DTRPAC Report page i 

Desert Tortoise Recovery Plan Assessment 

Tracy, C.R., R. Averill-Murray, W. I. Boarman, D. Delehanty, J.
 

Heaton, E. McCoy, D. Morafka, K. Nussear, B. Hagerty, P. Medica
 
 

DTRPAC Report page ii
 

Dedication 

This report is dedicated to our colleague and friend David Morafka. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page iii 

Assessment Committee
 

C. Richard Tracy (Chair) 

Professor of Biology 

University of Nevada, Reno 

Reno, Nevada 

Roy Averill-Murray William I. Boarman 

Biologist Biologist 

Arizona Game and Fish Department U.S. Geological Survey/ BRD 

Phoenix, Arizona San Diego, California 

Dave Delehanty Jill Heaton 

Assistant Professor of Biology Assistant Professor of Geography 

Idaho State University University of Nevada, Reno 

Pocatello, Idaho Reno, Nevada 

Jeff Lovich Earl McCoy 

Biologist Professor of Biology 

U.S. Geological Survey University of South Florida 

Flagstaff, Arizona Tampa, Florida 

Phil Medica Dave Morafka 

Biologist Research Associate 

U.S. Geological Survey California Academy of Sciences 

Las Vegas, Nevada San Francisco, California 

Ken Nussear Bridgette Hagerty 

Research Ecologist Ph.D. Student 

U.S. Geological Survey University of Nevada, Reno 

Las Vegas, Nevada Reno, Nevada 
 

 

 

 

 

 

 

 

 

 

DTRPAC Report page iv 

Table of Contents 

DESERT TORTOISE RECOVERY PLAN ASSESSMENT................................................................... I
 

DEDICATION ......................................................................................................................................II
 

ASSESSMENT COMMITTEE.......................................................................................................... III
 

TABLE OF CONTENTS ................................................................................................................... IV
 

TABLE OF TABLES ........................................................................................................................XII
 

TABLE OF RECOMMENDATIONS............................................................................................ XIII
 

ACKNOWLEDGEMENTS ............................................................................................................ XIV
 

BULLETED ABSTRACT OF FINDINGS AND RECOMMENDATIONS .............................. XVI
 

EXECUTIVE SUMMARY ............................................................................................................XVII
 

1. INTRODUCTION ............................................................................................................................ 1
 

1.1 Charge of the Desert Tortoise Recovery Plan Assessment Committee .................................................1
 

1.2 Desert Tortoise Recovery Plan Assessment Committee Members ........................................................2
 

1.3 Scientific Evaluation of the Recovery Plan ................................................................................................7
 

1.3.1 Recovery Prescriptions from the Recovery Plan ...................................................................................7
 

1.3.2 Topics Addressed in the Scientific Evaluation ......................................................................................9
 

1.3.3 Overview of Observations from the Assessment.................................................................................11
 

2. QUANTITATIVE LITERATURE REVIEW: THE STATE OF KNOWLEDGE..................... 16
 

2.1 Translocation ................................................................................................................................................19
 

Translocation Recommendations ....................................................................................................22
 

3. DISTINCT POPULATION SEGMENTS..................................................................................... 27
 

3.1 Definition and intentions of Distinct Population Segments...................................................................27
 

3.1.1 Background ............................................................................................................................................27
 

3.1.2 Discreteness............................................................................................................................................28
 

3.1.3 Significance............................................................................................................................................30
 

Direct Life-History Measures:...................................................................................................................32
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page v 

Ecological/Demographic Indicators:.........................................................................................................32
 

Possible Environmental Correlates: ..........................................................................................................32
 

3.1.4 Conservation Status ...............................................................................................................................32
 

3.2 DPSs of the Desert Tortoise........................................................................................................................33
 

3.2.1 Reappraisal of 1994 Recovery Units ....................................................................................................33
 

3.2.2 Provisional Revised List of DPSs.........................................................................................................36
 

DPS Recommendations ...................................................................................................................38
 

4. STATUS AND TRENDS............................................................................................................... 40
 

4.1 Recovery Plan Implementation .................................................................................................................40
 

Recovery Action Review and Implementation Recommendations: .............................................44
 

4.2 Trend Analyses of Populations ..................................................................................................................46
 

4.2.1 History of Long-Term Study Plots .......................................................................................................46
 

4.2.2 Trends Range-wide (East and West) ....................................................................................................51
 

4.2.3 Trend Analyses by Recovery Unit........................................................................................................52
 

Upper Virgin River Recovery Unit (and DPS) ........................................................................................54
 

Northeastern Mojave Recovery Unit ........................................................................................................55
 

Eastern Mojave Recovery Unit .................................................................................................................56
 

Northern Colorado Recovery Unit ............................................................................................................56
 

Eastern Colorado Recovery Unit...............................................................................................................57
 

Western Mojave Recovery Unit (and DPS) .............................................................................................58
 

4.2.4 Trend Analyses by Distinct Population Segment ................................................................................59
 

Lower Virgin River DPS ...........................................................................................................................59
 

Eastern Mojave and Colorado DPS...........................................................................................................60
 

Northeastern Mojave DPS .........................................................................................................................61
 

4.2.5 Summary of Trend Analyses.................................................................................................................61
 

4.3 Spatial Analyses............................................................................................................................................62
 

4.3.1 History of Desert Tortoise Transects....................................................................................................63
 

Total Corrected Sign Transects .................................................................................................................63
 

Distance Sampling Transects ....................................................................................................................64
 

4.3.2 Observation Rates ..................................................................................................................................66
 

4.3.3 Presence/Failure to Detect.....................................................................................................................68
 

4.3.4 Conditional Probability of Live Encounter ..........................................................................................70
 

Resampling .................................................................................................................................................70
 

Logistic Regression ....................................................................................................................................71
 

4.3.5 Kernel Analyses .....................................................................................................................................73
 

4.3.6 Nearest Neighbor Clustering.................................................................................................................84
 

4.4 Implications of Population and Spatial Analyses....................................................................................86
 

Plot and Spatial Analysis Recommendations .................................................................................88
 

4.5 Status and Trends of Habitat and Environmental Setting for Tortoise Populations .......................89
 

4.5.1 Road Case Study ....................................................................................................................................89
 

Road Case-Study Recommendations ..............................................................................................91
 

4.5.2 Patterns of Precipitation Case Study................................................................................................97
 

Patterns of Precipitation Case Study Recommendations...............................................................99
 

4.5.3 Disease Case Study...........................................................................................................................99
 

What is known and what is not known? ............................................................................................100
 

Risk from disease threats ....................................................................................................................103
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Disease Case-Study Recommendations........................................................................................105
 

5. LINKING IMPACTS, HABITAT, AND DEMOGRAPHY TO RECOVERY ....................... 108
 

5.1 Cumulative, Interactive, and Synergistic Impacts of Multiple Threats............................................109
 

5.1.1 Threats Network...................................................................................................................................112
 

Threats Recommendations.............................................................................................................119
 

6. MONITORING, EVALUATING, AND DELISTING.............................................................. 122
 

6.1 Strategies of Desert Tortoise Monitoring ...............................................................................................123
 

6.1.1 Historical Background for Desert Tortoise Monitoring ....................................................................123
 

6.1.2 Scope and Purpose of Modern Monitoring ........................................................................................124
 

6.1.2 Categories of Monitoring ....................................................................................................................126
 

6.2 Monitoring Desert Tortoises ....................................................................................................................128
 

6.2.1 Monitoring Desert Tortoise Populations ............................................................................................128
 

Long-Term Study Plots............................................................................................................................129
 

Distance Transect Sampling ....................................................................................................................130
 

6.2.2 Monitoring Individual Desert Tortoises .............................................................................................134
 

Condition indices......................................................................................................................................134
 

Behavior....................................................................................................................................................134
 

Behavior of Embryos and Neonates...................................................................................................136
 

Behavior of Juveniles..........................................................................................................................136
 

Behavior of Adults ..............................................................................................................................137
 

6.3 Habitat monitoring ....................................................................................................................................138
 

Monitoring Recommendations ......................................................................................................138
 

6.4 Delisting Criteria........................................................................................................................................142
 

Criterion 1 .................................................................................................................................................142
 

Criterion 2 .................................................................................................................................................142
 

Criterion 3 .................................................................................................................................................142
 

Criterion 4 .................................................................................................................................................142
 

Criterion 5 .................................................................................................................................................142
 

7. INTEGRATING RESEARCH AND MANAGEMENT............................................................ 146
 

7.1 Synopsis of Recommendations.................................................................................................................146
 

7.1.1 Research and Monitoring ....................................................................................................................146
 

• Re-evaluating the status of DPSs and the positioning of DWMAs....................................................146
 

• Improve population sampling methods ................................................................................................146
 

• Develop tools .........................................................................................................................................147
 

• Improve the focus on the recovery goal ...............................................................................................147
 

• Improve information gathering .............................................................................................................148
 

• Improving information dissemination ..................................................................................................148
 

• Improve the utility of monitoring efforts .............................................................................................149
 

• Improve the focus on recovery goals....................................................................................................149
 

• Develop research agendas .....................................................................................................................149
 

• Employing “outside” expertise .............................................................................................................150
 

• Improve information dissemination/access..........................................................................................150
 

7.1.3 Data Management ................................................................................................................................150
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page vii 

• Improve information dissemination/access..........................................................................................150
 

• Re-evaluate the status of DPSs and the positioning of DWMAs .......................................................150
 

• Improve the focus on the recovery goal ...............................................................................................150
 

7.2 Adaptive Management ..............................................................................................................................151
 

7.2.1 Ingredients of Inventory, Monitoring, and Research.........................................................................151
 

7.2.2 Relationships among Inventory, Monitoring, Research, and Adaptive Management.....................153
 

7.2.3 Definitions ............................................................................................................................................153
 

7.2.4 Inventory ..............................................................................................................................................154
 

7.2.5 Monitoring............................................................................................................................................154
 

7.2.6 Research ...............................................................................................................................................156
 

7.2.7 Adaptive Management Decision Making...........................................................................................156
 

7.2.8 The Circle of Status and Trends and of Monitoring ..........................................................................157
 

7.3 Cooperation and Coordination ................................................................................................................157
 

7.3.1 Desert Tortoise Recovery Office ........................................................................................................160
 

7.3.2 Science Advisory Committee..............................................................................................................160
 

7.4 Data Management ......................................................................................................................................163
 

7.4.1 Distribution of Monitoring Resources................................................................................................163
 

7.4.2 Data Management Plan........................................................................................................................164
 

7.4.3 Types and Sources of Errors ...............................................................................................................164
 

7.4.4 Errors Detection and Correction .........................................................................................................166
 

APPENDIX A. DTRPAC RESPONSES TO COMMENTS ......................................................... 168
 

APPENDIX B. DTRPAC MEETING MINUTES.......................................................................... 177
 

LITERATURE CITED ..................................................................................................................... 237
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page viii 

Table of Figures 

Fig. 2.1 Distribution of all literature types before and after the publication of the Recovery Plan. .............17
 

Fig. 2.2 Distribution of literature among the major research categories........................................................17
 

Fig. 2.3 Distribution of professional journal literature in the research categories before and after the
 

publication of the Recovery Plan. The proportion of Recovery Plan prescriptions associated with each 

major research topic are included for comparison with the distribution of professional journal literature.18
 

Fig. 2.4. Percent of early life stage documents in professional journals that focused on ecology and
 

autecology.............................................................................................................................................................19
 

Fig. 3.1. Depiction of recovery units proposed in the 1994 Recovery Plan. Green outlines within the 

recovery units are proposed DWMAs. ................................................................................................................34
 

Fig. 3.2. Ratio of rainfall in winter compared to summer in the Mojave Desert. Weather stations, and the
 

longitudes for those stations, are given in the table. .........................................................................................35
 

Fig. 3.3 Map of the proposed distinct population segments for desert tortoise. .............................................37
 

Fig. 4.1 Relative number of threats to desert tortoises in each critical habitat unit (i.e., DWMA), as
 

identified by the Recovery Plan in 1994. ............................................................................................................40
 

Fig. 4.2 Relative number of threats to desert tortoises in each critical habitat unit (i.e., DWMA), as
 

identified by the Desert Tortoise Management Oversight Group in 2003. ......................................................41
 

Fig. 4.3 Relative numbers of management actions recommended for each DWMA in the 1994 Recovery
 

Plan. ......................................................................................................................................................................42
 

Fig. 4.4 Relative numbers of management actions by DWMA reported to the USFWS that have been at
 

least partially implemented by 2002. ..................................................................................................................43
 

Fig. 4.5 Locations of desert tortoise permanent study plots within the federally listed range of desert
 

tortoises in the southwestern United States........................................................................................................47
 

Fig. 4.6 Trends in relative population densities for desert tortoises in the eastern and western permanent
 

study plot sites. .....................................................................................................................................................52
 

Fig. 4.7 Active (green tortoise symbols) and discontinued (orange triangles) permanent study plots
 

grouped within the 1994 Recovery Units............................................................................................................54
 

Fig. 4.8 Plot of adult densities over time for the City Creek permanent study plot located within the Upper
 

Virgin River Recovery Unit. Error bars are 95% confidence intervals for the density estimate. ..................55
 

Fig. 4.9 Plot of adult densities over time for the study plots located within the Northeastern Mojave
 

Recovery Unit. Error bars are 95% confidence intervals for the density estimate. ........................................55
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Fig. 4.10 Plot of adult densities over time for the study plots located within the Eastern Mojave Recovery
 

Unit. Error bars are 95% confidence intervals for the density estimate..........................................................56
 

Fig 4.11 Plot of adult densities over time for the PSPs located within the Northern Colorado Recovery
 

Unit. Error bars are 95% confidence intervals for the density estimate..........................................................57
 

Fig. 4.12 Plot of adult densities over time for the PSPs located within the Eastern Colorado Recovery Unit.
 

Error bars are 95% confidence intervals for the density estimate. ..................................................................57
 

Fig. 4.13 Plot of adult densities over time for the permanent study plots located within the Western Mojave
 

Recovery Unit. Error bars are 95% confidence intervals for the density estimate. ........................................58
 

Fig. 4.14 Active (green tortoise symbols) and discontinued (orange triangles) study plots grouped by
 

Distinct Population Segment. ..............................................................................................................................59
 

Fig. 4.15 Plot of adult densities over time for the Lower Virgin River Distinct Population Segment. Error
 

bars are 95% confidence intervals for the density estimate..............................................................................60
 

Fig. 4.16 Plot of adult densities over time for the Eastern Mojave and Colorado Distinct Population
 

Segment. Error bars are 95% confidence intervals for the density estimate. ..................................................60
 

Fig. 4.17 Plot of adult densities over time for the Northeastern Mojave Distinct Population Segment. Error
 

bars are 95% confidence intervals for the density estimate..............................................................................61
 

Fig. 4.18 The ratio of carcasses to live tortoises for DWMAs..........................................................................67
 

Fig. 4.19 Presence/”Failure to Detect” tortoises and carcasses for combined distance sampling (2001-

2003) and total corrected sign (1998, 1999, and 2001) transects. Dark green areas are those in which a
 

tortoise and/or scat were present. Light green areas are those in which a tortoise and/or scat and carcasses
 

were present. Red areas indicate only carcasses were present. White areas indicate no tortoises, scat, or
 

carcasses were found. Light tan areas indicate no distance sampling or total corrected sign transects were
 

conducted..............................................................................................................................................................69
 

Fig. 4.20 Results from the resampling analysis - Areas depicted in red are points in bins 6 and 12, which
 

had lower than average probabilities of live encounters; green points are bins 7 and 16, which had higher
 

proportions of live animals. Points in all other bins are blue in color.............................................................71
 

Fig. 4.21 Results from the logistic regression analysis. Cooler colors indicate higher probabilities of
 

encountering a live tortoise, and warmer colors indicate a lower probability................................................73
 

Fig. 4.22 Kernel analysis for the Upper Virgin River DWMA. The 95% kernel for live animals is indicated
 

by the green polygon; the 95% kernel for carcasses is indicated by the red outlined polygon. Transects that
 

were sampled for which no tortoises (live or dead) were found are indicated by the letter X on the map. ...75
 

Fig. 4.23 Kernel analysis for the Beaver Dam Slope / Mormon Mesa / Gold Butte-Pakoon DWMAs. The
 

95% kernel for live animals is indicated by the green polygon; the 95% kernel for carcasses is indicated by
 

the red outlined polygon. Transects that were sampled for which no tortoises (live or dead) were found are
 

indicated by the letter X on the map. ..................................................................................................................76
 

Fig. 4.24 Kernel analysis for the Coyote Springs Valley DWMA. The 95% kernel for live animals is 

indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined polygon. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Transects that were sampled for which no tortoises (live or dead) were found are indicated by the letter X 

on the map. ...........................................................................................................................................................77 

Fig. 4.25 Kernel analysis for the Piute-Eldorado Valley DWMA. The 95% kernel for live animals is 

indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined polygon. 

Transects that were sampled for which no tortoises (live or dead) were found are indicated by the letter X 

on the map. ...........................................................................................................................................................78 

Fig. 4.26 Kernel analysis for the Chuckwalla DWMA. The 95% kernel for live animals is indicated by the 

green polygon; the 95% kernel for carcasses is indicated by the red outlined polygon. Transects that were 

sampled for which no tortoises (live or dead) were found are indicated by the letter X on the map. ............79 

Fig. 4.27 Kernel analysis for the Pinto Mountain and Joshua Tree DWMAs. The 95% kernel for live 

animals is indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined 

polygon. Transects that were sampled for which no tortoises (live or dead) were found are indicated by the 

letter X on the map. ..............................................................................................................................................80 

Fig. 4.28 Kernel analysis for the Chemehuevi DWMA The 95% kernel for live animals is indicated by the 

green polygon; the 95% kernel for carcasses is indicated by the red outlined polygon. Transects that were 

sampled for which no tortoises (live or dead) were found are indicated by the letter X on the map. ............81 

Fig. 4.29 Kernel analysis for the Ivanpah DWMA. The 95% kernel for live animals is indicated by the 

green polygon; the 95% kernel for carcasses is indicated by the red outlined polygon. Transects that were 

sampled for which no tortoises (live or dead) were found are indicated by the letter X on the map. ............82 

Fig. 4.30 Kernel analyses for Fremont-Kramer / Superior-Cronese, and Ord-Rodman DWMAs. The 95% 

kernel for live animals is indicated by the green polygon; the 95% kernel for carcasses is indicated by the 

red outlined polygon. Transects that were sampled for which no tortoises (live or dead) were found are 

indicated by the letter X on the map. ..................................................................................................................83 

Fig. 4.31 Nearest Neighbour Hierarchical Cluster analysis for the Western Mojave. Green areas are 

clusters of living tortoises; red outlines are clusters of carcasses. ..................................................................85 

Fig. 4.32 Routes in the Western Mojave DWMAs in 1985-87. Blue routes were designated as open, brown 

as either closed, limited, undetermined, or non-route. Large roadless areas such as southwest OrdRodman, and the most southwestern portion of Fremont-Kramer were not without roads in 1985-87, but 

were instead not inventoried. On the other hand, the DTNA was designated by the BLM as an Area of 

Critical Environmental Concern and fenced in the late 1970’s, thus creating a roadless area.....................92 

Fig. 4.33 Routes in the Western Mojave DWMAs in 2001. Orange routes were designated as open, brown 

as either closed, limited, or non-BLM owned routes. The most southwestern portion of Fremont-Kramer 

remains un-inventoried as does portions of northern Fremont-Kramer, excluding the DTNA. .....................93 

Fig. 4.35 Comparison of 1985-87 and 2001 designated open BLM routes. The red routes represent 2001 

routes not formally designated as open in 1985-87. The lack of designation as open in 1985-87 could be a 

result of the fact that the route was inventoried in 1985-87 but not designated as open, not inventoried in 

1985-87 but existing, or not existing in 1985-87. ..............................................................................................95 

Fig. 4.36 Comparison of 2001 and 1985-87 designated open BLM routes. The blue routes represent 1985-

87 routes not formally designated as open in 2001. The lack of designation as open in 2001 could be the 

result of the fact that the route was inventoried in 2001 but not designated as open, not inventoried in 2001 

but existing, or not existing in 2001....................................................................................................................96 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xi 

Fig. 4.37 Seasonal rainfall in the Mojave Desert, 1930-2000..........................................................................98
 

Fig. 5.1 Network of threats demonstrating the interconnectedness between multiple human activities that
 

interact to prevent recovery of tortoise populations. Tier 1 includes the major land use patterns that
 

facilitate various activities (Tier 2) that impact tortoise populations through a suite of mortality factors
 

(Tier 3). ...............................................................................................................................................................113
 

Fig. 5.2 A section from the Threats Network from Fig. 5.1 that shows how multiple land uses and human
 

activities provide food subsidies to predators on tortoises, thereby increasing mortality............................115
 

Fig. 5.3 A section from the threats network from Fig. 5.1 showing just the primary activities associated 

with utility corridors. The causes of tortoise mortality associated with physical structures are also shown. 

.............................................................................................................................................................................117
 

Fig. 5.4 A subsection of the Threats Network shown in Fig. 5.1 that illustrates the mortality factors directly
 

associated with unpaved roads used for maintenance of utilities...................................................................118
 

Fig. 5.5 A much more complex web showing the interconnectedness among many activities associated with
 

utilities and their impacts on tortoise populations...........................................................................................119
 

Fig. 6.1 Idealized population trends before recovery planning implemented, as a result of implementing
 

recovery planning, and after delisting. .............................................................................................................123
 

Fig. 6.2 Dimensions of elements important to recovery, and therefore, needing monitoring. .....................125
 

Fig. 6.3 Kernel analysis of presence data for living desert tortoises (green polygons) and carcasses (red
 

outlines................................................................................................................................................................128
 

Fig.6.4 Simulated population growth at a 2% growth rate with (a) a 10% coefficient of variation around
 

the trend and (b) a 40% coefficient of variation around the same trend. ......................................................129
 

Fig. 6.5 Tortoise activity measured over a three year period at Bird Spring Valley, NV. Tortoise activity is
 

expressed as the proportion of animals active for each hour during each week of the year and ranges from
 

0 to 1. The gray areas represent times for which tortoise activity was not sampled. Warmer colors indicate
 

high proportions of animals active, and cooler colors indicate fewer animals active. .................................132
 

Fig. 7.1 Relationships among the desired objectives of a recovery program, a conceptual model of the
 

functional relationships among species, and monitoring activities in the adaptive management................155
 

Fig. 7.2 Relationships among factors contributing to disease important to demography of the desert
 

tortoise. ...............................................................................................................................................................159
 

Fig. 7.3 Relationships among offices, teams, committees, etc. functioning to produce strategies for recovery
 

and implementation of the listed species. .........................................................................................................162
 

Fig. 7.4 Kinds of activities associated with monitoring. .................................................................................163
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xii 

Table of Tables 

Table 1.1. Schedule of DTRPAC meetings ...........................................................................................................1
 

Table 2.1 Research categories used in quantitative literature review. ............................................................16
 

Table 4.1. Recovery actions listed in the Recovery Plan (and DWMA supplement) reported by management
 

agencies as implemented through 2002 (Redlands Institute (2002a-f). 0 = No Implementation; 1 =
 

Implementation Initiated; blanks indicate actions not applicable to that unit, according to the Recovery
 

Plan. ......................................................................................................................................................................45
 

Table 4.2 Years surveyed on permanent study plots for desert tortoises. A number (0 or 1) indicates that
 

data were taken at this plot. A zero indicates that the data are not available or sufficient for analysis, and a
 

one indicates that data were available for analyses in this report. ..................................................................48
 

Table 4.3 Citations for sources of data used in permanent study plot analyses..............................................50
 

Table 4.4 Study plots from which data were used to assess trends in population size in the original
 

Recovery Plan.......................................................................................................................................................51
 

Table 4.5 Summary of data, year, and region used for each analysis. TCS = total corrected sign surveys;
 

LDS = line distance sampling. ............................................................................................................................63
 

Table 4.6 Percentages of live animals and dead animals found on LDS transects. The third column is the
 

ratio of the percent of dead animals encountered to the percent of live animals encountered.......................66
 

Table 4.7 Observed ratios of live to dead tortoises. The P values indicate bins of transects in which the
 

ratios were different from that expected at random. The sign of the observed value indicates the direction of
 

the difference. .......................................................................................................................................................70
 

Table 4.8 Statistical table for the logistic regression analysis. ........................................................................72
 

Table 4.9 The estimated coefficients for the logistic regression model............................................................72
 

Table 4.10 Weather stations in the Mojave Desert used in analysis of precipitation (Fig. 4.37). .................97
 

Table 7.1 Summary of sources and types of error that have been found in Line Distance Sampling. .........165
 
 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xiii 

Table of Recommendations 

Bulleted Abstract of Findings and Recommendations xv
 

Recommendations on Translocations 23
 

Recommendations on Distinct Population Segments 38
 

Recommendations for Recovery Action Review and Implementation 44
 

Recommendations on Study Plot and Spatial Analyses Techniques 88
 

Recommendations from Road Case Study 91
 

Recommendations from Precipitation Case Study 99
 

Recommendations from Disease Case Study 105
 

Recommendations for Dealing with Threats 119
 

Recommendations on Monitoring 138
 

Considerations for Delisting Criteria 143
 

Synopsis of Overall Recommendations 146
 
 

 

 

 

 

 

 

 

 

DTRPAC Report page xiv 

Acknowledgements 

We would like to thank U.S. Fish and Wildlife Service staff, which assertively provided 

an interface between the DTRPAC and the public during the process leading to this 

report. The Biological Resources Research Center at the University of Nevada, Reno 

provided most of the logistic support for the process of creating this report. The 

University of Redlands, the Redlands Institute, and Lisa Benvenuti helped in producing 

maps. The Western Ecological Research Center of The U.S. Geological Service provided 

some financial and staff support. The Arizona Heritage Fund and a State Wildlife Grant 

(USFWS) supported Roy Averill-Murray as a member of DTRPAC. U.S. Fish and 

Wildlife Service provided funds for this project. 
 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xv 

Preface 

This report of the assessment of the Desert Tortoise Recovery Plan of 1994 is the result 

of more than a year of work by a committee who spent many hours conducting analyses 

and writing the report. A thorough understanding of the assessment process and products 

requires reading the entire report. Appendix B contains the minutes of all working 

meetings of the committee. This appendix allows a general tracking of the discussions 

and the process by which the report was assembled. For those who wish only to read the 

recommendations resulting from the report, there are three sources of recommendations. 

There is a one-page bulleted list of the general recommendations on page xv. The 

Executive Summary on page xvi presents an abstract of the report. All recommendations 

associated with each chapter of the report can be located by using the Table of 

Recommendations on page xii. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xvi 

Bulleted Abstract of Findings and Recommendations 

• The Recovery Plan of 1994 was fundamentally sound, but some modifications for 

contemporary management will likely make recovery more successful. 

• Complex meta analyses of tortoise distributions and abundances indicate trends leading 

away from recovery goals in some parts of the species range. These results indicate a 

need for more aggressive initiatives to facilitate recovery. 

• A USFWS Desert Tortoise Recovery Office (DTRO) should be established to facilitate 

and coordinate recovery efforts based upon an adaptive-management approach with 

advice from a Science Advisory Committee (SAC). 

• Many of the original prescriptions of the Recovery Plan were never implemented. These 

prescriptions continue to be appropriate and they should be implemented. However, 

synergistic, interacting, and cumulative threats, not appreciated by the original Recovery 

Team, also must be addressed and new prescriptions should be prioritized from analyses 

of analyses of “threats network topologies” assembled by the DTRPAC to assess 

redundancies and synergies within individual threats. 

• Recovery planning should reflect distinctness of population segments within the species 

range. The genetic distinctness of tortoise populations and of their pathogens must be 

assessed to guide all manipulative management (e.g., head starting, translocation, habitat 

restoration, corridor management, etc.). A newly proposed (by the DTRPAC) 

delineation of DPSs should be revised with new scientific information. 

• Status and trends of populations/metapopulations within DPSs are potentially impossible 

based only upon assessment of tortoise density because assessing density of populations 

for rare and cryptic species is exceedingly difficult (and potentially impossible). Thus, 

monitoring the efficacy of management actions should be based upon a comprehensive 

assessment of the status and trends of threats and habitats as well as population numbers. 

• A new definition of recovery is needed as assessing recovery defined in terms of a 

population that is demonstrably increasing or remaining stable may not be possible. The 

new definition should be based upon achievable assessment of progress toward recovery 

as assessed in the status and trends of threats, habitats, and population distribution and 

abundance. 

• The original paradigm of desert tortoises being recovered in large populations relieved 

of intense threats may be flawed as tortoises may have evolved to depend upon 

metapopulation dynamics. Assessing the appropriateness of the metapopulation 

paradigm is very important as management under this paradigm could require more 

intense actions (including head starting, genetics management, habitat management and 

facilitated dispersal, herd immunization, and other artificially facilitated ecosystem 

processes). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xvii 

EXECUTIVE SUMMARY
 

The Desert Tortoise Recovery Plan Assessment Committee (DTRPAC) was appointed by 

the U.S. Fish and Wildlife Service (USFWS) in 2003 and charged with carrying out a 

scientific assessment of the Desert Tortoise Recovery Plan published in 1994. The 

assessment committee consisted of credentialed academic and agency scientists with 

expertise in ecology, tortoise biology, conservation biology, geography and GIS 

technologies, scientific ethics and philosophy of science, the Endangered Species Act of 

1973 as amended and the implementation of that law, and desert natural history. 

Additionally, the assessment committee solicited input from nationally recognized 

scientists to provide expert advice and opinion in highly technical areas central to tortoise 

recovery including tortoise epidemiology, remote sensing, and multi-scale population 

monitoring. 

The resultant assessment reviews the Recovery Plan in the context of scientific and 

analytical advances made since the Recovery Plan was published in 1994. The primary 

goal of this assessment is to provide a critical scientific evaluation of the Recovery Plan 

prior to any renewal or revision of the plan. The assessment produced by DTRPAC is not 

a Recovery Plan, and it does not seek to make social, legal, or political decisions on 

desert tortoise recovery. Rather, the assessment is a scientific evaluation of the current 

state of scientific knowledge regarding tortoise recovery, and the assessment reveals 

directions, via analytical examples, towards the scientific knowledge necessary to achieve 

desert tortoise recovery. The committee explicitly demonstrates how recent analytical 

advances can be applied to desert tortoise recovery by carrying out original and rigorous 

analyses of existing data. Not only are these analyses meant to provide a detailed 

scientific perspective for a possible future recovery plan panel to consider, the examples 

also demonstrate the power of analyses now available for tortoise recovery when 

appropriate data exist and the true loss in potential information incurred when tortoise 

data acquisition is poorly planned or only intermittently carried out. 

The DTRPAC found that original Recovery Plan was fundamentally strong but could 

benefit substantially from modification. Modifications center on the following areas: (1) 

recognition of new patterns of diversity within the Mojave desert tortoise population, (2) 

explicit implementation of original Recovery Plan prescriptions, (3) greater appreciation 

of the implications of multiple, simultaneous threats facing tortoise populations, and (4) 

applying recent advances in analytical techniques to desert tortoise recovery. 

Much of the inability to implement the original Recovery Plan owes to the lack of 

coordinated, range-wide tracking and reporting of management implementation. The 

DTRPAC recommends that a much more aggressive coordination and facilitation effort 

should become the responsibility of the USFWS. A Desert Tortoise Recovery Office 

(DTRO) should be established in the USFWS to implement the needed oversight, 

tracking, and reporting of new information about the efficacy of management actions and 

the methods by which that efficacy is assessed. This office should empanel a Science 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xviii 

Advisory Committee (SAC - including members from academia and USGS) to serve in 

an advisory role to the DTRO. 

Research and management efforts can and should be integrated to increase the likelihood 

of tortoise recovery. It appears that many opportunities to accumulate scientifically 

rigorous data to examine tortoise and habitat trends, as well as to explore mechanisms 

underlying tortoise population dynamics, have been missed. Recovery depends upon a 

substantially greater understanding of tortoise behavior, genetics, disease transmission, 

and demography, and the DTRO should facilitate increased scientific understanding in 

these areas by increasing research activity outlined in the original Recovery Plan and 

here, and working to improve cooperation between managers and research scientists. 

Scientists need to emphasize research that will address urgent management needs and 

their efforts will benefit from consulting with managers on their “on-the-ground 

knowledge” of tortoise populations. Managers can contribute to recovery by 

collaborating and consulting with researchers on data acquisition, storage, and access. 

Additionally, sophisticated data oversight and management as well as independent 

expertise in data acquisition design and statistical analysis are essential to the process 

leading to desert tortoise recovery. 

The recovery prescriptions of the original Recovery Plan were only partially 

implemented and, as implemented, the Recovery Plan neither appears to be leading to 

desert tortoise recovery, nor is it likely to do so. In particular, explicit recommendations 

for research designed to provide rigorous data essential to understanding desert tortoise 

demography and population dynamics were not carried out. The failure to implement 

research recommendations means that the understanding of desert tortoise demography 

and population dynamics has advanced very little. The call for rigorous data was an 

essential part of the adaptive management approach at the core of the original Recovery 

Plan. In adaptive management, management actions are modified based upon incoming 

data that assesses whether or not current management actions are working. Establishing 

an aggressive DTRO will help us avoid missing more opportunities to facilitate recovery. 

Desert tortoises face an array of threats, which act simultaneously and synergistically. 

The far-reaching implications of this concept were not fully appreciated in the original 

Recovery Plan. Multiple, simultaneous threats are particularly insidious to formulating 

recovery actions because it is possible that potential gains made in tortoise numbers 

through one action can be lost when potentially “saved” tortoises perish or fail to 

reproduce due to a different threat not alleviated by the management action. The 

synergism of multiple threats refers to the biological fact that effects from one threat can 

be magnified when the threat co-occurs with another threat. The original Recovery Plan 

does not fully appreciate that threats to tortoises can act in this non-additive way. 

Due to the natural progression of science, the original Recovery Plan does not incorporate 

technological and analytical techniques now available. The DTRPAC reviewed the 

scientific literature, sought to acquire recent data in the “gray” literature (agency reports, 

etc.), and applied a suite of analytical techniques to existing desert tortoise data. These 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xix 

analyses were meant to yield new insights into desert tortoise biology and recovery, to 

provide examples of approaches that a new recovery plan could employ, and also to 

underscore the true need for, and benefit of, rigorous and scientific data that directly 

address issues underlying desert tortoise recovery. 

The assessment presents a modified set of desert tortoise Distinct Population Segments 

(DPS) relative to the original Recovery Plan. The new DPS delineations reflect the 

committee’s review and interpretation of recent desert tortoise and conservation biology 

literature. The DTRPAC delineations reflect the prevailing concepts of subpopulation 

“discreteness, “ and “significance,” and incorporate morphological, behavioral, genetic, 

and environmental information. The DTRPAC suggestion reduces the number DPSs from 

six to five by leaving the original Upper Virgin River and Western Mojave units intact 

and recombining the four central units into three reconfigured units. 

The assessment provides a highly detailed meta-analysis of desert tortoise population 

status and trends. The DTRPAC found the data on status and population trends often to 

be statistically unwieldy due to inconsistencies in data collection, suboptimal data 

collection design, and the truly daunting task of measuring animals that are difficult to 

detect and that occupy a harsh environment. Because much of the data currently available 

to address tortoise recovery was originally collected for purposes other than tortoise 

recovery, the DTRPAC analyses are meta-analyses using data of mixed quality. To adjust 

for very low statistical power in current data sets, DTRPAC used transect sampling 

carried out by various agencies and managers to derive tortoise occurrence data, then 

used spatial analysis of tortoise occurrence to map tortoise status and possible trends. 

Results are complex, but resulting maps suggest that in many areas tortoise populations 

appear be facing continued difficulty. Spatial analyses did not indicate zones of recovery. 

Kernel analyses of transect data – limited to only one year due to lack of additional 

sufficient data – identified several regions that may have experienced significant local 

die-offs. Statisticians consulting with DTRPAC derived an original analysis called 

“Conditional Probability of Being Alive” that spatially illustrated regions of low, 

intermediate, and high probability of encountering live tortoises during surveys. These 

analyses identified large regions within historic desert tortoise habitat as being associated 

with having a low probability of detecting live tortoises during surveys. In other words, 

probably few tortoises occur in these areas currently. The West Mojave recovery unit 

stood out within overall tortoise range as unambiguously experiencing continued 

population decline. 

The DTRPAC also performed spatial analyses of habitat and other geographic trends with 

special emphasis on potential impacts of roads and disease: two issues of historic 

importance in desert tortoise recovery. GPS technology and renewed survey effort 

indicate that more roads currently are documented in the western Mojave zone of tortoise 

decline than were documented in 1987. Some portion of the increase in roads probably 

represents legal or illegal road creation from 1987-2001. Some portion probably 

represents new documentation of previously existing roads. The relationship between 

road type and road density to tortoise decline needs to be clarified. Expert consultation 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xx 

with wildlife disease epidemiologists and emerging evidence from tortoise studies 

indicate that the relationship between ELISA-positive assays of live tortoises, 

Mycoplasma infection, and tortoise decline is not a simple and easily predicted 

relationship. Disease experts sought out by the DTRPAC described a growing awareness 

that the probability of infection leading to death in tortoises may be a function of chronic 

stress (e.g., malnutrition) and the strain of infectious agent. This means that the presence 

of disease alone is not sufficient to explain tortoise die-offs. For example, it is possible 

that habitat degradation results in physiologically stressed tortoises that then succumb to 

disease agents that are normal at background levels in healthy populations. The 

relationships between disease, physiological status, and tortoise death are scientifically 

tractable, but they have not been rigorously addressed. 

The assessment presents a threats network topology. This network illustrates the 

profoundly daunting array of threats facing the desert tortoise and should discourage a 

future recovery team, if it is necessary to form one, from viewing threats in overly 

simplistic way. A substantial body of evidence indicates that tortoises face a complex 

suite of threats. It is naïve to propose a recovery action that addresses a single threat and 

then anticipates straightforward additive increases in tortoises as a response to the 

management action. 

It is also clear that effective desert tortoise monitoring and the creation of an effective 

restoration strategy will entail a new and greater level of cooperation and coordination 

among managers and scientists. Currently, no group is charged with managing scientific 

data on the desert tortoise, and data often are collected and reported in ways that make 

them difficult to use in conjunction with other data. Currently, important desert tortoise 

data are widely scattered among state and federal agencies and the scientific community. 

Data have been gathered, “organized”, and stored in a multitude of ways. Some data have 

been organized and other still exists in raw, unanalyzed states. Accessibility of data for 

managers, scientists, and the public is highly variable. In short, a great deal of important 

long-term data cannot be used readily. Organizing and “mining” currently existing desert 

tortoise data could be highly productive and helpful. Establishing a DTRO would help 

focus attention towards learning from existing data and promoting new scientific 

initiatives. 

The current definition of desert tortoise recovery requires populations within recovery 

units to be stable or increasing for at least 25 years (one tortoise generation). To 

demonstrate recovery based on population stability, scientists must be able to distinguish 

among populations that are truly stable as opposed to populations that superficially 

appear to be stable because monitoring data are not sufficiently rigorous to detect 

declines when in fact declines are occurring. A new multi-dimensional monitoring 

strategy may be the most effective approach for redefining and verifying recovery. The 

monitoring approach presented in the assessment refers to three tiers of monitoring. Tiers 

1 and 2 perform status and trend monitoring by using repeated measures taken over time 

(tier 1) and inferential statistics applied across broad geographical areas (tier 2). These 

are designed to meet current management objectives and also to monitor changes over 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page xxi 

long time periods. Tier 3 is research monitoring designed to detect or to verify 

mechanistic links between actions and tortoise responses. Both population and habitat 

monitoring will require multi-scale approaches to achieve information needed for 

adaptive management and assessment of recovery. 

It is no longer clear that the original population paradigm upon which definitions of 

recovery were based is correct. Existing data do not exclude the possibility that tortoise 

populations evolved to be distributed in metapopulations instead of single, large 

populations. The dynamics of metapopulations, and the conservation prescriptions for 

metapopulations are entirely different from single, large populations. Thus, the original 

Recovery Plan prescribed establishing large wildlife management areas and reducing 

threats within those areas. For metapopulations, it may be additionally necessary to 

protect corridors among habitat patches, and to recognize that natural metapopulation 

dynamics require areas suitable for desert tortoises, but periodically vacant of tortoises. 

Thus, new data and analyses are needed immediately to determine the biological basis for 

defining recovery in light of the possibility that unforeseen ecosystem processes need to 

be protected as part of recovery. 
 

 

DTRPAC Report page xxii
 

“Science can only state what is, not what should be.” 

Albert Einstein, Out of My Later Years. (1950) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 1 

1. Introduction 

The original Desert Tortoise Recovery Team recognized the importance of including new 

data and analyses for recovery efforts as they become available. Indeed, the Recovery 

Team called for the Recovery Plan to be reassessed every three to five years to ensure 

that recommendations to management were made with the best available scientific 

information (USFWS 1994, p. 37). Since the Recovery Plan's publication in 1994, there 

have been no overt efforts to revise the Recovery Plan in light of new information 

pertinent to desert tortoise recovery, despite the fact that there has been new research on 

many aspects of desert tortoise ecology, threats, conservation biology, and monitoring, as 

well as public challenges to the validity of the Plan. 

1.1 Charge of the Desert Tortoise Recovery Plan Assessment Committee 

The U.S. Fish and Wildlife Service (USFWS) initiated a two-step process to revise the 

1994 Desert Tortoise Recovery Plan. Step 1 is a review and assessment of new research 

and information gathered on many aspects of desert tortoise ecology, threats, 

conservation biology, monitoring, and recovery actions. Step 2 will be the revision of the 

Recovery Plan by a newly established recovery team of scientists, agency resource 

specialists, and stakeholders, if a future recovery team is necessary. 

Following is a description of Step 1 of the process that has been initiated by the Desert 

Tortoise Recovery Plan Assessment Committee (DTRPAC). The charge of the DTRPAC 

is to review the entire Recovery Plan in relation to contemporary knowledge and, based 

on that review, prepare recommendations about which parts of the Recovery Plan need 

updating. Under this charge, the DTRPAC was to assemble and review all new literature 

pertinent to the Recovery Plan, to hold meetings to conduct an in-depth review of 

selected topics (disease, monitoring, etc.), and submit a final report to the USFWS. A 

schedule of DTRPAC meetings, including focal topics for each meeting is shown in 

Table 1.1. The minutes from each meeting are contained in Appendix B. 

TABLE 1.1. Schedule of DTRPAC meetings 

Topic Dates Location 

Orientation and Agenda 11 April 2003 San Francisco, CA 

Distinct Population 

Segments and Threats 

15-16 May 2003 Palm Springs, CA 

Disease Workshop Debrief, 

Disease, Status of Threats 

9-10 June 2003 San Francisco, CA 

Status of Populations, 

Demography, Finalize 

Threats 

31 July – 1 August 2003 Truckee, CA 

Monitoring and Delisting 

Criteria 

4-5 September 2003 Monterey, CA 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 2 

Habitat Conservation 

Planning, Research 

2-3 October 2003 Tucson, AZ 

Review and Report 

Preparation 

6-7 November 2003 Las Vegas, NV 

Report Preparation 26-27 February 2004 Reno, NV 

Report Preparation 22-23 April 2004 Carlsbad, CA 

Address Public Comments 26-27 May 2004 Reno, NV 

Finalize Report 14-15 June 2004 Reno, NV 

1.2 Desert Tortoise Recovery Plan Assessment Committee Members 

The DTRPAC was purposely assembled with scientists and experts diverse in terms of 

State representation, institutions of employment, gender, and scientific expertise. Some 

members were chosen who are not doing research on the desert tortoise. The committee 

was assembled with representatives with the following characteristics: 

1. expertise and experience with the desert tortoise and/or ecosystems containing 

desert tortoises, 

2. expertise and experience in conservation biology and other areas important to the 

DTRP evaluation process, 

3. ability to serve as “internal peer-reviewers” (i.e., scientists serving as general 

science analysts whose job it will be to keep tortoise scientists from becoming 

myopic while focusing on new data, analyses, and opinions for the desert tortoise), 

4. academic and agency scientists, 

5. representation of the original Recovery Team, 

6. broad representation from the geographic range of the listed species. 

The committee included the following members: 

C. Richard Tracy (Ph.D.), [Chair of the Committee] Professor of Biology and Director 

of the Biological Resources Research Center, University of Nevada, Reno, NV 

Dr. Tracy is the former Director of the Ecology, Evolution, and Conservation Biology 

Graduate Program at the University of Nevada, Reno. He currently serves as the 

science advisor for the Clark County Desert Conservation Program in Nevada. He 

earned his B.A. and M.S. from California State University, Northridge and his Ph.D. 

from the University of Wisconsin. He has served on faculties at Colorado State 

University, the University of Wisconsin, the University of Washington, the 

University of Puerto Rico, Pepperdine University, the University of Nebraska, and the 

University of Michigan. He has been honored as a Guggenheim Fellow, as a 

Distinguished Scholar at Pepperdine University, and as a Fellow of the Association of 

Western Universities. He also has received an American Society of Zoologists 

Service Award, a Desert Tortoise Council Conservation Award, a Service Award 

from the U.S. Fish and Wildlife Service, and he has served in leadership roles in the 

Ecological Society of America and the American Society of Zoologists. Dr. Tracy is 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 3 

an ecologist who has published more than 140 articles and book chapters on a wide 

range of topics in ecology, population biology, physiology, biophysics, and natural 

history of animals (mostly amphibians and reptiles), and whose studies have included 

research on herbivorous reptiles since 1977, and on desert tortoises since 1988. He 

was a member of the original Desert Tortoise Recovery Team, and he is a member of 

the Houston Toad Recovery Team. He has served as major professor for 37 masters 

and Ph.D. students, and he has directed theses, dissertations, and postdoctoral 

research of several graduate students and postdoctoral scholars who have studied the 

desert tortoise. 

Roy C. Averill-Murray (M.S.), Amphibians and Reptiles Program Manager, 

Arizona Game and Fish Department, Phoenix, AZ 

Mr. Averill-Murray earned his B.S. in Wildlife and Fisheries Sciences (cum laude) 

from Texas A&M University in 1990. In 1993 he earned his M.S. in Wildlife and 

Fisheries Science from the University of Arizona, where he completed his thesis on 

estimating density and abundance of desert tortoises in the Sonoran Desert. He began 

working for the Arizona Game and Fish Department in 1995 as the Nongame 

Branch's Desert Tortoise Coordinator. As Desert Tortoise Coordinator, he directed 

the state's population monitoring program; conducted research on desert tortoise 

ecology, especially reproduction; and co-chaired the Arizona Interagency Desert 

Tortoise Team. He has published 8 peer-reviewed scientific papers on desert 

tortoises, including 3 chapters in the new book The Sonoran Desert Tortoise: Natural 

History, Biology, and Conservation. He assumed the duties of Amphibians and 

Reptiles Program Manager in 2002, and he is responsible for the management of all 

amphibians and reptiles in Arizona. He is also co-chair of Partners in Amphibian and 

Reptile Conservation's Southwest Regional Working Group. 

William I. Boarman (Ph.D.), Research Wildlife Biologist, U.S. Geological Survey, 

Western Ecological Research Center, San Diego, CA 

Dr. Boarman received his Ph.D. in ecology from Rutgers University. He has worked 

for the Department of Interior for 13 years studying the ecology, behavior, and 

management of the desert tortoise and common raven. His desert tortoise research 

focuses on the impacts of roads on desert tortoise populations and the effectiveness of 

barrier fences and culverts at recovering desert tortoise populations. The association 

between raven ecology and anthropogenic resources to develop means to reduce 

raven predation on juvenile tortoises is the aim of his work with ravens. He has 

written a comprehensive evaluation of the state-of-the-art of our knowledge of threats 

to desert tortoise populations. He is also involved in research on the Salton Sea 

ecosystem, prairie falcon ecology, and marbled murrelet conservation. He has 

published 25 papers in peer-reviewed scientific journals. 

Dave J. Delehanty (Ph.D.), Assistant Professor of Biology, Idaho State University, 

Pocatello, ID 

Dr. Delehanty received his Ph.D. from the Ecology, Evolution, and Conservation 

Biology Program at the University of Nevada, Reno in 1997. He has taught 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 4 

Conservation Biology at UNR and ISU, and he is well known for his innovative 

approach to this important subject. He has studied mechanisms underlying behavior 

and the physiological importance of dietary carotenoid pigments on steroid-mediated 

physiological events involved with sexual maturation, sexual behavior, and 

reproductive performance in vertebrates. Importantly, he seeks to develop an 

improved understanding of animal behaviors integral to the success of conservation 

actions. He is implementing Nevada restoration programs for mountain quail and 

Columbian sharp-tailed grouse, two native species extirpated from all or part of their 

historic ranges. This includes developing new restoration techniques that account for 

behavioral and life history constraints. He is a critical thinker whose prowess in 

ecology, conservation biology, genetics, statistical analyses, research design, as well 

as species repatriation makes him an excellent member for the DTRPAC. 

Jill S. Heaton (Ph.D.), Assistant Professor of Geography, University of Nevada, 

Reno, NV 

Dr. Heaton was previously an assistant professor in Environmental Studies at the 

University of Redlands. She was Principal Investigator for the Redlands Institute (RI) 

Desert Tortoise Project (DTP). The RI and DTP are comprised of numerous research 

analysts, ecologists, GIS analysts, programmers, and systems analysts, among other 

positions. She and her DTP research team are building a desert tortoise decision 

support system. This system uses a scientific knowledge base linked to geospatial 

data within an application framework allowing users to evaluate decision and 

management options as well as identify knowledge and data gaps, thus clarifying 

research priorities. She is an arid lands ecologist, with degrees in biology and 

geography. She earned her B.S. and M.S. in Biology from the University of North 

Texas, in 1993 and 1996, respectively. Dr. Heaton earned her Ph.D. in Physical 

Geography from Oregon State University in 2001. Her research career has been spent 

in the arid southwest working with mammals in the Chihuahuan Desert and reptiles in 

the Mojave. She is experienced in applying quantitative and statistical techniques to 

ecological problems, and integrating ecological theory and principles with the spatial 

and temporal complexity of the natural environment. She has experience and 

expertise in habitat modeling, statistical modeling, environmental issues on military 

installations, urban and development biodiversity boundary interactions, and issues 

relating to land use and conservation. She is trained in GIS applications, primarily the 

suite of ESRI GIS products, remote sensing and image analysis, and traditional 

statistical and geo-statistical analyses. She has extensive fieldwork experience and 

strives to spend a quarter of her time in the field conducting research. 

Jeffrey E. Lovich (Ph.D.), Chief, Grand Canyon Monitoring and Research Center, 

U.S. Geological Survey, Flagstaff, AZ 

Dr. Lovich is the former Director of the U.S. Geological Survey, Western Ecological 

Research Center. Headquartered in Sacramento, California, the Center employs a 

staff of over 100 employees, located at 14 duty stations in California and Nevada. He 

started his federal career in 1979 at the National Museum of Natural 

History/Smithsonian Institution in the Division of Amphibians and Reptiles while still 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 5 

an undergraduate student at George Mason University. After finishing his B.S. in 

Biology, he stayed on at George Mason, earning an M.S. in Biology. From there, he 

went to the University of Georgia, obtaining a Ph.D. in Ecology in 1990. Most of his 

tenure at the University of Georgia was spent at the Savannah River Ecology 

Laboratory, a research facility of the University of Georgia in South Carolina. After a 

brief Post Doctoral fellowship at the Savannah River Ecology Laboratory, he went to 

work for the Bureau of Land Management, first as a staff biologist at the California 

Desert District Office in Riverside, then as the Lead Wildlife Biologist in Palm 

Springs. As a charter member of the National Biological Survey (now Biological 

Resources Division of USGS), he conducted research on desert tortoises and desert 

ecology in southern California. His research on turtles and tortoises spans almost 25 

years. During that time he published over 60 scientific papers, most on the ecology 

and evolution of North American and Asian freshwater turtles. He discovered and 

formally described three of the world's 280 or so turtle species, including two in the 

United States and one in Japan. In addition he published two books. He is co-author 

of the book "Turtles of the United States and Canada" published by the Smithsonian 

Institution Press in 1994, and co-editor of, and contributor to, the book "Biological 

Diversity: Problems and Challenges" published by the Pennsylvania Academy of 

Science the same year. 

Earl D. McCoy (Ph.D.), Professor of Biology, University of South Florida, Tampa, FL 

Dr. McCoy earned a B.S. in Biology at Florida State University in 1970, a M.S. in 

Biology at the University of Miami in 1973, and a Ph. D. in Biology at Florida State 

University in 1977. He has published over 100 peer-reviewed publications, many of 

which focus on the ecology and conservation biology of gopher tortoises. He has also 

published extensively on the philosophy of science and the basis of experimental 

design in ecology, including the book Method in Ecology: Strategies for Conservation 

Problems. He is currently on the editorial board for three journals, including Ecology 

and Ecological Monographs. He has been at the University of South Florida since 

1977. He has been the associate Chairman for the Department of Biology since 1992. 

He has also been a Visiting Assistant Professor at the University of Virginia on 

several occasions. He has mentored three postdoctoral students, 10 Ph.D. students, 

and 27 masters students. He is currently the primary investigator or a collaborator on 

several research projects, including a large multi-disciplinary project examining the 

field epidemiology of the Upper Respiratory Tract Disease in the gopher tortoise. 

David J. Morafka (Ph.D.), [deceased] Research Associate, Department of 

Herpetology, California Academy of Sciences, San Francisco, CA 

Dr. Morafka was the Lyle E. Gibson Emeritus Professor of Biology, CSU, 

Dominguez Hills. He earned his B.S. in Biology (with honors) at the University of 

California at Berkeley in 1967, and a Ph. D. at the University of Southern California 

in 1974. He was a member of the original Desert Tortoise Recovery Team and a 

member of the IUCN Freshwater Turtle and Tortoise Conservation Group. He had 

more than 50 publications and one book on North American desert reptiles and their 

conservation. He was the principal investigator on neonatology and hatchery nursery 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 6 

studies of the desert tortoise at Ft. Irwin and Edwards Air Force Base, and of the 

endangered Bolson tortoise in Mexico. 

Ken E. Nussear (Ph.D.), Research Ecologist, U.S. Geological Survey, Western 

Ecological Research Center, Las Vegas Field Station, Las Vegas, NV 

Dr. Nussear is a recent graduate from the Ecology, Evolution, and Conservation 

Biology Program at the University of Nevada, Reno. He received his B.S. in Zoology 

(summa cum laude) from Colorado State University. He has published several peerreviewed publications on the physiology of desert reptiles. He has worked on many 

research projects involving desert tortoises since 1995. His research has focused on 

conservation biology, nutritional ecology, and physiological ecology of desert 

tortoises. These research projects included a multi-site, multi-state translocation 

project designed to examine the efficacy of translocation as a conservation tool for 

desert tortoises. The study looked within and beyond the geographic range of desert 

tortoises and gives insights into the habitat requirements of this species. His work is 

being used to develop management strategies for desert tortoises in the face of the 

fastest growing human populations in the country. He had a pre-doctoral fellowship 

from the University of Redlands to continue his research. This research involves 

applied biophysical-ecology studies of tortoises to enhance our understanding of 

tortoise activity and how this impacts monitoring efforts. This work will help to refine 

desert tortoise monitoring efforts throughout the range of the listed population. 

Bridgette E. Hagerty, Ph.D. Student, University of Nevada, Reno (DTRPAC 

manager) 

Ms. Hagerty is a current doctoral student in the Ecology, Evolution, and 

Conservation Biology Program at the University of Nevada, Reno. She earned her 

B.A. in Biology (magna cum laude) from St. Mary’s College of Maryland in 2000. 

Prior to beginning her graduate studies, she was an Environmental Management 

Fellow with the Chesapeake Research Consortium and staffed committees at the 

EPA Chesapeake Bay Program. Her research focuses on the use of indirect methods 

to quantify movement among desert tortoise populations in the Mojave Desert. The 

results of her genetics research will be used to help make decisions concerning 

distinct populations segments of the desert tortoise. 

Phil A. Medica (M.S.), Biologist, U.S. Geological Survey, Western Regional 

Research Center, Las Vegas Field Station, (USFWS liaison representative) 

Mr. Medica is a Wildlife Biologist with the U.S. Geological Survey, Western 

Ecological Research Center, at the Las Vegas Integrated Science Office. He received 

his B.S. in Wildlife Management (Game Management) and his M.S. in Biology 

(Herpetology) from New Mexico State University in 1964 and 1966, respectively. He 

has worked on reptiles and small mammals throughout the southwestern U.S. for the 

past 40 years. He began his career working at the Nevada Test Site (NTS) in 1966 as 

a field technician for Brigham Young University, Department of Zoology, and was 

subsequently employed as a Staff Research Associate by UCLA, Laboratory of 

Nuclear Medicine and Radiation Biology from 1967-1981. While with UCLA at 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 7 

NTS, he studied the effects of gamma irradiation upon natural populations of animals 

and plants at the Rock Valley facility, documented sterility among the lizard 

inhabitants, and conducted lizard demographic and reproductive studies. He 

developed and implemented environmental research studies on natural populations of 

lizards and small mammals in conjunction with drought upon the ecosystem as well 

as disturbances, i.e., roads, fire, grading, cratering, and irradiation. From 1992-1993, 

he served as an Ecologist with the Bureau of Land Management, Las Vegas District 

Office, and was transferred to the National Biological Survey in 1993. As a Research 

Wildlife Biologist with the National Biological Survey, subsequently 

USGS/Biological Resources Division (1993-2000), he conducted extensive field 

studies pertaining to desert tortoise translocation, reproduction, and survivorship. 

Most recently, he served as the Mojave Desert Tortoise Coordinator for the U.S. Fish 

and Wildlife Service (2000-2004), initiating rangewide population monitoring using 

the Line Distance Sampling technique. He has authored or co-authored 70 reports, 

scientific papers, and peer reviewed journal articles pertaining to the ecology of 

desert reptiles and small mammals of the southwestern United States. 

1.3 Scientific Evaluation of the Recovery Plan 

1.3.1 Recovery Prescriptions from the Recovery Plan 

The passage in the following text box is taken directly from the Recovery Plan of 1994. 

This passage expresses the core of what needs to be compared with current management 

and knowledge. The comparison we present in this document is meant to be a scientific 

evaluation of the Recovery Plan in relation to contemporary knowledge of (a) the biology 

of the desert tortoise and (b) the extent to which the Recovery Plan was implemented. 
i. Develop monitoring plan

ii. Implement monitoring plan

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 8 

“The desert tortoise was listed as threatened primarily because of a variety of human 

impacts that cumulatively have resulted in widespread and severe desert tortoise 

population decline and habitat loss. The destruction, degradation, and fragmentation of 

desert tortoise habitat and loss of individual desert tortoises from human contact, 

predation, and disease are all important factors in the decline of the Mojave population. 

If the desert tortoise is to be recovered within its native range, the causes of the decline 

must stop, at least within the DWMAs. Some factors are likely more important than 

others; for instance, urbanization has probably caused more habitat loss than light 

cattle grazing. However, eliminating all factors that are deleterious to desert tortoise 

populations will certainly result in faster recovery than will selective elimination of a 

few. 

Accomplishing the prescribed recovery actions is needed to reduce or eliminate 

human-caused impacts in the recovery units and to implement the recovery strategy 

described in the Recovery Plan. 

1. Establish DWMAs and implement management plans for each of the six recovery 

units 

a. Select DWMAs 

b. Delineate DWMA boundaries 

i. Reserves that are well-distributed across a species' native range will be more 

successful in preventing extinction than reserves confined to small portions 

of a species' range. 

ii. Large blocks of habitat, containing large populations of the target species, 

are superior to small blocks of habitat containing small populations. 

iii. Blocks of habitat that are close together are better than blocks far apart. 

iv. Habitat that occurs in less fragmented, contiguous blocks is preferable to 

habitat that is fragmented. 

v. Habitat patches that minimize edge to area ratios are superior to those that 

do not. 

vi. Interconnected blocks of habitat are better than isolated blocks, and 

linkages function better when the habitat within them is represented by 

protected, preferred habitat for the target species. 

vii. Blocks of habitat that are roadless or otherwise inaccessible to humans are 

better than blocks containing roads and habitat blocks easily accessible to 

humans. 

c. Secure habitat within DWMAs. 

d. Develop reserve-level management within DWMAs. 

e. Implement reserve-level management within DWMAs. 

f. Monitor desert tortoise populations within recovery units. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 9 

2. Establish environmental education programs. 

a. Develop environmental education programs. 

b. Implement environmental education programs. 

3. Initiate research necessary to monitor and guide recovery efforts. 

a. Obtain baseline data on desert tortoise densities both inside and outside of 

DWMAs. 

b. Develop a comprehensive model of desert tortoise demography throughout 

the Mojave region and within each DWMA. 

i. Initiate epidemiological studies of URTD and other diseases. 

ii. Research sources of mortality, and their representation of the total 

mortality, including human, natural predation, diminishment of required 

resources, etc. 

iii. Research recruitment and survivorship of younger age classes. 

vi. Research population structure, including the spatial scale of both genetic 

and demographic processes and the extent to which DWMAs and 

recovery units conform to natural population subdivisions. 

c. Conduct appropriately designed, long-term research on the impacts of grazing, 

road density, barriers, human-use levels, restoration, augmentation, and 

translocation on desert tortoise population dynamics. 

d. Assess the effectiveness of protective measures (e.g., DWMAs) in reducing 

anthropogenic causes of adult desert tortoise mortality and increasing 

recruitment. 

e. Collect data on spatial variability of climate and productivity of vegetation 

throughout the Mojave region and correlate this information with population 

parameters (e.g., maximum sustainable population size, see Appendix G). 

f. Conduct long-term research on the nutritional and physiological ecology of 

various age-size classes of desert tortoises throughout the Mojave region. 

g. Conduct research on reproductive behavior and physiology, focusing on 

requisites for successful reproduction.” 

1.3.2 Topics Addressed in the Scientific Evaluation 

The DTRPAC reviewed the Recovery Plan to determine which parts required 

modification based on new knowledge. As a result of this review, the topics listed in 

Table 1.1 were addressed. To conduct the topic reviews most efficaciously, the 

committee invited outside experts to help conduct the reviews. This effectively expanded 

the panel of experts to very large numbers and provided the expertise needed to conduct 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 10 

an extremely thorough review of the Recovery Plan. The expertise brought to bear on the 

topics represented the highest level of scientific expertise available. The panel included: 

• Elliott Jacobson, DVM, Tortoise disease 

• Mary Brown, Ph.D., Mycoplasma 

• David Rostal, Ph.D., Tortoise reproduction 

• David Thawley, Ph.D., Veterinary epidemiology 

• Kristin Berry, Ph.D., Desert tortoise biology 

• Barry Noon, Ph.D., Conservation biology of endangered species 

• Michael Reed, Ph.D., Conservation biology, population modeling 

• Jim Sedinger, Ph.D., Population biology 

• Chuck Peterson, Ph.D., Herpetology, reptile ecology 

• Mary Cablk, Ph.D., Remote sensing 

• Ron Marlow, Ph.D., Conservation planning 

• Ann McLuckie, M.S., Conservation planning 

• Ray Bransfield, M.S., Conservation planning 

• Bryan Manly, Ph.D., Statistics (consultant for user groups) 

• Lyman MacDonald, Ph.D., Statistics (consultant for user groups) 

USFWS also invited diverse stakeholders to send representatives as observers to the 

DTRPAC meetings. Some of those representatives contributed substantively to 

discussions or report preparation and review. Representatives and observers included: 

• Clarence Everly, Consultant for the Department of Defense 

• John Hamill, Department of Interior and Desert Managers Group 

• Rebecca Jones, California Department of Fish and Game 

• Ron Marlow, Ph.D., Clark County Habitat Conservation Plan 

• Ann McLuckie, Utah Division of Wildlife Resources 

• Karen Phillips, U.S. Geological Survey 

• Lewis Wallenmeyer, Clark County Habitat Conservation Plan 

• John Willoughby, Bureau of Land Management 

After completion of the scientific evaluation, the DTRPAC focused on the following 

major topics for the report. 

1.	 Distinct Population Segments (DPS) in relation to the Recovery Units designated 

by the original Recovery Team. Recovering the Mojave population of desert 

tortoise in all its diversity (genetic, ecological, behavioral) in relation to 

conservation challenges is basic to a recovery plan. The concept of distinct 

population segments was mentioned in the original Recovery Plan, but the distinct 

population segments were referred to as recovery units. The original Recovery 

Plan suggested that genetic resolution of those recovery units was necessary. 

Research has been conducted since the original Recovery Plan, so this area 

certainly needs revisiting by the DTRPAC. 

2. Knowledge advances since the listing of the desert tortoise occurred in the
 

following areas: (a) populations and demography, (b) impacts to habitats, (c)
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 11 

literature, and (d) recovery plan implementation. Ten years have passed since the 

original Recovery Plan, so new research and conservation planning needed to be 

reviewed to assess whether new knowledge naturally leads to old conservation 

prescriptions or whether new knowledge requires new directions in conservation 

and management prescriptions. 

3. Linking impacts, habitat, and demography to recovery (Specific threats and their 

mitigations with special attention to impacts resulting from interactions among 

individual threats; the relationships among threats and the importance of disease) 

The original Recovery Plan attempted to list specific threats and link those threats 

to specific places. For 10 years, the identified threats have been the subject of much 

debate and planning. Insofar as some evidence has been that some populations are 

still declining, it was clear that threats needed reevaluation. 

4. Monitoring, evaluating, and delisting. Monitoring provides the information 

necessary to adapt management. Nevertheless, monitoring has been elusive and 

contentious. The ability to monitor rare and cryptic species has always been 

difficult, and new approaches to monitoring have been suggested since the original 

Recovery Plan. 

5. Integrating research needs and management. Numerous research needs were 

published in the original Recovery Plan. Some of those needs have been pursued 

vigorously and others neglected. This area needed updating and evaluation in light 

of years of experience. 

It is important to note that this summary is intended to serve as a “strategic” review of 

the current Plan. Although, we have conducted several new analyses of existing data to 

understand current status better or to illustrate various points, this report primarily 

provides recommendations for consideration in revising and more effectively 

implementing the Plan. 

1.3.3 Overview of Observations from the Assessment 

What follows in this report are evaluations of the original Recovery Plan in light of 

contemporary knowledge. Immediately below, we make eight general observations that 

bear on difficulties of implementing the original Recovery Plan or of lack of attempt to 

implement the original Recovery Plan. The remainder of the report is a more detailed 

summary of conclusions from this committee. 

The desert tortoise invokes three fundamental challenges in understanding its biology 

and managing its recovery: time scale, detectability, and metapopulation structure. 

Time Scale – Desert tortoise recovery is fundamentally a demographic problem. 

Diminished populations require some period of population growth (average lambda 

> 1.0) to recover. Populations that are stable and secure may fluctuate in size in 

response to local, prevailing conditions, meaning that population growth rate 

(lambda) will vary around an overall stable mean (lambda = 1.0). However, desert 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 12 

tortoise natural history is not well suited to demographic analysis using short-term 

study. Individual tortoises grow slowly, take many years to reach sexual maturity, 

and have low reproductive rates during a long period of reproductive potential. This 

means that studies of 1-10 years, or even longer, do not necessarily yield data of 

sufficient statistical power to reveal population trends. 

Detectability – Desert tortoise behavior and morphology make them very difficult to 

detect and observe. Other than in the Upper Virgin River Recovery Unit, where 

tortoise population densities have been high, the personnel and resources necessary to 

overcome the problem of low detectability have not been appropriate to allow precise 

estimates of population size of desert tortoise within the Mojave Desert. If desert 

tortoise density declines in the Upper Virgin River, even this recovery unit may 

ultimately suffer from problems of low detectability. 

Population paradigm – The original paradigm about how tortoise populations are 

organized, and the prescriptions made within that paradigm might be wrong and 

dangerously misleading. Existing data are consistent with the possibility that tortoises 

have evolved to exist in metapopulations. The original Recovery Plan and the original 

paradigm conceived desert tortoises to be distributed in large populations that 

required large areas and large densities to recover. Metapopulation theory, on the 

other hand, conceives that tortoises are distributed in metapopulation patches 

connected with corridors that allow inefficient and asynchronous movements of 

individuals among the patches. This paradigm conceives that some habitat patches 

within tortoise range will have low population numbers or no tortoises at all, and 

others will have higher population numbers. Movement among the patches is 

necessary for persistence of the “system.” If desert tortoises evolved to exist in 

metapopulations, then long-term persistence requires addressing habitat 

fragmentation caused by highways and satellite urbanization. Indeed, mitigating 

abrogations of natural corridors among habitat patches might require active 

management of tortoise densities in habitat patches. 

Desert tortoises face simultaneous, multiple threats. Tortoises face an array of threats 

and these threats act simultaneously. This concept is central to recovery, because it 

portends profound difficulties in formulating effective recovery actions. In particular, a 

management action that alleviates one threat may not yield meaningful recovery, 

because the deleterious effects of another threat operating simultaneously suppress the 

gains sought by the original management action. In other words, one threat can 

negatively compensate for another threat when threats are simultaneous. 

Threats to desert tortoises are interactive and synergistic. The magnitude of the 

deleterious effects of one threat can be a function of another threat. For example, if 

increased mortality reduces the lifetime fecundity of a female tortoise by removing that 

female from the population before she reaches her period of maximum annual fecundity, 

then deleterious factors to other life stages (e.g., raven predation on neonatal tortoises) 

may have a greater effect on tortoise demography. Why? The negative effect on neonates 

by raven predation, for example, now affects a larger proportion of neonates in the 

population, because new neonates are not produced when adults are killed. Also, disease 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 13 

may only be an important contributor to population declines during years of drought or to 

populations stressed by invasion of exotic plants or by off-road vehicles or any number of 

other stresses. In other words, threats to tortoise populations are complex, because the 

threats interact to cause impacts rather than creating impacts just directly. 

Recommendations made in the original Recovery Plan for carefully controlled 

experiments to generate data and analyses important to monitoring and recovery 

have not been implemented. The original Recovery Plan recommended a suite of 

experimental approaches which, if carried out, could have provided key data and 

analyses needed for understanding tortoise population dynamics, especially relevant to 

management effectiveness, important in guiding current recovery. Many of these 

recommendations appear to have been largely ignored. Unfortunately, ten years of 

opportunity to collect critical data and perform critical analyses have been diminished 

or lost for a variety of reasons. 

Much of the data currently available to address tortoise recovery was originally 

collected for purposes other than tortoise recovery (hence we are doing meta-analyses 

using data of mixed quality to perform analyses that would be more efficacious using 

data from well designed studies). Perhaps for historical reasons, certain tortoise studies 

have been carried out more-or-less continuously. For example, permanent study plots 

have been used to study demography and biology of tortoises in non-random sites. 

Various forms of distance sampling have been carried out at mixed levels of magnitude 

and intensity. A more efficient approach for the future might be to design studies using 

statistical and scientific expertise expressly to obtain key data to address central 

problems. 

Mapping of even poorly collected data reveals very important apparent patterns. 

Technological advances since the first Recovery Plan have resulted in powerful analytical 

tools that bear directly on analyzing and monitoring desert tortoise populations. In 

particular, GIS analyses of data diligently derived from large, disparate data sets that 

were collected by various agencies are yielding intriguing patterns. “Mining” historical 

data and applying powerful new analyses or applying older analyses in new ways will be 

helpful in prescribing recovery actions. As demonstration of the substantial value of this 

approach, we present several new analyses from existing data. These include (i) a kernel 

analysis of spatial distribution of live and dead tortoises, (ii) a cluster analysis of spatial 

distribution of live and dead tortoises, (iii) a spatial analysis of the probability of finding 

live versus dead tortoises, (iv) a multi-dimensional, multi-scale approach to monitoring, 

(v) a threats network topology, (vi) a quantitative literature review of all available tortoise 

literature, (vii) a weighted analysis of variance (ANOVA) of tortoise density from 

permanent study plots across 24 years, and (ix) a spatial analysis of the implementation 

of recovery actions from the first Recovery Plan. 

No group is charged with managing scientific data on the desert tortoise. Currently, 

important desert tortoise data are widely scattered among state and federal agencies and 

the scientific community. Data have been gathered, organized, and stored in a multitude 

of ways. Some data have been reviewed, collated, or otherwise organized. Other data 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 14 

have not. Accessibility of tortoise data to managers, scientists, and the public is highly 

variable. In short, a great deal of important long-term data cannot be readily used. This is 

an ineffective data management strategy for species recovery. A new infrastructure for 

ensuring quality, accessibility, and analyses of data is desperately needed. These 

observations apply equally well to information on and status of recovery action 

implementation. 

Scientific information important for recovery is entirely ad hoc. In general, new 

knowledge acquisition seems frequently to be directed at land-management agency 

mandates vis-à-vis management decisions. Thus, the limited supply of tortoise biologists 

is frequently absorbed into contracts for local issues (e.g., DOD needs for data to comply 

with NEPA). However, there is a real need to pursue the research agenda outlined in the 

Recovery Plan of 1994. Some HCPs have scientific oversight and direction, but there is 

essentially no coordination of the scientific enterprise conducted in different management 

units in a way to get more than accidental accumulation of necessary knowledge 

important for recovery of the desert tortoise and its ecosystems. 
 

 

 

 

DTRPAC Report page 15 

“Scientific principles and laws do not lie on the surface of nature. 

They are hidden, and must be wrested from nature by an active and 

elaborate technique of inquiry.” 

John Dewey, Reconstruction in Philosophy. (1920) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 16 

2. Quantitative Literature Review: the state of knowledge 

The most recent annotated bibliography (Grover and DeFalco 1995) published on desert 

tortoises (Gopherus agassizii) identified trends in research prior to 1991 and mentioned 

gaps in knowledge that influenced research prescriptions in the Desert Tortoise Recovery 

Plan (1994). The original Recovery Team made several recommendations for research 

necessary to fill information gaps important to the recovery of desert tortoise populations. 

These items included: 

•	 long-term demography (particularly recruitment and survivorship of 

younger age classes, sources of mortality, and epidemiology), 

•	 population structure (spatial scale of genetics and demography), 

•	 long-term analysis of impacts, 

•	 effectiveness of protective measures, 

•	 spatial variation in climate and vegetation, 

•	 nutritional and physiological ecology, 

•	 reproductive behavior and physiology, and 

•	 restoration, augmentation, and translocation. 

The Recovery Plan highlighted the need for long-term studies, which are necessary to 

capture temporal variation and ecologically relevant trends. In addition, the Recovery 

Plan prescribed research on non-reproductive age classes. Few studies have been 

conducted on survivorship or recruitment rates in young Gopherus tortoises due to their 

cryptic morphology and behavior. 

A recent literature review employed a quantitative approach to 1) compare the foci of 

research before and after the publication of the Recovery Plan, and 2) identify present 

gaps in desert tortoise knowledge (Hagerty, Sandmeier, and Tracy in prep.). Available 

desert tortoise literature, obtained by the Clark County Multi-Species Habitat 

Conservation Plan database (1378 total papers), was classified by age class, literature 

type, and one or more research categories (Table 2.1). Contingency table analyses were 

performed to determine differences among the types of research before and after the 

Recovery Plan was published. 

TABLE 2.1 Research categories used in quantitative literature review. 

Research Category Relevant topics included in each category 

Ecology life history characteristics, demography, ecology 

Autecology physiology, behavior, morphology 

Conservation threats, management, effectiveness of conservation efforts 

Systematics molecular and morphological systematics 

Disease pathology, veterinary procedures, pharmacology 

History natural history, evolution, fossil record, paleoecology 

Bibliographies literature reviews and annotated bibliographies 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report	 page 17 

Academic researchers and agency biologists studying desert tortoises communicate their 

results in professional journals, government documents, Desert Tortoise Council (DTC) 

symposia, and other professional society meetings. Overall, 22% of catalogued desert 

tortoise literature was published in professional journals. After the Recovery Plan, the 

percentage of literature published in professional journals increased, while the percentage 

of gray literature decreased (Fig. 2.1). The latter result may be an artifact of the 

availability of government reports, however there was an increased trend for researchers 

to publish their results in professional journals. 

• DTC symposia 60 . Gray 

52.3 D Professional Journal 

50 

Fig. 2.1 Distribution 

of all literature types 

0 40 before and after the 

publication of the Vl 31.9 31.0 c Recovery Plan.	 (]) 30 

E 

U 

0 19.0 

16.7 

10 

0 

Pre Recovery Plan Post Recovery Plan 

Further, professional journal documents were dominated by autecological research, while 

other documents contained mainly conservation and ecological studies (χ2 = 154.115, df 

= 6, p<0.0001) (Fig. 2.2). This result may suggest a dichotomy of research being done 

within agencies and academia, respectively. Tortoise conservation studies consisted 

mainly of descriptions of threats to tortoises and how these threats are being managed. 

Population density and habitat studies, which are typically performed by government 

agencies, are also 

included in the gray 50 

literature category. • Other 

40 D Professional journals 

- Ql 

E 30 

0 

20 Fig. 2.2 Distribution 

of literature among 

the major research 10 

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DTRPAC Report page 18 

The Recovery Plan prescriptions for future research did appear to have a limited impact 

on desert tortoise research. After the Recovery Plan was published, more documents in 

professional journals focused on ecology and implementation of conservation, with a 

continued emphasis on autecology (χ2 = 25.88, df = 5, p<0.0001) (Fig. 2.3). A change in 

the distribution of gray literature corresponding to the publication of the Recovery Plan 

was marginally significant (χ2 = 13.49, df = 7, p<0.06). 

60 

• Pre recovery plan 

50 • Recovery plan prescriptions 

• Post recovery plan 

Ul 40 C 

(]) 

E 30 U 

o 

o 

20 C 

o 10 

o
 

Fig. 2.3 Distribution of professional journal literature in the research categories before and after 

the publication of the Recovery Plan. The proportion of Recovery Plan prescriptions associated 

with each major research topic are included for comparison with the distribution of professional 

journal literature. 

Since the Recovery Plan was published, there has been considerable research on some 

aspects of tortoise biology, in particular nutritional ecology, reproductive physiology, and 

the effects of several specific impacts on tortoise populations. However, very little 

research has been published on other recommended topics, such as long-term 

demography, the effectiveness of recovery actions, translocation (but see below), and 

climatic and vegetative variability. Virtually no research has been conducted or published 

on other important topics, such as epidemiology and many long-term impacts on tortoise 

populations. Some additional areas that have been the topic of active research yet were 

not identified in the Recovery Plan prescriptions, include disease and health status, 

habitat conditions, and fire ecology. In the case of disease, recent studies have focused on 

pathology instead of the focus on epidemiology that was prescribed by the Recovery 

Plan. These new areas of research are important and may need to be continued at some 

level, however not in place of the recovery plan recommendations. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 19 

Research prescriptions in the Recovery Plan also emphasized the need for research on 

immature age classes within the categories of ecology and autecology. In particular, the 

Recovery Plan recommended research on recruitment and survival rates of nonreproductive age classes and their nutritional and physiological ecology. After the 

Recovery Plan, an increase in the percentage of studies on immature age classes 

corresponded to general prescriptions in these areas, suggesting that the Recovery Plan 

prescriptions were followed (Fig. 2.4). However, no studies included in the analyses were 

conducted that focus specifically on recruitment and survival of young age classes. A 

quantifiable deficiency in knowledge of the ecology of non-reproductive tortoises 

remains a missing link to understanding desert tortoise population structure and 

dynamics. Literature on early life stages is under represented in all age-relevant 

categories, with only 5% of documents focusing exclusively on immature life stages. 

Fig. 2.4. Percent of 

early life stage 

documents in 

professional journals 

that focused on ecology 

and autecology. 

0

5

10

15

20

Ecology Autecology

Early life stage journal documents (%) 

Pre recovery plan

Post recovery plan

Implementation of effective management strategies to recover the Mojave population of 

the desert tortoise requires an accurate characterization of population structure, threats to 

population persistence, and the effectiveness of protective measures. Determining life 

history characteristics, such as age-specific survivorship, is critical and requires large 

sample sizes and long study periods. In addition, hypothesis-based experiments on the 

long-term effects of recovery actions are also necessary. These gaps in knowledge were 

identified in the Recovery Plan, have not been addressed, and remain important 

prescriptions for research. 

2.1 Translocation 

There were many topics for research recommended by the Recovery Plan that have been 

the subject of active research and publication over the last decade. Translocation of desert 

tortoises has recently come to the forefront because of the impending expansion of Ft. 

Irwin in the West Mojave and the continued urbanization of the Las Vegas Valley. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 20 

Because no peer reviewed papers on recent research on translocation of desert tortoises 

have been published yet on this topic, and at the request from several reviewers of the 

draft DTRPAC report, we include a brief synopsis of recent translocation studies here. 

Translocation was regarded by the Recovery Team as both a threat and as a potential 

conservation measure to mitigate take of tortoises, to augment depleted populations, and 

re-colonize extirpated populations (USFWS 1994). 

Prior to the publication of the Recovery Plan, few studies of the effects of translocation 

on desert tortoises had been conducted, and no study was extensive enough to evaluate 

translocation as a conservation tool for this species. The results of previous efforts are 

generally reported in government documents (Berry 1974, Berry 1975, Berry 1976), as 

anecdotes (e.g., see Cook et al. 1978), or unpublished accounts (Crooker 1971, Bryan and 

West 1972, McCawley and Sheridan 1972, Cook et al. 1978, Corn 1991, SAIC 1993). 

Because of the dearth of literature on translocation of desert tortoise, the potential for 

success of translocation in this species had not previously been thoroughly examined, and 

as a result translocation as a tool for conservation has remained controversial (Berry 

1986, Dodd and Seigel 1991, USFWS 1994). Nevertheless, the Recovery Plan recognized 

the potential of the technique for augmenting populations with tortoises taken outside of 

DWMAs, and the plan recommended that more thorough research on translocation be 

conducted. 

The definition of success of translocating a species is typically taken to be the ability of 

the translocated or augmented population to become self-sustaining in the long-term 

(Griffith et al. 1989, Dodd and Seigel 1991, Fisher and Lindenmayer 2000). Success, 

however, may be measured at several temporal scales, which may be important 

precursors to judging the long-term success of a translocation program (Tasse 1989, 

Dickinson and Fa 2000, Fisher and Lindenmayer 2000). For example, there may be some 

level of initial mortality above which a translocation study is judged to be unsuccessful 

(Platenberg and Griffiths 1999). In addition, other goals may be used to judge success in 

the short-term, such as the colonization of a particular site (Lohoefener and Lohmeier 

1986), the social integration of translocated animals into the existing population (Berry 

1986, Reinert 1991), and the ability of the animals to find mates and reproduce (Berry 

1986, Pedrono and Sarovy 2000). 

Extensive translocation studies have been conducted in Nevada and Utah that quantified 

survivorship, growth, pre-release conditions, reproduction, microhabitat use, and 

movements (one index of behavior, which can be especially important to land-management 

decisions) of translocated and resident animals in six locations spanning elevations from 

500 to 1500 meters (Field 1999, Field et al. 2003, Nussear 2004, Nussear et al. in prep.). 

These projects included tracking more than 300 tortoises (resident and translocated) for 

several years. Some tortoises were translocated to habitats with vegetation not normally 

associated with desert tortoise populations (in order to assess the mechanistic determinants 

of geographic range in tortoises). Some tortoises were translocated into areas cleared of any 

resident tortoises and some into areas containing populations with resident tortoises (to 

assess the effect of translocation both on the animals translocated and on the tortoises 

already present in the habitat). Some translocated tortoises were formerly pet tortoises 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 21 

moved from urban settings to wild locations, and some tortoises were wild tortoises 

translocated from one wild location to another (to assess the potential to repatriate tortoises 

that had been removed from the wild for long periods prior to their release into the wild). 

Tortoises were translocated into the wild in three seasons of the year (in order to assess the 

extent to which season predicts success in translocation) (Field et al. 2003). Only tortoises 

certified as not having an immune response to Mycoplasma agassizii were translocated, and 

all areas studied had populations with resident tortoises having immune responses to 

Mycoplasma agassizii. 

In general, translocated tortoises had the same survivorship and reproductive success as 

resident animals. This result was the same in drought years and in El Niño years. 

Tortoises moved to atypical habitat generally moved until they reached habitat more 

commonly associated with desert tortoise presence. Even when desert tortoises were 

translocated into typical tortoise habitat, they tended to move greater distances in the first 

year after translocation, but their movements in the second year were indistinguishable 

from resident tortoises. Knowing how translocated tortoises displace after translocation is 

necessary in order to plan for any needed fencing of managed areas, or to determine the 

size of translocation release areas. Important in any of these measures of success are 

comparisons between translocated and resident animals in the area. This allows the effect 

of translocation to be statistically separated from factors normally expected in resident 

populations in particular areas. 

The results of these translocation studies indicate a very optimistic potential for success in 

translocating individual tortoises in a wide variety of circumstances. The mortality 

documented in previous translocation experiments on desert tortoises was largely because 

animals were translocated during the most stressful thermal environments of the year (e.g., 

when the weather is stressfully hot). The results of these recent studies suggest that both 

wild and pet tortoises can thrive and reproduce after translocation. These results also 

suggest that it is necessary to plan for translocated tortoises to move great distances in the 

first year after translocation. It is especially important to recognize that tortoises cannot be 

moved to unnatural habitats and expected that the tortoises will remain in those habitats 

(unless confined by fencing). Indeed, the fact that tortoises do not accept being 

translocated to atypical habitats suggests that some needs for the tortoises are only met in 

more typical habitat. 

Knowing that it is possible to translocate tortoises successfully is important in 

conservation planning. Translocation should not be substituted for habitat protection as a 

conservation measure, but translocation can be important as a means to supplement 

existing populations that may have declined abnormally (e.g., in regions formerly heavily 

used by recreationists or by construction projects such as gas pipelines, etc.). 

Translocation can be used to create new populations in areas where populations are 

known to have existed in the historic past, however, creating new populations always 

should be regarded as experiments until the reasons why historic populations are absent 

are known and logic and science suggests that a new population can thrive in the area. 

Future translocations could be used as an experimental tool to assess the effects of certain 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 22 

management prescriptions (e.g., fencing, ablation of cattle grazing, reducing the density 

of unpaved roads, etc.). 

The remaining cautions, vis-à-vis translocation, are that the process of translocation may 

disrupt community interactions and that the impacts of those alterations might be difficult 

to predict. In other words, we know that individual and population responses to 

translocation are generally benign and suggest that translocation can be an effective tool 

in the conservation arsenal for a land manager, but we do not yet know all that is needed 

about community interactions potentially modified by translocation. Thus, translocating 

tortoises into an area containing, for example, a strain of pathogen that is foreign to the 

translocated tortoises may alter the balance between host-pathogen relationships in ways 

that might not be easily predictable and potentially dangerous. Thus, additional research 

is needed to increase our understanding of host-pathogen relationships and other 

community-level interactions (e.g., competition, predator-prey, pathogen, etc.) to support 

carefully considered translocation programs. 

Translocation Recommendations 

• Translocation should not be substituted for habitat protection as a conservation measure 

but rather as a last resort to mitigate the take of displaced animals. 

• Translocation can be used to supplement or augment depleted populations, but all 

translocations should be conducted as an experiment with research to ensure that the 

threats originally causing the depletion have been removed. 

• Translocation can be used as an experimental tool to assess the effects of certain 

management prescriptions, or to assess the presence of threats that affect the 

population. 

• Translocated animals are likely to have large movements in the first two years. If 

tortoises are translocated near roads with high traffic volume, these roads should be 

fenced. In addition, if the goals of the translocation project are to retain animals in a 

relatively small area, then experimental fencing should be used for a few years as given 

in the translocation guidelines (Recovery Plan Appendix B). 

There are seven guidelines for translocation given in the Recovery Plan (see appendix B). 

These guidelines, while well intentioned have little chance of all being applied 

simultaneously. The use of these guidelines requires the knowledge of measures that are 

currently unavailable, or have poor precision for desert tortoises such as historic densities 

and carrying capacity. We recommend that these guidelines be revisited in light of recent 

information on translocation in desert tortoises, and in light of the consideration of 

realistic management constraints and conditions where translocations are likely to occur. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 23 

A summary of each guideline with commentary on its applicability is given below. 

Guideline 1 “Experimental translocations should be done outside experimental 

management zones. No desert tortoises should be introduced into DWMAs—at least 

until relocation is much better understood.” 

• Unless experimental management zones, or other areas within DWMAs can be used 

for translocation, translocated tortoises cannot be assured protection into the future. 

This is particularly important when long-term conservation of translocated 

populations comes into conflict with changes to the environment by humans such as 

urbanization or flood control projects. 

Guideline 2 “All translocations should occur in good habitat where the desert tortoise 

population is known to be substantially depleted from its former level of abundance. 

Translocation of reproductively competent adults into depopulated areas can have 

beneficial effects on population growth. Before population growth can occur, however, 

individuals must establish home ranges and enter into any existing social structure. 

Desert tortoises should be periodically evaluated against a defined health profile 

(proportional weight/size, fecal scans, and blood panels).” 

• These criteria have two possible limitations. First it tacitly assumes an explicit 

knowledge of the former abundance of animals (this is usually unavailable for most 

of the listed range of the tortoise). Second, if this guideline is strictly followed, then 

tortoises displaced from an area could be translocated to areas where tortoises could 

have different population composition. 

Guideline 3 “Areas into which desert tortoises are to be relocated should be surrounded 

by a desert tortoise-proof fence or similar barrier. The fence will contain the desert 

tortoises while they are establishing home ranges and a social structure. If the area is not 

fenced, past experience suggests that most animals will simply wander away from the 

introduction site and eventually die. (Fencing is not cheap; estimates range from $2.50 to 

$5.00 per linear foot). Once animals are established some or all of the fencing can be 

removed and probably reused.” 

• The final sentence of this guideline has not been scientifically evaluated. The goals of 

each proposed translocation should be considered individually. If one of the goals of a 

translocation program is to populate a specific area, then fencing the area may be 

desirable (but should be tested scientifically). If however the goal is to move tortoises 

to a non-specific area, such as a large valley, then fencing may be impractical, and 

un-necessary. 

Guideline 4 “The best translocations into empty habitat involve desert tortoises in all age 

classes, in the proportions in which they occur in a stable population. Such translocations 

may not always be possible, since young desert tortoises are chronically underrepresented 

in samples, often due to observer sampling error, and may now actually be 

underrepresented in most populations due to poor recruitment and juvenile survivorship 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 24 

during the last several years. Desert tortoises smaller than the 7-year age-size class are 

particularly vulnerable to predation and may be a poor investment for translocation, 

unless predator exclusion (fencing, for example) is incorporated into such endeavors. 

Mature females would probably be the best sex/age class to introduce into below carrying 

capacity extant populations because of their high reproductive value (low potential 

mortality, high potential fecundity for many years).” 

• This guideline seems to provide different recommendations. First it recommends that 

the best case would be to translocate all size classes, but it also suggests that juveniles 

may be a poor investment. Fencing of translocated tortoises is recommended as a 

protection from predation but this has not been confirmed. It is unlikely that most 

predators would be excluded using fencing, and juveniles have been reported to suffer 

from avian predation from ravens and other large birds. The concept of carrying 

capacity may not be appropriate for desert tortoise, and it would be extremely 

difficult to measure. It is difficult to reconcile the reportedly high tortoise densities 

prior to the 1980s with the concept of carrying capacity. 

Guideline 5 “The number of desert tortoises introduced should not exceed the predecline density (if known). If the pre-decline density is not known, introductions should 

not exceed 100 adults or 200 animals of all age classes per square mile in category 1 

habitat (Bureau of Land Management designation for management of desert tortoise 

habitat) unless there is good reason to believe that the habitat is capable of supporting 

higher densities. Post-introduction mortalities might be compensated by subsequent 

introductions if ecological circumstances warrant this action.” 

• Caution should be used if persistent post-introduction mortality continues over long 

periods of time. This may signal that threats originally causing are still present. If 

threats persist, the situation should be considered an opportunity to more about the 

importance of threats. 

Guideline 6 “All potential translocatees should be medically evaluated in terms of 

general health and indications of disease, using the latest available technology, before 

they are moved. All translocatees should be genotyped unless the desert tortoises are to 

be moved only very short distances or between populations that are clearly “genetically” 

homogeneous. All translocated animals should be permanently marked, and most should 

be fitted with radio transmitters so that their subsequent movements can be closely 

tracked.” 

• The application of radio transmitters should depend on the experimental design of the 

translocation project, and the questions that are to be asked of the translocated 

animals. If, for example, the study is to be used for the sole purpose of measuring 

long-term population genetics, then the costs and the intensive labor required to 

monitor all of the translocated animals monthly are probably not warranted. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 25 

• All translocations should be guided by a genetic management plan. Such a plan will 

help to ensure that translocated individuals are moved conservatively among 

populations that are genetically similar. 

Guideline 7 “If desert tortoises are to be moved into an area that already supports a 

population—even one that is well below carrying capacity—the recipient population 

should be monitored for at least 2 years prior to the introduction. Necessary data include 

the density and age structure of the recipient population, home ranges of resident desert 

tortoises, and general ecological conditions of the habitat. 

Areas along paved highways can serve as good translocation sites, if properly fenced. 

Many such areas support good habitats, but vehicle-caused mortalities and/or collecting 

have substantially reduced or totally extirpated adjacent desert tortoise populations. Any 

translocation sites should be isolated by a desert tortoise barrier fence or similar barrier 

next to the highway or road. The purpose of fencing the highway is obvious—to keep 

translocated animals from being crushed by vehicles on the road. However, fencing the 

other sides of the translocation area is critical for establishment. If a fenced area or strip 

of habitat approximately 0.125 to 0.25 mile wide is established along highways, some 

translocatees should establish home ranges and a social structure within this strip. When 

the inside fence is removed, the translocated desert tortoises and those from the extant 

population farther away from the road will eventually expand their home ranges into the 

remaining low-density areas. A second reason for inside fencing is to prevent any 

diseased, but asymptomatic, desert tortoises from infecting nearby, healthy populations. 

In the event that disease is an issue and a resident population is present nearby, double 

inside fencing should be considered." 

• Guideline 7 appears to address two topics. The first topic (monitoring residents) 

should be the focus of an experiment and not a criterion for all. As with guideline 6, 

the conditions of this monitoring should be guided by the experimental design for 

each specific translocation project. 

The second part of this guideline seems overly specific and speculative. While it is 

true that habitat reclaimed by fencing of major highways could provide receptive 

habitat, it is unknown if the threats associated with traffic are alleviated by fencing. 

For example, are tortoises affected by air pollution from traffic, or are raven 

populations artificially elevated near highways due to the presence of trash, and other 

animals killed on the road? Until these and other questions are answered the 

conditions of this guideline may constitute a sound research suggestion not a routine 

guideline. 
 

 

 

DTRPAC Report page 26 

“If Einstein had to go through all that is necessary to do science 

today, who knows what ‘e’ would equal.” 

President Josiah Bartlett, West Wing. (2003) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 27 

3. Distinct Population Segments 

3.1 Definition and intentions of Distinct Population Segments 

Given the Endangered Species Act’s definition of “species” to include “any distinct 

population segment of any species of vertebrate fish or wildlife which interbreeds when 

mature,” the 1994 Recovery Plan identified six recovery units of the Mojave population 

of the desert tortoise. These recovery units were identified under the concept of 

evolutionary significant units (ESU), as described by Waples (1991) and Ryder (1986), 

but a specific policy on how distinct population segments (DPS) would be defined and 

applied would only be formally proposed six months after the publication of the Plan 

(USFWS and National Oceanic and Atmospheric Administration 1994). A final policy 

was published in 1996 (USFWS and National Marine Fisheries Service [NFMS] 1996). 

Two issues arise from the identification of recovery units as DPSs or ESUs prior to a 

final DPS policy. First, the current policy identifies specific criteria that must be met in 

defining a DPS. The current recovery units need to be evaluated in light of these criteria. 

Second, the Recovery Plan stated that each recovery unit, considered to be separate 

DPSs, may be individually delisted upon meeting the recovery criteria listed in the Plan. 

However, DPSs must be designated through a formal listing (or delisting) process. 

Because the tortoise was listed as a single population throughout the Mojave Desert 

(USFWS 1990), recovery units may not now be individually delisted without formal DPS 

designation. This chapter addresses these two issues. 

3.1.1 Background 

USFWS and NFMS (1996) defined DPSs based upon three elements for recognizing 

individual sub-populations of a single species for differential protection under the 

Endangered Species Act (ESA): 

(1) discreteness of the population segment in relation to the remainder of the species to 

which it belongs, 

(2) significance of the DPS relative to the species to which it belongs, and 

(3) conservation status of the population in relation to the ESA standard for listing. 

The criterion of discreteness must be satisfied as prerequisite to recognizing both the 

physical existence (= geographical reality) and the biological/conservation significance 

(criteria #2 and 3) of a proposed DPS. The Congressional intent of the DPS provision of 

the ESA was that “the interests of conserving genetic diversity would not be well served 

by efforts directed at either well-defined but insignificant units or entities believed to be 

significant but around which boundaries cannot be recognized” (U.S. Court of Appeals, 

Ninth Circuit 2003). 

DPSs and ESUs were until 1994 largely equated with one another and are still treated as 

synonyms by NMFS. Since 1994, ESU has become much more narrowly defined in the 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 28 

discipline of comparative biology, where it is most often used. Typically, ESU refers to 

conspecific populations that are distinguishable by substantial and mutually 

monophyletic differences in their mitochondrial or nuclear DNA sequences (Moritz 1994, 

2002; see also its use by Avise 2000), differences sufficient to reflect past geographical 

isolation by “vicariance events” (Berry et al. 2002). Currently only NMFS still utilizes a 

narrow, genetic definition to designate DPS status, most prominently for salmonid fish 

(Pennock and Dimmick 1997) and fresh water mussels (Nammack 1998). For most taxa, 

both Services apply the much broader definition of DPS, provided above, for reasons 

reviewed by Pennock and Dimmick (1997). In terms of legal policy, agency and court 

precedence, and practicality, it is the broader definition of DPS that is particularly 

appropriate for defining subdivisions of the desert tortoise (Berry et al. 2002). Regardless 

of the historical divergence of ESU from the broader DPS, these concepts share a 

common objective of conserving genetic diversity and divergent evolutionary trajectories, 

whether these trajectories are demonstrated specifically through DNA (ESU sensu 

stricto) or inferred through both direct and indirect evidence (DPS sensu lato). In some 

sense, these units replace the poorly defined and highly subjective anachronism of 

subspecies (Frost and Hillis 1990, Frost et al. 1992). Influenced in part by the traditional 

use of morphology, and more recently genetics, in defining subspecies, USFWS and 

NMFS cite the use of these lines of evidence as appropriate parameters by which to 

define DPSs. However, these criteria were not to exclude other important information. 

The expressed Congressional intent was that differential protection of DPSs be applied 

“sparingly” to avoid important losses of genetic diversity. While genetics is generally 

recognized as the primary determinant of distinction, the definition and precedent use of 

DPSs for the ESA allows genetic, and by extension, evolutionary significance, to be 

inferred from other parameters. Even compelling differences in conservation status among 

subdivisions of a species may be invoked both to define and justify a DPS (e.g., 

differential conservation across international boundaries). 

Difficulties in the application of the term DPS largely hinge on the following questions. 

(1) What degree of genetic/evolutionary distinctness, either demonstrated or inferred, 

justifies DPS designation for a specific spatial entity as “discrete”? 

(2) What degree of ecological or behavioral differentiation, conservation status, and/or 

internal homogeneity would make a DPS significant? 

(3) To what extent do our existing databases for the desert tortoise subpopulations north 

and west of the Colorado River make it possible to discern distinctness and 

document both ecological significance and conservation status? 

3.1.2 Discreteness 

Resolution of the issue of discreteness is the first requirement in the justification of a DPS. 

A population may be considered discrete if 1) it is markedly separated from other 

populations of the same taxon as a consequence of physical, physiological, ecological, or 

behavioral factors, which may be evidenced by genetics or morphology, or 2) it is 

delimited by international boundaries within which significant differences in control of 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 29 

exploitation, management of habitat, conservation status, or regulatory mechanisms exist 

(USFWS and NFMS 1996). Determining discreteness is intrinsically challenging, because 

it involves diverse criteria, subjective judgments about degrees of distinctness, and a 

perspective from comparative biology that places discreteness in context of its particular 

taxonomic unit. The difficulty of determining distinctness has been exacerbated by the 

historical commingling of terms like DPS, ESU, and Recovery Unit as in the 1994 

Recovery Plan (Pennock and Dimmick 1997, Berry et al. 2002). Furthermore only core 

areas of most DPSs are resolved by current databases; discrete borders of DPSs are less 

easily delineated (see McLuckie et al. (1999) for illustration of the complexity of even 

using the Colorado River as boundary). 

Discreteness traditionally has referred to reproductive isolation from other conspecific 

population units (Nammack 1998). Yet, by definition, DPS units are recognized as 

conspecific, so reproductive isolation may be less than complete reproductive 

incompatibility. Reproductive isolation may be based on geographical, ecological, 

physiological, or behavioral difference(s), and quantitative genetics or morphology may 

be used as evidence of such difference(s). Although quantitative genetics is an arbiter to 

assist determination of discreteness (e.g., Spidle et al. 2003), other evidence of 

reproductive isolation may be considered (e.g., Haig et al. 2002), especially in the context 

of current policy definition of DPS. In the case of the desert tortoise, quantitative 

biochemical/genetic information is available (Rainboth et al. 1989, Britten et al. 1997, 

Lamb and Lydehard 1994, and McLuckie et al. 1999), and it should be used as the 

primary database. 

A second obvious source of comparative data is morphology. Morphological/meristic 

differences are traditional tools of taxonomists. Indeed, virtually all chelonian species and 

subspecies have been defined almost exclusively in terms of morphology. Such evidence 

may be misleading, especially at the subspecies level, particularly given the susceptibility of 

tortoise shell ontogeny to environmental factors (e.g., diet, seasonality, temperature regimes, 

etc., see Berry et al. 2002 and Jackson et al. 1976) that are not heritable. If, however, 

reproductive isolation is not detected because of incompleteness of genetic or morphological 

sampling, recentness of the isolating mechanism, anthropogenic translocations of 

individuals, or other reasons, then a case may be made for (1) additional quantitative genetic 

sampling in specific locations and/or (2) recognition of a DPS based on other criteria. 

However, such designations would be difficult justify, because they would require extensive 

knowledge of organism-environment interactions (actually it might well require more 

knowledge than we are able to obtain within the foreseeable future). 

The more generous definition in current use by USFWS (Pennock and Dimmick 1997) 

conveys “discreteness” to DPS units using criteria that would not justify discreteness in a 

literal evolutionary sense, but which are very relevant both to the conservation of species 

like the desert tortoise, in particular. Examples include recognizing populations 

fragmented or isolated by international boundaries and those demonstrating marked 

physical, physiological, ecological, or behavioral differences. Behavioral and ecological 

differences among populations may be used both to infer genetic/reproductive isolation 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 30 

and to establish the ecological significance of a proposed DPS, but the two concepts are 

so intertwined that they will be discussed together in the following section. 

In most cases, only DPS core areas may be defined but their boundaries are rarely 

discerned. Both spatially inadequate and genetically incomplete sampling precludes the 

resolution of such boundaries. This task needs to be addressed for many reasons, but 

especially when new DPS units are being subdivided from old, or when a pre-existing 

unit is subsumed into another. 

3.1.3 Significance 

Ecological and behavioral criteria need to be considered under the current definition of 

DPS. Genetic evidence generally comes from small samples of the genome of the 

species, and phenotypic differences in ecology and behavior also can provide evidence of 

genetic distinctness. Ecological differences help establish the “significance” of 

differences among populations. Thus, if a sub-population already has been demonstrated 

to be genetically “distinct,” when should it be considered ecologically “significant”? The 

USFWS and NFMS (1996) determine the significance of a discrete population by 

considering the following non-exclusive factors. 

(a) Persistence of the discrete population segment in an ecological setting unique or
 

unusual for the taxon.
 

(b) Evidence that loss of the discrete population segment would result in a gap in the
 

range of a taxon.
 

(c) Evidence that the discrete population segment represents the only surviving natural 

occurrence of a taxon that may be more abundant elsewhere as an introduced 

population outside its historic range. 

(d) Evidence that the discrete population segment differs markedly from other
 

populations of the species in its genetic characteristics.
 

A “significant” subdivision refers to evolutionary legacy. Thus, a DPS should either 

represent an independent component in the evolution of the species (Nammack 1998) or 

an irreplaceable component in the conservation of the species in its full diversity 

(Pennock and Dimmick 1997). 

What would be convincing ecological evidence that a DPS represents an independent 

evolutionary component or irreplaceable component in the conservation of a species? We 

propose that an important piece of evidence would be a difference in life history trait(s) 

such that individuals in the putative DPS may be affected differently from individuals 

elsewhere when faced with the same threat(s) to population persistence. Unfortunately, this 

criterion is not independent of existing threat(s) because data prior to the existence of 

threats are lacking. Thus, a more tractable criterion might be difference(s) in life history 

trait(s) such that individuals in the putative DPS may be affected differently from 

individuals elsewhere when faced with new threat(s). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 31 

Life history traits are adaptations influencing survivorship and reproduction. These 

adaptations include age and size at reproductive maturity, length of reproductive life, clutch 

size and size of hatchlings, number of clutches per year, sex ratios, mating systems and 

sperm storage, etc. Differences in these traits are the result of selection in different 

environments. Thus, life-history theory predicts that when stochastic selective pressures 

differentially select against young tortoises, then there should be life-history adaptations to 

increase the length of reproductive life of adults. Alternatively, when stochastic selective 

pressures differentially select against adult tortoises, then there should life-history 

adaptations to produce larger clutches of eggs. When there are differences in life histories 

among populations, and when there are threats to a sensitive species, then the adaptations 

to environments can be inadequately matched to environments. Thus, the life-history traits 

most likely to contribute to the evolutionary independence of a sub-population are those 

that reflect the adaptation to place and contribute to ecological success. 

Sometimes an understanding of these important life-history traits can be captured with a 

small number of population-level attributes. For example, age-specific mortality rates, 

clutch size and number of clutches each year, bodily growth rate, body size at 

reproductive maturity, and primary and secondary sex ratios (e.g., Tanner 1978). More 

recently, ecologists have been able to infer much of importance in ecological attributes 

contributing to the evolutionary independence of a sub-population from genetics, 

dispersion and dispersal, and size and arrangement of habitat patches (see Krebs 1994 and 

Ricklefs and Miller 1999). A fundamental list of population-level attributes for monitoring 

species recovery would be very similar and include population size, demographic rates, 

mode of reproduction, and age at sexual maturity (e.g., Hoekstra et al. 2002). 

Even though the information needed to understand the basic ecology of a species is 

reasonably clear, lack of knowledge about the basic biology of rare species often plagues 

recovery plans (Tear et al. 1993, Schemske et al. 1994, Crouse et al. 2002). While such 

information is largely lacking or inadequate to characterize existing DPS units within the 

threatened Mojave tortoise population, a robust set of life-history characteristics, both 

stable and pronounced in their differences, distinguish the Mojave desert tortoise from its 

counterpart in the Sonoran desert. The degree of isolation between populations east and 

west of the Colorado River correlates well with parallel genetic data used to separate the 

two currently conspecific groups of populations (Lamb and McLuckie 2002). For this 

reason, we do not entirely discount the eventual discovery of similar, if less pronounced, 

life history differences within Mojave tortoise populations. 

With the list of important population-level attributes in hand, we are in a position to 

develop a hierarchy of ecological evidence that can be used to determine if a putative 

DPS actually represents an independent evolutionary component. A suggested list 

follows, arranged from the most- to the least-convincing evidence. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 32 

Direct Life-History Measures: 

(a) survivorship 

(b) fecundity (clutch size and frequency) 

(c) dispersion rates 

(d) seasonality of mating and hormonal cycles 

(e) size at reproductive maturity 

(f) bodily growth rate and sex ratio 

Ecological/Demographic Indicators: 

(a) age distribution/size distribution 

(b) population growth rate 

(c) sex ratio/mating system 

(d) age at sexual maturity/generation time 

(e) reproductive value (per age class) 

(d) body size/number of clutches/timing of reproduction 

(e) population density 

Possible Environmental Correlates: 

(a) vegetation – both for diet/shelter 

(b) rainfall 

(c) soils 

(d) burrow size, shape, and orientation; hibernacula 

(e) other habitat variables (slope, proximity to ephemeral water channels, etc.) 

At least three caveats accompany this list. (1) Short- and long-term variability in any of 

these measures, indicators, or correlates could be important in concert with each other or 

independently. (2) It is not likely that direct demographic measures will be available from 

throughout a putative DPS, so establishing boundaries may require use of indicators and 

correlates, once their relationships to direct demographic measures have been established. 

Likewise, the establishment of long-term (10-20 year) study sites could verify correlates 

(they could even serve to ”ground truth” remote sensing inferences). (3) Standard 

statistical techniques can be used to establish significant differences in any of these 

measures, indicators, or correlates between locations. 

3.1.4 Conservation Status 

The conservation status of the species, as measured by the five listing factors identified in 

Section 4 of the ESA, provides final justification for its legal protection as a discrete and 

significant entity (i.e., DPS). Particularly germane to desert tortoise populations, so many 

of which are differentially affected by upper respiratory tract disease and other health 

threats, is the fact that health status should be used to recognize an individual population 

as discrete and significant (Pennock and Dimmick 1997). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 33 

The emphasis on threat(s) is further re-enforced by recent evaluations of recovery plans. 

These evaluations have led to several recommendations for improving the use of science 

in recovery plans (Clark et al. 2002). These recommendations include: (1) make threats a 

primary focus, (2) specify monitoring tasks for species status and recovery tasks, (3) 

ensure that species status-trend data are current, quantitative, and documented. 

3.2 DPSs of the Desert Tortoise 

3.2.1 Reappraisal of 1994 Recovery Units 

The 1994 Recovery Plan identified six Recovery Units (Fig. 3.1): Northern Colorado, 

Eastern Colorado, Upper Virgin River, Eastern Mojave, Northeastern Mojave, and 

Western Mojave. The current Recovery Units represent appropriate hypotheses of 

discreteness. Certainly all of the Desert Wildlife Management Areas (DWMAs) within 

these recovery units are valuable to the conservation of the desert tortoise. However, each 

of the Recovery Units must be reviewed under the more current and elaborate definition 

of DPS provided above. 

How well justified are these recovery units in terms of modern application of DPSs: 

should some be split, merged, or eliminated? At the species-wide scale, major differences 

in genetics, morphology, ecology, and behavior separate Mojave, Sonoran, and Sinaloan 

assemblages of the tortoise (Woodbury and Hardy 1948, Burge 1977, Jennings 1985, 

Turner et al. 1986, Weinstein and Berry 1987, Lamb et al. 1989, Glenn et al. 1990, 

Germano 1993, Lamb and Lydehard 1994, Wallis et al. 1999, Averill-Murray et al. 

2002a, Averill-Murray et al. 2002b, Averill-Murray 2002a,). These major genetic 

assemblages were resolved with a parsimony approach, using relative mitochondrial 

DNA differences exhibited by the other North American tortoise species (Lamb et al. 

1989). Recognizably different shell morphology between populations east and west of the 

Colorado River corresponds to the two described assemblages north of Mexico 

(Weinstein and Berry 1987). Each assemblage occupies a unique ecological setting 

(Berry et al. 2002). There is overwhelming support from several facets of science, which 

point to a clear separation between the Mojave and Sonoran assemblages of the desert 

tortoise. Within the Mojave assemblage, finer-scale genetic, morphological, ecological, 

and behavioral differentiation has been acknowledged in the Desert Tortoise Recovery 

Plan (USFWS 1994). 

The Western Mojave, Eastern Colorado, Northern Colorado, and the eastern end of the 

Eastern Mojave recovery units have poor justification as separate DPSs from each other, 

despite the geographical importance of their DWMAs, based on current genetic data 

(Lamb et al. 1989). Currently, the Eastern Mojave Unit combines distinctive California 

and Nevada haplotypes. We expect the Western Mojave Recovery Unit to be genetically 

discrete from other units, but additional research needs to be conducted to confirm 

genetic differences. Tortoises in the western Mojave Desert produce relatively larger 

eggs, produce fewer eggs overall, and lay their second clutches later than tortoises in the 

adjacent eastern Mojave Desert (Wallis et al. 1999). Behaviorally, western Mojave 
 

 

 

 

 

 

 

 

 

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" used ;, 3""1y$;'

Recovery Un~s

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DTRPAC Report page 34 

tortoises are much less active during summer than in other recovery units. Extremely 

winter-dominant rainfall and resultant effects on the vegetation community, as well as its 

position on the western end of the distribution, contribute to the significance of this 

recovery unit (USFWS 1994). Furthermore, range reduction already observed at the 

western edge of the species’ distribution (Bureau of Land Management et al. 2003, Map 

3-10) contributes to the significance of this putative DPS on the basis of the gap in the 

range that would be created by the loss of the DPS if not recovered. 

PSP In 

*

psp 

Current 

.. 

_ ... 

_ 

- 0 ­

... 

• • . 

Fig. 3.1. Depiction of recovery units proposed in the 1994 Recovery Plan. Green outlines within 

the recovery units are proposed DWMAs. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 35 

The entire complex east of the Baker Sink needs more data and analyses, as well as 

comprehensive reevaluation in terms of genetic diversity and ecological geographic 

boundaries. An attractive division line for the Western Mojave Recovery Unit runs along 

a line from Saline Valley in California in the north, then south through Death Valley, 

Silurian Valley, Baker Sink, and Cadiz Valley. It is particularly attractive because the 

lower elevations and extremely hot climates along this line divides the ecological western 

Mojave Desert with its quite variable winter-spring precipitation regime, lower 

elevations, and Mojave River hydrology, from the more eastern Mojave Desert, subject to 

more predictable winter and summer monsoon precipitation, more variable elevations, 

and closed basin and Colorado River hydrology. Rainfall pattern differences (Fig. 3.2) 

induce profound vegetation differences, forage, and possibly reproductive differences 

(seasonality of mating, egg clutch size, frequency, and timing). Furthermore, rainfall 

differences create the potential for different interactions among threats (Section 5). 

Station Latitude 

Adelanto 117.4167 

Apple Valley 117.2167 

0.8 0 Barstow 117.0333 

Cantil 117.9667 

0 China Lake 117.6833 0.6 

0 El Mirage 117.6333 

Hesperia 117.3000 

0 

0 Inyokern 117.8167 

0.' 0 0 Lucerne Valley 116.9500 0 

Mojave 118.1667 

0 Randsburg 117.6500 0.2 

Trona 117.3833 

Victorville 117.3000 

Boulder City 114.8500 0.0 

DNWLR 115.3667 ·119 ·118 -117 -116 -115 -114 

Dunn Siding 116.4333 Longitude Kyle Canyon 115.6000 

Las Vegas 115.1500 

Little Red Rock 115.4167 Fig. 3.2. Ratio of rainfall in winter compared to 

Mitchell Caverns 115.5500 summer in the Mojave Desert. 

Weather stations, and the longitudes Mountain Pass 115.5500 

for those stations, are given in the North Las Vegas 115.1167 

table. Red Rock Canyon 115.4667 

Searchlight 114.9167 

Sunrise Manor LV 115.0833 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 36 

While life history patterns and strategies should be expected to differ in tortoise 

populations east and west of the Baker sink, they have not yet been demonstrated other 

than for aspects of reproductive ecology noted above between sites in the Western and 

Eastern Mojave Desert Recovery Units. Tortoises are rare in the lowlands comprising this 

division, yet they are not entirely absent. Furthermore, neither allozyme nor mitochondrial 

comparisons yet support differentiation across this axis of potential separation (Rainboth 

et al. 1989, Lamb and Lydehard 1994). 

The western ends of each of the Northeastern Mojave and Eastern Mojave recovery units 

are indistinguishable genetically (Lamb et al. 1989, Britten et al. 1997). On the other 

hand, the eastern end of the Northeastern Mojave Recovery Unit falls out genetically 

distinct from the western end of this unit (Britten et al. 1997). A distinct shell phenotype 

occurs in the Beaver Dam Slope region of this unit (USFWS 1994). 

While we expect that significant differences in genetics and morphology exist, additional 

study is needed to quantify differences between the Upper Virgin River Recovery Unit 

and the Northeastern Mojave Recovery Unit (Berry et al. 2002). The Upper Virgin River 

Recovery Unit is discrete on the basis of behavioral/ecological factors (USFWS 1994) 

and also has a unique and unusual vegetation community, topography, and soil type 

(USFWS 1994). Loss of this unit would result in a gap at the northeastern extent of the 

species’ distribution. 

3.2.2 Provisional Revised List of DPSs 

We offer here a provisional recognition of a new set of DPS units (Fig. 3.3): Upper 

Virgin River Desert, Lower Virgin River Desert, Northeastern Mojave Desert (including 

Amargosa Valley, Ivanpah Valley, and Shadow Valley), East Mojave and Colorado 

Desert, and Western Mojave Desert. These include two of the original units (Upper 

Virgin River and Western Mojave) and add or revise four other units, based largely on 

the best resolving biochemical/genetic data of Rainboth et al. (1989), Lamb et al. (1989), 

Lamb and Lydehard (1994), and Britten et al. (1997). We do not consider these divisions 

definitive. These suggested revisions will require more data and analyses, as well as 

evaluation and expansion of the analyses of Britten et al. (1997), and may result in 

additional modification. Prior genetic studies pertinent to the foregoing case and others 

are largely piecemeal, confined to mtDNA, or limited to allozyme or morphological data. 

They provide us with little insight with regards to gene flow or discrete boundaries. 

Depending on the outcome of future studies, various DWMAs could be reassigned to 

different DPSs than currently proposed. In addition, we note that our provisional 

recommendations leave a single DWMA within the revised Northeastern Mojave Desert 

DPS, without specific habitat protection throughout the northern half of this segment. All 

of the DWMAs/critical habitat units remain well justified to sustain survival of G. 

agassizii: it is only their assignment to particular DPSs that concerns us. 

Although we recommend that additional data be collected to refine or revise these 

proposed DPSs, the evidence for particular DPS designation does not need to be absolute 

and incontrovertible. Note that an agency must have discretion to rely on the reasonable 
 

 

 

 

 

 

 

 

 

 

 

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East M<Jjave & CoIo<adQ D&$art

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DTRPAC Report page 37 

opinions of its own qualified experts even if a court might find contrary views more 

persuasive. Courts, however, must set aside agency actions that are arbitrary, capricious, 

an abuse of discretion, or otherwise not in accordance with law. The standard for reversal 

of an agency action is if the agency has “relied on factors which Congress has not 

intended it to consider, entirely failed to consider an important aspect of the problem, 

offered an explanation for its decision that runs counter to the evidence before the 

agency, or is so implausible that it could not be ascribed to difference in view or the 

product of agency expertise” (U.S. Court of Appeals, Ninth Circuit 2003). Note also “the 

fact that the evidence is weak, and thus not dispositive, does not render the agency’s 

determination arbitrary and capricious” (U.S. Court of Appeals, Ninth Circuit 2003). 

.... 

,.. 

psp In * 

,Revised DPS Units 

Vrgn RIVer 

Virgin 

• .­

,.­

• 

Fig. 3.3 Map of the proposed distinct population segments for desert tortoise. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 38 

DPS Recommendations 

We recognize that DPSs may not officially be designated in a recovery plan, but revision 

of the 1994 Plan should lay sufficient groundwork so that DPSs may be formally 

proposed in future delisting proposals as delisting criteria are met for each DPS (e.g., 

USFWS 2003). Future revisions will need to respond to the three criteria by which 

modern DPS units are defined: discreteness, significance, and conservation status. The 

mechanisms are as follows: 

• Genetic core units need to be assessed using both nuclear and mitochondrial genes 

(Berry et al. 2002). 

• The genetic boundaries and gene flow among units need to be critically examined. 

• Once these data are available, ecological, morphological, and behavioral attributes 

should be assigned to each of these genetic units. Correlations should be evaluated 

among established genetic units and carefully quantified and standardized 

ecological affinities, health status, life history patterns, and stereotypic behaviors. 

• The natural history of host-parasite associations for the major disease relationships 

for desert tortoise should be more deeply elucidated, including the genetics of hosts 

and strains of pathogens. 

• At least three disparate, long-term study sites should be established within each 

proposed DPS to verify the reality, consistency, homogeneity, and variability of 

these defining traits. 

• DWMAs within each DPS should be geographically revised to maximize their 

conservation potential in consultation with ecologists and local resource 

administrators including the USFWS for coordinating recovery efforts range wide. 
 

 

 

DTRPAC Report page 39 

“An experiment is a question which science poses to Nature, and a 

measurement is the recording of Nature’s answer.” 

Max Planck, Scientific Autobiography and Other Papers. (1949) 
 

 

 

 

 

 

 

D Urban Ar",as r

Degree

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DTRPAC Report page 40 

4. Status and Trends 

4.1 Recovery Plan Implementation 

The Recovery Plan identified specific management actions for each DWMA to address 

perceived threats identified during the listing of and recovery planning for the desert 

tortoise. If sheer numbers of threats are used as an indication of threatened status, all but 

the Chuckwalla DWMA have seen increased numbers in the intervening years between 

1994 and 2003 (Fig. 4.1 and 4.2). 

of Threat 1994 

.

- -

' .

.­

•• 

Fig. 4.1 Relative number of threats to desert tortoises in each critical habitat unit (i.e., DWMA), 

as identified by the Recovery Plan in 1994. 
 

 

 

 

 

 

 

 

 

 

 

 

InSlallalion

o Areas

0 2Lew

'''' ~'''''- 0 '

HIQIl

- - Recovery Un'/:

DTRPAC Report page 41 

• 

_•5 

Degree of Threat 2003 

j Milrtary • 

Urban 

Fig. 4.2 Relative number of threats to desert tortoises in each critical habitat unit (i.e., DWMA), 

as identified by the Desert Tortoise Management Oversight Group in 2003. 

In answer to these threats the Recovery Plan recommended a number of management 

actions per DWMA. The relative numbers of recommended management actions are 

illustrated in Fig. 4.3. In 2002 land and wildlife management agencies responded to a 

questionnaire from the USFWS to document implementation of the Plan (Redlands 

Institute 2002a- 2002f). Survey responses were not specific enough to quantify the level 

of implementation for specific actions. Therefore, we did not attempt to interpret the 

degree to which agencies actually implemented each action, only whether some action 

had been taken. We intend this brief analysis to simply represent a “first-cut” review of 

the general status of recovery plan implementation without delving into a comprehensive 

analysis of each recommendation in the Plan. 
 

 

 

 

 

 

 

 

 

 

 

o

,

=':"li/,-nD

DTRPAC Report page 42 

• ,

.-

Recovery Actions 

Number Recommended 

27 28 

0 29-30 

_ 31 -32 

Fig. 4.3 Relative numbers of management actions recommended for each DWMA in the 1994 

Recovery Plan. 

Based on survey responses in 2002, it appears that implementation has been uneven 

relative to recommended management (Fig. 4.4, Table 4.1). Many reviewers of the prior 

draft of this report made it clear that they disagreed with the representation of Recovery 

Plan implementation in Fig. 4.4 and Table 4.1, both by not crediting implementation 

where it had occurred and by giving credit for implementation where it may have been 

negligible. Our main conclusion from this survey is not the specific degree to which the 

Recovery Plan has been implemented in any given area. Rather, it is clear that the 

USFWS and other management agencies need to better document and quantify recovery 

efforts recommended in the Recovery Plan or its revision (Section 4.5.1) provides a 
 

 

 

 

 

 

 

 

 

 

,

_--f 44

MII ary

o Urban

DTRPAC Report page 43 

specific example of this), because to date the only source of collated and easily accessible 

information on the degree to which the Plan’s management recommendations have been 

implemented is a questionnaire that inadequately addresses Plan management 

recommendations. 

• ,

.-

Recovery Actions 

Percent Implemented 

50 

0 51-75 

_ 76 - 100 

- - Recovery Unit 

InstallatIon 

Areas 

Fig. 4.4 Relative numbers of management actions by DWMA reported to the USFWS that have 

been at least partially implemented by 2002. 

If left to this questionnaire as the only source of information from which to compare 

range-wide implementation efforts, we would be forced to conclude that little if any 

implementation has occurred within the western Mojave Desert (Fig. 4.4), even though 

the Recovery Plan called for a relatively high degree of management in this area (Fig. 

4.4). In fact, once again if left to this questionnaire alone, an average of 36% (n = 12; 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 44 

Coyote Springs Valley is combined with Mormon Mesa and Joshua Tree not included) of 

the management recommendations per DWMA were not reported as having been 

implemented as of 2002, ranging from 100% (at least partial) implementation at Upper 

Virgin River to only 32% implementation at Ord-Rodman (Table 4.1). Only 38% of 

recommended management actions were reported to be implemented overall in the 

Western Mojave Recovery Unit, and tortoise populations in this region have shown the 

most dramatic declines (Section 4.2 or Fig. 4.13). 

Recovery Action Review and Implementation Recommendations: 

With better planning and implementation of a new questionnaire that specifically 

addresses Recovery Plan implementation, we will be better able to assess the level of 

implementation of management recommendations. We offer the following specific 

recommendations regarding recovery action review and implementation: 

•	 Land managers and policy makers should undertake a coordinated, range-wide 

effort today, not waiting for the possible formation of a future recovery team, to 

assess the level to which Plan recommendations have been implemented within 

each DWMA. This effort should be directly correlated to Recovery Plan 

management recommendations. Without this effort, it will be impossible to assess 

the level of Plan implementation and thus objectively assess the reasons why the 

desert tortoise continues to appear to be declining throughout much of its range. 

•	 At the same time, if a future recovery team is formed, it will be essential that the 

team review and revise recovery recommendations for each DWMA and/or 

provisional DPS to ensure that recommended recovery actions address relevant 

site-specific impacts or threats. 

•	 Most recovery actions should be implemented in an experimental framework (in 

at least some areas) to determine the effectiveness of those actions. Appropriate 

response variables (e.g., tortoise numbers or density, reproductive output, 

nutrition, juvenile survival, etc.) may vary depending on the action. Likewise, the 

necessary study duration may vary depending on the action and response variable; 

long-term studies should be expected, given the life history of the tortoise. 

•	 The USFWS and other management agencies should develop a forward-looking, 

quantitative recovery actions database. Database development should begin during 

the Recovery Plan revision process with site-specific baseline measures (e.g., miles 

of authorized/unauthorized roads and trails, number of landfills in a particular 

DWMA) for each recovery action. Subsequently, agencies should document in the 

database specific levels of recovery action implementation (e.g., miles of roads 

closed, number of landfills closed or managed appropriately in a particular 

DWMA). Lundquist et al. (2002) and Hatch et al. (2002) found that recovery tasks 

and monitoring were significantly more likely to be implemented for plans with a 

recovery coordinator or committee and a centralized recovery database. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 45 

Table 4.1. Recovery actions listed in the Recovery Plan (and DWMA supplement) reported by management agencies as implemented through 2002 (Redlands 

Institute (2002a-f). 0 = No Implementation; 1 = Implementation Initiated; blanks indicate actions not applicable to that unit, according to the Recovery Plan. 

Recovery Action 

1 Prohibit Vehicles off Roads 

2 Prohibit Competitive/Organized 

Events 

3 Prohibit Surface Disturbance 

4 Prohibit Grazing 

5 Prohibit Burros/Horses 

6 Prohibit Vegetation Harvest 

7 Prohibit Collection 

8 Prohibit Dumping/Littering (+ 

cleanup) 

9 Prohibit Releases 

10 Prohibit Uncontrolled Dogs 

11 Prohibit Discharge of Firearms 

12 Restrict New Roads 

13 Close Roads 

14 Designate Roads 

15 Fence Roads/Install Culverts 

16 Law Enforcement 

17 Restore Habitat 

18 Sign/Fence Boundaries 

19 Landfill Management 

20 Environmental Education 

21 Withdraw Mining 

22 DWMA Mgt. Plan 

23 Secure Non-federal 

Lands/Habitat 

24 Halt Unauthorized ORV Use 

25 Halt Vandalism of Tortoises 

26 Install Railroad Barriers/Culverts 

27 Install Aqueduct Barrier 

28 Monitor Health of Population 

29 Evaluate Raven Use 

30 Install Urban/Other Barriers 

31 Raven Control 

32 Distribution/Density Surveys 

Chemehuevi 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0 

0 

0 

1 

1 

0 

1 

0 

0 

1 

1 

0 

1 

1 

0 

0 

1 

1 

Chuckwalla 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0 

0 

0 

1 

1 

0 

1 

0 

0 

1 

1 

0 

1 

1 

0 

0 

1 

0 

1 

Upper 

Virgin 

River 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

Fenner 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0 

0 

0 

1 

1 

0 

1 

0 

0 

1 

1 

0 

1 

1 

0 

0 

1 

0 

1 

Ivanpah 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0 

1 

1 

1 

0 

1 

1 

0 

1 

1 

0 

1 

1 

0 

0 

1 

1 

PiuteEldorado 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0 

1 

1 

1 

0 

1 

1 

1 

1 

1 

0 

1 

1 

0 

1 

1 

Beaver 

Dam 

Slope 

1 

1 

1 

1 

0 

1 

1 

1 

1 

0 

0 

1 

1 

1 

1 

1 

0 

1 

0 

1 

0 

1 

0 

0 

1 

0 

1 

Gold 

ButtePakoon 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0 

0 

1 

1 

1 

0 

1 

1 

1 

1 

1 

0 

1 

0 

1 

1 

Mormon 

Mesa 

1 

1 

1 

0 

0 

1 

1 

0 

0 

0 

0 

1 

0 

1 

0 

1 

0 

0 

1 

1 

0 

1 

0 

0 

0 

FremontKramer 

0 

0 

0 

0 

0 

0 

1 

1 

1 

1 

1 

0 

0 

0 

1 

1 

0 

0 

1 

1 

0 

0 

1 

0 

0 

0 

1 

1 

1 

1 

OrdRodman 

0 

0 

0 

0 

0 

0 

1 

1 

1 

0 

0 

0 

0 

0 

0 

1 

0 

0 

1 

1 

0 

0 

1 

0 

1 

0 

0 

1 

SuperiorCronese 

0 

0 

0 

0 

0 

0 

1 

1 

1 

0 

1 

0 

0 

0 

1 

1 

0 

0 

1 

1 

0 

0 

1 

0 

0 

% Partially Implemented 67% 64% 100% 64% 78% 85% 67% 80% 44% 47% 32% 36% 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 46 

4.2 Trend Analyses of Populations 

No existing data or analyses are adequate to estimate long term status or trends in (a) desert 

tortoise populations, (b) habitat for desert tortoises in any recovery unit, and/or (c) threats 

to tortoise populations regionally. However, we assembled as much data as was possible, 

within the time constraints for preparing the DTRPAC report, to perform the equivalent of 

meta-analyses on existing information (Hunter et al. 1982). Our analyses consist of two 

general approaches: 1) evaluation of long-term trends in the densities of desert tortoises 

within Recovery Units and within the Distinct Population Segments that are proposed by 

the DTRPAC, and 2) evaluation of qualitative and quantitative spatial analyses of the 

presence of live and dead tortoises on transects for (a) “total corrected sign” and (b) 

distance sampling. These analyses provide insight as to where, within larger management 

units, tortoises may be doing better or worse than in other areas. The successes of these 

analyses portend efficacious approaches for exploring data in new and innovative ways that 

can be terrifically important to the future successes of monitoring programs. 

4.2.1 History of Long-Term Study Plots 

Long-term permanent study plots were established in California in the early 1970’s as part 

of an inventory of Bureau of Land Management (BLM) resources (Berry 1984). 

Permanent study plots were also established in Arizona, Nevada, and Utah (Fig. 4.5). 

These plots originally were established to generate data on demography and population 

trends as well as ecological relationships with abiotic and biotic factors (Berry 1984). 

Various methods were used to assess population size in the initial surveys on those plots 

(e.g., 30-day spring surveys, 20-day fall surveys, and winter den surveys), but eventually a 

standard method became a 60-day spring survey of a one square mile plot. In this protocol, 

survey effort was divided into two periods of roughly equal times (capture and recapture 

periods). Tortoise density has been estimated using the Lincoln-Peterson calculation 

(Turner and Berry 1984); analyses for most plots limit abundance estimation to tortoises 

>180 mm MCL, due to reduced capture probabilities for smaller tortoises, but abundance 

of tortoises of all sizes on California plots is often estimated with a stratified Lincoln 

Index (Overton 1971). Additional data collected on study plots include health profiles, 

burrow or cover characteristics, tortoise size, information on carcasses, and vegetation on 

the plots. Few of these latter data have been analyzed beyond descriptive summaries. 

Plots typically were located on public lands and in areas containing “adequate tortoise 

densities for sampling,” sometimes explicitly where many tortoises had been reported; 

however, some plots were originally located in areas where strip-transect surveys had 

previously documented little or no tortoise sign (Berry 1984). Plots were located in areas 

generally considered to have been the least disturbed “representative habitats” within the 

desert ecosystems (e.g., Mojave Desert, Colorado Desert, etc.). Several plots on which 

few tortoises were found have been discontinued (K.H. Berry, pers. comm. 2003). Sixtyday plot surveys began in California in the early 1970’s, in Nevada and Utah in 1981, and 

in Arizona in 1987. Only a small subset of the plots has been surveyed in any one year, 

and fixed survey intervals have not been maintained (Table 4.2). 
 

 

 

 

 

 

 

 

 

'I.... •

,

not used ,., onolysls * used In an!'Jiy<is

CJ ~M

DTRPAC Report page 47 

Fig. 4.5 Locations of desert tortoise permanent study plots within the federally listed range of 

PSP 

PSP 

desert tortoises in the southwestern United States. 

Permanent study plot data were used to give the committee some insight into the rangewide status of tortoises over the most recent two decades. Density estimates and 

confidence limits for those estimates were collected from published literature, reports, 

and from personal communications with researchers who supervised surveys of the 

permanent study plots within the listed range of the desert tortoise from 1979 to 2002 

(Table 4.2). Not all plots were sampled in all years, and not all data were calculated or 

obtainable for plots that were sampled in some years (Table 4.2). 
 

 

 

 

 

 

 

 

DTRPAC Report page 48 

Table 4.2 Years surveyed on permanent study plots for desert tortoises. A number (0 or 1) indicates that 

data were taken at this plot. A zero indicates that the data are not available or sufficient for analysis, and a 

one indicates that data were available for analyses in this report. 

Study Site State 71/72 76/77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 

Southern Argus CA 0 

Fremont Valley CA 0 0 1 1 1 1 

DTNA (interior) CA 1 1 1 1 1 1 

DTNA (inter. Center) CA 1 1 1 1 0 0 

Fremont Peak CA 1 1 1 1 1 

Kramer Hills CA 1 1 1 1 1 

Stoddard Valley CA 1 1 1 

Lucerne Valley CA 1 1 1 1 

Johnson Valley CA 1 1 1 1 

Shadow Valley CA 0 1 1 1 

Ivanpah Valley CA 1 1 1 1 1 

Fenner Valley (Goffs) CA 0 1 0 0 0 0 1 1 1 

Ward Valley CA 1 1 1 1 1 

Chemehuevi CA 0 0 1 1 1 1 0 

Chuckwalla Valley CA 1 1 1 

Chuckwalla Bench CA 0 0 1 1 1 1 1 0 1 

Last Chance NV 0 

Sheep Mountain NV 1 1 1 1 

Piute Valley NV 0 0 1 1 1 

Christmas Tree NV 1 1 1 

Coyote Spring NV 1 1 1 

Gold Butte NV 1 1 1 

Sand Hollow NV 1 1 

Mormon Mesa NV 1 1 

Trout Canyon NV 1 1 

Eldorado Valley NV 1 

LMNRA 

Tassi NV 0 

Road 152 NV 0 0 

Road 149 NV 0 

Road 60 NV 0 0 

Road 58 NV 0 0 0 

Road 42 NV 0 0 

River Mountains NV 1 0 1 1 

Pinto Valley NV 0 

Overton NV 1 1 

Lake Las Vegas NV 0 

Grapevine NV 1 1 1 0 0 0 0 0 

Government Wash NV 0 

Dupont Mine NV 0 

Cottonwood NV 1 1 1 0 0 0 0 0 0 

Cat Claw NV 0 

Bitter Springs NV 0 0 0 

Pakoon Basin AZ 0 

Virgin Slope AZ 1 1 0 

BDS Exclosure AZ 0 1 0 

Littlefield AZ 0 0 1 1 

City Creek UT 1 1 

Woodbury-Hardy UT 0 1 1 1 

Beaver Dam Slope UT 1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 49 

Data on population densities on permanent study plots were assembled from numerous 

sources (Table 4.3). Data from these plots have limits to their value for scientific 

assessment of status and trends for several reasons. For example, the plots are not random 

samples of desert tortoise habitat, so extrapolations from them cannot be made. The plots 

were not sited to address specific hypotheses about management actions so it is not clear 

to what the contained tortoises are responding. The plots were not censused in the same 

years, and the timing of measuring the plots makes comparisons among plots of limited 

value. Detectability of tortoises was never measured which further limits temporal 

comparisons of status and trends. In spite of the inadequacies of these data, and with some 

caveats, they can be used to estimate the status and trends of desert tortoise populations 

with appropriate caution. When the Recovery Plan was assembled, information regarding 

the status of desert tortoise populations largely depended upon analyses of tortoise 

densities from permanent study plots. While these data showed that populations 

experienced significant declines in the western extent of the listed range (i.e., California, 

see USFWS 1994, Page 4, Fig. 1), no trend in adult densities for the eastern portion was 

discernable at that time (see USFWS 1994, Appendix C, Page C9, Fig. C4). 

Interpretations of analyses of data from permanent study plots have been controversial 

(Corn 1994, Bury and Corn 1995), and new sampling methods were advocated. Permanent 

study plots continued to be sampled in the years following the publication of the Recovery 

Plan, and many continue to be sampled. However, many of the study plots in Nevada, and 

Utah were not sampled beyond ~ 1996, as new methods of density estimation were 

implemented. Thus, the status of tortoise populations in California, as measured by data 

taken from study plots, is more current than that from Nevada or Utah. Nevertheless, data 

beyond those relied upon by the Recovery Team in 1994 are available and are analyzed 

herein, and those analyses show similar patterns in trends of desert tortoise densities to 

those published in the 1994 Plan. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 50 

Table 4.3 Citations for sources of data used in permanent study plot analyses 

Advantage Environmental Consulting. undated (1992) 

Bashor, A.N. undated (1991) 

Berry, K.H. 1989
 

Berry, K.H., T. Shields, and C. Knowles. In prep.
 

Duck, T.A., and E. Schipper. undated (1989)
 

Duck, T.A., and J.R. Snider. undated (1988) 

Foreman, L. (pers. comm.)
 

Fridell, R.A., and M.P. Coffeen. undated (1993)
 

Haley, R., and M. Boyles (pers. comm.)
 

Berry, K.H. 1990
 

Berry. K.H. 1992
 

Berry. K.H. 1995
 

Berry, K.H. 1996
 

Berry, K.H. 1999
 

Berry, K.H., L.L. Nicholson, S. Juarez, and A.P. Woodman. 1986
 

EnviroPlus Consulting. 1995
 

EnviroPlus Consulting. 1994
 

Fridell, R.A. 1995
 

Fridell, R.A., and J.A. Shelby. 1996
 

Fridell, R.A., J.R. Snider, K.M. Comella, and L.D. Lentsch. 1995
 

Fridell, R.A., M.P. Coffeen, and R. Radant. 1995
 

Goodlett, G., and P. Woodman 2003
 

Goodlett, G., M. Walker, and P. Woodman. 1997
 

Goodlett, G., P. Woodman, M. Walker, and S. Hart. 1996
 

K. Berry (pers. comm.) 

K. Phillips (pers. comm.)
 

Longshore, K.M. 2003
 

Medica, P.A. 1992
 

Minden, R.L., and S.M. Keller. 1981
 

Nickolai, J.L., and R.A. Fridell. 1998
 

P. Medica (pers. comm.) 

Rourke, J.W., C. Hillier, J. Merriam, and T.A. Duck. undated (1993) 

Turner, F.B., and K.H. Berry. 1985 

USFWS, Ventura Office Annual Permit Reports 

Woodman, P. 1997 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 51 

4.2.2 Trends Range-wide (East and West) 

Permanent study plots that have been sampled for an extended period, from which data 

were used in the original Recovery Plan, and can be divided into those in the eastern and 

western part of the desert tortoise range (Table 4.4), as was done in the original Recovery 

Plan. When the 1994 Recovery Plan was written, there were documented population 

declines in the Western Mojave and this downward trend appears unabated (Fig. 4.6). In 

addition, there is now a guarded concern for populations in the East Mojave (in California), 

particularly due to a single recent data point at the Goffs site (Fig. 4.6). This concern has 

highlighted the need for more data to assess the importance of data points that could either 

be outliers or could be indicators of new trends. In these areas, desert tortoises appear to be 

affected by various combinations of threats or the cumulative effects of many threats. 

Table 4.4 Study plots from which data were used to assess trends in population size in the original 

Recovery Plan. 

Eastern Western 

Chemehuevi Valley Desert Tortoise Natural Area (Interior) 

Chuckwalla Bench Desert Tortoise Natural Area (Visitors Center) 

Chuckwalla Valley Fremont Valley 

Ivanpah Valley Fremont Peak 

Upper Ward Valley Johnson Valley 

Christmas Tree Kramer Mountains 

Coyote Springs Lucerne Valley 

Gold Butte Stoddard Valley 

Piute Valley 

Sheep Mountain 

Trout Mountain 
 

 

 

 

 

 

 

 

 

 

 

 

 

6 a Wcst Mojaw Sitcs

. OTHAif

Oi • OTNA

C • .. FtemOf7f PIc

A tVM e

c C V.,

KntmfN

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0 c. a

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'" 6

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a: • • • 

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DTRPAC Report page 52 

1.00 • • 0

• • 3 

0.80 

. a Johnson 0 

a HI. 0 0.60 

• • 0 

o • 

0 0.40 •

> • 

0.20 

0.00 

1980 1985 1990 1995 2000 

Year 

1.00 • • • • Sites

• 0 

0.80 • 

•

• •

• •

• • 

• 

C 

0 0 0.60 • 0 . a . o 

o 0.40 0 • 

o 

• 0.20 

Beh 0 

0.00 

1980 1985 1990 1995 2000 

Year 

Fig. 4.6 Trends in relative population densities for desert tortoises in the eastern and western 

permanent study plot sites. 

4.2.3 Trend Analyses by Recovery Unit 

The DTRPAC analyzed for trends in tortoise population densities at a finer spatial scale 

than just the eastern and western portions of the listed range (as was done in the Recovery 

Plan). It is important to recognize that analyzing permanent study plots individually is 

largely meaningless except to learn about processes only on the plot (generally not valuable 

for conservation planning). Thus, analyzing permanent study plots cannot give insight into 

population trends occurring within larger management areas (Manly 1992, MacDonald and 

Erickson 1994, Underwood 1997) unless the plots are randomly placed within the area for 

which generalization is needed. Nevertheless, for our analyses, study plots were treated as 

though they were random samples of regions. Because the permanent study plots actually 

were not randomly placed (Berry 1984), this somewhat limits the extent to which it is 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 53 

possible to generalize from analyses (Manly 1992). Regardless of the limitations to 

analyses from these plots (the only data available), the data from the plots were analyzed in 

a way that reduced bias as much as possible. The geographic areas that we examined 

included the Recovery Units specified in the original Recovery Plan (Fig. 4.7), and the 

Distinct Population Segments (Fig. 4.14) suggested by the DTRPAC (see Section 3). For 

each Recovery Unit and DPS, we constructed a weighted general linear model with one 

continuous and one categorical variable (results below). Estimates of the population 

densities of adult tortoises (carapace lengths > 208 mm) were the response variable, and 

time (years) and the study plot were predictor variables. The model was weighted by the 

inverse of the half-width of the upper confidence limit relative to the magnitude of the 

density estimate. This weighting caused more precise density estimates to have greater 

influence on the model than those with poor precision. Repeated measures analysis of 

variance was also considered for these analyses, however the data from study plots were 

collected in different years and for differing numbers of years, which made this type of 

analysis untenable. The graphs of adult tortoise density for each Recovery Unit and 

Distinct Population Segment given below are bivariate plots of the raw density estimates 

and their confidence limits and not the results of analyses on the data. 

Some of the Recovery Units, or proposed Distinct Population Segments, did not have 

sufficient study plots within them to permit analysis, or had too few study plots to provide 

enough power to produce conclusive analyses. For example, the Upper Virgin River 

recovery unit and proposed DPS contained only one plot (City Creek), for which we had 

density estimates for only 1988 and 1994. Thus, no analyses were conducted for this 

Recovery Unit/DPS. In addition, the Eastern Colorado Recovery Unit and the Northern 

Colorado Recovery Unit each contained only two plots, and results for analyses from this 

small sample lack power and ability to generalize. The Western Mojave Recovery Unit 

contained the same set of permanent study plots as the proposed Western Mojave Distinct 

Population Segment, and therefore new analyses were not necessary for the DPS. 
 

 

 

 

 

 

 

 

.,.

,_ P.....

! • not used ",.,.lys

" used In analy$io

Recovery Un~s

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DTRPAC Report page 54 

PSP In .. 

*

psp 

Current 

.. 

_ 

- ... 

• , .... 

• . 

Fig. 4.7 Active (green tortoise symbols) and discontinued (orange triangles) permanent study plots 

grouped within the 1994 Recovery Units. 

Upper Virgin River Recovery Unit (and DPS) 

There was only one PSP represented in the Upper Virgin River recovery unit (City Creek; 

Fig. 4.7), and therefore no analysis was generated for this recovery unit. The density 

estimates for this site are given in Fig. 4.8. 

The Upper Virgin River DPS contains the same permanent study plot (City Creek) as the 

recovery unit (Fig. 4.7). No analysis was conducted for this DPS and Recovery Unit. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report	 page 55 

Upper Virgin River
 

Recovery Unit
 

Fig. 4.8 Plot of adult densities over 

time for the City Creek permanent 

study plot located within the Upper 

Virgin River Recovery Unit. Error 

bars are 95% confidence intervals 

for the density estimate. 

Northeastern Mojave Recovery Unit 

300	 0 City Creek I 

250	 I f/) 

Q) 

f/) I

200
 

150
 Q) 

0 

Q) 

f/) 100 

I50
 

0
 

1975 1980 1985 1990 1995 2000 2005 

Year 

The Northeastern Mojave Recovery Unit contained the Beaver Dam Slope (exclosure), 

Beaver Dam Slope, Coyote Springs, Gold Butte, Littlefield, Mormon Mesa, Overton, River 

Mountain, Sheep Mountain, Trout Canyon, Virgin Slope, and Woodbury Hardy permanent 

study plots (Fig. 4.7). 

The overall analysis was significant (F12,14 = 8.1, P = 0.0002), which was entirely due to the 

effect of site (F11,14 = 8.7, P = 0.0002). There was no significant statistical trend in adult 

density over time (F1,14 = 

0.008, P = 0.93; Fig 4.9). 

Fig. 4.9 Plot of adult densities 

over time for the study plots 

located within the Northeastern 

Mojave Recovery Unit. Error bars 

are 95% confidence intervals for 

the density estimate. 

Northeast Mojave Recovery Unit 

160 o	 60S Excl05ure 

•	 Beaver Dam Slope 

o	 Coyote Springs 140 •	 Gold Butte Littlefield 

•	 Mormon Mesa 

OVerton 

•	 River Mountain
 

Sheep Mountain
 

Trout Canyon
 

Virgin Slope
 

WH 

! j I 

20 I 

__ 

1975 1980 1985 1990 1995 2000 2005 

Year 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0L

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DTRPAC Report page 56 

Eastern Mojave Recovery Unit 

The Eastern Mojave Recovery Unit contains the Christmas Tree, Goffs, Ivanpah, Shadow 

Valley, and Piute Valley permanent study plots (Fig. 4.7). 

The overall analysis for the Eastern Mojave Recovery Unit was significant (F5,11 = 10.3, P = 

0.0007). This result was entirely due to the significance of the site effect (F4,11 = 11.7, P = 

0.0006). There was no significant effect of year in the model, indicating that there was no 

trend in adult density estimates over time (F1,11 = 0.2, P = 0.65; Fig. 4.10). 

East Mojave Recovery Unit 

300 

250 0 Christmas Tree

• 

0 Ivanpah Fig. 4.10 Plot of adult densities Q) Shadow Valley • Plute Valley over time for the study plots 200 j located within the Eastern Mojave 

Recovery Unit. Error bars are 95% 

150 confidence intervals for the density Q) 

estimate. Q) 

100 II I­ II

50 

0 I

1975 1980 1985 1990 1995 2000 2005 

Year 

Northern Colorado Recovery Unit 

The Northern Colorado Recovery Unit contained two permanent study plots, Chemehuevi 

and Ward Valley (Fig. 4.7). This limits how generalizable the results from this analysis can 

be and again highlights one of the weaknesses of using data from permanent study plots to 

discern long-term trends for management areas. 

The overall model for the Northern Colorado Recovery Unit was significant (F2,7 = 23.29, P 

= 0.0008), and the effect of site was significant (F1,7 = 39.6, P = 0.0004). There was no 

significant effect of year, indicating no statistical trend of adult tortoise density over time 

(F1,7 = 1.3, P = 0.3; Fig. 4.11). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 57 

Northern Colorado Recovery Unit 

300 

250 

200 

Fig 4.11 Plot of adult densities 

over time for the PSPs located 150

0

within the Northern Colorado 

Recovery Unit. Error bars are 95% 100 

confidence intervals for the ldensity estimate. 

50 I

0 

I

1975 1980 1985 1990 1995 2000 2005 

Year 

Eastern Colorado Recovery Unit 

The Eastern Colorado Recovery Unit contained two permanent study plots, Chuckwalla 

Bench and Chuckwalla Valley (Fig. 4.7). As in the Northern Colorado Recovery Unit 

analysis, this limits how generalizable the results from this analysis can be and highlights 

one of the weaknesses of using data from permanent study plots to discern long-term trends 

for management areas, whether they are Recovery Units or Distinct Population Segments. 

The overall model for the Eastern Colorado Recovery Unit was significant (F2,6 = 21.0, P = 

0.002), with significant effects Eastern Colorado Recovery Unit 

of both site (F1,6 = 19.18, P = 250 

0.005) and year (F1,6 = 20.24, P 0 Chuckwalla Bench = 0.004; Fig. 4.12). This Chuckwalla Valley • 200 indicated that there was a 

statistical decline in adult 

densities over time, which 150 

appears to be due to the effect 

of Chuckwalla Bench. 0 100 

Fig. 4.12 Plot of adult densities I- 50 Ij Ij over time for the PSPs located 

within the Eastern Colorado I

Recovery Unit. Error bars are 95% 0 

confidence intervals for the density 1975 1980 1985 1990 1995 2000 2005 

estimate. Year 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 58 

Western Mojave Recovery Unit (and DPS) 

The Western Mojave Recovery Unit included the DTNA Interior, DTNA Interpretive 

Center, Fremont Peak, Fremont Valley, Johnson Valley, Kramer Hills, Lucerne Valley, and 

Stoddard Valley Permanent Study Plots (Fig. 4.7). 

The overall analysis was significant (F8,25 = 7.2, P < 0.0001), and the year effect yielded a 

significantly negative trend in adult density estimates over time (F1,25 = 20.52, P = 0.0001 

(Fig. 4.13). There was also a significant contribution of site to the model (F7,25 = 4.46, P = 

0.003). This analysis indicates that, taken together, tortoise densities on the permanent 

study plots located within the Western Mojave Recovery Unit are declining, as was 

suggested in the Recovery Plan (Recovery Plan, Appendix C, page C10, Figure C5). This 

pattern suggests that recovery actions implemented since the Plan have not resulted in the 

reversal of this declining trend. 

The study plots included in the proposed Western Mojave Distinct Population Segment 

(Fig. 4.14) are the same as those in the Western Mojave Recovery Unit (Fig. 4.7). 

West Mojave Recovery Unit 

250 

Fig. 4.13 Plot of adult 200 0 DTNAf3l DTNA 4 • 

I 0 Fremont Peak 

Fremont Valley 

densities over time for the 

• permanent study plots Johnson Valley Kramer Hills

located within the Western ­

o Lucerne Valley 

-

­ 150 • Stoddard Valley

Mojave Recovery Unit. 

Error bars are 95% 

confidence intervals for o 

the density estimate. 

­

o 

IYear 
 

 

 

 

 

 

 

• ., ,

- ",

'-'M'fr-

<I. not YSed anal:isis

uMd Il ana!:l'"

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DTRPAC Report page 59 

4.2.4 Trend Analyses by Distinct Population Segment 

psp In 

• psp 

Revised DPS Units 

Vi gn 

Virgin 

& 

• • . 

Fig. 4.14 Active (green tortoise symbols) and discontinued (orange triangles) study plots grouped 

by Distinct Population Segment. 

Lower Virgin River DPS 

The Lower Virgin River Distinct Population Segment contains the Beaver Dam Slope 

(Exclosure), Beaver Dam Slope, Coyote Springs, Gold Butte, Littlefield, Mormon Mesa, 

Overton, River Mountain, Virgin Slope, and Woodbury Hardy permanent study plots (Fig. 

4.14). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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•

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DTRPAC Report	 page 60 

The overall analysis was not significant (F5,6 = 3.7, P = 0.07). Indicating that there was no 

effect of site, and importantly there was no significant trend in adult tortoise density over 

time (F1,6 = 0.29, P = 0.61; Fig. 4.15). 

Lower Virgin River DPS 

160 

140 

120 

Fig. 4.15 Plot of adult densities over time 

100 for the Lower Virgin River Distinct 

Population Segment. Error bars are 95% so 

confidence intervals for the density 

estimate. 

Eastern Mojave and Colorado 

DPS 

The Eastern Mojave and 

Colorado DPS contains the 

Chemehuevi, Christmas Tree, 

Chuckwalla Bench, Chuckwalla 

Valley, Goffs, Piute Valley, 

Ward Valley permanent study 

plots (Fig. 4.14). 

The overall analysis was 

significant (F7,20 = 11.89, P < 

0.0001), which was entirely due 

to the effect of site (F6,20 = 

13.46, P < 0.0001). There was 

no significant trend in density 

estimates over time (F1,20 = 2.22, 

P = 0.15; Fig 4.16). 

o 

Q)	 60 I 40 

20 

o 80S Exclosure • Beaver Dam Slope 

Littlefield 

Mormon Mesa Overton 

• River Mountain 

Year 

Eastern Mojave and Colorado Desert DPS 

300 0	 Chemehuevi
 

Christmas Tree
 •

0 Chuckwalla Bench (\J Chuckwalla Valley • Piute Valley Ward Valley 

250 

Q) 

200 II j 150 Q) 

0 

Q) 

100	 I I!! 

I50 I

0 

1975 1980 1985 1990 1995 2000 2005 

Year 

Fig. 4.16 Plot of adult densities over time for the Eastern 

Mojave and Colorado Distinct Population Segment. Error 

bars are 95% confidence intervals for the density estimate. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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0

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0 Sheep Mountain 

140 • Trout Canyon 

Q) 120 

100 

80 Q) 

0 

Q) 60 !

1 Ij I 40 

20 

0 

DTRPAC Report page 61 

Northeastern Mojave DPS 

The Northeastern Mojave Distinct Population Segment contains the Ivanpah, Shadow 

Valley, Sheep Mountain, and Trout Canyon permanent study plots (Fig. 4.14). 

The overall analysis was significant (F4,9 = 26.52, P < 0.0001), which was entirely due to 

the effect of site (F3,9 = 35.35, P < 0.0001). There was no trend in adult densities as a 

function of time (F1,9 = 0.06, P = 0.82; Fig. 4.17). 

Northeast Mojave DPS 

160 0 tvanpah

Shadow Valley 

Fig. 4.17 Plot of adult densities 

over time for the Northeastern 

Mojave Distinct Population 

Segment. Error bars are 95% 

confidence intervals for the 

density estimate. 

1975 1980 1985 1990 1995 2000 2005 

Year 

4.2.5 Summary of Trend Analyses 

From the trend analyses a few key conclusions can be drawn. First, the downward trend in 

adult tortoise densities in the Western Mojave clearly dominates the analyses, whether 

considered by dividing the listed range into eastern and western sections (Fig 4.6), or 

analyzed at the level of the Recovery Unit/DPS (Fig 4.14). There were several Recovery 

Units that contained too few permanent study plots to allow meaningful analyses and some 

that could not be analyzed. This speaks to the inadequacy of the historical placement of the 

permanent study plots in light of the current needs of range-wide monitoring. One caveat to 

the weighting procedure should be pointed out, however. Low point estimates with high 

variance are often obtained when few animals are captured or recaptured, so real tortoise 

declines may have had little effect on some models. For example, in the Northeastern 

Mojave Recovery Unit (or Lower Virgin River DPS) plot surveys on the Beaver Dam 

Slope Exclosure in 2000 and the Virgin Slope in 2003 produced too few live tortoises to 

even produce a population estimate that could be included in the analyses presented here. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 62 

This, combined with the fact that many more carcasses were found than in prior surveys,
 

suggests that recent declines have occurred on those plots.
 

Second, the variation in density estimates using study plots does not appear to be less than 

the variation from line distance sampling. Thus, it is unlikely that plot analyses would have
 

sufficient power to detect the subtle trends that are assumed to be associated with recovery 

of desert tortoise populations (see Monitoring section).
 

Finally, the resolution of the analyses that can be conducted with data from permanent
 

study plots is currently limited due to the relatively few plots established, the lack of
 

random placement of existing plots, and the fact that plots were not established to test
 

hypotheses concerning recovery. Newer research and monitoring using spatial analyses
 

requires the more extensive transect sampling promoted by USFWS since 2001. However,
 

a robust monitoring program requires exploring novel analyses, particularly those that can 

be conducted with existing data (or with little modification of current monitoring methods).
 

New methods could become increasingly important as new hypotheses-driven research and 

monitoring is required for recovery.
 

4.3 Spatial Analyses 

We conducted several GIS and spatial analyses to explore spatial variation within tortoise 

populations at different scales on the landscape and in different management units. Spatial 

analyses were based upon transect data generated for distance sampling and for surveys for 

total corrected sign (TCS), (see tortoise transect history below). The analyses that we 

conducted provide both qualitative and quantitative conclusions about the spatial nature of 

tortoises relative to carcasses, and of the relative presence and absence (viz., failure to 

detect) of tortoises in DWMAs. 

Specific analyses included: 

1) An Observation Rates analysis, which compared distance sampling transects in which 

live tortoises were observed relative to the number of transects in which only carcasses 

were observed. 

2) A Presence/Failure to detect analysis to examine the recent spatial distribution of the 

presence of live tortoises and carcasses using transect data from surveys of total corrected 

sign (TCS). 

3) Two Conditional Probability of Live Encounter analyses consisting of two 

approaches with the same goal. These analyses were used to estimate the probability that an 

observation was a living tortoise as a function of location within the Western Mojave DPS 

using Line Distance Sampling (LDS) data from 2001. 

4) Kernel analyses, which are quantitative analyses in which the distributions of live 

tortoises and carcasses were smoothed to qualitatively search for areas where distributions 

of live tortoises and carcasses do not overlap. These non-overlapping areas may indicate 

areas that have experienced recent die offs or expansions of populations. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 63 

5) Nearest Neighbor Clustering, which is a quantitative search for statistical clusters of 

live animals and carcasses. Analyses included searching the degree of overlap (or 

separation) of these clusters. 

Each of these analyses carries unique limitations concerning the extent to which transect 

data can be used. For example, Nearest Neighbor Hierarchical Clustering requires that the 

data be spatially random or regularly distributed. Thus, cluster analysis was restricted to 

using only LDS data from 2001. Table 4.5 lists data used in our spatial analyses. 

These analyses are neither intended to be an exhaustive exploration of all spatial analysis 

techniques suitable for TCS and LDS data, nor are they an exhaustive attempt to analyze all 

possible data and/or regions. Instead, our objective is to investigate alternative, and 

primarily novel, spatial analysis techniques that should be explored further by the 

subsequent recovery team. There are very likely more types of spatial analyses that could 

be explored and perhaps better spatial analyses that are more appropriate given the different 

sources of data that we had available. If a future recovery team is formed, we recommend 

that all of the data available to them, and future monitoring efforts be explored to the fullest 

extent possible, as the detection of trends alone (given current sampling precision, see 

Section 6) seems at this time untenable. 

Table 4.5 Summary of data, year, and region used for each analysis. TCS = total corrected sign 

surveys; LDS = line distance sampling. 

Analysis Transect Data Years Region 

Presence/Failure to Detect TCS, LDS All years West Mojave 

Observation Rates LDS 2001-2003 Range-wide (excluding Upper 

Virgin River) 

Kernel LDS 2001 Range-wide 

Cluster LDS 2001 West Mojave 

Conditional Probability of Being 

Alive: Re-sampling 

LDS 2001 West Mojave 

Conditional Probability of Being 

Alive: Logistics Regression 

LDS 2001 West Mojave 

4.3.1 History of Desert Tortoise Transects 

Total Corrected Sign Transects 

There have been several transect methods used to estimate the relative presence of 

tortoises, especially in the Western Mojave. Prior to, and later in support of, the draft West 

Mojave Plan (BLM et al. 2003), many transects were surveyed with the goal of measuring 

tortoise sign. These data typically are referred to as total corrected sign (TCS). Historically, 

estimates of relative tortoise density have been estimated from the “corrected” sign of 

tortoises. This correction was based upon comparison of sign counts from areas of 

unknown density and areas with both sign counts and estimated density. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 64 

Transect surveys for TCS transects were conducted in 1998, 1999, and 2001 by the Bureau 

of Land Management West Mojave Planning team in support of development of the draft 

West Mojave Plan (WMP) habitat conservation plan and the California Desert 

Conservation Area Plan amendment (BLM et al.2003). The transect method was developed 

by Berry and Nicholson (1984) to determine relative tortoise densities. However, the West 

Mojave Plan planning team restricted the use of the data for various reasons to depict 

relative “patterns of occurrence” for tortoises (BLM et al. 2003). The transects are typically 

walked in the Autumn, to allow for greater amounts of tortoise sign (i.e., scat and burrows) 

to accumulate during the activity season. In addition to observations of scat and burrows, 

observations of live tortoises and carcasses were also recorded. 

For the purposes of analyses conducted herein only the raw sign data were used. In other 

words, data were not “corrected”, and no density estimates were derived from the data. 

Distance Sampling Transects 

In February 1995 during a workshop on tortoise monitoring in Reno, Nevada (sponsored by 

the Biological Resources Research Center at the University of Nevada, Reno), tortoise 

biologists, statisticians, and monitoring experts reviewed previous methods used to monitor 

tortoise populations and possible methods to use in the future. At this workshop, the 

method of “Distance Sampling” (Buckland et al. 1993) was introduced as a way to mitigate 

the problems of the permanent study plots. At a second meeting in Laughlin, Nevada, in 

October 1998, the Management Oversight Group (MOG) proclaimed Distance Sampling to 

be the method that would be used on public lands for estimating density of desert tortoise 

populations. In June 1999, the MOG endorsed the use of Distance Sampling using program 

“Distance” as the method to be employed in range-wide sampling of desert tortoise 

populations. However, the appropriateness of the technique for sampling desert tortoises 

(especially in areas with low population densities) was, and remains, contentious (see 

Section 6). 

In January 2001 a monitoring workshop was held in Las Vegas, Nevada, to explain the 

sampling techniques that would be used in 2001 to conduct the first years effort of Line 

Distance Sampling range wide. This meeting was attended both by agency and contractor 

personnel. A handbook was prepared by the Desert Tortoise Coordinator and provided in 

March 2001 to serve as the manual for conducting the distance sampling in 2001. In March 

of 2001, two training workshops were conducted. Approximately 40 people attended each 

of the two four-day workshops. These training workshops provided practice for conducting 

the Distance Sampling technique by using styrofoam tortoise models (styrotorts) placed in 

natural habitats near Jean, Nevada. This technique had been used as part of an earlier 

demonstration workshop conducted in October 1998 (Anderson et. al. 2001). Finally, the 

tortoise transects were sampled range-wide beginning in 2001 by Chambers Group; Kiva 

Biological Consultants; the Mojave National Preserve; the University of Nevada, Reno; 

and the Utah Division of Wildlife Resources. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 65 

The Utah Department of Wildlife Resources instituted a monitoring program similar to that 

of the rest of the listed range of tortoises (using transects to monitor tortoises and the 

distance technique to estimate densities of tortoise populations) at the Red Cliffs Desert 

Reserve within the Upper Virgin River Recovery Unit (McLuckie et al. 2002). A pilot 

study was initiated in 1997, and reserve-wide monitoring was initiated in 1998. 

For most of the listed range (excluding the Upper Virgin River Recovery Unit) LDS 

transects (Buckland et al. 2001) were conducted for the years 2001-2003 by the USFWS in 

support of the range-wide sampling of tortoises within DWMAs. Transects were conducted 

in the spring, corresponding to periods of high tortoise activity. Data from these transects 

can be used to calculate density estimates at several scales (e.g., for each DWMA or 

Recovery Unit; Anderson et al. 2001). Transects for 2001 were randomly selected from a 

400m grid within each DWMA with the following exclusions: areas greater than 4,200 ft in 

elevation, slopes ≥30%, permanent water bodies, playas, major roads, private land, and 

restricted areas within military reservations. 

Density estimates for the 2001 distance sampling for the West Mojave indicate 

approximate densities of 7.3 tortoises/km2 (95% CI = 5 – 10) for the Fremont-Kramer 

DWMA and 9.6 tortoises/km2 (95% CI = 7 – 13) for the Ord-Rodman DWMA (Medica 

pers. comm.). These numbers are relatively comparable to those given for permanent study 

plots near the same two DWMAs (DTNA Interior for 2002 = 2 tortoises/km2 (95% CI = 1-

4), Fremont Valley for 2001 = 5 tortoises/km2 (95% CI = 2-9) (Berry pers. comm.). 

However, the sampling design for monitoring for most of the range (excluding the Upper 

Virgin River Recovery Unit) using transects was flawed in such a way that samples from 

subsequent years (2002 and 2003) cannot be considered representative of the DWMAs as a 

whole. Therefore, density estimates for 2002 and 2003 were not part of our analyses. The 

“flaws” in data collected in 2002 and 2003 reflect weaknesses in the system of 

constructively adapting monitoring each year to increase efficacy. In particular, several 

processes contributed to problems in 2002 and 2003. The lack of certainty in year-to-year 

funding of range wide monitoring contributed to an atmosphere of last-minute adjustments 

to monitoring methods. Adjustments to field techniques often emphasized logistics instead 

of needs for solid scientific design and statistical validity. Only as part of the DTRPAC 

process did we learn that adjustments in monitoring methods to improve logistics actually 

nullify the statistical validity of spatial analyses from those data. This experience reveals 

the pressing need for a consistent, high-level, scientific advisory capability as part of range 

wide monitoring overseen by USFWS. 

The data provided by distance sampling transects sampled in 2001 and the TCS transects 

from other years provide a capacious source of information for spatial analyses. For 

example, we found that the spatial data from both the relative sign and distance sampling 

transects could be used to understand better the information regarding the declining density 

estimates of tortoises as provided by the permanent study plots, especially in the West 

Mojave. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 66 

4.3.2 Observation Rates 

(distance sampling transects; range-wide, excluding Upper Virgin River; 2001-2003). 

The objective of this analysis was to ascertain the percentage of transects in which live 

tortoises were observed in comparison to the number of transects on which only carcasses 

were observed. Spatial randomness was not required for this analysis, so the data from 

distance sampling transects for 2001 through 2003 were used (Table 4.6). Although data 

from corrected sign transects also contain observations of live and dead tortoises, the 

difference in sampling period relative to distance sampling transects (Autumn for sign 

transects and spring for distance sampling transects) disproportionately biases against live 

observations compared to those observed on the distance sampling transects, which could 

skew the live/carcass ratios. For this reason we limited our analysis to LDS data only. 

The percentage of transects with observations of live tortoises and those with observations 

of carcasses are presented in Table 4.6. Note that high/low percentages should not be 

confused with high/low numbers of live tortoises or carcasses. For example, 29% of the 

transects in Fremont-Kramer in 2001-2003 had live tortoises and 67% of transects had 

carcasses (Table 4.6). 

We also calculated the ratio of carcasses to live tortoises for the same areas (Table 4.6, Fig. 

4.18). A low ratio (i.e. close to 1) does not mean that there are a low number of carcasses; it 

instead means that there were approximately equal numbers of carcasses and live tortoises. 

There was a continuum of ratios ranging from 1.08 for the Pinto to 3.67 for Fenner (Table 

4.6). 

Table 4.6 Percentages of live animals and dead animals found on LDS transects. The third column 

is the ratio of the percent of dead animals encountered to the percent of live animals encountered. 

DWMA % Live %Dead Ratio Dead/Live 

Beaver Dam Slope 5 6 1.25 

Chemehuevi 41 70 1.71 

Chuckwalla 24 46 1.94 

Chocolate Mountains 45 68 1.51 

DTNA 41 59 1.51 

Fenner 20 74 3.67 

Gold Butte 8 15 1.88 

Fremont-Kramer 29 67 2.29 

Ivanpah 16 46 2.87 

Joshua Tree 23 33 1.40 

Mormon Mesa 21 34 1.58 

Ord-Rodman 46 56 1.22 

Pinto Mountains 32 34 1.08 

Piute-Eldorado 15 48 3.23 

Superior-Cronese 29 46 1.60 
 

 

 

 

 

 

 

 

, , - - Recovery Unrt

MilRary Installatioo

o Urban

DTRPAC Report page 67 

The transects revealed patterns of discrepancy between observations of live tortoises and 

observations of carcasses. This analysis is based upon the premise that tortoise populations 

with equal numbers of live animals and carcasses are in a better state than those with 

disproportionately larger carcass numbers. It is worth noting that carcasses are purposely 

removed from active permanent study plots in California. In this case, the small analysis 

area and presence of two active study plots at the DTNA (one sampled in 1997 and 2002 

and the other in 2002 only) could contribute to the low ratio of carcasses to live tortoises. 

Carcass 10 Li ve Ratio 

0 1.08- 1.25 

1.26 • 1.75 

_ 1.76-3.68 

• , , Areas , .. 

Fig. 4.18 The ratio of carcasses to live tortoises for DWMAs. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 68 

4.3.3 Presence/Failure to Detect 

(total corrected sign and distance sampling transects, Western Mojave, all years). 

This analysis graphically assesses the recent spatial distribution of live tortoises and 

carcasses, but is not a statistical analysis of this distribution. Although burrows have been 

shown to be significantly correlated with live tortoises (BLM et al. 2003), we restricted our 

analysis of presence or “failure to detect” tortoises on transects with observations of live 

tortoises or scat. We used the presence of scat as an indication of live tortoises in a given 

area when live tortoises were not actually observed. This method assumes that where there 

is scat, there must have been a tortoise (recognizing that scat can be moved by wind, water, 

or other animals) within a relatively short time frame (assuming scat degradation rates of 1-

2 yrs). 

This analysis was restricted to the Western Mojave for two reasons. First, the DTRPAC 

had access to spatially referenced distance sampling data for the West Mojave, but not for 

other areas. Second, though the DTRPAC had access to distance sampling data throughout 

the entire listed range of the desert tortoise, an analysis of distance transects alone would 

not have been comparable to the combined transect data for the West Mojave due to the 

disparity in their sampling periods. 

All transects were assigned to one square mile analysis grids. Each grid cell was assigned a 

different color based on the composition of the observations of tortoises, scat, and carcasses 

found within the grids (Fig. 4.19). 

The presence/”failure to detect" analysis illustrates patterns of 1) tortoise or scat presence, 

2) tortoise or scat and carcass presence, 3) carcasses only, and 4) failure to detect either 

tortoises or scat or carcasses. Areas containing tortoises included the DTNA, the southern 

portions of Fremont-Kramer, south and east Superior-Cronese, and most areas of OrdRodman (Fig. 4.19). Large sections of Superior-Cronese have not been recently sampled 

(as near as we can determine). It is likely that many of these areas have been sampled by 

other research and/or compliance projects, however data from these areas were not 

available for analysis by the committee. Maintenance of a master desert tortoise location 

database would enhance the ability to track areas of tortoise and carcass occurrence. 
 

 

 

 

 

 

Edwards Air

Fo",,,Sas,,

MCAGCC

29j>aI",s

DTRPAC Report page 69 

Fig. 4.19 Presence/”Failure to Detect” tortoises and carcasses for combined distance sampling 

(2001-2003) and total corrected sign (1998, 1999, and 2001) transects. Dark green areas are those 

in which a tortoise and/or scat were present. Light green areas are those in which a tortoise and/or 

scat and carcasses were present. Red areas indicate only carcasses were present. White areas 

indicate no tortoises, scat, or carcasses were found. Light tan areas indicate no distance sampling 

or total corrected sign transects were conducted. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 70 

4.3.4 Conditional Probability of Live Encounter 

(distance sampling transects, Western Mojave, 2001). 

Resampling 

For this analysis the Western Mojave was divided into a grid consisting of 18 cells. Using 

the 2001 LDS data, the proportion of tortoises that were alive (i.e., live tortoises/[live + 

dead tortoises]) was then calculated for each cell. A test statistic was then derived for each 

cell, which consisted of the observed proportion of tortoises that were alive in each cell 

minus the proportion calculated from all cells combined (0.284). 

The test statistics for each of the 18 cells (Table 4.7) were tested for significance using a 

randomization method. To produce a randomized set of data the 609 transects were 

randomly reallocated to the 18 cells. This was done 10,000 times. The p-value for the 

statistic from the i

th cell was then the proportion of times that the randomized sets of data 

gave a value as far or further from zero than the observed test statistic. In addition, a 19th 

statistic was calculated, which consisted of the maximum of the absolute values of the 

statistics for the individual cells. This was then used to calculate an overall test of 

differences between the cells and for all of the data. 

As shown in Table 4.7, there are significant results for cells 6, 7, 12, and 16, and for the 

maximum statistic. There is also a nearly significant result for cell 15. It is more 

compelling to view the data graphically. Distinct areas, as defined by groupings of points 

with the same color with lower (red) or higher probabilities (green) of live encounters are 

clearly identifiable in Fig. 4.20. 

Table 4.7 Observed ratios of live to dead tortoises. The P values indicate bins of transects in which 

the ratios were different from that expected at random. The sign of the observed value indicates the 

direction of the difference. 

Bin Observed Value P-value Bin Observed Value P-value 

1 0.08 0.45 10 0.09 0.09 

2 -0.13 0.24 11 0.01 0.85 

3 0.10 0.47 12 -0.14 0.04 

4 0.06 0.30 13 -0.06 0.56 

5 0.10 0.47 14 0.05 0.43 

6 -0.28 0.002 15 -0.21 0.07 

7 0.29 0.008 16 0.52 0.001 

8 0.03 0.75 17 0.05 0.54 

9 0.05 0.54 18 0.22 0.09 

Max 0.52 0.004 
 

 

 

 

 

 

 

 

 

Ed",~m, Ai, Fo

wI

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P.'",~

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DTRPAC Report page 71 

• B 

( 

C ... 

• • 

• • ••

•

AGCC 

01 . , 

• 

• than 

• 

_ 

Fig. 4.20 Results from the resampling analysis - Areas depicted in red are points in bins 6 and 12, 

which had lower than average probabilities of live encounters; green points are bins 7 and 16, 

which had higher proportions of live animals. Points in all other bins are blue in color. 

Logistic Regression 

Another analysis was possible based upon logistic regression. The regression calculates the 

probability of a tortoise being live at a distance E km east and N km north from easting 

414493 and northing 3825771 and is given by 

P(E,N) =exp(ß0 + ß 1E + ß 2N + ß 3E.N + ß 4E2 + ß 5N2)/{1 + exp(ß 0 + ß 1E + ß 2N + ß 3E.N + ß 4E2 + ß 5N2)}. 

Data for this analysis were restricted to transects on which both live and/or dead tortoises 

were observed. Each of these transects then provided one observation on the number of 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 72 

tortoises that were live in a sample of n tortoises. It is possible that higher order polynomial 

terms are needed in the equation to describe better the spatial changes in the probability of 

a tortoise being live. This was not investigated. 

The following analysis of deviance shows that the model accounts for a significant amount 

of the variation in the data (Tables 4.8 and 4.9). The mean deviance is much larger than 

one, indicating that part of the variation in the data is not properly accounted for. This 

confirms that it would be worth investigating adding higher order polynomial terms into the 

equation. A kriging surface mapping the conditional probability of being alive in 2001 are 

presented in Fig. 4.21. 

This analysis asks the question, if a tortoise is found on a transect, what is the probability 

that it is a live tortoise? The region in the northern portion of the Fremont-Kramer DWMA 

and the northwestern portion of the Superior-Cronese DWMA had noticeably lower 

probabilities of encountering a live tortoise relative to other portions of the DWMAs. 

Table 4.8 Statistical table for the logistic regression analysis. 

df Mean 

deviance 

Deviance Deviance 

ratio 

Approx chi 

pr. 

Regression 5 47.8 9.56 9.56 <.001 

Residual 300 820.5 2.74 

Total 305 868.3 2.85 

Table 4.9 The estimated coefficients for the logistic regression model. 

Estimate s.e. t(*) t pr. 

Constant 1.966 0.63300 3.11 0.002 

E -0.02214 0.00506 -4.37 <.001 

N -0.02654 0.00979 -2.71 0.007 

EN 0.0000791 0.0000251 3.15 0.002 

E2 0.0000480 0.0000133 3.61 <.001 

N2 0.0000348 0.0000427 0.82 0.414 
 

 

 

 

 

 

 

 

 

 

 

•

ErJ ...~trl< Air FM"

Ch/mt "'-H Fl ...

•

'",",

DTRPAC Report page 73 

• B. 

• 

AGee 

!I In 

Fig. 4.21 Results from the logistic regression analysis. Cooler colors indicate higher probabilities 

of encountering a live tortoise, and warmer colors indicate a lower probability. 

4.3.5 Kernel Analyses 

(distance sampling transects, range-wide, 2001). 

The analyses presented above are useful for comparisons among DWMAs, but do not 

indicate where within an individual DWMA one would be more likely to find live tortoises. 

The kernel, cluster, and conditional probability of being-alive analyses presented below 

however, do indicate where within a DWMA one would expect to find live tortoises. This 

type of within-DWMA spatial analysis requires that the sample transects be significantly 

spatially random or regularly distributed. As such (for reasons given above), only the 2001 

LDS data were used. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 74 

This analysis used adaptive kernels (frequently used for home range analyses) to smooth 

the distributions of the observations of live tortoises and carcasses on the distance sampling 

transects to look for lack of overlap in regions of these two smoothed distributions. Data 

were separated into groups of adjacent DWMAs that had similar numbers of transects per 

area. Observations from these groups were separated into two datasets, one for live 

observations and one for carcass observations. Kernel analyses were conducted for both the 

live tortoises and carcasses for each of the groupings. The kernels were created using the 

Animal Movement Extension (v 2.04b, Hooge and Eichenlaub 2001) for ArcView 3.2 

(ESRI, Redlands, CA). The smoothing factor (H) was reduced to a value below that of the 

default to constrain the kernels to areas that were close to the boundaries of the sampled 

areas. These smoothing factors were taken to be the same for the carcass and live kernels 

for each area. Separate kernel analyses were conducted for the following areas which are 

generally denoted by the DWMAs included therein: 1) Upper Virgin River (Fig. 4.22); 2) 

Beaver Dam Slope/Mormon Mesa/Gold Butte-Pakoon (Fig. 4.23); 3) Coyote Springs (Fig. 

4.24); 4) Piute-Eldorado Valley (Fig. 4.25); 5) Chuckwalla (Fig. 4.26); 6) Joshua 

Tree/Pinto Mountain (Fig. 4.27); 7) Chemehuevi (Fig. 4.28); 8) Ivanpah (Fig 4.29); and 

Fremont-Kramer/Superior-Cronese, and Ord-Rodman (Fig. 4.30). 

The kernel analyses revealed several areas in which the kernel estimations for live tortoises 

and carcasses did not overlap. The pattern of non-overlapping kernels that is of greatest 

concern are those in which there were large areas where the kernels encompassed carcasses 

but not live animals. These regions represent areas within DWMAs where there were likely 

recent die-offs or declines in tortoise populations. This pattern occurred in half of the areas 

for which kernel analyses were conducted (Figures 4.24, 4.25, 4.29, 4.30). It should be 

noted that a few of these areas had relatively few transects (Fig. 4.25, 4.29), and that the 

data underlying all of these results come from only one year of sampling (2001). 

Kernel analyses for the Upper Virgin River (Fig. 4.22), Chemehuevi (Fig. 4.28), Joshua 

Tree/Pinto Mountain (Fig. 4.27), and Chuckwalla (Fig. 4.26) DWMAs had distributions of 

live and dead animals that were more like what we expect to occur in “normal” tortoise 

populations, in that carcasses occurred in the same areas as live animals and not in 

extensive areas absent of live animals. 
 

 

 

 

lOS

v

live OilsefvaHon

Observahon

)( 2001

0 95%

Live

o 2001 Sludy Bound"';..

Militury 1""'. 11 .1;00

o Areas

DTRPAC Report page 75 

• 2001 

• 2001 Ca rcass 

No Observation 

2001 Carcass Probability 

2001 Probability 

_ 95% 

lDS 

i. Urb." 

Fig. 4.22 Kernel analysis for the Upper Virgin River DWMA. The 95% kernel for live animals 

is indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined 

polygon. Transects that were sampled for which no tortoises (live or dead) were found are 

indicated by the letter X on the map. 
 

 

 

 

.,

-~ "I

I" '"

)'11 'f

I'

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,

'~~';/"> ..,~;;;;;;;;;;;:j Live O!l$efV~hoo ~OOl Observshon

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0 2001

_'1 Military Insto ll el,,,., if' 0 Areas

DTRPAC Report page 76 

• Beaver Dam Slope

x x 

I 

2001 

• Ca rcass 

2001 Carcass P r obability

2001 Live P ro bability

_ 95% 

lDS SludY _ 

Urban 

Fig. 4.23 Kernel analysis for the Beaver Dam Slope / Mormon Mesa / Gold Butte-Pakoon 

DWMAs. The 95% kernel for live animals is indicated by the green polygon; the 95% kernel 

for carcasses is indicated by the red outlined polygon. Transects that were sampled for which 

no tortoises (live or dead) were found are indicated by the letter X on the map. 
 

 

 

 

fiMf/sA,r

Foru8ase

"

" .:._-

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/

M ormonMe.a

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Clrc... Ob.e<vation

2001 Qb..,rnr""

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C] 95%

o 2001 Bound"';..

Military 1,,"'" 11 81;00

o Areas

DTRPAC Report page 77 

2001 L.ive Probability 

_ 95% 

lDS Sludy 

., Urban 

• 2001 

2001 

X No 

2001 Probability 

Fig. 4.24 Kernel analysis for the Coyote Springs Valley DWMA. The 95% kernel for live animals 

is indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined 

polygon. Transects that were sampled for which no tortoises (live or dead) were found are 

indicated by the letter X on the map. 

J 

I 
 

 

 

 

-,

•

LIVe Observauon

1001 Carcass ObseNalion

x No 0!>w<v3~

D '"

. ", ':rr,'

0 2001 Boundari...

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o Urban

DTRPAC Report page 78 

Piute - Eldorado 

\ 

• 2001 

• 

2001 

2001 Carcass Probability 

•
 

( • 

2001 Live Probability 

LOS Study 

Installatlon " 

Areas " 

Fig. 4.25 Kernel analysis for the Piute-Eldorado Valley DWMA. The 95% kernel for live 

animals is indicated by the green polygon; the 95% kernel for carcasses is indicated by the red 

outlined polygon. Transects that were sampled for which no tortoises (live or dead) were found 

are indicated by the letter X on the map. 
 

 

 

 

Live ObSefVlltion

2001 Carcass Observation

~lNo~~

02001 Study Ba.lndari es

InslallaHon

Chaco/Me

MI.

Cenrro

Si Se

o Areas

DTRPAC Report	 page 79 

AGR 

\ 

Ion 

• 200 1 

7B	 • 

X 

2001 Carcass Probability 

0 95% 

2001 Live Probability 

_ 95% 

E/ 

LOS 

Military 

Urban 

Fig. 4.26 Kernel analysis for the Chuckwalla DWMA. The 95% kernel for live animals is 

indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined 

polygon. Transects that were sampled for which no tortoises (live or dead) were found are 

indicated by the letter X on the map. 
 

 

 

 

2001 LIIre Observation

2001 Observation

2001 No Ol>~rvalion

CJ 95%

......._--1_95%

02001 Study Ba.lndaries

Inslallalion

o Areas

Twenlynlne

I

•

" Pi rf

Mounta'lns

J. --

"

DTRPAC Report page 80 

, 

Palms 

, 

.
 

X X 

X 

X . X X X X X

X 

X 

X 

• 

• Carcass 

x 

2001 Carcass Probability 

2001 L. ive Probabi lity 

LOS 

Military 

Urban 

Fig. 4.27 Kernel analysis for the Pinto Mountain and Joshua Tree DWMAs. The 95% kernel 

for live animals is indicated by the green polygon; the 95% kernel for carcasses is indicated 

by the red outlined polygon. Transects that were sampled for which no tortoises (live or dead) 

were found are indicated by the letter X on the map. 
 

 

 

 

!

Live Observation

1001 ObseNalion

x No~a~

0 95%

_ 95%

0 2001 Bounda ri...

Mil itary

o Urban

8ul/Mad

" . '1<

•

"x

#

,

~!4~.t

DTRPAC Report page 81 

I 

• 2001 

• Carcass 

2001 

2001 Carcass Probability 

2001 live Probability 

LOS Study 

Installatlon 

; 

Areas 

x 

elll' 

o 

• 0 •

• 0 • 0 0 

0 0 ••

• 0

• 0 0 ' 

0 

0 0 0 

0 0 .. 0 • 0 

0 • 0 

0 

0 -..•

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0 

0 

.. 

Pinto-Mo untaIns 

Fig. 4.28 Kernel analysis for the Chemehuevi DWMA The 95% kernel for live animals is 

indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined 

polygon. Transects that were sampled for which no tortoises (live or dead) were found are 

indicated by the letter X on the map. 
 

 

 

 

ut Eldorado

o Urban

Live Observation

1001 ObseNalion

x No~a~

0 95%

_ 95%

------ 2001 Boundari...

Mil itary

•

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DTRPAC Report	 page 82 

Sea hi hr 

I 

•	 2001 

•	 Carcass 

2001 

2001 Carcass Probability 

'.­

• , 

• 

_ 

2001 Live Probability 

LOS Study 

Installatlon 

Areas 

Fig. 4.29 Kernel analysis for the Ivanpah DWMA. The 95% kernel for live animals is 

indicated by the green polygon; the 95% kernel for carcasses is indicated by the red outlined 

polygon. Transects that were sampled for which no tortoises (live or dead) were found are 

indicated by the letter X on the map. 
 

 

 

 

'"

UVf!' Observlltion CllrclIss

Observ<ltlons

x

'/~(11 CJ 95~ ~j~r::(J J i j :-.

, ;et'~. :JG!C" ,,%

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DTRPAC Report page 83 

o 

o 0

e 

Observation • 2001 • 2001 _ 

2001 No 

2001 Carcass P ro bability

. . 

/' 2001 Livl! Pro ba bility _ 

Urban 

( 

DTNA 

• 

AI' 

o·. eO 

Fig. 4.30 Kernel analyses for Fremont-Kramer / Superior-Cronese, and Ord-Rodman DWMAs. 

The 95% kernel for live animals is indicated by the green polygon; the 95% kernel for 

carcasses is indicated by the red outlined polygon. Transects that were sampled for which no 

tortoises (live or dead) were found are indicated by the letter X on the map. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 84 

4.3.6 Nearest Neighbor Clustering 

(distance sampling transects, Western Mojave, 2001). 

Nearest Neighbor Hierarchical Clustering analysis was used to identify clusters of live 

tortoises and carcasses within the Western Mojave. These analyses were performed using 

CrimeStat II (Levine 2002). Spatial randomness of distance sampling data (2001-2003) and 

total corrected sign data (1998, 1999, and 2001) was tested. The tests included analysis of 

each year, all years, and both. All analyses were using the ArcView extension Animal 

Movement (Hooge and Eichenlaub 2001). The results of these tests confirmed that distance 

sampling transects in 2001 were randomly distributed. However, all other years and all 

combinations of years and methods were statistically spatially clustered. Thus, only data 

from 2001 were analyzed. As with the kernel analyses, where one finds live animals one 

would expect to find carcasses at some level, although the draft West Mojave Plan (BLM et 

al. 2003, Appendix L) reported that carcass counts were not correlated with transect live 

tortoises counts. However, our analyses were conducted for presence and absence and not 

for densities. Where one finds carcasses and no live animals there is cause for concern, 

suggesting recent die-offs in these areas. 

The Nearest Neighbor Hierarchical Spatial Clustering routine used by CrimeStat is a 

constant-distance clustering routine that groups points together on the basis of spatial 

proximity (Levine 2002). The threshold distance (i.e., the confidence interval around a 

random expected distance of a pair of points) was set to 0.95 (i.e., fewer then 95% of the 

pairs could be expected to be as close or closer by chance). Only pairs of points that are 

closer together than this threshold distance are grouped together as clusters. The minimum 

number of points required to create a cluster was set to 5. The size of the ellipse around the 

cluster was set to one standard deviation, which would cover about 65% of the points. 

The Cluster analysis revealed numerous patterns of statistically significant live and carcass 

clusters, and these clusters did not overlap in several areas. These include; central FremontKramer, western Superior-Cronese, and numerous areas within the Western Mojave (Fig. 

4.31). 
 

 

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DTRPAC Report page 85 

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Fig. 4.31 Nearest Neighbour Hierarchical Cluster analysis for the Western Mojave. Green 

areas are clusters of living tortoises; red outlines are clusters of carcasses. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 86 

4.4 Implications of Population and Spatial Analyses 

The spatial analyses provided in this report are examples of the kinds of analyses that 

should be considered by a possible future recovery team and by the science advisors to the 

USFWS. We recommend that similar analyses be conducted for the rest of the listed range. 

We also recommend analyses with additional years of data when suitable data become 

available. Time and data limitations have prevented the DTRPAC from completing all 

possible analyses for this report. 

The Western Mojave (Recovery Unit/DPS) has experienced marked population declines 

over time (Fig 4.6). This was indicated in the original Recovery Plan and continues today. 

Spatial analyses of the West Mojave show areas with increased probabilities of 

encountering dead rather than live animals (Fig. 4.18, 4.19, 4.20, and 4.21), areas where 

kernel estimates for carcasses exist in the absence of live animals (Fig. 4.31), and extensive 

regions where there are clusters of carcasses where there are no clusters of live animals 

(Fig. 4.31). Collectively, these analyses point generally toward the same areas within the 

West Mojave, namely the northern portion of the Fremont-Kramer DWMA and the 

northwestern part of the Superior–Cronese DWMA. Together, these independent analyses, 

based on different combinations of data, all suggest the same conclusion. The management 

strategy and implementation of recommended management actions over the last decade in 

West Mojave Recovery Unit have not slowed the decline of tortoise populations, and 

tortoise numbers are plummeting. Indeed the Draft West Mojave Plan (WMP) points out 

problems within the same areas highlighted in our analysis. For example, despite 

historically high densities of tortoises (BLM et al. 2003, map 3-7) within some portions of 

the West Mojave Recovery Unit, analyses in the West Mojave Plan indicate recent die offs 

(BLM et al. 2003, map 3-12) and higher-than-average sign counts (BLM 2003, map 3-8) in 

the same regions as presented by our independent analyses of the data. 

Data are not currently available (i.e., they either do not exist or are not easily accessible) 

with the same detail for most of the range of desert tortoises. Nevertheless, it is possible to 

compile and digitally catalog corrected sign data for other recovery units within the listed 

range, but not without considerable time and money. We had additional historical data for 

permanent study plots and recent data from distance sampling surveys for these regions, 

and they were similarly analyzed but not reported. Kernel analyses of DWMAs within 

other Recovery Units and Distinct Population Segments also show areas of nonoverlapping carcass and live animal distributions (e.g., Fig. 4.24, 4.25, 4.29 and 4.30) and 

this signals reason for concern for these areas. Ivanpah (Fig. 4.29) and Piute–Eldorado 

Valley (Fig. 4.25) contained study plots that were analyzed in the East Mojave Recovery 

Unit analysis (Fig. 4.6). While there was no overall statistical trend in adult density over 

time, the 2000 survey at Goffs and the 2002 survey at Shadow Valley indicate low 

densities of adult tortoises relative to earlier years. Unfortunately there are no data in the 

latter years for all five study plots within this recovery unit, and therefore, while there is no 

statistical trend in adult densities, we cannot conclude that tortoises have not experienced 

recent declines in this area. The probability of finding a carcass on a distance sampling 

transect was considerably higher for Ivanpah, Chemehuevi, Fenner, and Piute-Eldorado 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 87 

which make up the Eastern Mojave Recovery Unit and portions of the Northeastern Mojave 

and Eastern Mojave/Colorado Desert DPSs (Table 4.6). 

The kernel analysis for the Piute-Eldorado Valley (Fig 4.25) indicated large areas where 

there were carcasses, but no live animals were found. For this entire area in 2001, there 

were 166 km of transects walked, and a total of six live and 15 dead tortoises were found, 

resulting in a live encounter rate of 0.04 tortoises per km for this area. This encounter rate 

was among the lowest for that year for any of the areas sampled in the listed range. 

Analyses of the study plots for the Eastern Mojave Recovery Unit (Fig. 4.6) and the East 

Mojave and Colorado DPS (Fig. 4.16) do not indicate significantly declining densities of 

adult tortoises prior to 1997. The kernel analysis for the Ivanpah DWMA also indicates 

large areas where only carcasses were found and smaller areas where live animals occurred 

(Fig. 4.29). Analyses of the study plots for the Lower Virgin River DPS (Fig. 4.19) and the 

Eastern Mojave Recovery Unit (Fig. 4.6) do not indicate significant declines in adult 

density over time (although note the apparent declines on the Beaver Dam Slope Exclosure 

and Virgin Slope plots noted in Section 4.2.5). 

The Coyote Springs Valley DWMA is included in the Lower Virgin River DPS plot 

analysis. While the kernel analysis for this region showed areas where the distributions of 

carcasses and living tortoises do not overlap (Fig. 4.24), densities of adult tortoises for the 

region do not show a statistical trend over time (Fig. 4.6). Thus, while there may be a local 

die-off occurring in the northern portion of this DWMA, this does not appear to influence 

the overall trend in the region as interpreted by study plot data. However, as stated above, 

the data for permanent study plots for this region were discontinued after 1996. Thus, if 

there have been recent declines in numbers, they are not reflected in our analyses of study 

plots. Nevertheless, we did not see large regions of non-overlapping carcass and live 

tortoise kernels in the regions adjacent to the Coyote Springs Valley DWMA (Fig. 4.24). 

The probability of finding either a live tortoise or a carcass was relatively very low for 

Beaver Dam Slope and Gold-Butte Pakoon and moderately low for Mormon Mesa/Coyote 

Springs Valley (Table 4.6) all within the Lower Virgin River DPS. 

The Eastern Colorado Recovery Unit contained only two study plots, and analyses of adult 

densities over time indicate that there may be declines in this area (Fig. 4.12). From 

inspection of the density data, it appears that this is likely due to declines in adult density 

for the Chuckwalla Bench plot, but not the other plot (Fig. 4.12). The kernel analysis of this 

area shows that the distributions of the living tortoises and carcasses overlap for most of the 

region sampled by LDS (Fig. 4.26). The Chuckwalla Bench study plot is outside of the 

distance sampling study area, and this creates a problem in evaluating what may be 

occurring in that area of the DWMA. However, the few transects walked in that portion of 

the DWMA yielded no observations of live or dead tortoises. This illustrates our concern 

for drawing conclusions from areas represented by too few study plots and leaves us with 

guarded concern for this region. The percentage of transects with live animals was 

relatively high for most DWMAs within the Eastern Colorado Recovery Unit (Table 4.6). 

In addition, the ratio of carcasses to live animals was low within this recovery unit relative 

to others (Fig 4.18). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 88 

Desert tortoise populations defy definition in terms of population dynamics even after 30 

years of data from a wide variety of studies. In particular, the existing paradigm and the 

original Recovery Plan treated desert tortoise population dynamics and planned for 

recovery as individual populations. However, the temporal dynamics revealed in existing 

data and theory, and the clear indication that populations of tortoises respond remarkably 

slowly, suggest that this original paradigm needs re-evaluation. Specifically, it is not 

known if desert tortoises have evolved to exist in single large populations or in 

metapopulations. The prescriptions for recovery in the Plan were for individual populations 

and assumed that preserving large blocks of habitat and managing threats in that habitat 

would be principally all that would be necessary to recover the species. However, that 

original paradigm, and the prescriptions made within that paradigm, may be wrong and 

dangerously misleading and ineffective. Consider, for example, that existing data have 

revealed population crashes occurring asynchronously across the range. There are reports 

that some populations, which have crashed previously, have subsequently increased in 

population density. Additionally, everywhere where populations have been dense, those 

populations have crashed. This suggests that density-dependent mortality occurs in desert 

tortoise populations, and that population dynamics may be asynchronous. 

These characteristics indicate that tortoises may exist in a classic metapopulation (Hanski, 

1999, Levins and Culver 1971, Levins et al. 1984), and this should portend profoundly 

different prescriptions for recovery. In particular, if desert tortoises have historically 

existed in metapopulations, then connections among habitat patches are a necessary part of 

conservation prescriptions. Additionally, habitat suitable for tortoises, but without tortoises, 

should be regarded as equally necessary for recovery. Assessing the state of a 

metapopulation (including the long-term persistence of the species) will be entirely 

different and needs to be the subject of future research and consultation. Long-term 

persistence cannot be determined from tortoise density or tortoise numbers alone, but 

assessment must include the complexities of metapopulation dynamics and the habitat 

characteristics that promote metapopulation dynamics (habitat connectivity through 

inefficient corridors (i.e., partial connectivity), asynchrony of subpopulation dynamics, 

several separate habitat patches, and others). Some of the characteristics of proper 

metapopulation function may already have been obviated by proliferation of highways, and 

habitat fragmentation due to satellite urbanization. Thus, management may require 

artificially facilitating metapopulation processes such as movement among patches. Insofar 

as having the correct paradigm is central to recovery success, this is a critical area requiring 

attention by science consultants to the USFWS. 

Plot and Spatial Analysis Recommendations 

1.	 There were several recovery units and proposed DPSs that contained too few 

permanent study plots to be analyzed either with any power, or at all. If study 

plot sampling is to continue, it would be better if there were enough study plots 

to represent the different scales of management areas. As a study plot is in itself 

only a sample, and not representative of an entire area, it would be beneficial to 

have several plots within each area upon which future analyses are to be 

conducted, for example a DPS, or even for DWMAs within DPSs. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 89 

2.	 If permanent study plots are to be continued (see, for example, 

recommendations in Section 3), then there should be some agreement among 

the surveying agencies to share the data for the greater good of the tortoise 

species. Permanent study plots played a key role in this committee's 

interpretation of the current status of tortoise populations, but it is possible that 

some of the conclusions reached as a result of our analyses could be different 

had additional years of data been available. However, the trend from the 

Western Mojave is a solid conclusion that cannot be disputed. 

3.	 We found the exploration of new analyses, especially those that can be 

conducted with existing data or with little modification of current monitoring 

methods, to be extremely valuable toward understanding the status of tortoise 

populations and the inadequacies of current monitoring. These types of analyses 

should be part of any future reporting on status and trends of desert tortoise to 

the MOG, DMG, and/or Congress. These kinds of analyses should be prepared 

by a body like the recommended Desert Tortoise Recovery Office discussed in 

Section 7.3 of this report, so that regular advice can provide a means towards 

improved monitoring. 

4.	 The paradigms of population/metapopulation dynamics need to be re-evaluated. 

This may require explicit experimental research to dissect the driving ecosystem 

processes important to long-term persistence of desert tortoise populations or 

metapopulations. 

4.5 Status and Trends of Habitat and Environmental Setting for Tortoise 

Populations 

An efficacious monitoring program should be multidimensional, including monitoring of 

populations, monitoring the extent and condition of habitat, and monitoring threats to 

tortoises. Monitoring habitats and threats has not previously been part of the protocols for 

monitoring the desert tortoise, so analyses of past efforts is not possible. However, it is 

possible retrospectively to provide examples of how such analyses can be conducted. We 

present the examples below as “case studies.” 

4.5.1 Road Case Study 

Habitat monitoring considers variables related to the physical environment of the desert 

tortoise. These variables can include natural processes, such as climate and weather, and 

anthropogenic threats, such as presence of roads, livestock grazing, urbanization, etc. In 

this case study, we explore the temporal distribution of routes (i.e., roads) inventoried 

between the mid 1980s and 2001 and the co-occurrence of above average vehicle impact 

areas with higher density TCS and die-off regions as presented by the West Mojave Plan 

(BLM et al. 2003). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 90 

Roads are conduits by which humans come into contact with tortoises. Hence, 

understanding the relationship between the presence of roads and tortoise population 

dynamics may be important to formulating desert tortoise recovery strategies. The original 

Recovery Plan recommended: 1) prohibiting vehicles from driving off roads; 2) restricting 

proliferation of new roads; 3) closing vehicle access to all but designated routes; and 4) 

implementing emergency closures of unpaved roads and routes as needed to reduce human 

access and disturbances in areas where human-caused mortality may have caused negative 

population trends. The plan also specifically highlighted the need to halt unauthorized ORV 

use in the Fremont-Kramer DWMA (USFWS 1994, Table 4.3). 

The comparisons made in this case study use the best data available to the DTRPAC. 

However, we are aware that both road and tortoise data are imperfect, thus we identify 

possible scenarios resulting from these imperfections and geographic regions within the 

Western Mojave that yield contradictory relationships between the presence of roads and 

tortoise sign. 

The following data were used in this case study: 1985-87 (Fig. 4.32) and 2001 routes (Fig. 

4.33) provided by the BLM. Above average vehicle impact areas, areas identified as higher 

then average sign counts, and areas with recent die-offs (Fig 4.34) were taken from the 

West Mojave Plan. In the following section, inventory and any of its variants, is used to 

represent routes (i.e., roads) without dealing with official designation (i.e., open, closed, 

undetermined, etc.). Different methods were used by the BLM to inventory routes between 

1985-87 and 2001. In particular, Global Positioning System (GPS) and Geographic 

Information Systems (GIS) were used for locating and mapping roads in 2001 but not in 

1985-87. Thus, the 2001 inventory is likely to be more detailed and more accurate than the 

initial 1985-87 inventory. Despite this discrepancy, the data used for this case study 

represent the best available data, data for which management and policy decisions have 

been made, and data for which management and policy decisions are being made currently 

(e.g., WMP and West Mojave Route Designation). 

The 2001 inventory of roads (Fig. 4.33) indicates that a higher density of roads currently 

exists within DWMAs in the West Mojave than was documented in 1985-87 and also that 

more roads are currently documented than were documented in 1985-87 (Fig. 4.34). One 

explanation for the increase in road density in the Western Mojave is that the number of 

roads increased during this period. Based on the increased human population in the western 

Mojave during this time, an actual increase in roads is a plausible and likely explanation for 

the increase in inventoried roads. This is especially likely considering the popularity of 

vehicle-based recreation in the desert leading to the legal and illegal creation of single and 

two-track routes. However, an important alternative explanation exists. It is plausible and 

likely that at least some of the recently mapped roads are historic rather than newly created, 

especially considering the effectiveness of GPS-based mapping and increased survey effort 

in recent years. This alternative hypothesis is important because arithmetically it is possible 

that the rate of discovery of established roads (better technology and greater effort) 

exceeded the rate of road closures (management action) and resulted in more apparent 

roads. It is possible that the question of recent road creation could be resolved by analyzing 

consistently collected data such as satellite and aerial surveys that documented the presence 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 91 

or absence of roads in the Western Mojave from 1987-2001.The DTRPAC encourages 

management agencies to consider performing this analysis. 

The tortoise population dynamics information for the western Mojave also has caveats. In 

particular, the “higher density TCS areas” may have used burrow counts as well as 

sightings of live tortoises and tortoise scats. Hence, it is possible that higher than average 

TCS may be inflated relative to other surveys techniques. This is an example of the 

difficulties that arise when data are inconsistently collected, named, and reported. 

The number of inventoried routes increased significantly between 1985-87 and 2001 (Fig. 

4.32 and 4.33). The spatial location of open routes between 1985-87 and 2001 has changed 

significantly (Fig 4.35 and 4.36). The red lines in Fig. 4.35 represent 2001 officially 

designated open routes that were not similarly designated as such in 1985-87. In some 

cases these routes may have existed in 1985-87 but failed to be inventoried, or if 

inventoried they were not designated as open. The blue lines in Fig. 4.36 represent 1985-87 

officially designated open routes that were not officially designated as open in 2001. In 

some cases these routes may no longer exist, they exist but were not inventoried in 2001, or 

they may still exist but were not officially designated as open in 2001. 

We identified 6 regions within the western Mojave roads case study that each indicate a 

different potential relationship between roads, higher then average TCS densities, and 

tortoise die-off regions (Fig. 4.34). We identify tortoise die-off regions within and outside 

vehicle use areas (Fig. 4.34, regions A and B, respectively); higher then average TCS 

densities within and outside of vehicular areas (Fig 4.34, regions C and D, respectively); 

areas simultaneously with high die-off, high TCS, and vehicle use (Fig. 4.34, region E); 

and areas with simultaneous high die-off, high TCS, and no vehicle use (Fig. 4.34, region 

F). A superficial explanation for these results is that vehicle use is unrelated to higher than 

average density TCS and/or die-off regions. This interpretation is incongruous with other 

indications that tortoise mortality is linked to human encounters via roads and would 

require a reinterpretation of other studies. Alternatively, there are many kinds of vehicle 

use and some uses are relatively innocuous to tortoises whereas other uses are deleterious. 

It is also possible that the data in this comparison lack sufficient resolution to detect the 

real and complex relationships between TCS, carcasses, roads, and vehicle use. 

Road Case-Study Recommendations 

1.	 Management agencies should compare historic satellite and aerial surveys to 

better document changes in road density. 

2.	 Despite ambiguities in the current case study, a similar approach could be 

employed using rigorously collected data to reveal real and important 

relationships between tortoise population dynamics and presence of roads or 

other aspects of, or impacts to, desert tortoise habitat. 
 

 

 

 

 

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DTRPAC Report page 92 

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Fig. 4.32 Routes in the Western Mojave DWMAs in 1985-87. Blue routes were designated as open, 

brown as either closed, limited, undetermined, or non-route. Large roadless areas such as southwest 

Ord-Rodman, and the most southwestern portion of Fremont-Kramer were not without roads in 

1985-87, but were instead not inventoried. On the other hand, the DTNA was designated by the 

BLM as an Area of Critical Environmental Concern and fenced in the late 1970’s, thus creating a 

roadless area. 
 

 

 

 

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Fig. 4.33 Routes in the Western Mojave DWMAs in 2001. Orange routes were designated as 

open, brown as either closed, limited, or non-BLM owned routes. The most southwestern portion 

of Fremont-Kramer remains un-inventoried as does portions of northern Fremont-Kramer, 

excluding the DTNA. 
 

 

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DTRPAC Report page 94 

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recent die-off regions as reported by the West Mojave Plan (BLM et al 2003). Letters are explained 

in the text. 

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Fig. 4.35 Comparison of 1985-87 and 2001 designated open BLM routes. The red routes 

represent 2001 routes not formally designated as open in 1985-87. The lack of designation as 

open in 1985-87 could be a result of the fact that the route was inventoried in 1985-87 but not 

designated as open, not inventoried in 1985-87 but existing, or not existing in 1985-87. 
 

 

 

 

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Fig. 4.36 Comparison of 2001 and 1985-87 designated open BLM routes. The blue routes 

represent 1985-87 routes not formally designated as open in 2001. The lack of designation as 

open in 2001 could be the result of the fact that the route was inventoried in 2001 but not 

designated as open, not inventoried in 2001 but existing, or not existing in 2001. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 97 

4.5.2 Patterns of Precipitation Case Study 

It is important to assess the natural variation in the physical environment as well as the 

anthropogenically-altered environments. Drought has been hypothesized potentially to cause 

population declines in desert tortoise populations. To assess the extent to which there have 

been trends in precipitation, we obtained data on precipitation from all known weather 

stations in the Mojave. These data were parsed into cumulative rain that would affect 

production of spring annual plants (precipitation within November to April) and rain 

resulting from summer monsoonal thundershowers (precipitation within May to October). 

These data were assembled for three locations in the Mojave (Table 4.10) and averages for 

each region and for each season were plotted in Fig. 4.37. Clearly, the regions have different 

patterns of rainfall, as the West Mojave has almost all of its rainfall in the winter season. 

Also, clearly, there is no long-term trend in rainfall amounts or in patterns of drought 

duration. The variability of precipitation from year-to-year is very large, and the only 

apparent conclusion one can draw from the data is that the amount of precipitation and the 

occurrence of drought are not especially predictable measures for any place in the Mojave. 

Thus, the absence of a clear pattern suggests that precipitation alone (i.e., not in concert with 

other stressors) cannot account for downward trends in population sizes in the Mojave. 

Table 4.10 Weather stations in the Mojave Desert used in analysis of precipitation (Fig. 4.37). 

Northeast-Sonoran East Group West Group 

BEAVER DAM BOULDER CITY ADELANTO 

BULLHEAD CITY DESERT NATL WL RANGE APPLE VALLEY 

BUNKERVILLE DUNN SIDING BARSTOW 

CALLVILLE BAY KYLE CANYON RANGER STN CANTIL 

DAVIS DAM LAS VEGAS MCCARRAN INTL AP CHINA LAKE NAF 

ECHO BAY MITCHELL CAVERNS EL MIRAGE 

KINGMAN MOUNTAIN PASS HESPERIA 

LAKE HAVASU NORTH LAS VEGAS INYOKERN 

LAUGHLIN RED ROCK CANYON ST PK LUCERNE VALLEY 1 WSW 

LITTLEFIELD 1 NE SEARCHLIGHT MOJAVE 

LOGANDALE SUNRISE MANOR LAS VEGAS RANDSBURG 

LYTLE RANCH SHOSHONE TRONA 

MESQUITE VICTORVILLE PUMP PLANT 

NEEDLES 

OVERTON 

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PIERCE FERRY 17 SSW 

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TEMPLE BAR 

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DTRPAC Report page 98 

1250 

A. West Mojave November to April 

• May to October 1000 

B. East Moj ave 

1000 

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1250 

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1000 

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1980 1990 2000 

Fig. 4.37 Seasonal rainfall in the Mojave Desert, 1930-2000. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 99 

Patterns of Precipitation Case Study Recommendations 

This type of analysis should be conducted for other specific threats to desert tortoise 

populations, as well as ecological variables that may also influence tortoise population 

status (e.g., rainfall, Fig. 4.37). Such analyses will provide managers and scientists with a 

comprehensive database of the current environmental setting under which tortoise recovery 

is taking place and will provide the basis for future hypothesis-based monitoring of tortoise 

populations relative to threat mitigation and environmental change. 

4.5.3 Disease Case Study 

Because disease has been such a prevalent issue throughout the range of the desert tortoise, 

it seems appropriate to consider it in some depth here, as an aspect of the status of the 

species’ environmental setting. The Recovery Plan mentions two diseases specifically, 

shell dyskeratosis (section I.B.3) and upper respiratory tract disease (sections I.B.3 and 

II.D.3.b.1, appendix D.IV.C). Other potentially important diseases not mentioned 

specifically include herpesvirus (THV) (Pettan-Brewer et al. 1996), iridovirus (Westhouse 

et al. 1996), and fungus (Homer et al. 1998, Rose et al. 2001) infections. Diseases in 

general are mentioned or implied for topics such as sources of mortality (USFWS 1994, 

Section II.D.b.2) and translocation (USFWS 1994, Appendix B.6). 

Shell dyskeratosis is not uncommon in both the desert tortoise and the gopher tortoise. The 

disease may be related to nutrient deficiency or to toxins (Jacobson et al. 1994, Homer et 

al. 1998, Christopher et al. 2003; E.R. Jacobson, pers. comm.). A direct connection 

between shell dyskeratosis and population decline in tortoises has not been established. A 

correlation between the presence of shell dyskeratosis and a die-off of individuals has been 

reported for a site in California (Berry 1997), yet numerous other threats (Boarmann 2002) 

are also present at that site. In addition, no correlation exists between frequency of shell 

dyskeratosis and population declines in the Sonoran Desert (Arizona Game and Fish 

Department, unpublished data). 

Little was known about the relationship of Mycoplasma to tortoise disease when the 

Recovery Plan was developed. Likewise, the potential relevance to the desert tortoise of 

studies of Mycoplasma in the gopher tortoise was little appreciated when the Recovery Plan 

was developed. Upper respiratory tract disease (URTD) now is confirmed to be the result 

of infection by Mycoplasma agassizii in both the desert tortoise and gopher tortoise (Brown 

et al. 1994, 1996). Furthermore, another, closely related, species of Mycoplasma, M. 

cheloniae, has been isolated from tortoises, and two more species of mycoplasma are 

known from tortoises, but not as yet isolated (Brown et al. 2002; M.B. Brown, pers. 

comm.). Important studies of respiratory mycoplasmal infection in tortoises published since 

1994 include Jacobson et al. (1995), Berry (1997), Epperson (1997), Lederle et al. (1997), 

McLaughlin (1997), Schumacher et al. (1997, 1999), Smith et al. (1998), Brown et al. 

(1999), and Diemer-Berish et al. (2000). A direct cause/effect relationship between 

respiratory mycoplasmal infection and population decline in tortoises has not been 

established, although a provocative correlation between the presence of URTD and die-offs 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 100 

of individuals of both the desert tortoise and the gopher tortoise has been documented at 

some locations (Jacobson et al. 1995, Berry 1997, Rabatsky and Blihovde 2002, Seigel et 

al. 2003; K.H. Berry, pers. comm.; J.E. Diemer-Berish, pers. comm.). 

Mycoplasma agassizii is easily transmitted horizontally by direct contact between host 

individuals (McLaughlin 1997, Brown et al. 2002). Although other Mycoplasma are known 

to be transmitted vertically from host mother to offspring and via fomite, such modes of 

transmission have not been demonstrated for M. agassizii (Brown et al. 2002). Because M. 

agassizii is so easily transmitted horizontally, isolating infected individuals is an 

appropriate means to control spread. Isolation of infected individuals is only a part of the 

general strategy for control of an infectious disease, which should include diagnosis, 

quarantine, culling or segregation, physical separation, sentinels, and long-term monitoring 

(M.B. Brown, pers. comm.). How much time, effort, and funds are put into implementing 

this strategy for a particular disease depends, in large part, on the perceived risk to the host: 

the greater the perceived risk, the larger the commitment. For example, although the 

viruses that can cause another upper respiratory tract infection, the “common cold” in 

humans, are extremely contagious, virtually no control strategy for the pathogens has been 

implemented, because the perceived risk is low, despite the fact that individuals sometimes 

develop secondary infections and occasionally succumb to the – largely indirect – effects of 

the viruses. Assessing risk is particularly difficult in situations, such as those surrounding 

both the desert tortoise and the gopher tortoise, in which many of the relevant facts that 

bear on the assessment simply are uncertain or unknown. We return to assessing risk later. 

What is known and what is not known? 

A great deal has been learned about the relationship of Mycoplasma to tortoise disease, 

mostly since the Recovery Plan was developed. It is certain (Brown et al. 2002) that: 

•	 Mycoplasma agassizii (strains PS6 and 723) is a cause of URTD 

•	 The pathology of mycoplasmosis involves hyperplastic and dysplastic lesions of the 

upper respiratory tract 

•	 Clinical signs of URTD vary in onset, duration, and severity 

•	 Mycoplasmosis has a chronic phase and may be clinically silent (subclinical) in 

adult tortoises 

•	 Infection with M. agassizii elicits specific antibody responses that can be detected 

by ELISA 

•	 The current ELISA may not be able to detect exposure of all tortoises to 

mycoplasmas other than M. agassizii, although some cross-reactions do occur 

•	 The antibody responses to M. agassizii are detectable by ELISA beginning eight 

weeks after experimental infection 

•	 Under experimental conditions, gopher tortoises become ill quicker after repeated 

exposure to M. agassizii 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 101 

•	 Colonization of the upper respiratory tract with M. agassizii may be detected by 

culture and PCR, but assay sensitivity is not as high as the ELISA 

•	 Mycoplasmosis is a horizontally transmissible disease 

Note, first, that the important information that we know with certainty relates entirely to 

individual tortoises and not to populations. We return to current understanding at the level 

of the population later. Secondly, important uncertainties and unknowns remain even at the 

level of individual tortoises. For example, it is probable, but not clearly established (Brown 

et al. 2002) that: 

•	 Pathogenic and nonpathogenic tortoise mycoplasmas exist 

•	 There is variation among strains of Mycoplasma agassizii in their ability to cause 

URTD 

•	 Other species of Mycoplasma (such as M. cheloniae) also can cause URTD 

•	 Specific antibodies against M. agassizii may not confer protective immunity 

•	 Mycoplasma may be transmitted by some forms of indirect contact 

•	 Mycoplasma may not persist in burrows of infected tortoises 

Many of the uncertainties and unknowns at the level of individual tortoises warrant 

increased attention (Brown et al. 2002; M.B. Brown, pers. comm.; E.R. Jacobsen, pers. 

comm.). In particular, more information is needed about: vertical transmission of tortoise 

pathogens (on-going studies are examining vertical transmission of both M. agassizii and 

THV), tortoise immunobiology (need information on reagents and functional assays, 

normal versus abnormal values, and the cellular immune system), tortoise pathophysiology 

and hemosiderosis, modes of transmission of tortoise pathogens other than M. agassizii, 

and relative importance of tortoise pathogens (need information on the virulence of species 

and strains). 

Although accruing information about the effects of URTD and other diseases on 

individuals is an important undertaking, sound management decisions about species 

recovery require accruing information about the effects of diseases on populations. 

Unfortunately, virtually nothing still is known about the demographic consequences, either 

direct or indirect, of URTD. It is suspected that respiratory mycoplasmal infection can 

affect desert tortoise and gopher tortoise life history traits (survival, fecundity, migration) 

directly and, therefore, affect population dynamics directly (Brown et al. 2002; M.B. 

Brown, pers. comm.), but establishing such a connection, if it indeed does exist, requires a 

more concerted effort than has been made to date. This cause-and-effect relationship has 

two linkages: Disease  Individual  Population. A suitable research plan, therefore, 

would need to be designed first to establish that disease affects the life history traits of 

individuals, and second, to establish that the changes in life history traits of individuals 

cumulatively affect population dynamics. Although some tortoises with respiratory 

mycoplasmal infection clearly have died with what appear to be abnormal deaths (Jacobson 

et al. 1995, Berry 1997, Rabatsky and Blihovde 2002, Seigel et al. 2003; K.H. Berry, pers. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 102 

comm.; J.E. Diemer-Berish, pers. comm.), other tortoises with the infection have lived 

what appear to be normal lives for extended periods (e.g., at sites at which seropositive 

individuals occur, yet at which no substantial declines in population size can be 

documented; McCoy et al. in review). Unfortunately, the nature of the research to date has 

been such that cases of the absence of population decline, in the face of respiratory 

mycoplasmal infection or of subsequent recovery from URTD, have not been well 

reported. Neither have the fates of random samples of ill – defined broadly – and healthy 

individuals from the same populations been mapped, as far as we can tell. The connection 

between the disease and survival of individuals, therefore, remains inferential, and whether 

or not disease is an important source of mortality (section II.D.3.b.2) remains largely 

unknown. Declines in the fecundity of tortoises with acute respiratory mycoplasmal 

infection have occurred, but the best available evidence indicates that they eventually 

recover (Schumacher et al. 1999; D.C. Rostal, pers. comm.). The connection between the 

disease and fecundity of individuals, therefore, remains problematic. No studies to date 

have explored the potential connection between disease and migration of individuals. 

Tortoises with respiratory mycoplasmal infection may display abnormal physiological 

responses, such as increased water loss, or behavioral responses, such as reduction in 

appetite, reluctance to leave burrows, and irregular basking and burrowing, however, which 

could influence movement patterns (Brown et al. 2002; M.B. Brown, pers. comm.; E.R. 

Jacobson, pers. comm.). 

It seems clear that the dearth of information on the linkage between disease and life history 

traits of individuals would reduce the linkage between changes in life history traits of 

individuals brought about by disease and resulting population dynamics largely to 

speculation. The best-published attempt to relate tortoise demography to disease was by 

Berry (1997). She presented convincing evidence that desert tortoise population densities 

had declined substantially at two sites (but see the discussion of permanent study plots and 

measurement of population densities presented elsewhere). Some individuals at one of the 

sites were seropositive and/or clinically ill with URTD, and some individuals at the other 

site exhibited varying degrees of shell dyskeratosis. She concluded (p. 94) that “between 

1988 and 1992 the declines of adults [at the site with seropositive and/or clinically ill 

individuals] are clearly attributable to URTD caused by M. agassizii.” She is more reserved 

in her conclusion about the second case (p. 95): “the population decline appears to be 

linked to the appearance of shell lesions on the tortoises.” The evidence that she presents 

for the cause-and-effect relationship between tortoise population decline and disease in the 

first case is: (1) prior to 1988, before the appearance of acute URTD, few individuals ever 

were observed with overt signs of illness or in a dying state; (2) individuals displaying 

clinical signs of URTD were distributed throughout the site and in adjacent areas; and (3) 

of 27 individuals in a health profile research program, fitted with radio transmitters, 6 died 

and 11 disappeared between 1989 and 1992. We suggest that this evidence supports a more 

conservative conclusion, one that is nearer the conclusion that Berry (1997) reached for the 

other site: the population decline appears to be linked to the appearance of URTD in the 

tortoises. Note that this conclusion still is immensely important and demonstrates that, at 

present, disease threats deserve consideration on par with other threats. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 103 

Risk from disease threats 

It appears that URTD is a complex, multi-factorial disease, interacting in some 

circumstances with other stressors to affect tortoises (Brown et al. 2002; M.B. Brown, pers. 

comm.). Hypothesized factors contributing to mycoplasmal transmission and URTD 

disease severity include different critical thresholds of exposure among tortoise 

populations; difference in virulence among microbial species and strains; prior exposure, 

which probably limits the ability to control disease severity; variable clinical expression, 

both temporally and spatially; differences in sex ratios, age structures, and behaviors 

among tortoise populations; exacerbating factors, such as drought; and tortoise nutritional 

status (M.B. Brown, pers. comm.). 

At present, the accumulating evidence about URTD is a mass of seeming contradictions. 

No data indicate that URTD is moving through Mojave Desert tortoise populations in a 

wavelike pattern typical of mycoplasmal spread (E.R. Jacobson, pers. comm.); yet, failure 

to identify the pattern may have resulted from inadequate serological sample sizes, 

inadequate spread of sampling effort throughout the range of the desert tortoise, or other, 

similar, problems (E.R. Jacobson, pers. comm.; see Diemer-Berish et al. 2000, McCoy and 

Mushinsky in review). Tortoises in the genus Gopherus may have maintained a long-term 

coexistence with the pathogens causing URTD (E.R. Jacobsen, pers. comm.; McCoy and 

Mushinsky in review); yet, in some places, such as Ft. Irwin, tortoises seem to have been 

isolated from at least Mycoplasma agassizii (E.R. Jacobson pers. comm.; see McCoy and 

Mushinsky in review), and, in many ways, respiratory mycoplasmal infection in tortoises 

resembles a new interaction between host and pathogen (D. Thawley, pers. comm.). In 

general, respiratory mycoplasmal infections have high morbidity but low mortality (Brown 

et al. 2002); yet, in some places, severe population declines have been hypothesized to be 

linked to URTD caused by M. agassizii (e.g., Berry 1997). 

These seeming contradictions reinforce the emerging picture of URTD as a complex, multifactorial disease. First, as we have seen, demonstrating the two important cause-and-effect 

relationships Disease  Individual  Population is not easy, and the difficulty is 

compounded by inadequate sample sizes and inadequate experimental design. Second, the 

potential effects of URTD, either for individuals or for populations, are inextricably 

intertwined with potential effects by numerous other threats, and teasing out individual 

effects, when several factors co-vary, is a difficult analytic problem. Third, changing 

ecological conditions, whether connected with human activities (e.g., habitat degeneration, 

McCoy et al. in review) or not (e.g., malnutrition, Jacobson 1994, Oftedahl et al. 2002); 

drought, Berry et al. 2002), may stress individuals and result in more severe clinical 

expression of URTD (Brown et al. 2002). Fourth, mycoplasmal infections often are density 

dependent (e.g., Hochachka and Dhont 2000), and URTD is seen mostly in relatively dense 

populations (M.B. Brown, pers. comm.), suggesting that some threshold density of tortoises 

may need to be reached before the infection becomes severe. Fifth, even if the mycoplasmal 

species responsible for URTD have maintained a long-term relationship with tortoises in 

the genus Gopherus, the pathogens appear to evolve rapidly into novel strains (Brown et al. 

2002), suggesting that demographically important pathogenic relationship may occur at the 

sub-specific level. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 104 

The complexity of the disease threat facing the desert tortoise, coupled with the uncertainty 

surrounding many of the key issues, and the fact that the tortoise is faced with many other 

threats, suggests that a conservative approach toward disease as a threat be adopted at this 

time. Although the evidence suggests that disease, especially URTD, could be an important 

force shaping the demography of desert tortoise populations, the evidence neither 

demonstrates that disease is a potent force, nor that it is the most important force, nor that it 

acts independently of others forces. A more balanced, adaptive, and focused approach to 

dealing with URTD is appropriate at this time, perhaps one modeled on the 

recommendations of McCoy and Mushinsky (in review) for dealing with the disease in the 

gopher tortoise. Such a balanced approach would take into account the risks, and associated 

costs, involved not only of transmitting Mycoplasma agassizii among tortoise populations, 

but also of transmitting it within populations or to other species. It would deal with the 

management practice of translocation and of dooming demographically valuable 

individuals to euthanasia simply because they are suspected of harboring the pathogen. It 

would deal with underestimating the importance of other pathogens (such as herpesvirus, 

THV) and of diverting attention and resources away from managing, acquiring, and 

restoring habitat. For example, if Mycoplasma agassizii has a long-term relationship with 

its tortoise host, then addressing the risks involving habitat loss, fragmentation, and 

degeneration is crucial for permitting recovery from URTD. Die-offs are likely to have 

occurred historically, and populations have obviously recovered. Under current conditions, 

large populations in good habitat likely could recover again, but small populations or 

populations in poorly managed habitat may be in serious danger of extinction. A more 

adaptive approach would take into account the evolution of knowledge about M. agassizii 

and URTD. Advances in knowledge may necessitate reevaluation of the risks facing the 

tortoise. For example, if strains of M. agassizii are variable in virulence, as evidence now 

suggests (Brown et al. 2002), then careful isolation of high-virulence strains on the one 

hand, and relaxation of the moratorium on translocation of the low-virulence strains on the 

other hand, may be warranted and wise. A more focused approach would take into account 

the ultimate goals of any actions taken against URTD. Different goals may dictate different 

weightings of the risks facing the gopher tortoise. For example, if the ultimate goal is for 

populations to be self-sustaining in the face of environmental pressures, including disease, 

then actions requiring persistent veterinary intervention may counter indicated and 

dangerous. 

The complexity of the disease threat facing the desert tortoise, coupled with the uncertainty 

surrounding many of the key issues and the fact that the tortoise is faced with many other 

threats, suggests that the disease threat will not be understood without bringing to bear all 

of the tools of modern epidemiology, particularly ecological epidemiology. Classical 

epidemiology primarily is concerned with the statistical relationship between disease 

agents, both infectious and non-infectious, while ecological epidemiology is concerned 

with the ecological interactions between populations of hosts and parasites (Swinton 1999). 

Epidemiologists are aware of the importance of the sociodemographic (classical 

epidemiology) or the ecological (ecological epidemiology) setting influencing the course 

that a disease takes in a population, and they are equipped with the statistical tools 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 105 

necessary to deal with diseases resulting from a variety of confounded and interdependent 

factors and to establish causal chains. 

Disease Case-Study Recommendations 

An immediate need exists to develop scientifically-based recommendations for 

management of healthy and ill -- defined broadly – wild tortoises so as to minimize the risk 

to both individuals and populations of uninfected tortoises (Brown et al. 2002), and by 

extension, risks both to individuals and populations of infected tortoises. The focus here is 

on the two recovery actions recommended in the Recovery Plan most relevant to disease 

threats in light of this need (see below). These two recommendations still are sound, but 

suffer from almost complete lack of implementation in the past decade. Here we also list 

additional recovery actions, which should be seen as simple extensions of the original 

actions based on new knowledge available today. 

a. Initiate epidemiological studies of URTD and other diseases (section II.D.3.b.1) 

•	 Refocus the general approach to research on disease, treating it as part of a network 

of threats to tortoise populations, which, because of negative and positive feedback 

loops to other threats, cannot be addressed effectively without reference to the 

threats network (see section 5.1.1). 

•	 Develop multi-disciplinary, long-term research agendas to understand the network 

of threats (a possible model, developed for studying URTD in the gopher tortoise, is 

in Section 7.3). 

•	 Develop tools to study disease which are not so expensive that they preclude needed 

resources to research the interactive effects of disease with other threats. 

•	 Develop more knowledge about the ecogeography of genetics of disease and hosts 

as a way to develop recommendations for translocation programs cognizant of the 

potential harm that can come from lack of information about mismatches between 

virulence of genetic strains of pathogens with different strains of host. 

•	 Include epidemiologists and population biologists in developing the research agendas. 

b. Research sources of mortality, and their representation of the total mortality, including 

human, natural predation, diminishment of required resources, etc. (section II.D.3.b.2) 

•	 Add health assessments to the information gathered in ecological studies and 

monitoring, perhaps using an existing protocol (Berry and Christopher 2001).
 

•	 Develop clear standards for determining whether individuals in a population are 

healthy or not and whether they have been stressed or not. 

•	 Continue current serological surveys for M. agassizii, adding screening for THV. 

Develop surveys for other Mycoplasma species as assays become available. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 106 

•	 Continue necropsies (the sample currently includes 74 individuals according to E.R. 

Jacobson). Develop a rationale for these necropsies in relation to the potential for 

information from them to affect new knowledge and management. 

•	 Continue developing, improving, and extending diagnostic tests. This includes
 

developing less expensive and more field-portable testing.
 

•	 Continue developing stress tests that are applicable to wild tortoises (e.g., 

adrenocorticotropin hormone (ACTH), phytohemagglutinen (PHA), and sheep red 

blood cell (SRBC) challenge experiments, to examine adrenal gland response, Tcell response, and B-cell response, respectively; P. Kahn, pers. comm.). 

•	 Inform researchers about both the qualities and the shortcomings of diagnostic tests 

(see Brown et al. 2002); for example, clinical signs of URTD may be non-specific 

or specific host responses to agents other than mycoplasmas; seropositive (ELISA) 

individuals may display no overt clinical signs of URTD; and that ELISA alone 

often is not sufficient, largely because they indicate only past exposure and not 

necessarily current infection. 

•	 Inform researchers about the value of different diagnostic tests in addressing 

different goals (see Brown et al. 2002); for example, different tests are appropriate 

for health assessment of an individual tortoise, for a population survey, for long 

term population monitoring, and for investigation of a mortality event. 

•	 Ensure that all important information is made accessible to researchers. 

•	 Ensure that the expedient course of killing seropositive, but otherwise healthy,
 

individuals is kept to a minimum.
 

A caveat to these recommendations is in order. Many modern epidemiologists do not think 

that epidemiology itself should be concerned with the delivery of services or with 

implementation of policy (e.g., Savitz et al. 1999). Regardless of whether or not one agrees 

with this viewpoint – which reflects a similar viewpoint common in conservation biology – it 

points to a separation between the scientifically-based accumulation of knowledge and the 

ultimate use of knowledge. The recommendations made here are for improving the science 

surrounding disease as a threat for the desert tortoise and may not necessarily provide an easy 

transition to management strategies. Designing management strategies for a complex disease 

threat, particularly one in which the factors contributing to the complexity may themselves be 

threats – which is an unusual situation – is a daunting task; however, the response to this 

daunting task must not be to ignore the complexity in the name of expediency. 
 

 

 

DTRPAC Report page 107 

“Science is a way of thinking much more than a body of knowledge. Its 

goal is to find out how the world works...” 

Carl Sagan, Broca’s Brain: Reflections on the Romance of Science. (1979) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 108 

5. Linking Impacts, Habitat, and Demography to Recovery 

The committee found that desert tortoises face a vast array of threats and that these threats 

interact with one another in highly complex ways that vary from place to place within the 

historic range of the desert tortoise. In fact, examples of species facing a single major threat 

are unusual among listed species. The complex nature of many threats is likely to make 

them difficult to both document and address in recovery plans. In addition to understanding 

complex ecological systems, mitigating threats often requires understanding and addressing 

interrelated social and economic factors, thus creating additional challenges in assigning 

tasks for species’ recovery (Lawler et al. 2002). The DTRPAC does not identify any simple 

and universal prescription for restoring and protecting desert tortoises across their range. 

Rather, the committee presents a threats matrix – a topology of the complexity of threats 

facing desert tortoises currently. The committee recognizes the importance of the on-theground knowledge that land managers will bring to developing management responses to 

threats. The committee urges management actions that recognize and account for the 

knowledge that land managers will bring to the table and that also account for the true 

complexity of formulating management actions for populations that face multiple, 

simultaneous, interacting threats. 

Desert tortoise recovery is fundamentally a demographic process. That is to say that 

recovery activities center on tortoise populations, particularly population size and whether 

or not they are increasing, decreasing, or stable. The fundamental recovery goal is for 

tortoise populations to have sufficient size and stability to ensure their continued existence. 

Tortoise populations increase, decrease, or remain stable largely because of the net effects 

of several important demographic factors: birth rate (natality), survivorship (recruitment 

into the breeding population), fecundity, and death rate (mortality). A population growth 

index called “lambda” summarizes the cumulative effects of these demographic factors. 

Lambda describes if and how quickly populations are changing. A population that is 

increasing has a lambda greater than 1. For example, a lambda of 2 would indicate that the 

population is doubling in size each generation (32 years for desert tortoises; Turner et al. 

1987). A population that is declining has a lambda that is less than 1. For example, a 

lambda of 0.5 means that the population is diminishing by half each generation. A stable 

population has a lambda of 1, i.e., the population is replenishing itself each generation. 

Most recovery actions for threatened and endangered species are designed to stabilize 

population size (lambda at 1.0 based on dynamics across several generations) where 

population size is sufficient to safeguard against extinction. If population size is small 

enough to threaten extinction, the recovery goal is to increase population size (lamba > 1.0) 

until the population is sufficiently large to ensure persistence. Then the population can be 

managed for a long-term lambda of 1. Population increase can be achieved through actions 

that increase natality, increase recruitment, increase fecundity, decrease mortality, or some 

combination of these. Because the management actions taken depend in part upon the 

factors responsible for population declines, it is important to know what forces are causing 

population declines or are preventing small populations from rebounding to stable 

population sizes. Forces influencing population dynamics were addressed in Appendix D of 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 109 

The Recovery Plan (USFWS 1994), by listing each identifiable force and presenting 

evidence that it is indeed a threat to population well being. 

5.1 Cumulative, Interactive, and Synergistic Impacts of Multiple Threats 

One of the most insidious problems preventing desert tortoise recovery is that tortoise 

populations face multiple threats. To grasp the complexity of threats facing desert tortoises, it 

is helpful to consider two important ways that these threats act: 

Individual populations face a suite of threats simultaneously. 

This means that ameliorating a prominent threat does not mean that the population has 

become secure. Another threat may replace, or “compensate” for, the threat that has been 

removed. Adding further complexity, each population may face its own suite of threats. 

Threats can interact with one another. 

The action of one threat can influence the degree to which another threat is expressed. 

Because threats are simultaneous, the degree to which a particular threat is expressed is partly 

a function of other active threats. The interaction of threats need not be simply additive. They 

can be synergistic. In other words, the combined application of two or more threats may 

cause an overall effect that is greater than the sum of each threat individually. 

Our task was to determine if new information would change the original Recovery Team’s 

(USFWS 1994) evaluation of threats to desert tortoise populations. For this analysis, we 

made use of a recent objective analysis of evidence pertaining to threats to desert tortoise 

populations (Boarman 2002) plus testimony of expert witnesses and knowledge of committee 

members. The Recovery Plan identified a large number of important threats to tortoise 

populations. Although some new information has been generated since then, we see little 

need to change the Recovery Team’s treatment of most individual threats. However, the 

original Plan did not fully appreciate the complexity of interactions of individual threats with 

each other and the insidious nature of the synergism that can occur among threats. In 

particular, the original Recovery Plan did not emphasize the degree to which one mortality 

factor can deleteriously compensate for another mortality factor when the first one has been 

mitigated through management actions. For example, the original Plan did not illustrate 

clearly that adult tortoises may die from an alternative mortality factor, such as vandalism, 

after being protected from another important mortality factor, such as being crushed by cars, 

in an environment of multiple anthropogenic threats. 

Some new information exists on the extent of threat posed by some specific activities. For 

example, feral and unleashed domestic dogs are now thought by many to pose an important 

threat to tortoises in some parts of the Mojave (Bjurlin and Bissonette 2001), but this issue 

was barely recognized in1994. Recent studies have shown that native vegetation biomass 

and other elements of the Mojave Desert ecosystem were higher in areas protected from 

grazing and OHV activities, while non-native grass biomass was greater outside the 

protected area (Brooks 1995, 1999). Another study found greater plant cover and desert 

tortoise abundance in an unused plot compared to an OHV-used plot (Bury and 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 110 

Luckenbach 2002). Lovich and Bainbridge (1999) reviewed effects of OHVs on desert 

ecosystems, as well as other anthropogenic effects. Translocation was portrayed as a likely 

threat to populations in 1994, but recent research has shown how it may be an important 

element in recovery programs (Field 1999, Nussear et al. 2000, Nussear 2004). More 

details are now available on disease (see Section 4.5.2 and many studies listed in Boarman 

2002), raven predation (Boarman 2003), fires (e.g., Brooks and Esque 2002), invasive 

weeds (e.g., D’Antonio and Vitousek. 1992, Brooks 2000, Brooks and Esque 2002), 

military activities (e.g., Krzysik 1998, Berry et al. 2000), and livestock grazing (e.g., Avery 

1997, 1998). A little more has been learned since 1994 about a number of other threats to 

tortoise populations including illegal collecting (Berry et al. 1996), kit fox predation 

(Bjurlin and Bissonette 2001), handling (Averill-Murray 2002b), release of captives (Field 

et al. 2000, Johnson et al. 2002), roads (Fig. 4.32, von Seckendorff Hoff and Marlow 

2002), and noise (Bowles et al. 1999). Most importantly, however, virtually nothing is 

known about the demographic impacts of any of the threats on tortoise populations or the 

relative contributions each threat makes to tortoise mortality. This dearth of knowledge is 

not surprising given the difficulty of estimating desert tortoise population sizes (see 

Chapter 4). We caution that the individual threat approach taken by the Recovery Plan 

(USFWS 1994) may have resulted in managers placing too much emphasis on political and 

practical trade offs involved in controlling individual threats; we believe tortoise recovery 

depends on emphasis being placed on managing multiple threats because of the interactive, 

synergistic, and cumulative effects of multiple threats. 

We recommend a significant modification to the Recovery Plan’s perspective on threats by 

strongly emphasizing the importance of cumulative, interactive, and synergistic threats to 

desert tortoise populations throughout the Mojave. We emphasize that multiple threats 

appear to act simultaneously to suppress tortoise populations at any given place in the 

desert. Simultaneous multiple threats represent an insidious threat to desert tortoise 

populations by diminishing the benefits of carrying out important management actions 

designed to relieve stress on tortoise populations. For example, overgrazing may suppress 

tortoise populations by reducing the availability of important forage plants (Avery and 

Neibergs 1997). However, tortoises that are “saved” by grazing reductions may be lost 

anyway due to shooting by public land users or crushing by vehicles driven on desert roads. 

Hence, even though grazing reduction was appropriate and necessary, it was not sufficient 

because saved tortoises were now available to be lost through the compensatory threat 

(called “compensatory mortality”). 

Multiple threats can also act synergistically. By synergism we mean that the deleterious 

effects of a given threat are substantially magnified when another threat is simultaneously 

acting. In other words, the cumulative threat effect is greater than the sum of the individual 

threats. One example of synergy between threats is raven predation and road mortality. 

While some tortoises are killed by ravens and others are crushed by vehicles on roads, the 

presence of tortoise (and other) carcasses on roads enhances the survival and reproduction 

of ravens which are then available to prey upon tortoises (Boarman 2003). Another 

possible important synergism is the suspected link between disease and nutrition or disease 

and drought (Brown et al 2002, M. B. Brown pers. comm., Duda et al. 1999). In this 

scenario, well-nourished tortoises may not necessarily die from URTD, but succumb when 

under nutritional stress. Nutritional stress, in turn, may occur in areas such as OHV open 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 111 

areas where forage availability has been significantly reduced. Multiple threats and their 

synergistic interactions may make it extremely difficult to identify and implement 

management actions that will most efficiently lead to recovery. 

Whereas the most obvious threats directly result in tortoise mortality (e.g., road mortality 

and poaching), the cumulative, interactive, and synergistic impacts of multiple threats is 

often manifested through indirect impacts that reduce survivorship and fecundity. Habitat 

degradation and the resulting reduced nutrition are two of those indirect impacts. Habitat 

degradation takes many forms, and often the occurrence of one form of degradation is 

correlated with the occurrence of other forms. Three kinds of habitat degradation are 

centrally important to tortoise conservation and tortoise population decline: habitat 

fragmentation, habitat loss, and habitat degeneration. Fragmentation refers to the parsing of 

habitat into separate segments. This is a spatial phenomenon, but does not refer to habitat 

loss per se. For example, a fence or road that forms a barrier to tortoise movement divides a 

tortoise population into two units without significant habitat loss. Habitat fragmentation is 

an issue of scale and has been shown to cause population declines in other reptiles (Fisher 

et al. 2002). 

Habitat loss refers to the destruction or conversion of previously suitable habitat into a 

form that is no longer suitable to tortoises. For example, urbanization leads to habitat loss 

for desert tortoises. Animals with large home ranges, such as the desert tortoise, typically 

are sensitive to habitat fragmentation and habitat loss. Both lead to population decline. 

Among the deleterious effects of habitat fragmentation are reduced movement and gene 

flow among breeding populations. Fragmenting a population increases the likelihood of 

local population extinction from a range of demographic and catastrophic events (Opdam 

1988, Hanski and Gilpin 1991). Habitat loss does not necessarily fragment a population, 

but habitat loss invariably leads to population decline due to net loss of space and resources 

available to tortoises. 

Lastly, habitat can degenerate, meaning its value for desert tortoise survival and 

reproduction is reduced, even if the habitat is not fragmented or destroyed. Reduced habitat 

quality can be a particularly insidious problem for wildlife managers because it can be 

difficult to recognize that seemingly suitable habitat is actually deficient in some important 

way. Habitat fragmentation, loss, and degeneration are all occurring throughout the Mojave 

Desert, but particularly in the western Mojave. Unfortunately, habitat protection has not 

been effectively implemented in many areas within the tortoise’s historic range (e.g., see 

Section 4.1). 

Nutrition is important to desert tortoise population biology because of the role it plays in 

growth, health, and fecundity. The availability of adequate nutrition to tortoises in the 

Mojave ecosystem is naturally variable in response to annual variation in precipitation, 

temperature, soil moisture, and plant community responses. Some years are forage rich and 

others forage poor, which in turn causes for annual differences in fecundity and 

survivorship. This is an example of a natural interaction between abiotic factors (weather) 

and biotic factors (native plant community) influencing tortoise populations through the 

indirect pathway of nutrition (see Fig. 5.1, Turner et al. 1984, Peterson 1994, Peterson 

1996a, Peterson 1996b). However, anthropogenic factors introduce a suite of factors that 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 112 

ultimately bear on tortoise nutrition through more complex synergistic effects. For 

example, the replacement of native forbs and grasses by introduced weeds may change the 

plant community response to precipitation and the nutritional value of the forage produced. 

Additionally, exotic plants change fire cycles, fugitive dust, the biological availability of 

water, and perhaps, tortoise movement. The demographic consequences of tortoise 

nutritional ecology may prove to be difficult to monitor directly, however the threats 

network described below may suggest proxy factors that can reasonably be monitored and 

managed. 

Focusing on individual threats has resulted in little positive change for desert tortoise 

populations. The individual threats approach has not contributed to a general recovery of 

the desert tortoise for several reasons. For example, the individual threats approach 

generally does not account for compensatory mortality in which one mortality factor takes 

tortoises that were “saved” from another mortality factor. A particularly troublesome 

consequence of using the individual threats approach is a problem we term “elevating the 

expedient to the important.” A simple listing of individual threats may prompt managers to 

attend first to those threats they view as most tractable, in light of available resources and 

political exigencies, but managing those threats may not necessarily produce the best 

results. For example, raven depredation of tortoises appears to be an important problem and 

raven control is a straightforward management action that can be quickly and easily 

implemented. However, raven control may not be the highest priority management action 

for every tortoise population. Finally, focusing on individual threats suffers from Leibig’s 

Law of the Minimum (Berryman 1993). By focusing on and removing only the one or two 

threats considered the most important, no response may be realized because the next most 

important threat becomes the limiting factor for population recovery (Leibig’s Law). Thus, 

we believe the most effective management will be based on recognizing the importance of 

addressing the multiplicity of threats impacting specific populations. 

5.1.1 Threats Network 

We illustrate the truly complex relationships among the array of threats to tortoise 

populations with a three-tiered conceptual model (Fig. 5.1). The model characterizes biotic, 

abiotic, and anthropogenic factors in a network of threats to tortoise populations. Overall, 

the network illustrates the interaction of biotic, abiotic, and human land-use factors in 

causing tortoise population decline. Major land-use categories appear in the top tier of the 

network. The second tier represents activities or threats that are indirectly linked to tortoise 

mortality and fecundity. The third tier represents mortality factors that lead directly to 

tortoise population decline. The model focuses on anthropogenic features that lead to 

tortoise population decline because these factors are central to developing effective 

recovery strategies. We do not illustrate tortoise population increases in the network, but 

we recognize that ameliorating the deleterious effects represented in the model may open 

the way for desert tortoise population increases through increased longevity and fecundity. 

It is important to note that this network model represents a hypothesis that needs regular 

reevaluation and modification. 
 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 113 

Biotic Anthropogenic AblaUc 

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TIER 2 

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Fig. 5.1 Network of threats demonstrating the interconnectedness between multiple human 

activities that interact to prevent recovery of tortoise populations. Tier 1 includes the major land use 

patterns that facilitate various activities (Tier 2) that impact tortoise populations through a suite of 

mortality factors (Tier 3). 

The threats network demonstrates that many human activities can have negative effects on 

tortoise populations through many pathways. Taking management actions that break one 

pathway, even though the pathway is real, may not be adequate to prevent the mortality 

factor from continuing to diminish a tortoise population. This is because alternative 

pathways exist to “compensate” by removing animals that were otherwise “saved” by a 

management action as with “compensatory mortality,” discussed above. Compensatory 

mortality is not the only way that multiple pathways make developing recovery actions 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 114 

difficult. Tortoise populations can also experience “indispensable mortality,” resulting from 

tortoise life history traits that are not under human control. In tortoises, reducing the 

influence of a mortality factor on younger age classes, for example, may not result in a 

commensurate increase in overall population size because high mortality among older, 

highly fecund individuals is the true constraint on the population. For example, 

“headstarting” of hatchling sea turtles is not particularly effective in reducing population 

decline, relative to protection of reproductive females (Frazer 1993), because of the very 

high mortality rates of intermediate-age individuals. Indispensable mortality accounts for 

why reducing raven predation alone likely will not result in significant increases in tortoise 

population size. 

Anthropogenic food provides a good example of how network analysis gives insight into 

the importance of recognizing alternative pathways before planning recovery actions. 

Figure 5.2 is a portion of the complete network (Fig. 5.1) and shows direct and indirect 

ways that human activities generate anthropogenic foods for predators that eat desert 

tortoises. Ranching, agriculture, and urbanization are probably the biggest direct land uses 

that provide food to ravens, coyotes, and feral dogs. Other land uses generate foods less 

directly through associated activities illustrated in Tier 2 of the network. Activities that 

generate food subsidies to tortoise predators include motorized and non-motorized 

recreational activities, railroads, and landfills. Taking a single threat approach, eliminating 

railroads as a source of food, may indeed reduce the amount of food available to ravens, 

but there are still many other compensatory sources of food the ravens could switch to: and 

no measurable reduction in juvenile mortality may be realized. As a further illustration, the 

presence of people facilitates raven presence and their likely predation on tortoises in other 

ways, such as water, nesting structures, roosting sites, and nesting materials. So, even if all 

anthropogenic sources of food were eliminated, human activities may still facilitate 

predation on tortoises by ravens. A multiple threats approach to tortoise recovery would 

evaluate the relative contributions each source makes to the availability of food. With the 

assistance of statistical analyses such as Path Analysis (Petraitis et al. 1996, Smith et al. 

1997, Wootton 1994) or Structural Equation Modeling (Maruyama 1997), sources can then 

be prioritized and the most important ones eliminated to maximize the positive benefit to 

tortoise populations. 
 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 115 

ranching agriculture urbanization 

landfills 

non-motorized 

recreation 

construction 

Ravens 

Fig. 5.2 A section from the Threats Network from Fig. 5.1 that shows how multiple land uses and 

human activities provide food subsidies to predators on tortoises, thereby increasing mortality. 

The network also illustrates a vortex of feedback loops in which mortality mechanisms 

from both natural and human impacts can reinforce one another. In particular, some factors 

affect age distribution through increased mortality of older individuals, which in turn 

affects population recruitment through the reduced fecundity of young individuals, which 

then makes the population more susceptible to threats that affect younger, smaller 

individuals. In other words, not only do impacts from threats cause a population decline, 

but a population may also lose much of its ability to rebound from the population decline. 

Lastly, an inability to rebound can be exacerbated when impacts differentially affect 

breeding female or juvenile segments of a population. Several demographic models 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 116 

indicate that tortoises require very high juvenile survivorship and recruitment into the 

breeding population to recover diminished tortoise populations (Congdon et al. 1993, Doak 

et al. 1994, USFWS 1994). The vortex of deleterious feedbacks among multiple threats 

represents a grave threat to tortoise recovery. 

There are several important caveats relative to using the threats network to formulate 

recovery strategies. First, the effects of some of the threats may have time lags that make 

the effects hard to discern early. Second, tortoise populations and habitats may respond to 

threats emanating from areas outside of DWMAs or other areas designated for management 

action. Third, cumulative or indirect effects caused by modification of ecosystems, may 

occur. Fourth, threats may have different effects in different areas. Fifth, the magnitude of 

various threats may depend upon the initial condition of the landscape and its changes 

through time. Sixth, the degree of threat by any one factor almost certainly changes in 

different combinations of interacting threats. Finally, the value of a management strategy 

depends on the particular problem being addressed. In other words, the threats matrix 

provides a general topology of the complex issue of threats. However, management actions 

to recover or protect individual tortoise populations likely will have to be custom designed 

for those populations and be based on the suite of threats and their interactive effects facing 

that population. We do not identify any simple and universal prescription for restoring and 

protecting desert tortoises across their range. 

To illustrate how the threats network can be interpreted, we provide three simplified 

examples. First, following a relatively simple thread, we see that four major elements are 

associated with utility corridors (Fig. 5.3): construction, physical structures (e.g., power 

towers, pump houses, etc.), people (e.g., involved in maintenance operations), and unpaved 

roads. Each one of those elements affects tortoises through various mechanisms. For 

example, physical structures cause loss of habitat and facilitate mortality from predation by 

providing nesting habitat for ravens (Boarman and Heinrich 1999). This example shows a 

relatively straightforward connection between utility corridors and tortoise population 

declines. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 117 

( (onstructlon ) 

Fig. 5.3 A section from the threats network from Fig. 5.1 showing just the primary activities 

associated with utility corridors. The causes of tortoise mortality associated with physical structures 

are also shown. 

Unpaved roads represent another contributor to threats associated with utility corridors 

further illustrating a much more complex web of connections. On the face of it unpaved 

roads have relatively few direct impacts on tortoise population. The crushing of tortoises, 

habitat loss, and air pollution (not illustrated) associated with unpaved roads do not appear 

to be the major causes of tortoise decline (Fig. 5.4). However, there are a host of important 

indirect impacts of unpaved roads that may be very important factors in tortoise decline, 

some of which are illustrated in Fig. 5.5). For example, unpaved roads, specifically the 

vehicles and the people they transport, cause fires (USFWS 1994, Brooks pers. comm.), 

which in turn kill tortoises and alter native and non-native vegetation (Brooks and Esque 

2002). Roads facilitate the spread of non-native plants (Brooks and Esque 2002, Gelbard 

and Belnap 2003), which may in turn suppress growth of some native species (Brooks 

2000). Unpaved roads also generate fugitive dust (Gillette and Adams 1983), which 

reduces productivity of plants (Sharifi et al. 1997) and may release contaminants (Forman 

et al. 2003). Roads facilitate non-motorized and motorized (OHV/ORVs) recreation, which 

can directly, and indirectly, impact tortoise demography (not illustrated in Fig. 5.5) 

(Boarman 2002). Finally, unpaved roads provide access to people, which can facilitate a 
 

 

 

 

 

 

 

/'

DTRPAC Report page 118 

large number of activities that may harm tortoises (e.g., vandalism, removals, release of 

diseased captives, habitat destruction, dumping of garbage and toxic chemicals, crushing 

burrows and animals, release of pet dogs that may become feral, etc.) (Boarman 2002). 

Hence, when viewed within the threats matrix, unpaved roads within desert tortoise habitat 

may be a key factor associated with tortoise decline. 

Fig. 5.4 A subsection of the Threats Network shown in Fig. 5.1 that illustrates the mortality factors 

directly associated with unpaved roads used for maintenance of utilities. 
 

 

 

 

 

 

 

 

 

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anthropogenic::

fugitive

rec::reallon

DTRPAC Report page 119 

lants 

OHV/OIIVs 

non-motoMzed 

food 

dust 

Fig. 5.5 A much more complex web showing the interconnectedness among many activities 

associated with utilities and their impacts on tortoise populations. 

Threats Recommendations 

The threats network represents a working hypothesis of how various factors impact tortoise 

populations, singly or interactively (as cumulative, synergistic, or interactive effects), 

whether biotic, abiotic, or anthropogenic. We encourage managers to think about 

management in terms of suites of threats. Our model first posits that many threats affecting 

desert tortoises include multiple factors or various aspects of individual factors. For 

example, “livestock grazing” includes both horses and burros. Second, not all possible 

impacts, or mechanisms of mortality, are depicted in the model (e.g., minor sources of 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 120 

mortality such as ant predation of eggs are not included). Third, all possible linkages 

important to describing interacting threats may not be included in this model. The 

connections we chose to include are only those with a more apparent probability of 

occurring (i.e., with strong empirical or theoretical support) and that likely do not occur 

only rarely (e.g., meteor falling on a burrow or a tortoise finding, swallowing, and being 

injured by a balloon). Finally, each linkage is illustrated as equi-probable and equally 

important; focused research and modeling should reveal relative strengths of the various 

linkages. 

An appropriate application for the model is to identify nodes that have many linkages 

(incoming and outgoing). Factors represented by these nodes may be key factors that merit 

focused and priority management action. The next step is to take an hypothesis-driven 

approach to determine what management actions will have the greatest effects on tortoise 

populations. If a future recovery team is formed, we see them using this model to make 

initial recommendations about priorities for management action. 

We offer the following recommendations for changes to the Recovery Plan: 

•	 Place a greater emphasis on the interactive, synergistic, and cumulative effects of 

the multiple threats that occur at any given space and time. 

•	 Research and management should, through a hypothesis-based approach, focus first 

on those sets of actions and threats that contribute to a greater number of mortality 

mechanisms (i.e., involve more linkages in Fig. 5.1) or that affect size structure or 

fecundity. 

•	 The relative strengths of hypothesized connections between threats and mortality 

should also be assessed (some individual linkages may be more important than 

multiple linkages from other individual threats). This assessment should be based 

on data from research designed specifically to elucidate relationships between 

threats and mortality. 

•	 Data from the previous two recommendations should be combined into a
 

classification system that characterizes threat by spatial extent, frequency,
 

predictability, and intensity.
 

•	 Develop and use innovative methods, including GIS and other types of visualization 

technologies, to visualize and display the temporal and spatial complexities of 

individual and interactive threats. 
 

 

 

DTRPAC Report page 121 

“The aims of scientific thought are to see the general in the particular 

and the eternal in the transitory.” 

Alfred North Whitehead, in A Dictionary of Scientific Quotations by Alan L. Mackay . (1991) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 122 

6. Monitoring, Evaluating, and Delisting 

The 1994 Recovery Plan (p. 3) identified the most serious problem facing the remaining 

desert tortoise populations in the Mojave region as 

the cumulative load of human and disease-related mortality accompanied by 

habitat destruction, degradation, and fragmentation. 

As a result, the Recovery Plan recommends a list of recovery actions for each DWMA, and 

many individual actions have been implemented (GAO 2002; but see Section 4.1). Many of 

these actions appear to have been selected due largely to their ease of implementation, 

rather than their effectiveness in improving tortoise status. Furthermore, an uncoordinated 

approach with a suite of management treatments and hit-or-miss assessment of 

effectiveness is rarely effective for species recovery. Specific diagnosis is needed to reveal 

the magnitude of how different factors (or combinations of factors) are affecting a species’ 

decline, and that diagnosis should guide priorities for the treatments (Caughley and Gunn 

1996). 

Recovery of threatened and endangered species must often be initiated with incomplete 

biological knowledge and in the face of multifaceted and intractable ecological, political, 

economic, and social challenges. Thus, it is difficult to predict with confidence the outcome 

of proposed management actions. Monitoring the subsequent response of the species to 

management is therefore essential (Campbell et al. 2002). The Recovery Plan specifically 

recommended the establishment of “experimental management zones” within DWMAs, in 

which certain otherwise prohibited activities would be allowed to occur in an experimental 

context. These zones would allow scientists and managers to determine the effectiveness of 

different management actions. Unfortunately, experimental management zones have not 

been created, and a primary criticism of desert tortoise recovery efforts to date has been the 

lack of necessary analyses assessing the effectiveness of specific recovery actions (GAO 

2002). 

The importance of data-based decision making is already recognized by the USFWS 

(Crouse et al. 2002). For example, the USFWS and NMFS habitat conservation planning 

(HCP) handbook identifies the need for syntheses of relevant biological data and specific 

methods for determining anticipated levels of incidental take when describing the impacts 

of the project covered by a given HCP (USFWS and NMFS 1996). Additionally, USFWS 

specifically recommends adaptive management (see Section 7.2) to adjust to uncertainty 

due to gaps in scientific information regarding the biological requirements of the species. It 

is important to allow for changes in mitigation strategies (or other recovery actions) that 

may be necessary to reach the long-term goals or biological objectives of conservation or 

other land management plans. Monitoring is essential in an adaptive management program, 

and it should be designed to ensure proper data collection and scientific analyses. The 

results of scientific monitoring analyses represent the basis for adjusting management 

strategies and can lead to more efficient recovery of a species, both in terms of time and 

money, because recovery actions that are closely monitored can be modified to ensure the 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 123 

desired results (Campbell et al. 2002). The need for hypothesis-driven experiments to 

assess the efficacy of management actions should not be under-emphasized in a revised 

recovery plan. Other than by coincidence, the effectiveness of recovery efforts depends on 

the accuracy with which the reasons for decline have been determined (see Section 5), and 

furthermore, we cannot know for sure without an experimental design that an action and 

any success were causally related (Caughley and Gunn 1996). 

6.1 Strategies of Desert Tortoise Monitoring 

6.1.1 Historical Background for Desert Tortoise Monitoring 

The keystone-delisting criterion in the Recovery Plan for Mojave Desert tortoises is: “As 

determined by a scientifically credible monitoring plan, the population within a recovery 

unit must exhibit a statistically significant upward trend or remain stationary for at least 25 

years (one desert tortoise generation)” (Fig. 6.1). This criterion was promoted by the 

original Desert Tortoise Recovery Team instead of a more common criterion specifying a 

target population size required for delisting (at the time when the desert tortoise was listed 

by USFWS, there was a downward trend in population size). The other four delisting 

criteria for desert tortoise relate to conservation actions required after an upward trend has 

been achieved. 

z 

us 

Fig. 6.1 Idealized population z trends before recovery planning 

implemented, as a result of 

implementing recovery 

planning, and after delisting. 

0. 

0. 

Historically, monitoring has centered on the tortoises themselves and not on monitoring 

their environments or threats. For example, the Desert Tortoise Recovery Plan, Appendix 

A, (USFWS 1994) outlined the need to determine regional densities of desert tortoises to 

determine if population sizes remain stable, increasing, or declining. Originally, desert 

tortoise populations were monitored using strip transects (Berry 1979) or plots (Berry 

1984). Both of these approaches have provided data on local desert tortoise densities with 

varying degrees of accuracy and precision, yet neither of these approaches were designed 

to provide regional density estimates. 

Modern monitoring requires going beyond simple tracking of population densities and 

expanding to document changes in three elements of importance to recovery: 

TIME 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 124 

1. size of populations 

a. population size includes measures of population density 

b. aerial extent of population 

2. habitat of the species 

3. threats to populations 

6.1.2 Scope and Purpose of Modern Monitoring 

The purposes for monitoring are manifold. For example, monitoring is necessary to assess 

the efficacy of management actions and can alert managers to catastrophic changes in 

population size, habitat loss, proliferation of threats, etc. Success must be assessed by 

comparing it to goals set in advance. Goals and management actions may evolve with 

additional knowledge, thus effective monitoring is carried out within an “adaptive 

management” framework (see Section 7.2). 

All monitoring should be hypothesis driven or designed to meet management objectives. 

There should be clearly defined questions and purposes, such as detection of trend or 

changes in abundance of desert tortoise over time. Note that monitoring for population 

trend detection should be based on the hypothesis that the population is changing at some 

rate, whether that is specified as 0% change (i.e., stable population) or some positive or 

negative rate, and therefore estimation methods must be sensitive enough to detect the 

desired trend with reasonable probability (power). Monitoring should never be conducted 

“to do monitoring” just for the sake of monitoring. 

Monitoring data and analyses will be the basis for delisting. Although population 

persistence is the ultimate goal of recovery, the current monitoring program is one 

dimensional, in that monitoring is only done for densities of tortoises and thus will never 

inform management to its full potential. We recommend that monitoring should be a 

multidimensional program, including monitoring of tortoises, but also monitoring the 

extent and condition of habitat and monitoring impacts to tortoises, as well. Each of these 

dimensions, in turn, involves multiple scales: individual, population, and species for the 

tortoise dimension; micro-scale, macro-scale, and landscape scale for the habitat 

dimension; low, moderate, and high for the impact dimension (Fig. 6.2). The goals of an 

effective desert tortoise monitoring program minimally should include: 

1. Monitoring to assess recovery status of the desert tortoise 

2. Monitoring in an adaptive management framework 

3. Monitoring that is multi-dimensional 

4. Monitoring that is multi-scaled. 
 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report	 page 125 

I
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Fig. 6.2 Dimensions of elements important to recovery, and therefore, needing monitoring. 

The types of questions that could be asked of a multi-dimensional, multi-scaled, recoveryfocused, and adaptive management-integrated monitoring program include, for example: 

1.	 Are there enough tortoises in the DPS for the population to be self-sustaining? 

2.	 Is the criterion of a 50% probability of persistence for 500 years the best criterion 

to define recovery? 

3.	 Is the condition of the habitat within a recovery unit improving or getting worse? 

4.	 Is the effective area of tortoise habitat contained within the DPS region being 

reduced? 

5.	 Are threats to tortoises increasing or decreasing in the DPS region? 

The ability to successfully manage tortoises, habitat, or impacts, and the importance of 

managing tortoises within an adaptive framework, increases as one moves across each axis 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 126 

of Fig. 6.2. As one moves from the light to dark shades, it becomes increasingly more 

difficult to manage along particular dimensions, and it becomes more important to manage 

within an adaptive framework. Monitoring should be targeted more towards the darker 

areas of the graph, as that information tends to be the most important for assessing recovery 

status. On the other hand, research should not neglect other areas of the box. Wherever 

possible, research should focus on topics that inform management needs or directly support 

monitoring to assess the recovery status of the desert tortoise. 

6.1.2 Categories of Monitoring 

Four categories of monitoring have been recognized in study of relationships of wildlife 

populations, habitat, and threats (e.g., Independent Scientific Advisory Board 2003, NMFS 

2002). 

Implementation Monitoring is monitoring of task completion in a specific project (e.g., 

miles of habitat fenced, miles of roads decommissioned, completion of reports, etc.). 

Implementation monitoring results must be presented for projects and need to be clearly 

documented and synthesized (see Section 4.1). However, sound science requires that 

project results also be measured in terms of benefits to desert tortoises and habitat. 

Tier 1 status and trend monitoring obtains repeated measurements on indicator variables 

over a period of time, with a view to quantifying trends or abrupt changes over time. For 

example, availability of water in a habitat improvement project might be measured in 

August every third year for a 21-year period. This can be a low level of monitoring on 

individual project sites or on a large area. For example, aerial photography or data layers in 

a GIS could be used for long-term trend monitoring of riparian or other terrestrial habitat 

over time. In general, Tier 1 monitoring does not establish cause and effect relationships 

(i.e., is not a “true” research experiment) and does not provide statistical inductive 

inferences to larger areas or time periods. It is not necessarily expensive or time consuming. 

However, Tier 1 mapping or trend monitoring on similar projects replicated over time and 

space can provide compelling evidence for general conclusions. Also, aerial photography or 

data layers in a GIS yield a census of the study area, thus eliminating the need for spatial 

sampling and classical statistical analysis at the scale studied. 

Tier 2 statistical monitoring provides statistical inferences to parameters in the study area 

as measured by certain data collection protocols (e.g., distance sampling for density of 

desert tortoises). These inferences apply to areas larger than the sampled sites and to time 

periods not studied. The inferences require both probabilistic selection of study sites and 

repeated visits over time. Individual proposals can support larger Tier 2 statistical 

monitoring projects by using the same field methods and methods to select study sites that 

contribute information to Tier 2 statistical monitoring. Tier 2 statistical monitoring will be 

required for estimation of parameters such as number of desert tortoises of reproductive age 

in an area, juvenile production, acres of noxious weed present, etc. 

Tier 3 research (effectiveness) monitoring is for those projects or groups of projects 

whose objectives include establishment of mechanistic links between management actions 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 127 

and population responses of the desert tortoise or its habitat condition. Tier 3 research 

monitoring requires the use of experimental designs incorporating “treatments” and 

“controls” randomly assigned to study sites. Generally, the results of Tier 3 research 

monitoring qualify for publication in the refereed scientific literature. Examples of Tier 3 

monitoring would include: 1) projects to evaluate the effects of different levels of predator 

control on survival of juvenile desert tortoises, with study areas selected randomly for 

reference and treatment; 2) projects to evaluate the survival rates of adult desert tortoises in 

areas treated by different management actions; and 3) projects to evaluate the effectiveness 

of various land restoration or management techniques. 

Tier 3 research and monitoring is that tier most necessary to be hypothesis-based. For 

example, hypothesis-based monitoring could be used to determine the effects of 

management actions such as highway fencing or removing grazing. Presence/absence data 

can be used to identify areas that could be targeted for repatriation or other research 

projects needed for assessing the efficacy of management (e.g., MacKenzie et al. 2002). 

For example, data on presence and absence of tortoises collected as part of a project to 

estimate population density of desert tortoises were used in a kernel analysis of distribution 

of the desert tortoise in the Western Mojave (Section 4.3). This analysis revealed areas in 

which tortoises were found formerly and now are largely absent. A similar kernel analysis 

of carcasses showed that the same geographic area had a wider distribution of carcasses 

than live animals. Thus, kernel analyses of presence and absence of live desert tortoises and 

carcasses show an example of where the distribution of desert tortoises was not maintained 

in parts of designated DWMAs and USFWS critical habitat. Specifically, in an area that 

was formerly in the range of desert tortoises, there appears to be no remaining population 

(Fig. 6.3). A GIS analysis of this extirpation illustrates that the consequence of this loss is 

greater than just the loss of the individual tortoises. For example, the Desert Tortoise 

Natural Area (DTNA) has become a fragment of habitat separated from the rest of the 

DWMA to which it belongs. The same damaging results have occurred in Eldorado Valley, 

Nevada. Time required for Tier 3 research monitoring may be relatively short (e.g., 

predator abundance following different control procedures) or long term depending on the 

response time (e.g., response of vegetation to burning treatments). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 128 

AI' 

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Fig. 6.3 Kernel analysis of presence data for living desert tortoises (green polygons) and 

carcasses (red outlines. 

6.2 Monitoring Desert Tortoises 

6.2.1 Monitoring Desert Tortoise Populations 

Tier 1 and 2 status and trend monitoring must have clear objectives for current 

management agencies, but should also provide information on status, trend, and change 

over relatively large regions and long periods of time. Ideally, the methods will remain 

useful for a minimum of 25-50 years. For example, the 2001 distance sampling for desert 

tortoise abundance provides Tier 2 monitoring allowing statistical inferences to be made to 

large areas of habitat of the desert tortoise. Assessing trends in population numbers is 

necessary to assess the efficacy of management actions or to determine when delisting is 

warranted. Additionally, trends must be discernable regardless of variation in periodic 

estimates of population size (whether that variation is caused by actual variation in 

population numbers or errors in estimates of population size). With little variation in data, 

statistically determining a population trend is a simple task (Fig. 6.4). However, large 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 129 

variance in population density estimates for desert tortoises can make determining a trend 

very difficult. The life history characters of desert tortoises make discerning population 

trends difficult over a short time (e.g., 25 years; see Fig. 6.4). This type of problem stems 

from a particular life history typical of desert tortoise (Kareiva and Klepetka1994) and has 

been previously demonstrated for bald eagle populations (Hatfield et al. 1996). 

a. -

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Fig.6.4 Simulated population growth at a 2% 

growth rate with (a) a 10% coefficient of •

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coefficient of variation around the same trend. b. • SD(40% ofD) I •

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Originally, desert tortoise populations were monitored using total corrected sign transects 

(Berry 1979) or plots (Berry 1984). Both of these approaches have provided data on local 

desert tortoise densities with varying degrees of accuracy and precision, yet neither of these 

approaches were designed to provide regional density estimates. As a result, range-wide 

distance sampling has recently been implemented to provide regional density estimates. 

However, modern population monitoring also requires going beyond simple tracking of 

population densities and should also include documenting changes in the aerial extent of 

populations. 

Long-Term Study Plots 

Permanent study plots (see Section 4), and the data gleaned from them, were extremely 

valuable in identifying the original problems with tortoise populations declining. Similarly, 

they remain important because of their historic data. However, there are also many 

problems with using permanent plots to determine population trends: 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 130 

 Plots cover a small percentage (0.2%) of tortoise critical habitat, though plots are 

separated far enough that tortoises from one plot cannot move to another. 

 Plots are neither randomly placed in critical habitat, nor are they placed to address 

hypotheses concerning threats or management actions (e.g., highway fencing, 

removing grazing, allowing fragmentation due to urbanization, etc.). 

 Replication of plots within years is inadequate for comparison. 

 Sample sizes of survey years are largely inadequate to yield enough statistical 

power to perform a regression of trends in any particular plot. High variability in 

point estimates within years contributes to the problem of detecting subtle upward 

or downward trends. 

 Several plots were abandoned early in the process because they had low tortoise 

counts. This creates a bias for analysis of trends. 

 Data from plots violate assumptions in mark-recapture techniques when applied to 

all size classes, and detectability of tortoises was not evaluated as part of the 

analyses. 

 The spacing of plots is different in different places, and the spacing may not
 

produce needed sensitivity to detect changes at different landscape scales.
 

Continued monitoring of permanent study plots may still be of value for other reasons, 

however. Consideration may need to be given to abandon sampling plots that do not 

address specific research or management issues other than “just because a particular plot 

has been surveyed for a long time.” 

o	 Long-term capture/recapture data from plots has tremendous potential for looking at 

mechanisms of trends and asking size-class survivorship questions. 

o	 In management or threat-related, hypothesis-based surveys, if data were parsed out 

from individual grids within plots, more power would exist to determine which 

threats or management activities are most important. 

Distance Transect Sampling 

Distance Sampling is a method of enumerating population density from data collected 

along transects. The method requires that measuring the perpendicular distance from the 

transect line to all tortoises sited (Anderson and Burnham 1996). Calculating animal 

density by distance sampling requires mathematical adjustments to account for the extent to 

which a population can be sampled. For example, one has to know the probability that 

tortoises on the transect line are available to be detected (active or visible in burrows) and 

the actual detection rate (termed g0 and often assumed to be 100% in distance sampling). 

Additionally, one has to measure detectability of tortoises which are some distance away 

from the immediate transect line, (termed Pa in distance sampling) which is the probability 

that animals can be seen by the person walking a transect (Anderson et al. 2001). 

The further a tortoise is located from the transect line, the more difficult it is to see. In 

distance sampling, the perpendicular distance from the transect to the animals can be used 

to estimate Pa by assessing proportion of tortoises seen as a function of distance from the 

transect. The proportion of observed tortoises is then adjusted assuming the proportion of 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 131 

tortoises on the transect line is 100%. The statistical approach to calculating Pa requires a 

sample size of about 60 – 80 observations to obtain a well-formed frequency distribution of 

observations in relation to distance from the transect line (Buckland et al. 2001). This is the 

recommended standard, but, in fact, as few as 15 observations have been used in analyses 

by the USFWS. In good years, a person must walk more than 400 km to see 60 tortoises in 

most of the listed range, and in some years, it is necessary to walk more than 1000 km to 

find 60 tortoises (Medica, pers. comm.). The relatively high densities found in the Upper 

Virgin River Recovery Unit result in much higher encounter rates for that region, and thus 

the density estimates from that area have greater precision. 

Mathematical and statistical research on properties of distance sampling has shown the 

pooling of data from multiple teams is robust to different abilities of teams to detect desert 

tortoises, so long as all teams have 100% probability of detection of available animals on 

the transect line. If desired, allowing for team differences with distance sampling is 

straightforward, although not with current versions of the program Distance. For example, 

double sampling with independent observers and logistic regression can be used to adjust 

for different abilities of teams and other characteristics of desert tortoises such as: tortoises 

found walking in the open and tortoises found in burrows (e.g., see Manly et al. 1996 for 

the use of this method in surveys of polar bear). This method can potentially be used to 

adjust for sources of error including the tacit assumption that tortoises in burrows have the 

same availability and detectability as tortoises found walking in the open. 

Some adjustment factors are also difficult to estimate. For example, the availability of 

tortoises on the transect line changes among sites, at different times of the day, at different 

seasons, and among years (Fig. 6.5). The probability of detection of available tortoises on 

the line may vary from one team to another. However, data from across the entire 

California and Nevada portion of the range are currently lumped to calculate correction 

factors for density estimates of tortoises for the entire Mojave range, exclusive of the Upper 

Virgin River (the Utah Division of Wildlife Resources has been estimating tortoise density 

independently of other recovery units since 1997). Tortoise activity is calculated using a 

small number of focal tortoises, which are monitored to find the proportion of animals that 

are active. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 132 

0 0.2 0.4 0.6 0.8 1.0 

20 

1997 

15 

Fig. 6.5 Tortoise activity 

measured over a three year 

period at Bird Spring Valley, 10 

NV. Tortoise activity is 

expressed as the proportion 

of animals active for each 5 

hour during each week of 20 

the year and ranges from 0 

to 1. The gray areas 15 represent times for which 

tortoise activity was not 0 

sampled. Warmer colors 10 indicate high proportions of 

animals active, and cooler 

colors indicate fewer 

5 animals active. 

20 

15 

10 

5 

•

Mar. May Aug. Oct. Dec. 

Month of the Year 

Although tortoise densities should be easy to calculate using distance sampling (because 

tortoises are diurnal, tortoises are found in open habitat, and their activity is linked to 

drought severity index), it is not always the case that tortoises are easy to enumerate. 

Tortoise positions that are cited while sampling include burrow (visible), deep (not visible), 

open, under vegetation, hidden, tortoise in the open but near burrow. For each recovery unit 

the percent activity of focal animals (n = 5-18) is measured. The mean of observations 

during when transects are surveyed is calculated. Unfortunately, the software used to 

calculate tortoise densities (Program Distance) currently allows the use of only one value of 

g0, and this is a serious limitation to the analyses. New software or data collection methods 

(e.g., double sampling with independent observers) need to be developed allowing those 

working with desert tortoises to account for all the variables affecting tortoise activity and 

detectability. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 133 

Power Analysis - A power analysis was performed to estimate the ability to detect trends in 

population size (Link and Hatfield 1990, Hatfield et al. 1996) in relation to different 

reasonable annual percent population growth rates (e.g., those given in the Recovery Plan, 

and in Doak et al. 1994), with ranges in error generally encompassing those currently 

encountered using distance sampling in the Mojave Desert (Nussear 2004). For an entirely 

reasonable gentle growth rate (1%), the coefficient of variation would have to be much 

lower (i.e., 12 %) than current technologies are producing (9.5 to 56.2%, average = 20%) in 

order to detect a trend statistically, based on current population sizes. Currently, those 

working on distance sampling are trying to reduce variance in estimates of Pa and g0, but it 

may be impossible to reduce variance enough to be able to detect subtle trends typical of 

the natural growth rates of tortoise populations. Therefore, transect methods minimally 

require modifications to increase the precision of population estimates to the point where 

they may be useful for analyses needed for delisting. The detection of steeper trends, such 

as those of tortoise populations in the West Mojave, is currently possible with the level of 

variation achieved using distance sampling. 

Various scientists are working on modifications to the way data are collected and exploring 

and evaluating new approaches to analyzing data. These modifications include the length 

and shape of the transects, the number of technicians working on the transects, the manner 

in which the data are collected, the configuration of random start locations for the transects, 

the areas included/excluded for sampling, etc. Each of these approaches needs to be 

evaluated in terms of the potential to discern subtle changes in population size. 

Modifications have been suggested based on the tradeoffs between the precision of data 

points and the number of data points. 

There is some doubt that precision of estimates from distance sampling is being evaluated 

correctly. The sampling unit is the transect, and the “sample size” is the number of 

transects in a particular study area, not the number of desert tortoises observed. Program 

distance should be used to obtain Pa. Then, given g0 and an independent estimate of the 

proportion of individuals missed on the transect lines, call this proportion Pt, the 

abundance on a given transect is ni/(Pa*g0*Pt*Area Searched), where ni is the number of 

desert tortoises seen on “the transect” and Area Searched in the denominator is adjusted 

for length and width of transect. Data might be pooled to estimate the factors: (Pa*g0*Pt), 

but the variance of the survey should be computed based on the values of ni/(Pa*g0*Pt) 

from each transect. Finally, this process should be bootstrapped to bring in the variation 

due to estimation of the components of (Pa*g0*Pt). Pooling the data and running it through 

program distance one time will give a model-based estimate of variance that does not 

reflect variation from transect to transect. Clearly, population enumeration via distance 

sampling needs refinement and evaluation, including evaluating the efficacy of the 

approach all together. This refinement can best be accomplished by establishing a 

science-savvy monitoring committee who can evaluate and direct change in approaches to 

monitoring methods and approaches. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 134 

6.2.2 Monitoring Individual Desert Tortoises 

Comprehensive monitoring programs allow biologists and managers to understand the 

dynamics of a species fully. If applied toward desert tortoises, this type of program would 

include asking different questions on many different scales, ranging from the level of the 

population to the individual level. This section discusses aspects of individual desert 

tortoise monitoring. 

Condition indices 

Examining changes and variation in the body condition of individuals may also provide 

another method for modeling and mapping habitat condition. It could be useful to develop a 

body condition index for individual desert tortoises that included more information about 

the health of the individual than do current indices. A condition index might lead biologists 

to mechanisms contributing to population dynamics. For example, snakes show strong 

correlations between body condition and reproductive fitness (C. Peterson, pers. comm.; 

but see Wallis et al. (1999) for contrasting results with regard to desert tortoise 

reproductive output). 

Measuring the condition of individuals need not be separate from monitoring population 

size. A condition index may provide evidence for mechanisms behind changes in 

population size. For example, a measure of condition could potentially link the risk of 

mortality to individual covariates. That risk could help contrast between a stable and 

declining population. Using a more formalized monitoring structure allows some pressure 

to be taken off of requiring high precision of density monitoring (i.e., density 

measurements are not relied upon to answer all questions about a population). Each scale 

that is monitored should have different objectives and a coordinated effort for addressing 

each objective. For example, following individuals (“sentinels”) could be used to determine 

extent of certain threats, but not to answer exhaustive questions. 

Behavior 

We also explored information about population viability contained in the behavior of 

individuals. Understanding desert tortoise behavior can be very important to developing 

means to achieve recovery. The actions of living tortoises within their habitats contribute to 

survival, growth, reproduction, and ultimately to population persistence. 

Tortoise behavior, as it relates to recovery, consists of the cumulative actions carried out by 

individual desert tortoises. The goal is to recognize critical and generalizable behavioral 

patterns among desert tortoises. This comes from the study of individual animals under 

natural and experimental conditions. 

The behavior of individual desert tortoises is the result of complex interactions among six 

factors. Behavior should be analyzed in the context of the interplay of these six effects. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 135 

1. Genetic Make-up - Individuals are endowed with a unique genotype that will result in 

future individualized responses. More importantly, natural selection and drift can 

result in genetically-derived behavioral differences among populations (e.g., 

burrowing in soil versus using caves in rocks). 

2. Developmental Conditions - Developmental conditions can strongly influence 

genetic expression and subsequent behavior. For example, maternally-derived 

nutrients and hormones, as well as environmental contaminants within the egg, 

influence neonate performance. 

3. Physiological Traits - The ability and manner by which a tortoise responds to 

environmental conditions, and exposure to disease, is a function of its physiological 

capabilities. Because physiological limits and capabilities themselves are determined 

by genes, development, age, sex, and past physiological events, behavioral responses 

of tortoises to prevailing conditions may not be predictable without detailed 

investigation (Zimmerman et al. 1994). Furthermore, as the demography of the 

population shifts or as the habitat is transformed, mean physiological responses 

across a population may shift. 

4. Morphological Traits - Genetic make-up, development, and past physiological events 

determine morphological characteristics. Morphology and behavior are deeply 

intertwined. Morphology biomechanically limits what behaviors can be performed 

(e.g., foraging performance, vagility, crossing barriers, etc.). 

5. Environmental Conditions - Generally, an animal will exhibit only a subset of its 

total behavioral repertoire. Behaviors often are cued by prevailing environmental 

conditions. Humans are introducing inordinate new cues into the Mojave ecosystem 

(e.g., intentionally placed barrier fences along highways and changes of vegetation 

due to invasions of exotic weed species). 

6. Cumulative Individual Experiences - With time, an animal accumulates a set of 

individual experiences that can strongly influence its behavioral response to a 

stimulus. For these kinds of flexible behavioral responses, older individuals will tend 

to express successful behavioral responses (natural selection). Although counterintuitive, net behavioral responses within a population can be a function of 

demography even after controlling for differences in 1-5. If tortoise lifespan has 

been shortened due to human-caused mortality, tortoises that once contributed most 

to reproduction (mature and experienced individuals) may now be lost on a regular 

basis. 

Most behaviors of primary conservation and recovery importance are poorly understood or 

unknown at this time. Because the recovery of the desert tortoise is intrinsically a 

demographic problem, it is valuable to take a demographic approach to tortoise behavior. 

Doing so illustrates the central role of behavior in the recovery of the desert tortoise and 

identifies significant gaps in knowledge of important tortoise behavior. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 136 

Behavior of Embryos and Neonates 

Post-hatch performance of young birds and turtles is linked to egg quality, which in turn is 

linked to adult female physiology and the time of egg formation. Egg size (Roosenburg and 

Kelley 1996), nutrient endowment to the yolk, and the endowment of maternally derived 

steroids (Pilz et al. 2003, Sockman and Schwabl 2000) affect the behavior and performance 

of neonates following hatch. Variation in neonate tortoise performance and its relationship 

to maternal quality are unknown. 

This seemingly obscure issue is linked to tortoise conservation and recovery in two 

important ways. Adult females that face poor quality foraging habitat likely will produce 

fewer or lower quality eggs. Secondly, if prevailing mortality patterns act to remove mature 

and experienced (i.e., high quality) females, egg quality and quantity likely will decline. 

Post-hatch movement and habitat selection of neonate tortoises appears to be largely 

unknown but likely is very critical to population dynamics. The Mojave environment is 

heterogeneous. It is plausible that only a small subset of the general environment is 

adequate for the survival and growth of neonate tortoises, so these special habitats become 

extremely important to conservation and recovery even though they may represent a small 

percentage of available habitat. Do neonate tortoises go on a “random walk?” Are they 

following cues to important habitat? Are they moving independently of one another? 

A corollary to this issue is nest-site selection by breeding females. Adaptively, one might 

predict that females will select nest sites close to suitable neonate habitat if such habitat is 

available and females have knowledge of it. Are females limited in nest-site selection? 

Possible limits might be: inexperience (older may do better), territoriality, loss of quality 

nest sites, barriers to movement to preferred sites. 

Behavior of Juveniles 

Desert tortoises have a long juvenile period. Prolonged juvenile periods in birds and 

mammals frequently are attributed to the need for learning as well as for time needed to 

grow to breeding size. Desert tortoises grow and reach sexual maturity faster when fed highnutrition diets (Christopher et al. 1998), and gopher tortoises do the same in high-nutrition 

habitats (Mushinsky et al. 1994). Apparently, little thought has been given to the possibility 

that the juvenile period in tortoises has important functions other than a prolonged effort to 

acquire the nutrients to grow to some predetermined breeding size (Wilson et al. 1999). 

Certainly, juvenile tortoises engage in a suite of behaviors central to future population 

dynamics. Most importantly: 

Movement - The degree to which juvenile tortoises move through their environment is 

critically important because of its link to three crucial phenomena. 

A) Juvenile dispersal - Dispersal determines gene-flow, the “connectedness” of 

populations, and the genetic signal which we attempt to decipher in evaluating 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 137 

populations. Without significantly better understanding of juvenile dispersal, 

informed recovery planning will be severely hampered. 

B) Disease transmission - It is likely that juveniles move more than adults in the 

process of finding a place to settle. It also is likely that juveniles encounter 

more tortoises in this process than do settled adults. Hence, juveniles moving 

through the environment and interacting (agonistically?) with other tortoises 

could be a central mechanism for disease transmission. We cannot verify or 

discount this plausible scenario without measuring juvenile movement. 

C) Information gathering - The juvenile period can be an important period of 

information gathering. Presumably, juveniles learn locations of food, water, 

shelter, potential mates, and other critical information during the juvenile 

period. If juveniles necessarily wander during this period of their lives, then 

their vulnerability due to wandering may remain high regardless of apparent 

environmental conditions. 

Foraging and seeking shelter to promote growth - Nutrition, water, and thermal needs 

differ for juveniles relative to adults. Do juveniles have special habitat needs related 

to this growth phase of their life? Are these habitat needs being met? 

Gender differences in juvenile behavior - Little to nothing is known here. 

Behavior of Adults 

Considerably more is known about adult behavior, although it remains insufficient for wellinformed conservation planning. Key issues are: 

Disease by behavior interplay - Disease regularly causes behavioral changes in animals 

(listlessness and other forms of morbidity, etc.). If disease changes behavior and 

detection during surveys, then surveys may fail to provide accurate information. 

Mating system - Effective population size and genetic signatures can be influenced by 

mating system. Mating systems can create differential vulnerability of the sexes during 

movements. Encounters with vehicles, barriers, or humans might be influenced by 

mating systems. Disease transmission might be affected by searching for mates and 

courtship. 

Sperm storage – With sperm storage, following insemination adult females become 

temporarily independent of males for reproduction. This independence lasts for the 

duration of effective storage. Furthermore, if males are polygynous, then adult male 

survival becomes relatively less important than female survival. 

Breeding dispersal – Especially, do females return to nest areas? Are some females 

“sinks” by returning to traditional sites that actually fail? 

Circannual rhythm – Circannual rhythm can affect detectability, interacting with good 

food years. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 138 

6.3 Habitat monitoring 

When threats to habitat exist, it may be as important to monitor habitat as it is to monitor 

the focal species. In this context, a bias toward monitoring of focal species is particularly 

undesirable, because problems with habitat loss that have immediate consequences are 

deprived of attention and resources (Campbell et al. 2002). 

Remote Sensing for Tier 1 monitoring of status and trends - Aerial photography, digital 

airborne data, and satellite data are all possible remote sensing technologies that could be 

used to monitor habitat (M. Cablk, pers. comm. 2003). Remote sensing will not work well 

unless habitat monitoring experts work within the decision-making process. Types of 

habitat features that could be measured using remote sensing include vegetation 

association, slope, elevation, micro-conditions, elevation limits, geomorphology, and 

urban/agricultural land, etc. Once tortoise experts have determined which features are 

important to measure, the spatial, spectral, and temporal resolution of those features must 

be determined. This approach makes it more likely to capture the essence of habitat and 

how best to measure it. Change detection analysis would be used to determine seasonal or 

annual differences. 

Habitat Modeling - New techniques have also been developed in environmental and habitat 

mapping/modeling (C. Peterson, pers. comm. 2003). These approaches determine key 

features and assess those features along an environmental gradient. This has been done well 

for some species using simple habitat variables like temperature and moisture. Analysis tools 

include estimation of probability of occurrence or abundance of desert tortoises by multiple 

regression on habitat variables. In addition, resource selection functions for habitat use can 

be estimated by contrasting GIS or “on the ground” data between transects with and without 

detection of desert tortoises (Manly et al. 2002). 

Monitoring Recommendations 

•	 A coordinated, integrated, collaborative, range-wide monitoring program is needed. 

This program must be comprehensive and multi-scaled in its approach. The elements 

of the program should include the aerial extent of population, density of populations 

within aerial extent, qualitative and quantitative gain/loss of habitat, quantitative trends 

for threats, and possibly a condition index of individuals as an indicator of the 

population status. 

•	 There should be a science team formed to advise USFWS and land managers on how 

to make, and keep, the monitoring efforts scientifically credible and to help adaptively 

manage monitoring efforts to be as efficacious as possible. This team should also help 

in the prioritization of monitoring efforts. To be most useful, study design and data 

collection protocols for Tier 1 and 2 monitoring should be standardized. 

•	 The monitoring program should include an outside panel of experts to evaluate and
 

recommend how data should be collected and analyzed. The DTRPAC and outside
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 139 

experts agreed that a monitoring program is not useful unless it has a centralized 

organization, which can provide USFWS with information needed to make informed 

decisions. 

•	 A centralized monitoring program should be rigorous and formal wherein agencies, 

counties, and municipalities contribute to a centralized fund from which integrated 

monitoring projects can be funded which adhere to consensuses on monitoring 

priorities, approaches, data standards, etc. It is imperative that sufficient funding is 

secured to implement a scientifically rigorous monitoring program, including not 

only field collection of data, but also quality control measures and data management. 

•	 There should be a top-down organization of personnel to conduct monitoring in such a 

way that a formalized process is followed for data collection, quality control, and data 

archival. Standardized data collection and data sharing will allow collaboration so that 

meta-analyses and analyses beyond the calculations of tortoise densities can be done. 

All parties who collect monitoring data should have an agreement for data 

sharing/pooling and documentation of metadata, as well as agreements on publication 

of the data/analyses. 

•	 All Tier 1 and 2 monitoring should be designed to meet current management 

objectives but should be general enough to monitor trend and changes over a relatively 

long time period, say 50 years. All Tier 3 monitoring should be hypothesis driven. In 

other words, Tier 3 research should be experiments to test pre- and post-management 

actions over relatively short time periods. 

•	 Protocols for Tier 3 research monitoring should include identification of specific 

statistical and modeling procedures for analysis of data collected. There should be 

anticipated analysis methods for Tier 1 and 2 status and trend monitoring, but these 

analysis methods are less critical than for Tier 3 research because Tier 1 and 2 

monitoring data should have utility over a relatively long time period. In fact, analysis 

methods for Tier 1 and 2 monitoring data that will be used in, say 2025, have probably 

not yet been envisioned. 

•	 Monitoring should be promoted to detect change at different scales or levels of 

integration (Allen and Hoekstra 1992). 

•	 Data on habitat and threats should be collected as part of tortoise density monitoring to 

extend the scope of density analyses and enhance the ability to develop correlationregression models between abundance of desert tortoise, habitat, and threats. This 

would include association of habitat and threat indicator variables (e.g., length of roads 

per unit area in buffers surrounding transects) with individual transects used in 

distance sampling. 

•	 There should be a workshop to bring experts on various kinds of monitoring together 

to map a plan for developing monitoring of habitat and threats. Additionally, there 

should be a summit on statistical approaches to density monitoring. This summit 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 140 

should bring together statisticians and tortoise biologists to map out a plan for
 

improving density monitoring.
 

•	 There is value in permanent study plots only if the data are used more fully. The use of 

permanent study plots should be evaluated relative to their utility in answering specific 

research or management questions. Some established plots may have outlasted their 

scientific usefulness, while others may need to be established to answer new questions 

(e.g., relative to threats and recovery action effectiveness or DPS differentiation). 

•	 The value of permanent study plots is also based on the availability of raw plot data. 

Without the ability to pool data from all areas and projects, plot data do not justify 

their expense. It is difficult to justify the amount of money spent on data collection 

from plots without having open access to the full data set. Inter-agency coordination 

should be imposed to acquire all necessary data for analyses. 

•	 Continue to use transect sampling, as these data are extremely valuable. Develop 

custom computer software to incorporate unique needs for tortoises (including 

modeling go and Pa). Currently, it is not possible to modify the computer software 

program DISTANCE. Do research to find ways to reduce variance in estimates of 

availability and detectability, including variance created due to the clumped 

distribution of tortoises in the landscape. Investigate the use of bootstrapping of 

individual transect lines to evaluate a design based estimate of variance of density and 

abundance of desert tortoises. 

•	 There should be continued work to modify distance sampling to get the most precise 

estimates possible. This includes, for example, improving detection rates and adding 

environmental covariates in models of population density. 

•	 There should be an attempt to determine the minimum rate of growth or decline 

detectable by the most optimistic methods. This would produce an answer to the 

question, “in the best of all worlds, is there power to detect a certain level of decline or 

increase?” 

•	 Distance sampling as implemented in 2001 combined with habitat and threats 

variables measured at the same sites continues to hold great promise for long-term 

status and trend monitoring. If distance sampling is shown not to have enough power 

to track population trends, then it may be necessary to redirect effort towards detecting 

trends in other objects or processes, such as changes in carcass density or tracking dieoffs, etc. The downside to this suggestion is that some objects or processes may have a 

time lag that would preclude seeing a decline in adequate time to respond with a 

change in management. 

•	 Transect sampling associated with distance sampling for abundance as implemented in 

2001 should be refined to collect considerably more data. Additional data could 

include habitat measures such as rainfall, vegetation, etc. as well as measures on 

individual tortoises such as blood samples for assessing stress, health, genetic 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 141 

distinctness, etc., and the ability to determine remotely sensed/GIS data such as linear 

density of roads in buffers surrounding transects. 

•	 Density monitoring needs to be recognized to have several components: training field 

crews, field collection of data using standardized data collection protocols, data quality 

assessment and quality control, data archival, metadata (methods) archival, and data 

analysis and reporting. Too frequently in the past, monitoring has expended virtually 

all funds on field collection of data, and the other components that should be included 

in a comprehensive monitoring program have been neglected. 

•	 If estimates of tortoise density are determined to be too variable to be useful in 

assessing effectiveness of management actions, then perhaps density estimates should 

be treated as “density indicators.” This approach should be used only after it has been 

determined that assessing density cannot be accomplished to obtain useful, precise, 

and accurate estimates. 

•	 There should be an attempt to assess the extent to which data on presence and absence 

of tortoises could be useful to the goals for monitoring. The method of MacKenzie et 

al. (2002, 2003) should be explored as a means to enhance monitoring. The methods of 

Manly et al. (2002) for estimation of resource selection functions should be considered 

as a means of relating habitat use to measured indicators of habitat quality/quantity or 

threats. 

•	 A health, or physiological status, index needs to be developed from body condition 

measurements of individual tortoises. The condition index of Nagy et al. (2002) may 

not be sufficient by itself, because it gives no information on levels of stress, immune 

system function, etc., and little information on changes in body mass not attributable 

to water gain/loss (see also Hayes and Shonkweiler 2001). 

•	 Initiate a rapid response program to investigate morbidity and mortality events, using 

existing programs (e.g., Biodefense, Foodnet) as models (i.e., develop standard 

operating protocols so that when a die-off event occurs, response actions happen 

quickly). Develop standard diagnostic and evaluation protocols to determine the nature 

and severity of a disease threat. Develop appropriate management strategies for 

containing or removing a disease threat, if necessary. Develop appropriate ways of 

evaluating the success of management strategies. 

•	 Habitat and threats monitoring by remote sensing should be researched. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 142 

6.4 Delisting Criteria 

As given in the Desert Tortoise Recovery Plan, five criteria must be met for delisting of the 

desert tortoise (USFWS 1994). 

Criterion 1 

“As determined by a scientifically credible monitoring plan, the population within a 

recovery unit must exhibit a statistically significant upward trend or remain 

stationary for at least 25 years (one desert tortoise generation).” 

Criterion 2 

“Enough habitat must be protected within a recovery unit, or the habitat and the 

desert tortoise populations must be managed intensively enough, to ensure long-term 

population viability.” 

Criterion 3 

“Provisions must be made for population management in each DWMA so that

population lambdas are maintained at or above 1.0 into the future.”
 

Criterion 4 

“Regulatory mechanisms or land management commitments have been implemented that

provide for adequate long-term protection of desert tortoises and their habitat.” 

Criterion 5 

“The population in the recovery unit is unlikely to need protection under the Endangered 

Species Act in the foreseeable future. Detailed analyses of the likelihood that a population 

will remain stable or increase must be carried out before determining whether it is

recovered. (a) Fluctuations in abundance, fecundity, and survivorship; (b) movements of

desert tortoises within the area and to or from surrounding areas; (c) changes in

habitat, including catastrophic events; (d) loss of genetic diversity; and (e) any other

threats to the population all might be significant and should be important elements that

should be considered in such an analysis.” 

All but the first criterion deal with securing habitat into “the foreseeable future” for the 

recovered populations and remain mostly relevant, except for changes in wording needed to 

accommodate a new first criterion. The first criterion may require replacement or 

modification. The Recovery Plan called for creation of areas for intensive management of 

tortoise populations that were large enough (at least 1000 square miles) to permit recovery 

of the populations within them after the populations had declined to minimum permissible 

population sizes, as determined by population viability analyses. Although this prescription 

followed logically from a heuristic model of what was known about population dynamics 

in the desert tortoise, statistical methods now available suggest that it may be impossible to 

monitor populations precisely enough to determine if the prescription was effective. Power 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 143 

analysis of current monitoring approaches to estimate tortoise population densities shows 

that it will be nearly impossible statistically to discern an upward or stable population 

trend, even over a 25-year time span, which is a requirement of the current criterion. On 

this basis, the first criterion needs to be modified, and the revised criterion should 

incorporate the following considerations. 

•	 The criterion of a population remaining at least “stationary” does not work well, 

insofar as high variance in population estimates often makes a population’s trending 

upward or downward statistically indistinguishable from its remaining “stationary.” 

•	 The criterion of a population remaining at least stationary draws attention 

exclusively to population size and excludes concern for changes in habitat and 

threats, which are significant components of a well-conceived recovery and 

monitoring program. 

•	 The criterion of a population remaining at least stationary ignores multiple scales of 

measurement, disregarding important information on population well being 

available at the levels of the individual (e.g., physiology and behavior of 

individuals) or landscape (e.g., ecosystem processes, such as habitat fragmentation 

and/or degeneration), and failing to define relationships among the components of a 

well conceived recovery and monitoring program. 

•	 The criterion of a population remaining at least stationary suffers statistically from 

lack of power and high levels of risk from both Type I and Type II statistical errors. 

•	 The definition of a “population” excludes the possibility of tortoise populations 

acting as metapopulations. 

These considerations highlight the fact that that the heuristic model of desert tortoise 

population dynamics used by the Recovery Team essentially is obsolete. In particular, the 

Recovery Plan may have (a) overestimated the importance of local population dynamics, 

(b) underestimated the importance of metapopulation processes (a concept in its infancy in 

1994), and (c) greatly underestimated the time required to observe evidence of recovery. 

Population die-offs appear to occur commonly, and local populations seem to recover from 

those die-offs at different rates. Some local populations appear historically to have 

achieved high densities and subsequently all to have suffered die-offs (this pattern has been 

seen especially in the Western Mojave and in Southwestern Utah, but it also may have been 

present in other places, such as Piute Valley, Ivanpah, Chuckwalla Valley, and Fenner 

Valley). These slowly accumulating facts suggest that the desert tortoise exists in an 

ecological system in which metapopulation dynamics may have been historically important 

to the long-term persistence. It may be the case that, for the desert tortoise, nobody has yet 

seen a single cycle of local population extirpation and re-colonization that may occur 

naturally as a part of metapopulation dynamics. Habitat fragmentation by satellite 

urbanization and high-density highways currently may be preventing natural 

metapopulation processes and, ultimately, species recovery. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 144 

The metapopulation model of recovery contrasts deeply with the heuristic model used by 

the Recovery Team. If the metapopulation model accurately describes the ecology of the 

desert tortoise, then it will be necessary to understand the dynamics of recovery for both 

local populations and for entire metapopulations, within an ecosystem that is permanently 

disrupted by habitat loss, fragmentation, and degradation. In this disrupted state, 

metapopulations are not likely to recover without artificial enhancement of metapopulation 

processes. For example, if fragmentation ablates normal processes of recolonization of 

local populations after die-offs, then it may be necessary to “head start” recolonization of 

local populations from hatchery stocks. This, and similar, management actions were not 

considered in the original Recovery Plan. Employing the metapopulation model will 

require considerable ecological wisdom, and we recommend that the new science advisory 

committee for the USFWS assemble appropriate expertise, perhaps in a workshop, to 

develop new prescriptions for management that will lead to delisting. It will be necessary 

for such a group to develop new criteria for assessing recovery of a metapopulation. In 

particular, it will be necessary to develop (1) indices of poor metapopulation function that 

do not suffer from the kinds of statistical and other inadequacies described above (perhaps 

indices that focus on extreme, i.e. minimum, values rather than on central tendencies); (2) 

monitoring schemes that are sensitive enough to reveal relatively subtle changes in 

demography, habitat, and threats (perhaps schemes that focus on presence/absence of 

critical size classes in a large number of small, widely spread quadrats rather than on 

quantitative assessment of population size in a small number of locations); and (3) 

management plans that compensate for ecosystem dysfunction (perhaps plans that, of 

necessity, incorporate currently controversial techniques such as head starting, 

translocation, and maintenance of so-called "assurance colonies"). 
 

 

DTRPAC Report page 145
 

“True science teaches, above all, to doubt and be ignorant.” 

Miguel de Unamuno, The Tragic Sense of Life. (1913) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 146 

7. Integrating Research and Management 

The mission of the DTRPAC was to analyze the current state of research on the desert 

tortoise, to identify important gaps in our knowledge about the desert tortoise, and to 

suggest ways in which those gaps could be filled. The results of the efforts of the DTRPAC 

to accomplish this mission are displayed in previous chapters. Although its mission did not 

include recommendations about management directly, the DTRPAC concluded that 

research and management are so closely intertwined that it would be remiss in not 

addressing relevant management issues. Furthermore, the DTRPAC strongly suggests that 

no matter how good and complete the research effort may become, it will be for naught if it 

does not become part of a well-conceived management plan. We begin by reviewing the 

research needs. 

7.1 Synopsis of Recommendations 

We collected the various recommendations in previous chapters, paraphrased them for 

clarity, and organized them topically, by Research and Monitoring, Cooperation and 

Coordination, Data Management, and Other Management Recommendations. The list of 

these recommendations follows (the chapter from which each need was extracted is 

included, in parentheses). 

7.1.1 Research and Monitoring 

• Improve understanding of genetics and the relationships between genetics and other 

attributes 

Genetic core units, boundaries, and gene flow need to be examined. (3) 

Patterns of differences in ecological. morphological, behavioral, demographic, and 

health status of each unit needs to be determined. (3). 

More about the ecogeography of genetics of pathogens and hosts must be learned (4). 

• Re-evaluating the status of DPSs and the positioning of DWMAs 

DWMAs within each DPS should be geographically revised to maximize their 

conservation potential (3). 

• Improve population sampling methods 

There should be enough study plots to represent the different scales of management 

areas (4). Alternatively, using 5-10 key permanent study plots as indices of change, 

while abandoning sampling of other plots, should be considered (6). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 147 

The data should be used more fully, and the raw plot data pooled from all areas and 

projects (6). 

Modify distance sampling analyses to get the most precise estimates possible, 

including modeling G0 and Pa (6). 

If distance sampling is shown not to have enough power to track population trends, 

then redirection of effort towards detecting trends in other objects, processes, or 

indices, such as changes in carcass density or tracking die-offs, should be 

considered (6). 

Determine the maximum rate of growth or decline detectable by the most optimistic 

methods (6). 

The method of MacKenzie et al. (2002), looking at presence/absence, should be 

explored as a means to enhance monitoring (6). 

Statistical tests need to include measures of power and deal with both Type I and 

Type II statistical errors (6). 

If densities are determined to be too variable to be useful in assessing effectiveness 

of management actions, then density estimates should be treated only as “density 

indicators.” (6). 

• Develop tools 

Innovative methods for the visualization and display of individual and interactive 

spatial and temporal threats, including GIS and other types of visualization 

technologies, should be developed and evaluated (5). 

Inexpensive and more field-portable tools and diagnostic tests to study disease 

should be developed (4). 

Stress tests that are applicable to wild tortoises (e.g., adrenocorticotropin hormone 

(ACTH), phytohemagglutinen (PHA), and sheep red blood cell (SRBC) challenge 

experiments, to examine adrenal gland response, T-cell response, and B-cell 

response, respectively), should continue to be developed (4). 

Habitat monitoring by remote sensing should be developed (6). 

• Improve the focus on the recovery goal 

In the threats network, the relative importance or hypothesized nature of each 

linkage between impacts and mortality sources should be weighted. Research and 

management should, through a hypothesis-based approach, focus on those 

actions/threats that are more heavily weighted (5). 

Refocus the general approach to research on disease, treating it as part of a network 

of threats (5). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 148 

Develop clear standards for determining whether individuals in a population are 

healthy or not and whether they have been stressed or not (4). 

A study of the epidemiology of URTD is badly needed. (2) 

Sources of mortality, particularly their importance relative to each other, needs to 

be better explored as age-specific survivorship. (2) 

The impact many threats have on tortoise populations is poorly known and in need 

of investigation to evaluate their relative importance and develop effective 

mitigations to reduce their impacts. (2) 

Alternative protective measures need to be compared experimentally to help ensure 

that useful methods are used. (2) 

Long-term studies, that include standard life-history traits, are needed on tortoise 

demography. (2) 

The natural history of host-parasite associations for the major disease relationships 

should be more deeply elucidated (3). 

All monitoring should be hypothesis driven (6). 

Recognize density monitoring as having several components: training field crews, 

field collection of data, data quality assessment and quality control, data archival, 

and data analysis and reporting (6). 

• Improve information gathering 

Health assessments should be added to the information gathered in ecological 

studies and monitoring. A health, or physiological status, index needs to be 

developed from bodily condition measurements of individual tortoises (6). 

Current serological surveys for M. agassizzi should be continued, adding screening 

for THV and other Mycoplasma species, as assays become available (4). 

Continue necropsies, if a rationale for these necropsies can be developed in relation 

to the potential for information from them to affect new knowledge and 

management (4). 

Data on habitat and threats should be collected as part of tortoise density 

monitoring, to extend the scope of monitoring (6).
 

Monitoring should be pitched to detect change at different scales or levels of 

integration (6). 

• Improving information dissemination 

Inform researchers about both the qualities and the shortcomings of diagnostic tests 

for Mycoplasma species and URTD (4). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 149 

Inform researchers about the value of different diagnostic tests in addressing 

different goals (4).
 

Explicit acknowledgment describing what data are not available should be made, to 

allow a more accurate assessment of uncertainty and risk in the planning process (6). 

7.1.2 Coordination and Cooperation 

• Improve the utility of monitoring efforts 

Coordination of effort on monitoring can be improved if USFWS would ensure that all 

monitoring data are reported annually as part of the federal permitting process. Then 

the USFWS could facilitate sharing data among researchers as part of the USFWS 

responsibility to obtain, analyze, and distribute reports on monitoring data (4). 

• Improve the focus on recovery goals 

Research and management should, through a hypothesis-based approach, focus on 

those actions/threats that are more heavily weighted (5). 

Provide quantitative biological goals for the conservation/management plan or recovery 

action (6). 

• Develop research agendas 

Develop multi-disciplinary, long-term research agendas to understand the network 

of threats. Include epidemiologists and population biologists in developing the 

research agendas (4). 

There should be a workshop to bring experts on various kinds of monitoring and 

statisticians together to map a plan for developing monitoring of habitat and threats (6). 

Initiate a rapid response program to investigate morbidity and mortality events (4). 

Ensure that killing seropositive, but otherwise healthy individuals, is limited (4). 

There should be coordinated effort to conduct monitoring, including having a
 

formalized process for data collection, quality control, and data archival (6).
 

A centralized, integrated, collaborative, range-wide monitoring program should be 

initiated (6). 

Recognize density monitoring as having several components: training field crews, 

field collection of data, data quality assessment and quality control, data archival, 

and data analysis and reporting (6). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 150 

• Employing “outside” expertise 

Include epidemiologists and population biologists in developing the research 

agendas (4).
 

There should be a science team to advise the USFWS on how to make and keep the 

monitoring efforts scientifically credible; to help adaptively manage monitoring 

efforts to be most efficacious; and help in prioritization of monitoring efforts (6). 

There should be external peer review by an independent panel of experts that would 

periodically review the monitoring program and the science advice given (6). 

The monitoring program should include an outside panel of expert analysts to 

evaluate and recommend how data should be collected and used (6).
 

There should be a workshop to bring experts on various kinds of monitoring and 

statisticians together to map a plan for developing monitoring of habitat and threats (6). 

• Improve information dissemination/access 

There should be imposed inter-agency coordination to acquire all necessary data for 

analyses (6). 

7.1.3 Data Management 

• Improve information dissemination/access 

Ensure that all important data exist, are accessible to researchers, and are explicitly 

summarized (4). 

Explicit acknowledgment describing what data are not available should be made, to 

allow a more accurate assessment of uncertainty and risk in the planning process (6). 

Information/data should be maintained in an accessible, centralized location (6). 

7.1.4 Other Management Recommendations 

• Re-evaluate the status of DPSs and the positioning of DWMAs 

DWMAs within each DPS should be geographically revised to maximize their
 

conservation potential (3).
 

• Improve the focus on the recovery goal 

Research and management should, through a hypothesis-based approach, focus on 

those actions/threats that are more heavily weighted (5). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 151 

The list of research needs suggests attention be directed to at least three management areas: 

adaptive management, cooperation and coordination, and data management. We discuss 

each of these areas successively. 

7.2 Adaptive Management 

Adaptive management can be defined as a flexible, iterative approach to long-term 

management of biological resources that is directed over time by the results of ongoing 

monitoring activities and other information. This means that biological management 

techniques and specific objectives are regularly evaluated in light of monitoring results 

and new information on species needs, land use, and a variety of other factors. These 

periodic evaluations are used over time to adapt both management objectives and 

techniques to better achieve overall management goals as defined by measurable 

biological objectives. 

Adaptive management of recovery efforts for the desert tortoise must be designed to 

provide an objective, quantitative evaluation of the effectiveness of management actions 

in attaining program goals (Kareiva et al. 1999). It should provide a scientifically sound 

approach to provide resource managers with objective scientific data and analysis upon 

which to base management decisions as well as scientifically valid evaluation of 

management actions. 

A critical element of any adaptive management program is the database upon which 

management decisions can be made. Such a database can provide a basis for evaluating 

species, habitat, and/or threats status and trends, and it can be used to evaluate 

management actions directed at recovery. Adaptive management requires an objective 

and scientifically-valid program for collecting data coupled with supervision of an 

accessible database by a competent scientific authority. 

A Desert Tortoise Recovery Office (DTRO) should be established in the USFWS to 

oversee collection, quality control, and archival of scientific data as well as analysis of 

data and generalization of results from data. This office should be advised by a Science 

Advisory Committee (SAC; see Section 7.3.2) composed of credentialed scientists who 

have expertise in conservation biology, statistics/experimental design, and herpetology. 

The DTRO would facilitate both collection and distribution of data from and to scientists, 

managers, and stakeholders. Additionally, this office should be in charge of data security. 

This office should appoint a database manager (potentially as a contract) that will be in 

charge of long-term maintenance of the database 

7.2.1 Ingredients of Inventory, Monitoring, and Research 

Inventory, monitoring, and research include six key steps, which when appropriately 

linked to decision making, will maximize the collection and integration of objective, 

reliable data into the decision-making process and is intended to minimize inappropriate 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 152 

or unnecessary management actions. 

• Identifying Explicit (Quantifiable) Scientific Goals and Objectives 

The goals of recovery programs include targets of study at a wide variety of spatial scales 

and levels of ecological complexity. For example, targets of study will range from highly 

restricted spatial scales for individual tortoises to broad spatial scales to include multiple 

DPSs (see section 3.0). 

• Identifying Likely Threats or Combinations of Threats 

The SAC should guide efforts to identify likely threats, or threat combinations (see Section 

5), for recovery. Threats, and threat combinations, will include both natural and 

anthropogenic phenomena including change in drought frequency, fire, toxic pollutants, 

flood, invasions of exotic species, poaching, disease, and so on. Identification and 

verification of threats, and threat combinations, will be the product of research to establish 

mechanistic links between environmental phenomena and threats to populations and 

ecosystems. 

• Constructing Conceptual Models Describing Crucial Ecological Interactions 

The models are important in developing an understanding of the key processes and 

properties of the ecological interactions between individuals, and/or populations, and their 

environments, and in developing understanding of how threats affect processes like 

extinction. The models will be important in delimiting the boundaries of what constitutes 

natural variation in population processes and the role of humans in stressing populations. 

Models should incorporate the latest scientific concepts and paradigms, which can keep 

costs low and scientific understanding high. 

• Identifying Indicators or Indices 

Indicators are surrogates of population responses to threats (Simberloff 1998). Indicators 

can be demographic properties or characteristics that are easy to measure and exhibit 

dynamics and responses that parallel those of more difficult to measure population 

properties or processes. Indicators must be selected because they demonstrate low natural 

variability, but they respond measurably to environmental change at reasonable cost. 

Indicators might include population sizes and distributions, and physical and biotic 

variables. Establishing indicators will require research into the correlation among 

population dynamics and ecosystem properties and processes. 

• Developing Sampling Design to Estimate Status and Trends of Populations, Habitats, 

Threats, and/or Indicators 

Hypothesis testing, trend analyses, model development, and statistical inference must come 

from rigorously scientific programs that should be subjected to independent scientific 

review. Monitoring exercises must be statistically rigorous so that the program will have 

the highest probability to detect ecologically important trends convincingly. Sampling 

design, hypothesis testing, and trend analyses are all scientific procedures that continually 

become better as general scientific knowledge increases. Thus, rigor in this area will 

require continuous reevaluation. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 153 

• Determining Threshold Values That Will Trigger Management Changes 

Quantitative levels of status and trends should be used to trigger adjustments land 

management and policy. This is the basis for adaptive management, and it provides 

recommendations for the appropriate bodies to establish dynamic policies and management 

aimed at producing the desired ecological condition and the conditions required by the 

USFWS. 

Appropriately integrated, this systematic program can use direct measurements and 

surrogate variables (indirect measures of the status of recovery) to determine the status and 

trends of the focal species. The resulting data and analyses should provide insight and lead 

to recommendations for adaptive management. It is critical to this process and to the 

assurances made to the USFWS that the long-term scientific integrity of inventory, 

monitoring, and research be assured because of the highest standards of scientific 

accountability and peer review. 

Inventory, research, and monitoring are necessary and important activities for recovery 

programs. Nevertheless, the lines defining the differences and similarities between 

monitoring and research are not sharp. Indeed, appropriate monitoring requires research 

methods to provide more than anecdotal information, and anecdotal information will be 

inadequate for both economy-seeking permit holders and for regulatory agencies. 

Additionally, where monitoring methods do not yet exist, research must be conducted to 

develop efficacious means to assess the effectiveness of the recovery efforts. 

7.2.2 Relationships among Inventory, Monitoring, Research, and Adaptive Management 

Inventory, research, and monitoring (IRM) are necessary and important activities for 

complex, long-term, recovery efforts. The lines defining the differences and similarities 

between monitoring and research are not sharp. Indeed, apposite monitoring requires 

research methods to provide anything more than anecdotal information, and anecdotal 

information will be inadequate for both economy-seeking permit holders and for regulatory 

agencies. Additionally, where monitoring methods do not yet exist, research must be 

conducted to develop efficacious means to assess the effectiveness of the recovery plan. 

Thus, this section will elaborate on the definitions, roles, and importance of IRM activities 

in conservation planning. 

7.2.3 Definitions 

• Inventory, a to Webster’s New International Dictionary (Merriam-Webster 1986), is 

an itemized list of current assets; as a survey of natural resources such as a survey of 

wildlife of a region. 

• Monitoring, a to Webster’s New International Dictionary (Merriam-Webster 1986), is 

to watch, observe, or check especially for a purpose. 

• Research, a to Webster’s New International Dictionary (Merriam-Webster 1986), is to 

search or to investigate exhaustively. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 154 

7.2.4 Inventory 

A recovery program designed to protect sensitive populations must be based upon 

knowledge of the status of populations. The size and spatial distributions of populations are 

critically important pieces of information upon which management prescriptions can be 

made. If the status of any population is not known, then aspects of that status can be 

assessed through an inventory of presence and absence, that inventory should be conducted 

at the earliest possible time in the planning process, and periodic inventories may need to 

be conducted to assess the distribution of presence. 

7.2.5 Monitoring 

Monitoring without a goal can result in misdirected management more than can result from 

no monitoring at all. Monitoring without goals can consume valuable resources that can be 

used constructively in other conservation actions (such as buying more habitat), and 

incorrect information from improper monitoring can mislead and direct dangerous 

management decisions. Additionally, monitoring must be conducted with adequate 

sampling and scientifically defensible sampling protocols so that any new data are 

sufficiently replicable that they can lead to conclusions with a determinable probability of 

being correct. 

There are numerous relevant goals of monitoring, and different kinds of monitoring are 

necessary and important to a successful recovery plan. Nevertheless, monitoring is 

important to validate management actions, to provide better data for adaptive management, 

and to get advanced knowledge of unforeseen circumstances that arise in the recovery plan. 

Monitoring can be categorized as implementation monitoring, effectiveness monitoring, 

and validation monitoring (NMFS 2002). The first two of these forms of monitoring meet 

the definition of monitoring, but the validation monitoring is actually a form of research 

(see below, Fig. 7.1). 

• Implementation Monitoring 

Implementation monitoring provides a permanent record of what mitigation and 

management is applied as part of the recovery plan. Implementation monitoring should 

occur continually and it should include details about the implementation actions undertaken 

in mitigation of take or as management for recovery. Implementation monitoring should 

assess actions such as fencing along roads, recreation restrictions within reserves, range 

improvements, pollution regulation, vegetation restoration, grazing management, etc. 

Implementation monitoring also should include “natural implementations” such as 

occurrences of drought, natural fires, and invasion of exotic species. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 155 

Actual Status

and Trends

Research

Validation

Monitoring/

Research

Results of

management actions

Adaptive

Management

Actions

Effectiveness

Monitoring

Desired Status

and Trends

from Management Actions

Conceptual Model

Implementation

Monitoring

Fig. 7.1 Relationships among the desired objectives of a recovery program, a conceptual model of 

the functional relationships among species, and monitoring activities in the adaptive management. 

• Effectiveness Monitoring 

Effectiveness monitoring is used to record change in recovery status caused by management 

actions and other important natural and anthropogenic events as well as random, year-toyear change. With sufficient data from different monitoring sites and from a series of years, 

analyses should be able to separate out the non-random change from a background of 

random change. For example, analyses of data from effectiveness monitoring could assess 

the efficacy of grazing restrictions on vegetation. They could estimate the impacts of natural 

and anthropogenic fires. They may assess the growth in animal populations freed from 

mortality caused by vehicles on roads passing through semi-natural areas. Importantly, 

analyses from effectiveness monitoring also should assess the loss of biological resources 

due to aggressive competition, predation, or parasitism by exotic species. 

Even if all populations being recovered were monitored to assess non-random change, that 

would not be enough as a test of the efficacy of recovery actions. Other populations or 

processes within the planning area could threaten the efficacy of a recovery program even 

before non-random change occurs in the populations. If habitats are invaded by a 

destructive exotic species, or a destructive change in pollution levels, or a destructive 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 156 

change in climate, then the existing management activities might not be adequate and 

might have to be changed as part of adaptive management. 

• Validation Monitoring 

Validation monitoring (NMFS 2002) is actually research. Its purpose is to determine if the 

“conceptual model” of the ecological systems of the recovery program is valid. The concept 

of validation is that, if the conceptual model is correct, then correct prescriptions for 

adaptive management can be made. Validation monitoring/research determines the extent to 

which predictions and assumptions of adaptive management are appropriate to attain the 

desired objectives. Validation monitoring/research generally requires experimentation and 

long-term monitoring to create a database essential to validate results from the effectiveness 

monitoring. Validation can be made regardless of whether or not the conservation objectives 

are met. For example, if a particular standing crop of non-woody vegetation is deemed (by 

the conceptual model) to be essential to provide shade for tortoises, and if this standing crop 

is not achieved even after a reduction in cattle grazing, then validation monitoring/research 

could be used to determine needs for additional changes in grazing. That is, validation 

monitoring/research is used to assure that benefits of management actions are not wrongly 

attributed to a given action or mechanism. 

Adaptive management of recovery efforts requires constant assessment of the effectiveness 

of management actions. That assessment occurs through monitoring, and some monitoring 

cannot occur without research. An effective monitoring program must have all three types 

of monitoring and research or else it is not possible to interpret data from the component 

parts of monitoring. Specifically, the efficacy of the recovery effort requires evaluation of 

the effects of management in light of hypothesized responses to that management and to 

the actual management actions. All of the different kinds of monitoring are required to 

make a decision to alter current management practices to reach the desired objectives of 

recovery. 

7.2.6 Research 

Research is necessary for the development, and continual correction, of the conceptual model 

of the recovery program. An incorrect conceptual model of recovery can lead to dangerously 

inappropriate adaptive management. Assumptions of which management actions will lead to 

the desired objectives of the recovery program need to be tested. For example, suppose that 

we hypothesized a conceptual model that posits that unpaved roads result in greater mortality 

of reproductive female tortoises. This hypothesis requires testing. The test would not simply 

assess the number of tortoises lost due to facilitated poaching or direct mortality from 

vehicles, etc. It would, additionally, assess threats to the persistence of desert tortoise 

populations given that some individual tortoises will die due to roads. 

7.2.7 Adaptive Management Decision Making 

Importantly, adaptive management must facilitate information transfer to decision makers 

and land and resource planners. The process involves five steps: 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 157 

• Provide a range of possible management responses. 

• Determine the potential alternative ecological outcomes associated with specific 

phenomena being monitored. 

• Assess the probabilities associated with each possible interpretation of monitoring data. 

• Identify the management decision that maximizes the overall “utility” of each 

decision and outcome (involving considerations of the costs of misinterpretations of 

monitoring data and costs of wrong decisions). 

• Propose research endeavors that are likely to result in identification of management 

actions which will allow species to be moved from evaluation to covered status. 

7.2.8 The Circle of Status and Trends and of Monitoring 

The circle of elements marked with blue arrows in Fig. 7.1 includes the major elements of 

adaptive management. Generally, it is necessary to develop goals for recovery, which 

generally will be the status and trends needed for delisting. Our understanding of the 

ecological interactions between the species and its environment represents our “model” of 

system. The model, then, represents what we know about the role of food resources, 

disease, predators, roads, etc. for population dynamics of desert tortoise. That model, and 

the goals for recovery, represent the ingredients needed to prescribe management actions to 

achieve those goals. Management actions might include fencing roads, managing access by 

off-road vehicles, habitat restoration of abandoned roads or mines, reducing the 

anthropogenic subsidies to ravens (e.g., garbage dumps, power lines), etc. The efficacy of 

these management actions needs to be monitored by effectiveness monitoring. 

Effectiveness monitoring does not assess the management actions per se, but assess the 

outcomes relative to the desired status and trends. Thus, the circle in Fig. 7.1 depicts the 

relationship between status and trends and monitoring as discussed in the next chapters. 

7.3 Cooperation and Coordination 

The interaction between environmental scientists and environmental managers often has 

been contentious, even though the ultimate goal of both groups is environmental protection 

(Cullen 1990; Dewberry and Pringle 1994; Shrader-Frechette and McCoy 1994a, b). Many 

factors, such as under-use of the reductionist approach by managers (Romesburg 1991), 

over-use of the reductionist approach by scientists (Miller 1993), perceived irrelevance of 

science to the environmental problem-solving process (Johannes 1998), and lack of 

consistency among scientists (Kaiser 2000b), may have contributed to this contentiousness. 

Despite the barriers between scientists and managers, which still are not easily overcome 

(Kaiser 2000a), cooperation between the two groups can return important dividends in 

dealing with species recovery (Ecological Society of America 1995, Hyman and Wernstedt 

1995, Kleiman and Mallinson 1998, Badalamenti et al. 2000). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 158 

Cooperation among scientists in different disciplines, like cooperation between scientists 

and managers, is likely to return important dividends in dealing with species recovery, yet 

such cooperation also is not easily fostered (Metzger and Zare 1999). Dealing with disease 

threats is an aspect of species recovery for which cooperative research would seem, 

potentially, to be particularly productive (Nicastri et al. 2001, Wallace 2001). Conservation 

efforts often could be improved markedly by involving wildlife health professionals (Kock 

1996, Deem et al. 2001), and disease control efforts often could be improved markedly by 

involving ecologists (Hoffman 2002, Wasserburg et al. 2002, Kazura and Bockarie 2003). 

The potential role for ecologists in dealing with disease threats is critical as we increasingly 

come to appreciate the ways in which local (e.g., Ross 2002) and global (e.g., Chan et al. 

1999) environments influence disease transmission and prevalence, and, in turn, we come 

to appreciate the role of environmental improvement in mitigating the consequences of 

disease (e.g., Woodroffe 1999). 

As an example of the potential value of cooperation and coordination, consider research on 

URTD. Researchers consisting of experts on mycoplasmas (Mary Brown, PhD, University 

of Florida (UF); Paul Klein, PhD, UF; Lori Wendland, DVM, UF; Dan Brown, PhD, UF), 

gopher tortoise ecology (Earl D. McCoy, PhD, University of South Florida (USF); Henry 

R. Mushinsky, PhD, USF; Joan Berish, MS, Florida Fish and Wildlife Conservation 

Commission (FFWCC)) and population modeling (Madan Oli, PhD, UF) are working 

cooperatively to fill in important gaps in our knowledge about the effects of respiratory 

mycoplasmal infection and URTD on the gopher tortoise. The cooperative research is 

funded by the joint NIH/NSF Ecology of Infectious Diseases Program for five years. The 

premise underlying the research is that URTD is a complex, multi-factorial disease, 

interacting in some circumstances with other stressors to affect tortoises (Fig. 7.2). 

Questions that the research is addressing include: do natural and anthropogenically-induced 

population characteristics influence disease transmission and prevalence; does habitat 

quality influence disease transmission and prevalence; does the disease negatively 

influence population demographics; and do mycoplasmas vary in virulence, and, if so, does 

the strain present influence disease transmission and prevalence? 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DTRPAC Report page 159 

Factors 

Transmission 

Population 

Host Factors Habitat Factors 

Fig. 7.2 Relationships among factors contributing to disease important to demography of the desert 

tortoise. 

Anthropogenic, habitat, host, and microbial factors all potentially affect the interaction 

between URTD and tortoise populations (Fig. 7.2). Anthropogenic factors include 

translocation of tortoises, surrounding urban development, fire suppression, and human 

predation. Means of studying anthropogenic factors include field surveys, fire history data, 

FFWCC translocation records, and current and historic aerial photographs. Habitat factors 

include size, fragmentation, management, and rainfall. Means of studying habitat factors 

are much the same as for anthropogenic factors. Host factors include size class, sex, health 

status, and serological status. Means of studying host factors include tortoise surveys, 

ELISA, CBC, chemistry panels, and physical examinations. Microbial factors include 

virulence, species, and strain. Means of studying microbial factors include culturing, PCR, 

molecular epidemiology, and infection studies. 

The data derived from the studies listed above will be used to develop causal and predictive 

models of the interaction between URTD and tortoise populations. The models elucidate 

the effects of URTD on population demographics (survival, reproduction, migration) and 

on population growth. The models also will evaluate the role of the major factors listed 

above in influencing URTD transmission and prevalence. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 160 

7.3.1 Desert Tortoise Recovery Office 

The DTRPAC review leads strongly to the opinion that USFWS needs to implement a 

Desert Tortoise Recovery Office (DTRO) made up of scientists, a recovery coordinator, 

GIS specialist, database specialist, and support staff (Fig. 7.3). Some part of that staff can 

be outsourced to contractors, and that may be desirable. However, the USFWS has had a 

history of failure on implementing recovery, because the effort is not commensurate with 

the magnitude of the task. The desert tortoise is more complex in terms of needs for 

recovery than any of the widest-ranging listed species in the US, such as northern spotted 

owl, red-cockaded woodpecker, or grizzly bear. Thus, unless extinction is an acceptable 

option, USFWS must devote more resources to recovery efforts. 

The DTRO should be directly responsible for concerted range-wide recovery efforts for 

desert tortoises. It would provide a focus to cause management of desert tortoises to be 

more efficient and effective. The proposed DTRO would provide a centralized point of 

contact, through which research, data compilation, and monitoring activities are 

coordinated, so as to maintain the highest level of knowledge about progress toward 

recovery of the desert tortoise. In addition, the DTRO would focus on identifying where 

new research and management should be focused to facilitate range-wide recovery of this 

species. The DTRO would consist of a Recovery Team leader, and a staff of specialized 

personnel charged with coordinating monitoring, research, Section 7 consultation, and HCP 

issues. The DTRO would also have the capability of GIS analysis of data, and data storage, 

compilation and synthesis, as well as public relations and staff support. As a core set of 

responsibilities, the DTRO would: 

• Advise, conduct, direct, and prioritize research where appropriate 

• Develop new techniques for monitoring desert tortoises, their habitat, and threats 

• Recommend management actions based upon the best available science 

• Standardize methods for data collection 

• Develop a centralized desert tortoise data repository and management system 

• Inform policy through recovery recommendations and plan reviews as directed 

• Address needs of agencies, local governments, MOG, MOG/TAC, DMG and other 

appropriate management organization 

• Create a point of contact for stakeholders groups, agencies, NGO's, Congress, GAO, 

etc. to address policy information needs 

7.3.2 Science Advisory Committee 

The DTRO would draw upon the expertise of a Science Advisory Committee (SAC) in 

order to benefit from the most current knowledge and information available. The SAC 

would be composed of appointed members from the USFWS, USGS-BRD, and academia, 

and the Desert Tortoise Coordinator (Fig. 7.3). The SAC would meet periodically to provide 
 

 

 

 

 

 

 

 

DTRPAC Report page 161 

scientific expertise and recommendations to the DTRO. As a core set of responsibilities, the 

SAC would: 

• Rank importance of threats and networks of threats 

• Assess the efficacy of monitoring 

• Prescribe needed research 

• Prioritize research-based recovery actions 

• Synthesize data 

• Assess progress of recovery 

• Consult outside scientific experts as necessary 

The SAC could be extremely valuable in addressing some of the critical research questions 

still remaining concerning the desert tortoise, particularly in the areas of spotting trends; 

identifying gaps in data; and understanding tortoise biology, environment, and threats. 
 

 

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Fig. 7.3 Relationships among offices, teams, committees, etc. functioning to produce strategies 

for recovery and implementation of the listed species. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 163 

7.4 Data Management 

Data management is crucial to producing meaningful and useful data to support desert 

tortoise recovery. Currently, important data from monitoring tortoise densities are widely 

scattered among state and federal agencies and the scientific community. Data have been 

gathered, organized, and stored in a variety of ways with no common approach. Metadata 

may or may not be available. Some data have been reviewed, collated, or otherwise 

organized. Other data have not. Accessibility of tortoise data to managers, scientists, and 

the public is highly variable. In short, a great deal of important data (both historical and 

recent data) cannot be readily used and may be at risk to being lost permanently unless the 

data are compiled, organized, quality assurance/ quality control documented, stored, and 

made easily accessible to authorized individuals. 

7.4.1 Distribution of Monitoring Resources 

Data management is centrally important to data oversight, but it must be done in the 

context of a coordinated monitoring and research program that systematically seeks to 

identify needs, generate hypotheses, design studies, collect data, conduct analyses, and 

report findings (i.e., scientific method). Translating the scientific method into on-theground monitoring and research activities requires funding to support the following 

activities: planning, training, data collection, data management, and analysis and reporting 

(Fig. 7.4). Size of the pie slices is not intended to represent amount of funding needed, but 

to represent that each slice is as equally important as any other slice. 

Fig. 7.4 Kinds of activities 

associated with monitoring. 

Planning

Training

Data 

Collection

Data 

Management

Analysis and 

Reporting

There is a natural tendency to think that data collection is the main activity in monitoring, 

but monitoring data do not reach their potential without all aspects of the monitoring 

process (Fig. 7.4). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 164 

7.4.2 Data Management Plan 

It is important to identify issues and potential solutions for improving the management of 

data collected for programs that monitor desert tortoise populations, threats, and habitat. At 

a minimum, creation of data management plan would generally include: 

 Guidelines to standardize data collection models and data management based 

upon scientific data collection needs 

 Guidelines to standardize and manage field data collection operations and 

methods. The implementation of these guidelines will insure that at a minimum 

the data will be evaluated for its completeness, correctness, and 

conformance/compliance against the method, procedures, and contractual 

requirements. 

 A Data Quality Assurance/Quality Control Plan (that specifies required 

management activities, procedures and identifies appropriate manual and 

automated methodologies for post-processing and database finalization) 

 A Data Administration Plan (that identifies how data should be consolidated and 

managed in a central data repository and the identification of responsible parties) 

7.4.3 Types and Sources of Errors 

Data are prone to errors. All data collection operations for desert tortoise monitoring can, 

nevertheless, be designed and conducted to prevent data entry errors and to automate the 

detection and correction of errors during processing. Data may exhibit numerous types of 

error that may be broadly classified into the following three categories: 

•	 Blunders –Mistakes in instrument reading, data entry, erroneous computation, 

careless observation and recording 

•	 Systematic Errors –A regular error introduced by instruments, measurement
 

conditions, or data processing techniques
 

•	 Random Errors –Resulting from accidental or unknown combinations of cause. 

Random errors are the most difficult to detect and correct. 

By process of example from 2001-2003 LDS data, Table 7.1 outlines the types of errors 

that need to be managed in any monitoring or research data collection effort. The 

development of the data management plan should include procedures of preventing, 

minimizing, and correcting each of these data error types. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 165 

Table 7.1 Summary of sources and types of error that have been found in Line Distance Sampling. 

Error Type Error Data Tables (ATTRIBUTES) Potential Source 

Positional 

Accuracy 

Illogical spatial locations 

Example: Transect locations in the 

Pacific Ocean 

Corner Coordinate, Observation  field crew data entry 

 GPS Data Error (bad 

coordinate values, etc.) 

Spatial Different projections, datums, and (EASTING, NORTHING,  GPS Setup (Incorrect 

Reference correction factors by area, by year, by 

contractor 

Example: A portion of the locations 

within the database are systematically 

shifted by 100m meters in the northing 

and 200m in the easting 

LATITUDE, LONGITUDE) Datum, Incorrect 

Projection) 

 Coordinate conversion 

(error in transforming raw 

field data during 

processing to unify into a 

common database) 

Attribute 

Accuracy 

Incorrect data values 

Example: Incorrect time of observation 

All tables and fields  PenDragon scripts 

 field crew data entry 

 incorrect PDA Time 

Completeness Missing data values 

Example: No distance from the line 

recorded 

All tables and fields 

All attributes without automated 

validation 

 Data not validated during 

data entry 

Consistency Non-standard values 

Example: Live and Carcass each have 

three different spellings in the database. 

Technically ‘LIVE’, ‘live’, and ‘Live’ all 

mean "live tortoises" 

Attributes are not within tolerances 

(acceptable parameters) 

Example: an MCL value of 10,000mm 

All tables and fields  Data entry 

 Data collection methods, 

contractors, and database 

schema changed each 

year 

 Contractors/data collectors 

interpret record and 

process data differently 

Relational 

Integrity 

(error in key 

relationship 

among records 

across tables) 

Missing or incorrect relationship key 

Example: Transect records do not have 

all related (corresponding) corner 

coordinate records, corner coordinate 

record does not have corresponding 

transect record, or relationship key is 

incorrect 

Transect and Corner Coordinate  Field crew does not create 

all corner coordinate 

records 

 Incorrect relationship key 

was entered 

Missing or incorrect relationship key 

Example: Observation record does not 

have corresponding transect record, or 

observation has incorrect transect 

relationship key 

Transect and Observation  Field crew does not create 

observation 

 Incorrect relationship key 

was entered 

Data Type and Invalid data type Observation  Database design is 

Precision Example: decimal numerical value 

stored as an integer 

incorrect 

 Data processing did not 

preserve data types (e.g., 

import or conversion 

resulted in rounded 

values) 

Lineage and No documentation Study-level tracking  Lack of convention 

Metadata Example: Inaccurate or missing field 

logs, table names, interim processing file 

names, GIS meta-data 

 Lost or missing logs 

 Failure to create 

documentation 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 166 

7.4.4 Errors Detection and Correction 

The most effective means to achieve a quality database is to prevent errors from occurring 

in the first place at each level of the workflow process. Prevention will require a 

combination of initiatives at each stage of data management to standardize data capture 

methods, to standardize the data storage model, and to standardize and automate data 

processing and storage. The principal steps in the data processing workflow are: 

• Data model and database design 

• Field data collection 

• QA/QC post-processing 

• Compile data into a common, finalized database 

References 

Principles of Error Theory and Cartographic Applications; reprinted June, 1968; 

United States Air Force, Aeronautical Chart and Information Center. 

Guidance on Environmental Data Verification and Data Validation (EPA QA/G-8); 

November 2002; United States Environmental Protection Agency, Office of 

Environmental Information. 

Guidance for Data Quality Assessment: Practical Methods for Data Analysis (EPA 

QA/G-9; QA00 UPDATE; EPA/600/R-96/084); July 2000; United States 

Environmental Protection Agency, Office of Environmental Information. 
 

 

DTRPAC Report page 167 

“Science is the great antidote to the poison of enthusiasm and 

superstition.” 

Adam Smith, The Wealth of Nations. (1776) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 168 

Appendix A. DTRPAC Responses to Comments 

We received one comment form and three letters in response to the DTRPAC presentation 

at the September 24, 2003, Desert Tortoise Management Oversight Group meeting in Las 

Vegas. We received 12 letters with comments on the working draft of the report. This 

appendix summarizes and addresses these comments. 

Many reviewers made editorial comments regarding typographical errors, clarifications, 

and omissions, including an Executive Summary, information on translocation and HCPs, 

and a more thorough discussion of delisting criteria. 

We revised the report where appropriate. 

Several reviewers requested that the DTRPAC’s goals and objectives be clarified in the 

report. 

We revised the report accordingly. 

Many reviewers commented that the U.S Fish and Wildlife Service’s policy on DPSs should 

be better incorporated into the DPS chapter and that the provisional revision of DPSs 

needed better justification. 

We revised the chapter to more explicitly reference and describe the USFWS’s DPS 

policy. The final report more clearly justifies the provisional DPSs according to the 

policy and identifies areas needing additional data or research to solidify or modify 

potential future DPS designation. If and when recovery units or DPSs are revised, 

existing DWMAs should be reevaluated relative to new recovery unit/DPS 

boundaries. 

A reviewer commented that, in the DPS chapter, discussion about life-history adaptations, 

which evolve over many generations, does not fit well within the context of recovery plans. 

Consideration of life-history traits in evaluating potential DPSs does not imply that 

DPS designation should anticipate evolution of new traits. Rather, differing lifehistory traits between potential DPSs indicate a level of adaptation that has already 

occurred and which contributes to the “significance” criterion of DPS designation. 

Therefore, this discussion is appropriate to the chapter. 

Some reviewers commented that the literature-review chapter added little to the assessment 

and should be moved to an appendix and that the topic of translocation should be included 

in the discussion. 

We were charged to review scientific information since the 1994 Recovery Plan 

was published. This chapter provides an overview of areas of research that have 

been conducted, as well as gaps relative to the 1994 Recovery Plan’s 

recommendations. As such, we have retained the chapter in the report and have 

added specific information on translocation. 

Many reviewers commented that the analysis and discussion of desert tortoise status and 

trends was not clear or was flawed in statistical methodology, included omissions in 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 169 

figures and specific analyses, and should include discussion on how to improve data 

collection and analysis methods. 

This section of the report has been greatly revised to address issues raised by the 

reviewers. Statistical methods in both the draft and final reports were reviewed by 

two outside statisticians. 

Some reviewers questioned whether a recommendation that the Western Mojave Recovery 

Unit of the tortoise should be uplisted to endangered status was within the scope of the 

DTRPAC’s charge. 

We agree that such a recommendation was not within the committee’s charge and 

have revised the report to simply emphasize that the current data indicate that desert 

tortoises in the Western Mojave Desert are continuing to decline. It is the USFWS’s 

responsibility to determine whether these data are sufficient to change the listing 

status of the species within this recovery unit/DPS. 

Some reviewers questioned whether all available data were used or pointed out several 

times where the DTRPAC failed to incorporate available data such as that in the 

West Mojave Plan, numerous Biological Opinions, and other formal or informal 

documents. 

We assessed important information that could be addressed given time constraints 

placed on the committee and invited groups to provide specific studies or data that 

bear on the assessment. If other specific reports were overlooked in this assessment, 

we ask that they be provided to USFWS so that a possible future recovery team can 

incorporate that information into the actual revision of the Recovery Plan. We 

regret the omission of West Mojave Plan data in the draft report. Where 

appropriate, much of these data and analyses have been included in the final report. 

Many reviewers questioned the accuracy of or methods behind the figures and tables 

summarizing desert tortoise threats and Recovery Plan implementation. Some reviewers 

commented that particular recovery actions were not reflected in the implementation table 

(Table 4.3 in the working draft) as having been implemented. Others questioned whether 

some actions recorded in the table as having been at least partially implemented have 

actually been implemented in a meaningful way. Most were unsatisfied with the simplified 

representation of actions having “no implementation” or “at least partial 

implementation.” 

We summarized Recovery Plan implementation as of 2002 based on information 

provided by the relevant management agencies. It was impossible to quantify the 

degree of implementation, given the nature of the information provided. We revised 

this section to clarify the sources of information used, but more importantly we 

emphasize recommendations to better document and quantify implementation of 

recovery actions in the future, rather than drawing final conclusions about specific 

levels of implementation based on incomplete and inadequate data. 

Many reviewers commented that the road case study was a flawed comparison between 

early route designations and more recent route inventories. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 170 

The road case study was revised to address concerns over comparisons across years. 

A more detailed explanation was provided on methods used to collect the data and a 

full exploration of the consequences of the differences was discussed. Additional 

information provided by the West Mojave was included in the analysis. 

A reviewer requested that historic (pre-1970s) land management information be compared 

to tortoise population data and subsequently commented that the report did not address, or 

otherwise determine, the efficacy of recovery actions implemented to date. Another 

comment noted that tortoise populations have continued to decline after grazing had been 

eliminated on most of the Mojave National Preserve and that no scientific basis has been 

given for vegetation thresholds for removing cattle. 

We are unaware of any pre-1970 data on tortoise population trends, though we are 

aware of some of the threats that were on the landscape at that time. Both the 

working draft and the final report repeatedly state that research needed to determine 

the effectiveness of recovery actions has not been conducted to date. The report 

specifically recommends that research and monitoring on threats and management 

effectiveness be implemented in the future. However, threat effects may not always 

be connected in space and time, and a fundamental challenge in evaluating 

responses to management is overcoming the extended time scales required for 

tortoise demographic processes to result in measurable population changes. 

We received comments indicating that significant data on URTD since 1994 must be 

reviewed and incorporated into the revised recovery plan and should guide 

management/recovery actions set forth in the plan, including the simple steps of halting the 

spread, determining the cause of, and developing a cure for the disease. 

We reviewed all desert tortoise disease studies, discussed the topic in detail, and 

provided specific recommendations to the USFWS and a possible subsequent 

Recovery Team in the report. It is important to note that even though URTD has 

been associated with tortoise population declines, the precise relationship between 

the disease and demographic effects is poorly known; tortoises have likely 

maintained a long-term coexistence with mycoplasmas; mycoplasmal infections are 

not typically associated with high mortality in other species (in fact, low-virulence 

strains may actually be beneficial to tortoise populations); and a cure or treatment 

for URTD in the wild is impossible at the population level. Management actions for 

desert tortoise populations in the face of disease must not be conducted outside the 

context of other threats. In this way, the condition of tortoise populations can be 

improved so that they can endure disease outbreaks. 

A reviewer commented that the DTRPAC should acknowledge the lack of a disease strategy 

and recommend that the formal recovery team consider all strategies for dealing with 

disease. 

The report covers a variety of strategies and makes some much more specific 

recommendations than were previously available. 

A reviewer commented that disease case study de-emphasizes disease relative to other 

threats, including OHVs, toward which the draft report reflects a strong bias, and that the 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 171 

draft report ignores correlations between disease incidence and tortoise population dieoffs, leading to a misguided recovery effort. 

The report clearly states that disease deserves attention on par with other important 

threats, especially given the observed correlations. We believe the report shows no 

bias against disease or any other threat. Nonetheless, there is overwhelming 

evidence that OHV activities of the nature that occurs within open areas causes 

great damage to tortoise habitat. There is considerably less showing what level of 

damage is caused by lighter activities that are mostly constrained to designated 

routes. This information is included in Boarman (2002), which is cited by the 

report, and its conclusions are not dependent on an assumption of a strong impact of 

grazing or OHV activities. 

A reviewer commented that the draft report suggests that epidemiology is an academic 

exercise only and that it has no place in directing wildlife management policy. The 

reviewer further commented that a statement in the draft report (that improvements in the 

science surrounding disease as a threat to desert tortoises may not necessarily provide an 

easy transition to management strategies) implies that more funding should be spent on 

research but not on on-the-ground management. 

The reviewer misinterprets the report on this subject. The report simply states that 

many epidemiologists and conservation biologists believe that their role as 

scientists is to maintain objectivity in providing scientific information by distancing 

themselves from the application of that information in policy decisions. The report 

goes on to say that designing effective management strategies will be a daunting 

task that should consider all the complexities of the disease threat, not a task that 

should be ignored in favor of additional research for research’s sake. 

Several reviewers commented that the draft report’s discussion of cumulative and 

synergistic threats to desert tortoises, and the associated threats network figure, has not 

been proven, is a “copout,” misdirects attention from disease, is otherwise too theoretical, 

or should have been replaced by a prioritized list of mortality factors and recovery 

measures. 

The rationale for “synergistic causes of desert tortoise declines” is described in 

detail in the report and should not be interpreted as misdirecting attention from 

disease or any other specific threat. We agree that a multiple threats, “death of a 

thousand cuts,” perspective is unsatisfying and difficult to accept. Unfortunately, 

we firmly believe that this is the situation we are forced to deal with. There are 

many things affecting tortoise populations, their relative impacts are extremely hard 

to assess, and the populations are not at all likely to respond significantly if only 

one threat is dealt with. We agree with commentors that little data currently exist to 

document specific interactions between threat factors, including relative magnitudes 

of effects, and we include important recommendations to correct this deficiency. 

With regard to a specific comment on potential interactions between tortoise 

nutrition and disease, we note that nutrition has well documented effects on growth, 

health, and fecundity of wildlife, including desert tortoises. We agree that data do 

not currently exist to document population-level effects of nutrition on disease and 

population declines, and recommend that such studies be conducted. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 172 

A reviewer commented that there has not been an attempt to correlate air pollution from 

the Los Angeles Basin and the southern San Joaquin Valley, and potential associated heavy 

metal toxicants, with desert tortoise declines. 

The links between air pollution and disease or tortoise health have been largely 

unexplored. It is unknown if the levels of heavy metals found in tortoise tissues 

represent toxic levels, nor if the spatial patterns are consistent with air pollution 

being the source. Furthermore, there is essentially nothing that desert managers can 

do about air pollution, which mostly derives from the Los Angeles Basin. 

A reviewer commented that “new information” with respect to feral dogs applies only to 

Twentynine Palms Marine Corps Base. 

The only published data we know of is from Twentynine Palms, at the interface 

between urban/rural and wild areas. There are observations by several biologists of 

dogs causing mortality in other areas, in both the Mojave and Sonoran deserts, 

including areas with a low density of human residences. These observations have 

not been quantified. We feel the evidence is sufficient to justify a need to 

implement actions to reduce dog predation in urban/rural – wildland interfaces like 

the area around the southern edge of Twentynine Palms. More work is required to 

further understand the threat. 

We received a comment disputing the role of habitat fragmentation in tortoise declines or 

as a threat to tortoise populations. 

Habitat fragmentation is an issue of scale and has been shown to cause population 

declines in other reptiles (Fisher et al. 2002). Animals with large home ranges, such 

as the desert tortoise, appear to be affected seriously by habitat fragmentation/loss, 

and habitat protection has not been effectively implemented in many areas within 

the tortoise’s range. Fragmentation can cause reduced movement and gene flow 

among breeding populations. It does not directly cause mortality, however there are 

documented indirect effects, such as introduced exotic plants and increased 

mortality on roads. von Seckendorff Hoff and Marlow (2002) demonstrated a 

reduction in tortoise sign with proximity to roads and a relationship between this 

reduction and the traffic level. Roads create linear “sinks” fragmenting tortoise 

populations. While it is intuitive that restricted genetic interchange caused by this 

fragmentation may have long-term population consequences, we agree that studies 

have not yet been conducted to determine the nature of those consequences. Section 

5 describes the need for studies evaluating the relative importance and interactions 

of these effects. 

Some reviewers noted geographic differences in particular threats or recommended that a 

regional assessment of threats be conducted, especially relative to the evolutionary history 

of the tortoise and populations at the margins of the current range. Another reviewer noted 

that available GIS data layers were not used in the analysis, other than in the road case 

study. 

The report explicitly discusses threats in a general, non spatially-explicit context. 

We recognize the importance of the spatial differences in threats for the desert 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 173 

tortoise and include this issue as a caveat to the threats network. However, we defer 

to the Recovery Team to more specifically address regional threats and mitigation 

under the guidance of recommendations provided in the report. The evolutionary 

history of the desert tortoise and the geologic history of the Mojave Desert have 

little bearing on the relevance of managing the tortoise under the current ESA. 

Desert tortoise adaptations (or exaptations sensu Morafka and Berry (2002)) ) do 

make them suitable for desert living, even at the margins of their current range. 

Populations at the edge of the species’ range can be different and important in many 

ways. We underscore our recommendation that the spatial component of threats and 

threat mitigation be taken into account and that management actions be monitored 

in a hypothesis-based approach to determine the effectiveness of the action. 

The GIS data of which we are aware and had readily available are primarily from 

the West Mojave plan, and other sources will be invaluable in identifying specific 

areas where certain threats are likely to exist. Even though a comprehensive 

analysis of region-by-region threats was beyond the scope of our task, we 

recommend that, if a future recovery team is formed, they undertake such an 

exercise within the context of multiple threats in a network for each region. 

A reviewer commented that more necropsies need to be performed on dead tortoises each 

year to better determine the cause of tortoise mortality. 

We agree more work on causes of death (including, but not limited to necropsies) 

are critically needed to test and refine the hypothesis of multiple interacting threats. 

This recommendation is made in the report. 

A reviewer commented that the draft report lacks an analysis of predation and predator 

control. 

The report and Boarman (2003) include discussions of what is known about 

predation. We agree that additional research is needed on predation and predator 

control (and its effectiveness in tortoise recovery). This recommendation is made in 

the report. 

A reviewer commented that the current difficulty in detecting trends in tortoise populations 

suggests that the original decision to list the desert tortoise as Threatened under the ESA 

had inadequate scientific support. 

Subtle population trends are difficult to detect for most desert tortoise populations 

with current methods. However, as the report states, dramatic population declines 

such as those observed before and since the listing of the tortoise are easy to detect. 

The GAO’s independent review of the listing decision found that the decision was 

appropriate. 

Several reviewers responded to a statement in the draft report that “all monitoring should 

be hypothesis driven” by suggesting that this excluded basic monitoring to detect 

population trends in the absence of an experimental study. 

We continue to emphasize that monitoring needs to be conducted in an 

experimental framework to determine the effectiveness of recovery actions, 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 174 

however we have clarified the report to indicate that population trend-detection 

monitoring is still appropriate as long as estimation methodologies are sensitive 

enough to detect the desired trend (e.g., reject a null hypothesis that the population 

is decreasing at a particular rate). 

Several reviewers commented on the difficulty of distance sampling to detect trends in 

tortoise populations and that the method is a waste of time and should be abandoned or 

that the report should better identify ways to improve the method. 

The report documents several supplemental analyses that make the distancesampling effort valuable, besides estimating tortoise density. We have revised the 

report to provide a more complete review of the method as it has been implemented 

for desert tortoises to date. The report also includes several recommendations for 

future research in improving the method for estimating density, as well as additional 

information that could be gained from the effort. 

Some reviewers questioned statements in the report that suggested that some permanent 

study plots should be abandoned. 

We recognize, and the report documents, value in permanent study plot data. 

However, given limited resources and a list of documented problems associated 

with the permanent study plots, the report recommends that plots that do not serve 

to answer specific research or management questions be discontinued. 

A reviewer commented that an observation in the draft report (that the current monitoring 

program has expended virtually all funds on field collection of data and little on quality 

control or data management) ignores the reality that funding is limited and that in reality 

the choice comes down to collecting as much data as possible or collecting insufficient 

data and managing them expensively. 

We recognize the need to obtain sufficient funding and emphasize efforts to do so 

in the report. However, the utility of data collected under any funding level is 

severely compromised if sufficient effort is not also directed to quality control and 

data management. Collecting “sufficient” data and managing them poorly is just as 

much a waste of money as collecting insufficient data and managing them 

expensively, because resources are not available to determine whether the data 

collected really are “sufficient.” 

One comment suggested that revision of the Recovery Plan carefully consider and analyze 

the importance of soils and ecological site descriptions to delineate desert tortoise habitat. 

We agree that a scientifically sound analysis should be conducted to determine 

which factors negatively impact populations of the desert tortoise. The report 

provides recommendations to accomplish this task, including recommendations for 

habitat monitoring at different scales. A possible future recovery team should 

consider soils and other ecological aspects of tortoise habitat in this monitoring 

effort. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 175 

We received a comment suggesting that data on tortoise reproduction and disease be used 

to reevaluate the 1.0 lambda originally calculated in the 1994 Recovery Plan to determine 

a more accurate recovery goal. 

As noted in the report, most recovery actions for threatened and endangered species 

are designed to stabilize population size (lambda at 1.0 across generations) where 

population size is sufficient to safeguard against extinction and to increase 

population size (lamba > 1.0) where population size is small enough to threaten 

extinction. By definition, lambas < 1.0 result in continued population decline. While 

we make no specific recommendations regarding modifying recovery criteria to 

reflect increased population lambas, we defer to a possible future Recovery Team to 

make a final determination. Nevertheless, we agree that disease and other relevant 

factors must be evaluated relative to population growth rates. 

Many reviewers commented on the lack of discussion on headstarting and translocation as 

potential recovery tools for the tortoise. 

The final report now includes a section on this topic. 

Several reviewers provided comments pertaining to topics such as public outreach, the 

need for an implementation schedule and costs of implementation, the need to review 

existing DWMAs, and prioritization of research. 

These comments are outside the scope of the DTRPAC’s charge and have been 

referred to the USFWS to be addressed by a subsequent Recovery Team, if one is 

necessary. 
 

 

DTRPAC Report page 176 

“Let science neither be a crown to put proudly on your head nor an axe 

to chop wood.” 

Talmud 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 177 

Appendix B. DTRPAC Meeting minutes 

Desert Tortoise Recovery Plan Assessment Committee Meeting

Friday, April 11, 2003 9:30am – 5:00pm 

California Academy of Sciences, Goethe Room 

Greeting and charge to the committee 

Bob Williams, Field Supervisor of the Nevada Field Station of the Fish and Wildlife Service 

(USFWS), presented the Desert Tortoise Recovery Plan Assessment Committee (DTRPAC) with a 

charge to use the best available scientific information to review the 1994 Recovery Plan. 

After this review, the team will provide a report with recommendations as to where the 1994 plan 

should be revised (if necessary) and provide any new relevant data useful to prepare the revision. 

These recommendations will be reviewed by Management Oversight Group (MOG), the Clark 

County MSHCP, the Washington County MSHCP, and the Desert Management Group (DMG). 

After the DTRPAC has submitted their report, USFWS will form a recovery team to draft a new 

recovery plan. Therefore, this assessment is a first and important step to determine revisions and 

future direction of desert tortoise recovery. 

USFWS will act as an interface between the team and the public. The need for stakeholder 

involvement in this process was highlighted. DMG representatives attended the DTRPAC meeting 

largely to reflect the interests of stakeholder groups in the process. They may attend future meetings 

to represent stakeholders participation and to facilitate an environment of openness and objectivity. 

It was noted that this assessment committee is not a recovery team. This assessment is only the first 

part of two-step process. The team will be working as peer reviewers of the 1994 Recovery Plan in 

light of contemporary knowledge. The second step in the recovery plan revision process will be to 

assemble a recovery team consisting of scientists, managers, and stakeholders who will complete a 

revision of the plan. 

A two-page summary of the current process will be provided on the on DMG website which will 

include the DTRPAC mission, scheduling of future meetings, briefings, and biographies of 

committee members. 

Process of evaluation 

A suggestion was made that there should be at the minimum, four or five more DTRPAC two-day 

meetings before a draft report deadline in November. The next deadline will be for a completed 

report to be delivered to the MOG by January for review. This committee does not include all the 

expertise that will be needed to complete this assessment. Therefore, ad hoc experts will be asked to 

brief the committee on topics where additional scientific expertise would be valuable. 

Open meetings 

All future DTRPAC meetings should be open to representatives of interested stakeholders who 

would like to observe. It was stated that by inviting representative stakeholders (one or two 

individuals) to observe and comment in their allotted time, they would then be able to convey 

DTRPAC proceedings to constituents. USFWS will invite stakeholders to future meetings, and 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 178 

provide minutes from each meeting through the DMG website. Meeting agendas, including invited 

speakers for each meeting will be announced in advance. 

One opportunity for public involvement will be an open call for requests for additional topics to be 

covered at DTRPAC meetings. A preliminary list of what the team plans to include in the 

assessment will be provided. If there is a good scientific basis, these additional topics will be 

included at the appropriate time during discussions. 

Invitations to stakeholder scientists 

If a stakeholder feels as though the team has missed information, they are invited to provide a 

scientist to present their issue as a briefing to the team. DTRPAC meetings will be topic oriented, 

so the scientist will be speaking about the specified topic of the meeting, and (s)he must bring 

references to publications that can be distributed to the team members prior to the meeting. 

Periodic briefings to DMG and MOG 

Briefings of the DTRPAC progress to the MOG, Clark County, Washington County, and the DMG 

will be completely open to the public. 

Location of meetings 

To provide convenience for local team participants, meetings will be sited in different locations. 

Possible locations include Las Vegas, Palm Springs, Reno, and San Francisco again. Depending on 

the discussion topics, field trips may be required. 

Advanced materials for each topic 

Materials for each meeting will be available via email, on a website, and in print for meeting 

participants. Materials for each meeting will be determined at the previous meeting. 

Writing assignments 

At the end of each topic discussion, different sections of the report will have to be written. Team 

members will alternate between writing and reviewing sections. 

Discussion of proposed six segments of assessment (tentative list) 

Following a discussion on the process of future DTRPAC meetings, the team began discussing and 

prioritizing, the tentative list of six proposed segments of the recovery plan assessment. This 

preliminary list, which will be subject to change following public comment and further team 

discussion, is attached at the end of the minutes. 

1. Delisting criteria 

Delisting criteria are found on the first page of recovery plan, and are goals that are critical to the 

recovery of the desert tortoise. A discussion of these criteria has three parts: 

a) Are the current Recovery Units biologically correct? 

b) Is the relationship between Recovery Units and delisting criteria appropriate? 

c) Are delisting criteria able to be implemented and sufficient? 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 179 

It was suggested that the Recovery Units of the 1994 plan should be revisited and modernized in 

light of the current USFWS definition of a distinct population segments (DPS). Currently, the 

recovery plan acknowledges six recovery units based upon genetic, morphological, behavioral, 

ecological, and geographic differences. Using the USFWS DPS definition, boundaries should be 

revisited, along with the number of DPSs, which may change with new data and DPS definition 

criteria. 

The clarification was provided that the Mojave desert tortoise was listed range wide, before the 

USFWS definition of DPS was established. Therefore, the USFWS currently can only delist the 

entire Mojave population. Legally, it is not possible to delist recovery units. DPSs are usually 

defined in the listing action, which would allow delisting by DPS. If the team finds, in accordance 

with contemporary USFWS policy, that distinct population segments need to be individually listed 

and there is adequate evidence that this is warranted, then the DTRPAC should attempt to provide 

information on redefining segment boundaries, characterize what data are missing for DPS 

designation, and how many specific DPSs are justified. If the species warrants DPS listings, the 

team should provide as much information as possible to the future Recovery Team as they make 

changes to the Recovery Plan. 

Meeting participants concurred that the team should review current literature and current recovery 

units and give basis for change in boundary and number of units. If the team comes to consensus that 

the tortoise populations should be distinguished as DPSs, then there should be a recommendation on 

how many units should be designated. There was also a suggestion that the team should operate under 

the (potentially “null”) hypothesis that there is only one large population. The preponderance of 

evidence will have to prove that the populations have fundamental differences in life history 

strategies with conservation consequences, if they are considered the same. It was noted that the 

assessment committee also must consider the consequences of not breaking down tortoise 

populations into DPSs, if it will be a downfall, and why. 

Different threats, niches, habitat, behavior, morphology, genetics, and ecology are possible 

characteristics defining DPSs. As a result, different management strategies may be necessary for 

each DPS. The USFWS policy lists the following as DPS criteria: discreteness, significance, and 

conservation relevant to listing factors. The committee must evaluate all these criteria. 

What information is needed for this topic? 

Genetics and morphology data 

ACTION: Dr. Morafka will take the lead on this issue and compile and distribute relevant literature 

on DPSs. The DTRPAC will discuss differences in definitions between the Recovery Plan and 

current definitions in the literature, and look at extent of where DPS boundaries need to be 

reconsidered. 

 Demographic status – Committee members should identify information gaps. The committee 

would like any data that suggests why populations are declining in certain areas, and results 

from any new demographic studies that occurred after the 1994 Recovery Plan. 

o	 Types of data needed (mean as well as within and between site variances): 

 size distribution 

 plot densities 

 sex ratios 

 health status 

 fecundity data/reproduction 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 180 

o	 How much? 

 All the data from as many populations as possible is needed, so that team can 

evaluate data, and recommendations can be based on best data available. 

 The DTRPAC is also interested in evidence of decline and from study plots, 

including information on placement of plots, number of visits, drought 

conditions during each year of study, and evidence of mortality including 

shells. 

o	 End product: 

 The team would like a map of total tortoise distribution with indicators of 

population status (arrows up/down/stable), and the evidence that led to each 

judgment. 

ACTION: Mr. Medica will be the lead on determining what status information is available, and
 

compiling permit reports from USFWS offices. Mr. Murray will provide study plot information
 

from Arizona, which will be scanned in electronically by Dr. Heaton.
 

NOTE: All electronic information should be sent to Ken Nussear (UNR). Dr. Heaton will aid in the 

collection of electronic data and scanning.
 

ACTION: Dr. Heaton will gather total live/carcass data, burrow data, lumped sign data, line 

distances sampling data, and encounter rates, and will incorporate them into a map; This type of 

map may be helpful with area occupied by tortoises (presence/absence) and threats.
 

Briefings:
 

The DTRPAC will require a briefing on all topics related to DPS units. Dr. Morafka will
 

collaborate with others to provide a briefing on distinctness. Other possible invited speakers would
 

be Taylor Edwards, Dr. Kristin Berry, and Dr. Dave Germano.
 

The briefing on demographic status should include status across the Mojave population’s range. Dr.
 

Berry will be asked by Dr. Lovich and USFWS to provide a complete review of California study
 

plots, particularly those that have had long-term monitoring, and any new studies. Mr. Medica will
 

provide equivalent information for Nevada. Mr. Murray will report on Arizona and Utah.
 

ACTION: Dr. Tracy will draft guidelines for what is needed by those giving briefs. He will then
 

email the draft to entire team for comments.
 

The following items need to be discussed and integrated before the DTRPAC can make any
 

recommendations regarding distinct population segments.
 

 Genetic, morphological, and biological differences among populations 

 Range wide demographic status of tortoise populations and threats 

 Determine the extent to which the results from the assessment differ from 1994 recovery 

plan 

As a result of the extensive amount of information needed to discuss DPSs, and the amount of time 

to prepare data, these topics will be broken up over several meetings. 

2. Threats 

The topic of threats to tortoise populations includes three components: definition of threats, status, 

and monitoring. Mojave populations of the desert tortoise population appear to be in a delicate 

balance. This may cause difficulty in ranking threats, especially when any number of combinations 

of threats may be the culprit of population declines. The following are viewed as threats to the 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 181 

desert tortoise: ravens, vehicle access, feral dogs, and grazing. The DTRPAC will discuss these 

threats separately, the interrelation of threats and groups of cumulative threats, as well as any new 

threats. Currently, there is a controversy over whether disease should be considered a threat or is 

manifested as an “exacerbating condition”, not a cause – or precipitant - of population declines. As 

a result, disease will be considered separately from threats. 

Disease update

The DTRPAC would like an update on ELISA testing and would like to discuss the following 

questions. 

 Is disease natural or an invasive? 

 If natural and largely existing in a chronic state, what exacerbates it into an acute state? 

 If an animal is tested, where is it located? (wild vs. pet populations) 

Regional Status on a by-threat basis 

Dr. Bill Boarman and Dr. Heaton will be asked to provide a brief on missing information in the 

most current threats document and where are threats located. 

West Nile Virus question and impact 

Dr. Delehanty will assemble a short report on changes in the West Nile Virus and the possible 

threats to ravens in the Mojave Desert. 

3. Monitoring: 

USFWS has identified (a) species populations, (b) habitat changes, and (c) threats as monitoring 

priorities. Monitoring issues will be covered during appropriate topic discussions. 

Habitat 

New information on habitat has become available since the 1994 recovery plan. The DTRPAC 

would like a clear picture of how tortoise habitat has changed. This would include information on 

the impacts of fire on tortoise habitat with the disappearance of shrubs. Estimations of habitat loss 

would also be helpful. Utah State University and the Desert Research Institute collaborated on a 

data set that provided estimations of development from 1980, 1990, and future projections. This 

data set may provide good regional indications by providing population information layered on top 

of urbanization. 

4. Remaining items to be covered 

 Habitat Conservation Plans (HCPs) – The team should be assigned to review that section of 

recovery plan and determine if it is on target. Members would like an update section on 

which HCPs are on the ground and the status of tortoise management. 

 Research needs and priorities/delisting criteria 

Scheduling of future meetings: 

(15% of each meeting will be devoted to planning the next meeting.) 

Meeting 1: 

May 15-16, Palm Springs, CA 

 Day 1: 

o	 First session on distinct population segment issues: biology, genetics, and 

morphology 

o	 No invited speakers for day 1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 182 

 Day 2: 

o	 Disease and associated topics (euthanasia, ELISA testing, and other management 

issues) 

o	 Due to a conflict with a major microbiology conference, it is not possible to be 

briefed on disease at the next meeting. Thus, Dr. Boarman will brief us on threats. 

o	 Prepare for monitoring of threats portion of Meeting 3 

Meeting 2: 

June 9-10, San Francisco, CA 

Both days will be spent on the regional status and monitoring of threats. THE DTPRAC will ask the 

question, “Does the original recovery plan adequately cover these issues and is there new 

information that would change views?” Due to the microbiology conference conflict, we will invite 

M. Brown, D. Brown, D. Rostal, and J. Heaton to present a briefing at this meeting instead of the 

Palm Springs meeting. 

Meeting 3: 

July 31-Aug 1, Tucson, AZ 

This meeting will focus on the demographic status of tortoise populations and habitat. Dr. Kristin 

Berry, Phil Medica, and Roy Murray will be asked to present demography data for CA, NV, AZ, 

and NM. A discussion of monitoring will begin at this meeting. 

Meeting participants at April Meeting 

Roy Averill-Murray, Arizona Game and Fish
 

Dave Delehanty, Idaho State University
 

Jill Heaton, University of Redlands
 

Jeff Lovich, USGS/BRD
 

Earl McCoy, University of South Florida
 

Phil Medica, USFWS
 

Dave Morafka, California Academy of Sciences
 

Ken Nussear, University of Nevada, Reno
 

Dick Tracy, University of Nevada, Reno
 

Bob Williams, USFWS
 

John Hamill, DMG
 

Bridgette Hagerty, UNR
 

Clarence Everly, DMG
 

For Reference: 

Possible areas of discussion 

1.	 Delisting criteria (do we need changes from those prescribed in the DTRP?)/ need to list by 

“Distinct Population Segment” (DPS)?/ different criteria for different DPSs? This topic is listed 

first because, even though the 1994 recovery plan suggested treating each recovery unit 

separately, the USFWS has not pursued legally treating each recovery unit separately. Insofar as 

differences among recovery units have become greater with time (some populations having 

declined to disastrous levels while others could be stable), and insofar as this is a topic that might 

require USFWS action before the recovery plan is revised, we need to discuss this topic. 

2.	 Habitat conservation planning including critical habitat designation, threats, and delisting 

criteria. This allows us to address the different needs in different recovery units. 
 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 183 

3. Updates on regional status of (a) population threats, (b) threats, (c) habitats. This forms the 

basis for most other topics. 

4.	 Monitoring of (a) tortoises, (b) threats to tortoise populations, and (c) changes in status of 

habitats. The prescriptions for monitoring in the 1994 recovery plan were sometimes naïve in 

light of today’s knowledge. This is a terrifically important, and sometimes controversial, topic. 

5.	 Details of specific threats and their mitigations with special attention to interactions among 

individual threats. This deals with the very controversial topics of the basis for listing and 

recovery. 

6.	 Research needs and priorities in the next decade. Assessment of research proposed in 1994 

DTRP and what is needed next. Most of what was recommended in 1994 has not been 

implemented. We need to reassess old and new prescriptions for science and research. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 184 

Desert Tortoise Recovery Plan Assessment Committee Meeting

Friday, May 15-16, 2003 

Wyndham Hotel, Palm Springs, CA 

Announcements and Introductions 

Bob Williams (USFWS) spoke about changes made in stakeholder involvement after the April 11th 

meeting. In order to implement the recovery plan consistent with the GAO report, the U.S. Fish and 

Wildlife Service (FWS) is working on a Memorandum of Understanding (MOU) among 

Department of Interior agencies and the states. A memo to the Management Oversight Group 

(MOG) and Desert Management Group (DMG) outlined a two-layer structure for stakeholder 

involvement in this process. The first layer consists of state and federal agencies, which would 

nominate representatives to observe the scientific expert panel. The second layer consists of 

representative stakeholders. This structure will be used to develop an open process for those 

collecting information and will aid in data gathering. The membership of the Desert Tortoise 

Recovery Plan Assessment Committee (DTRPAC) will not change. 

Presentation on distinct population segments issues (biology, genetics, morphology), led by Dr. 

David Morafka 

A synopsis was given of how distinct population segments (DPSs) are incorporated into the 1994 

recovery plan, as well as the language of the 1996 USFWS DPS policy. The terms DPS and ESU 

(evolutionary significant unit) were synonymous at the time the 1994 recovery plan was written. 

These were equated as a recovery unit in the 1994 plan, and all terms were used interchangeably. 

The USFWS has developed a legal definition for the DPS. The DPS designation is based on three 

criteria, and the term is to be used “sparingly” and only when warranted. The three criteria are: 1) 

discreteness, 2) significance (if criteria 1 is met, and 3) conservation status in relation to the Act’s 

standards for listing. 

The term “sparingly” is only discussed in terms of listing, not delisting. Therefore, if the DTRAPC 

recommends that the species warrants DPS designations, then implementation of delisting each 

segment may be possible. The other alternative would require relisting the desert tortoise, making 

redefining using DPS units more difficult. By writing delisting criteria in the recovery plan using 

USFWS DPS criteria, the DTRPAC could accomplish the same goals and with less difficulty. 

There are many examples where this is already occurring, such with the gray wolf. The USFWS 

recommendation to the DTRPAC is to make recommendations based on science. The USFWS will 

use those recommendations for appropriate actions. 

The DTRPAC has three tasks in relation to identifying DPSs: 1) make the best recommendation 

with current available information for the number of DPS units (if any) and the boundaries of those 

units, 2) determine gaps in information, and 3) produce a new protocol for how future recovery 

teams and assessment committees should handle DPS designations. In all discussions, the DTRPAC 

should be trying to reject the null hypothesis that there is no difference among units and should the 

term DPS “sparingly”. 

A summary was provided of current information on the status of ESU/DPS (see Pennock and 

Dimmick 1997). Previous genetic work on the desert tortoise has used mitochondrial DNA and 

allozyme markers. Currently, there is no uniform command for geneticists to perform tortoise 

studies using equivalent sample sizes, genetic markers, or study areas. As a result, uniform 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 185 

sampling has not occurred range-wide for the Mojave population. Data are incomplete and have 

inherent biases resulting from low scientific rigor. 

To designate a DPS, all three elements must be considered and satisfied in some way, but not 

necessarily equally. 

1)	 Discreteness: Genetics is a conservative place to start to look for evidence of population 

differences. Morphology may be different across the Mojave population, but can be subject 

to dietary and other environmental influences, as well as genetics. Behavioral differences 

are similar to morphological differences in that it may not be solely a function of genetics. 

2)	 Significance: The term significance can be taken very broadly, and unusual circumstances 

and ecological niches may be critical to DPS designations. Peripheral populations may 

warrant protection because of its distinct ecosystem; however, one must also take into 

account the probability of persistence. 

Discussion on distinct population segments (DPS) 

Currently the recovery plan designates six recovery units: Upper Virgin River, Northeastern 

Mojave, Eastern Mojave, Northern Colorado, Eastern Colorado, and Western Mojave. 

There was discussion concerning the table below and how the terms in the table relate back to DPS 

criteria. The table was constructed using published and available evidence. 

Table summarizing the criteria used to define Distinctive Population Segments. The criteria are 

ranked as poor or negative evidence (—), absent or ambiguous evidence (0), positive evidence (+), 

or highest priority. The data are taken from The Desert Tortoise (Mojave Population) Recovery 

Plan (Plan) (1994) and Britten et al. (1997). Possible changes to the table are highlighted in red. 

Initially the Conservation Need/Status columns were represented by one column, which notes that 

there is positive evidence for greatest need for conservation relative to the status of the unit. 

DPS Discreteness 

(I) 

Ecological 

Significance (II) (be 

more specific) 

Geographical 

Significance 

(II) 

Genetic 

Significance 

(II) 

Conservation 

Need (III) 

Conservation 

Status/existing 

regulatory 

mechanisms 

(III) (threats, 

etc) 

Northern Colorado — 0 + ? 0 

Eastern Colorado — + + — ++ 

Upper Virgin River + + + + ++ 

Eastern Mojave 0 0 0 — + 

Northeastern 

Mojave 

0 — + 0/+1 + 

Western Mojave 0 + + — ++ 1 Significant genetic units are embedded within the DPS. 

There was a discussion about additions to the table, including discreteness being separated into its 

component parts (behavior, morphology, ecology) and using the new DPS hypotheses based on 

genetics by adding a North Las Vegas unit. The conservation status column should include 

consideration of threats, which are important for determining the status (threatened/endangered) of 

each DPS. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 186 

The USFWS DPS Policy determines the order of discussion for designating DPSs. First the unit 

must be discrete. Once discreteness is determined, than significance must be, followed by 

conservation status. The DTRPAC came to consensus to use genetics used as first cut for 

determining DPS units, followed by the incorporation of other factors including morphology, 

ecology, and behavior. 

Maps showing the current situation and proposed changes were used to aid in the discussion. A 

suggestion for the DTRPAC to provide more detailed recommendations for the boundaries for DPS 

units, etc. was given because of the ability to use current GIS technology. 

The DTRPAC must resolve 1) if there is a legitimate basis for DPSs in the Mojave population, 2) if 

four conservative units are well-justified, 3) what data, in addition to genetics, are needed to make 

DPS designations, and 4) how can interested scientists improve on status quo. 

The DTRPAC suggested that the Upper Virgin River unit is well justified because it has 

discreteness in genetics, behavior, morphology, and habitat. In addition, the Western 

Mojave/Eastern Colorado units are distinct from the other units. The Northeastern Mojave unit 

requires resolution and revision. Finally, the Northern Colorado unit has poor justification to be 

designated different from the Western Mojave. 

In Southern Nevada, there is a wealth of local amphibian populations due to historical water 

complexity that has only recently been simplified. This suggests that it is a good place to look for 

desert tortoise distinctness. Britten et al. (1997) highlights complexity in S. Nevada, but not in a 

uniform way. Since the recovery plan there have been studies that present information on the 

division of recovery units in the Mojave population. Britten et al. (1997) use shell morphology, 

allozyme data, mtDNA data at a fine resolution and designate Amargosa, Piute, North Las Vegas, 

and South Las Vegas as separate areas. Lamb (1994) suggests that there are genetically distinct 

populations in NV (North Las Vegas/South Las Vegas), and in the northern part of the tortoise 

range. 

A suggestion was made to designate Coyote Springs/Mormon Mesa/ Gold Butte (North Las Vegas) 

as one DPS. Further genetics are needed to define the Gold Butte area. There would be another unit, 

South Las Vegas, and perhaps more than one (Piute Valley, Ivanpah, Amargosa). Historic land data 

vaguely supports this idea, but it is not an overarching cause. These DPS designations would be a 

working hypothesis. In order to provide more support for this hypothesis, it will be necessary to 

expand on Britten et al. (1997) and incorporate land formation data. 

Allozyme and mtDNA data suggest that most of California is strikingly homogeneous for many 

warm desert species. This may suggest that there was an over subdivision of recovery units in CA. 

The Colorado Desert has quite different vegetation from Western Mojave (Vasak 1984); however, 

there is little genetic difference. The differences could be local environmental adaptations to 

different environments, such as differences in rainfall. 

Some members of the committee continue to stress that threats are paramount to recovery. 

Although the DTRPAC has no problem with determining distinctness among the population, some 

members caution against excessively fine scale phylogenies. 

The DTRPAC came to an initial consensus on DPS designations, based on genetics using the 

current available data. These DPS hypotheses are subject to revision with new genetic, ecological, 

behavioral data. The genetic discreteness hypothesis is that there are four DPS units: Upper Virgin 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 187 

River, North Las Vegas, Western Mojave/Colorado Desert/Piute Valley (subject to revision), and
 

Amargosa/Eastern Mojave (Ivanpah).
 

Limitations and Deficits in DPS designations:
 

1) Program of uniform sampling (20-25 samples per local populations using all genetic markers,
 

including microsatellite information range wide)
 

2) Behavioral: a) burrow/microhabitat selection b) hibernacula
 

3) Ontogentic series characterizing morphological differences
 

4) Standardized morphological analysis
 

5) Behavioral differences among populations that affect gene flow
 

6) Geographically describe problematic areas (Southern Nevada, Colorado divisions)
 

Position paper recommendations:
 

1.Add a geneticist to the full Recovery Team to revise the 1994 plan.
 

2. Genetic core units need to be assessed using both nuclear and mitochondrial genes (Berry et al., 

2002). 

3. The genetic boundaries and gene flow between units needs to be critically examined. 

4. Once these data are available, ecological, morphological and behavioral attributes can be 

assigned to each of these genetic units. 

5. Finally, CHUs within each DPS should be geographically revised delineated to maximize their 

conservation potential in consultation with local resource administrators. 

The initial DPS hypotheses do not include ecological differences and boundaries. A suggestion was 

made to study behavior that is essential to gene flow, thus connecting genetics and behavior. 

Information would include fecundity, clutch frequency and size, mating system, sperm storage, 

connectivity, barrier crossing, and dispersal patterns for juveniles and adults. Another suggestion 

was that the DTRPAC should specify the need for or give specific objective ways to determine if a 

behavior or morphology is different among DPS units. This would requite targeted research. 

ACTION: Dr. Morafka will revise the position paper in light of today’s discussion, as well as add 

recommendations for future groups revising DPS units. Dr. McCoy will write an addition to the 

paper discussing problems with objectivity and the research necessary to overcome these 

difficulties. Dr. Delehanty will write an addition discussing the conservation biology point of view. 

Briefing on threats to Mojave desert tortoise population, Dr. Bill Boarman 

The DTRPAC will examine if there are significant changes that need to be made in a subsequent 

recovery plan in relation to threats. This possibly includes justification for the list of threats in the 

1994 recovery plan, and suggesting data collection that would allow for the prioritization of threats. 

The 1994 recovery plan does not show the complexity of threats or potential interactions among 

threats. 

Dr. Boarman was charged to evaluate all current knowledge on threats to desert tortoises for the 

West Mojave Planning Team. His 2002 report includes a literature search, an evaluation of sources, 

and a discussion on threats to desert tortoises. Ranking of threats and spatial/temporal information 

is not included in the report. Some sources used to support threats were weak (based on lack of 

data). Since 1994, more data have become available, which should be identified in the DTRPAC 

report. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 188 

Discussion of threats: 

DTRPAC’s report should recommend that the recovery team use Dr. Boarman’s 2002 literature 

review and Dr. Heaton’s work to update the recovery plan. For example, appendix D could be 

revised using Dr. Boarman’s literature review. 

Dr. Boarman highlighted new or increasing threats. The 1994 Recovery Plan may have 

underestimated the threat of feral dogs to desert tortoises. As a result of less space between desert 

fragments, there are regional changes in canids as a threat. Anecdotal information suggests an 

increase in feral dog populations, corresponding with an increase in human disturbance. Fire is also 

an increasing threat. The spatial and temporal distribution of fire should be examined, as roads may 

be causing the increase. 

In addition, Dr. Boarman noted threats that have diminished since the 1994 Recovery Plan. Direct 

impacts of livestock grazing have been eliminated due to action, except in certain areas in the West 

Mojave. Collecting by humans may no longer be a widespread population threat. Law enforcement 

data would be helpful to determine if collection is a localized problem. There is a need to compile 

poaching information to refine extent of the threat. 

The major inadequacy of the original plan was lack of discussion on synergies and interactions 

among threats. Instead a list of threats was provided. One of the substantial overall threats is the 

human access or road access to the desert. This threat incorporates components of the exotics, fire, 

poaching, and ORV threats. The reduction of cumulative effects as supposed to individual threats 

would be more effective. Cumulative threats were not emphasized in the 1994 recovery plan. 

Quantifying threat interactions experimentally will be the most difficult, expensive, and valuable. 

Designating research areas for science (experiments) to occur and recommending experimentation 

that has management payoff should be a priority. 

A suggestion was made to use modeling of threats and their effects on tortoise population. A 

current update of the model could be made using current available data (i.e. new raven predation 

data). The model could be used to evaluate relative effects of threats compared to each other (i.e. 

sensitivity analysis) in certain areas of the Mojave. Probability maps, predicting threats in certain 

areas of the desert in conjunction with modeling effects on tortoise populations would help assess 

potential for problems. In addition, an updated graph of roads vs. tortoise deaths showing an 

analysis on a spatial and temporal scale (roads, fires, exotics) to compare to other non-human 

caused threats. In order to rank threats, some form of commonality is needed. The DTRPAC should 

highlight overarching problems and what needs to be done on a more localized basis. 

ACTION: Dr. Tracy and Dr. McCoy will work on a modeling effort to assess the effects of ravens 

on tortoise populations. 

ACTION: NDEP historical data has not been available on line. Clarence Everly has been tasked 

with providing DTRPAC with data that has been previously unavailable (aerial photos). 

ACTION: The desert is a place of life that has vital components (desert blooms, seasonality) easily 

damaged by human contact. Desertification of the desert can wipe out species that are typically 

described as “desert species.” Dr. Morafka will write a paragraph explaining desert complexity. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 189 

Preparation for future DTRPAC meetings 

June 9-10 Meeting in San Francisco, CA: 

June 9 – Disease 

Invited guests: Dr. Mary Brown, Dr. Dave Rostal, Dr. Elliot Jacobson 

June 10 – Wrap up threats; Presentation on threats by Dr. Heaton 

Dr. Elliot Jacobson will be invited to speak about interaction between URTD and herpes virus. The 

workbook from the Disease workshop should be available for distribution at this meeting. The
 

disease discussion could be one day, and the team should have focused questions that deal with the 

recovery plan. The DTRPAC should focus on issues not discussed in the 1994 recovery plan such
 

as new diseases (e.g. herpes), alternative hypotheses of sources, synergisms, and types of stresses.
 

In order to write a report about the 1994 recovery plan with respect to new information on disease,
 

the DTRPAC will ask penetrating questions to the invited speakers.
 

ACTION: Dr. Morafka will contact Dr. Jacobson about attending the June meeting.
 

A suggestion was made to invite an outside epidemiologist to interact with Mycoplasm experts in
 

the tortoise field. DTRPAC would like to determine data are necessary to make further progress in
 

the tortoise disease. The epidemiologist will hopefully be able to determine if the current pattern of
 

outbreak and latency been documented elsewhere. In addition, the epidemiologist will be asked to
 

objectively evaluate current Mycoplasm hypotheses, which would launch into later discussion.
 

ACTION: Dr. Tracy will find an outside epidemiologist to attend the disease portion of the
 

meeting. Dr. McCoy will send Dr. Tracy a list of references for epidemiologists.
 

There was concern raised about ability to cover all threats, including a comparative analysis and
 

potential other threats. However, identified threats are already included in the 1994 Plan.
 

Cumulative effects and interactions among threats are lacking. A suggestion was made to identify
 

threats and how they affect life history strategies.
 

A Threats table should include basic information, management, monitoring, and mitigation, in order
 

to provide as much information as possible for the next recovery team.
 

ACTION: Dr. Heaton will put together a first draft of a threats matrix that will accompany the DPS 

table with respect to former recovery units (and/or new DPS).
 

Dr. Heaton is also working on a spatial population status map.
 

July 31-Aug 1 Meeting: This meeting has been moved to Truckee, CA.
 

July 31 – Demography/Population status 

Aug 1 – Threats wrap up 

ACTION: Dr. Tracy will invite Dr. Dan Brown to give briefing on disease phylogeny in the 

afternoon July 31 or morning Aug 1. 

There should be a gap analysis of demography data, as well as a discussion of ties between tortoise 

declines and threats status 

ACTION: Roy Murray has all materials for UT and AZ. Data in spreadsheet format will be given 

to Ken Nussear and Dr. Heaton by May 23. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 190 

September 4-5 Meeting in Monterey, CA: 

Topics to be discussed: 

Monitoring / Begin delisting criteria 

ACTION: Dr. Morafka will call Asilomar about accommodations. The Double Tree or Casa 

Munras Inn are other choices for accommodations. The Monterey Aquarium is another choice for a 

meeting place. 

October 2-3 in Tuscon, AZ: 

Topics to be discussed: 

Finish delisting criteria 

Research Needs 

Conservation Planning 

Invite: Mary Cablk (DRI) 

ACTION: Dr. Heaton will invite Mary Cablk. The Desert Research Institute has range-wide 

change detection analysis data. Mary will give a presentation on hyperspectral data.
 

The issue of tortoise habitat will be covered during the conservation planning discussion. A
 

suggestion was made to review critical habitat designations and determine if they are properly
 

designated. This could be determined by performing a comparative analysis of demographic data in
 

critical habitat vs. outside critical habitat. Reserve design could also be revisited in a similar 

manner. Management actions of other species that would affect tortoises will also be covered in
 

conservation planning.
 

ACTION: Roy Murray will call about meeting accommodations at Tumamac Hill or the USGS 

room at the University of AZ. Bridgette will call the Inn Suites.
 

November 6-7 in Las Vegas, NV:
 

Grand Wrap Up and final DPS designation discussion
 

Revisit discussion of DPS and desert tortoise threats 

By changing the number of DPS units, the number of needed management reserves may change. It 

is important to ensure that there is continuity in protection throughout the listed range, despite 

where boundaries are changed. 

An argument was made for breaking up Western Mojave based on other factors besides genetic 

factors. There is a special conglomeration of threats in the West Mojave, as well as ecological 

differences in the Colorado Desert (i.e. major climatic difference, 116 degrees longitude is a 

segregation point based on meteorological data in the Mojave). There is also corresponding data on 

desert flora and rainfall from Mojave botanists. A good reference for this is the June Lathrup (ed.) 

book on California Deserts. 

ACTION: Dr. Heaton will put together maps for each situation to show further delineation of DPS 

units after genetics using ecological (climate) and behavioral factors. Tortoise habitat will 

EXCLUDE everything above a certain elevation (5, 000 ft) to better show the available habitat, dry 

lakebeds, urban areas, and highways. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 191 

Determination of writing assignments: 

The DTRPAC began to assign sections of the final report by identifying products that would result 

for DTRPAC meetings. A rough draft of a Table of Contents is attached at the end of this 

document. There was a discussion on what topics should be included in the report and in what 

order. Additionally, products were discussed from the past meeting and this meeting. The section 

on research needs should be a portion of each of the writing assignments for each section, not one 

section at the end of the report. An introduction to the report will include a scientific overview of 

what is known about the desert tortoise comparing prior to the 1994 Plan to present, showing 

significant advances in the state of general knowledge. DTRPAC products will include an updated 

GIS range map for Desert Tortoise and a comprehensive bibliographic reference for all desert 

tortoise literature, including references published since the 1994 Plan. 

ACTION: Dr. Lovich will produce a rough draft of an introduction and distribute to the DTRPAC 

for review. 

Meeting participants: 

Roy Averill-Murray, Arizona Game and Fish
 

Dave Delehanty, Idaho State University
 

Jill Heaton, University of Redlands
 

Jeff Lovich, USGS/BRD
 

Earl McCoy, University of South Florida
 

Dave Morafka, California Academy of Sciences
 

Ken Nussear, University of Nevada, Reno
 

Dick Tracy, University of Nevada, Reno
 

Bob Williams, USFWS
 

Bridgette Hagerty, University of Nevada, Reno
 

Becky Jones, CA Dept of Fish and Game
 

Clarence Everly, DMG
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 192 

Desert Tortoise Recovery Plan Assessment Committee Meeting 

June 9-10, 2003 

Redwood Room, California Academy of Sciences, San Francisco, CA 

Discussion on tortoise disease with panel of guest speakers, Dr. Mary Brown, Dr. Elliott 

Jacobson, Dr. David Rostal, and Dr. David Thawley 

The following questions were asked of guest speakers prior to the meeting: 

1)	 What is the existing research and what future research is needed bearing on the alternative 

hypotheses concerning URTD? The alternative hypotheses are 1) Mycoplasmosis is a novel 

disease to natural populations of desert tortoise, or 2) Mycoplasma has persisted in wild 

populations of desert tortoise for a long time, occasionally breaking to acute status with some 

mortality. 

2) What existing research/future research bears on whether populations of desert tortoise (not 

individuals) are negatively affected by URTD? 

3) What research has been done and needs to be done to understand what stressors will cause 

chronically affected populations to become acute? 

4) What existing research/future research bears on the effects of different strains of Mycoplasma 

on clinical outbreaks v. environmental stressors? 

5) What management actions do the literature and your scientific opinion recommend to control 

the spread of URTD, and to recover affected populations? 

Dr. Elliot Jacobson gave a presentation on disease studies in the desert tortoise. At the time of the 

original recovery plan, very little was known about Mycoplasma in relation to tortoise disease. Two 

sections of the 1994 recovery plan apply to disease: 3.b.1 Initiate epidemiologic studies and 3.b.2 

Research sources of mortality. Little attention has been paid to epidemiologic studies since the 

recovery plan was written. 

There is no data to support the idea that Upper Respiratory Tract Disease (URTD) is moving 

through the populations of the Mojave desert tortoise. From the information available, it would 

seem that Mycoplasma has been in coexistence with the desert tortoise for extended periods of time; 

however, there may have been subsequent changes in the strains infecting tortoises. Evolutionarily, 

Mycoplasma can coevolve with their hosts. Current data only point to an association between death 

of tortoises and URTD. 

Mycoplasma agassizii is isolated in the upper respiratory track, which is unusual with Mycoplasma 

infections. Dr. Jacobson is interested in looking at the energetics of disease in the desert tortoise. 

Studies of water balance in sick tortoises appear to be critical to understanding the relationship 

between disease and environmental stress. 

Shell dyskeratosis is the only other disorder mentioned in the recovery plan. This disorder, which 

may be related to toxins, causes lesions that affect the formation of keratin. 

The following are on going projects related to desert tortoise disease: 1) necropsies of ill and dying 

tortoises (recommended in original Recovery Plan), 2) serologic survey of desert tortoises for 

exposure to Mycoplasma and Herpesvirus (THV) (prevalence of disease in captive tortoises), and 3) 

transmission of Herpesvirus and Mycoplasma through the egg of desert tortoises. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 193 

Dr. Jacobson gave some examples of tortoise disease, including hepatic and renal disease, and 

Herpesvirus. Herpesvirus may be a significant problem; however, there is no data on how 

Herpesvirus is affecting wild populations. 

Future studies on tortoise disease will include: 1) transmission of THV, 2) developing immunologic 

markers for heath assessment, 3) examination of tissues by PCR for retroviruses and other 

pathogens, and 4) understanding the pathophysiology of hemosiderosis. 

The need for epidemiologic studies was highlighted, however, to perform the appropriate studies, 

appropriate questions are needed. For example, is disease spreading across the Mojave? Although 

ELISA positive animals did increase across the Mojave desert, this may be an artifact of sampling. 

URTD is seen mostly in dense populations and may be drought associated. Another question would 

be is URTD an ultimate cause of tortoise mortality. 

There was a question of how information on tortoise disease will relate into management actions, 

considering this is a sparsely distributed wild population. It was noted that human intervention 

might only be a short-term fix. Over the long-term, human actions may not necessarily help the 

species. The difference between protecting populations and protecting individuals was noted. The 

response was that there is conservation value in containing the disease in particular areas which are 

protected. By setting up ways to limit disease transmission, this will aid in translocation studies by 

limiting exposure. Interim actions are necessary to create artificial source and sink populations 

cannot sustain themselves alone due to habitat fragmentation and other threats. Source and sink 

populations could be related to elevation, and subsequently to rainfall. 

There is a population of tortoises in Ft. Irwin which does not show antibodies for the disease. This 

suggests that it could be possible that Mycoplasma may be novel for the desert tortoise or that the 

population has cleared the disease. An alternative explanation is that the sample sizes could be too 

small or the test could not be detecting the strain that may exist in that population. There was a 

suggestion that URTD has all the characteristics of agents entering a population that have never 

come across a particular organism (non-resistant population). This may be a case of a very 

significant genetic change in the Mycoplasma in recent times. 

Dr. Mary Brown presented the need for a global perspective on tortoise disease. There are 

multifactor causes of morbidity and mortality events and disease is only one factor that contributes 

to mortality. Understanding how disease interacts with stress, drought, and nutrition is critical. 

There is a need for a rapid response program to investigate morbidity and mortality events. There 

are other response programs (Biodefense and Foodnet) which we can use as models. 

Components of rapid response could include: 

1) Standard operating protocols in place (permits, etc.) so that when an event happens, the 

response actions occur immediately. 

2) Diagnostic and evaluation protocols designed to determine the nature of the threat 

3) Appropriate management strategies for containment or removal of threat 

4) Plans for monitoring the success of the action 

This potential management action was not specified in the original recovery plan. If there is a 

disease outbreak in a protected area, this is a possible way to introduce controls to prevent 

spreading to conspecifics. Examples of possible actions are setting up a quarantine zone or 

removing actively shedding animals. These animals could be held for observation and possibly 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 194 

reintroduced in the long term. Using modeling as a tool also may be helpful for studying different 

outbreak scenarios. There is a need for interdisciplinary solutions to disease. In the future, models 

could be applied to use and test validity of predictive models, provide framework for management 

decisions, and use real outbreaks to provide a benchmark for efficacy of containment models. 

Strategies for the control of infection diseases include: 

 Diagnosis 

 Quarantine 

 Culling or segregation 

 Physical separation/barrier 

 Use of sentinel animals 

 Investigate the periphery of outbreak 

 Long-term monitoring – choose populations that will provide the most information, not 

solely disease monitoring (habitat, etc) 

Hypothesized factors contributing to URTD disease transmission and severity: 

 Critical threshold of exposure (differs among populations) 

 Microbial virulence 

 Microbial infections dose and lesion dose (wide variety of virulence) 

 Prior exposure (limited ability to control disease severity) 

 Clinical expression of disease 

 Gender, age, and behavior (individual behavior may affect) 

 Exacerbating factors – nutrition, drought, etc. 

 Nutritional status 

Although there is no definitive proof, the following are the potential population effects of URTD 

(long-term monitoring is needed): 

 Multifactorial disease 

 Directly Affects demographics and viability 

 May impact Survival and reproduction 

 May affect Physiology/behavior 

There are two Mycoplasma that have been isolated from wild tortoises: 

 Mycoplasma agassizii – confirmed etiologic role in URTD 

 Mycoplasma cheloniae – isolated; some strains may be pathogenic 

 Two additional Mycoplasma not yet isolated 

A cluster of closely related species may cause URTD, which is consistent with respiratory disease 

in poultry and small ruminants. This causes a diagnostic dilemma because the ELISA test may not 

cross react with all strains; clusters may vary regionally, and may vary in virulence. To understand 

differences in virulence among strains, new work is being done with virulence infection studies. 

1) Identification of virulence genes and development of virulence profiles 

2) Critical prognostic information and management decisions – identify gene products and 

develop prognosis checks, which may be an early detector for populations in trouble 

It is important to understand specific virulence factors so that scientists can: 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 195 

 Predict disease severity and at risk populations 

 Determine specific antigens occurring when “bad” Mycoplasma are present 

 Monitor changes over time 

o	 Mutations 

o	 Changes in microbe present due to new introductions 

Currently there are major gaps in knowledge including: 

 Tortoise immunobiology – reagents and functional assays, normal vs. abnormal values, 

cellular immune system 

 Infectious agents – different strains/species 

 Diagnostics testing 

 Long term effects in wild populations 

These gaps lead to directions for future research: 

 Development of genetic profile for virulence 

 Interactions with other agents 

 Rapid response 

Dr. David Rostal gave a presentation on URTD and reproduction in the desert tortoise. 

Reproduction studies occurred in 1991-1993 with a follow up in 2000-2001. Dramatic declines in 

reproduction were seen in acute animals; however, reproduction recovered in animals showing 

clinical signs of URTD over time. Animals showing acute symptoms were more likely to show 

symptoms in the follow up. These animals were not nesting, and therefore, were not functioning as 

a reproductive part of the population. In the follow up, a majority of sick individuals began to 

reproduce in a manner like ELISA negative animals. There was no difference in clutch size and no 

difference in hatchling size between formerly sick and always well animals. The ability to 

reproduce seems to recover in infected tortoises. 

Some observations from gopher tortoises at Ft. Stewart may provide insight for the desert tortoise. 

Reproduction, clutch size, and hatchling success were not affected by a five-year drought; however, 

multiple droughts can have a cumulative effect. Habitat is the most important component to tortoise 

health. There is a low probability that Mycoplasma can be vertically transmitted; however the 

antibody is passed from mother to offspring. Preliminary studies support this, but more data are 

needed. Moreover, outbreaks followed the introduction of animals into research groups, but 

individuals not introduced into groups did not show signs, suggesting that social stress can cause 

clinical signs. 

Stress, density, and nutrition affect wild populations with varying levels of ELISA positive 

(possibly different strains with different virulence). This may lead to an outbreak or not, with 

clinical (no reproduction) and subclincal (reproduction recovers) phases. It is important to 

determine the causes of outbreaks and to look further at the interaction between drought and 

disease. 

The discussion on disease pointed towards not ranking threats, but focusing on cumulative and 

interactive effects. Perhaps disease has always existed, however, it may be important to show that, 

possibly as a result of other threats, disease has become a problem. Long-term monitoring is 

necessary to answer some specific questions, determine specific management actions, and monitor 

their effectiveness. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 196 

A veterinary epidemiologist gave perspectives on tortoise disease from the epidemiologist’s point 

of view: 

 Determine the relevance of the questions concerning disease to the survival of the desert 

tortoise over the long term. 

 Place equivalent effort into answering what are the factors contributing to the decline in 

tortoise numbers. 

 There are challenges due to the nature of the host and the pathogen in this case 

o	 Widely spread host, which makes it difficult to get epidemiological data 

o	 Ranking causes of death 

 Ask how will the disease affect low density, long-lived species? 

 Determine how Mycoplasma behaves in a population of desert tortoise 

 Be wary of modeling too quickly with too little information, and be sure to use post hoc 

evaluation of models; possibly use modeling to assess knowledge base. 

 Pick representatives sites as examples, and design studies that collaborates between those 

studying individuals and epidemiology 

The following are possible changes in prescriptions for research that were not made in the original 

recovery plan: 

 The USFWS should be proactive in providing leadership using multi-disciplinary/multiyear efforts. Long-term research agendas and improve implementation are needed. 

 Use the study of healthy tortoises as a control to determine what is abnormal may have 

value, but killing healthy animals should be kept at a minimum. 

The following are possible changes in prescriptions for management actions that were not made in 

the original recovery plan: 

 There should be a slight rearrangement in organization of the approach towards disease, 

and threats in general. No longer a list of threats but an integrated approach (totality). 

 There are currently no standards for determining if a population is healthy or not and 

whether individuals were stressed or not. Is it possible to develop them? 

o	 Rapid response protocols 

o	 Integrating management and research; use a global perspective 

o	 Monitor health of populations in all DWMAs 

Briefing on the Disease Workshop 

Highlights were given from November 2002 workshop on desert tortoise health and disease. The 

disease workshop report will include lists of what we know, what we don’t know, and what we 

suspect for topics including, health, nutrition, general, URTD, and herpes. The report also includes 

research priorities and management actions. The document still needs several iterations, including 

addition of citations under the “what we know” section. 

Determination of writing assignments 

A discussion of DPS units continued from previous discussions in the prior meeting. A map 

showing four genetic units was discussed. Further ecological evidence is needed for dividing West 

Mojave from Colorado. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 197 

Presentation on desert tortoise threats, Dr. Jill Heaton 

The following five steps could be used begin to address threats and to set the stage for the 

complexity of threat interactions: 

1.	 Identify a list threats (* already complete) 

2.	 Visualize complexity of threats (GIS, etc) (**critical) 

3.	 Develop ways to describe and characterize threats and threat interactions (possible 

research priorities for long-term monitoring) 

4.	 Methods for prediction of threat spatial interactions 

5.	 Application of methods for description and prediction of past present future threats 

The potential starting point to handle the issue of description and characterization of threats 

(monitoring, mitigating) could be the questionnaire used to evaluate recovery plans (Ecological 

Applications on Recovery plans). The questionnaire would need to modify not to single out 

individual threats. There are serious difficulties with this approach due to questionnaire design. In 

addition, it will be difficult to obtain quantitative data from the questionnaire. This questionnaire is 

already approved from USFWS and can be used as a framework to characterize threats and 

differences in threats based on ages, but we are cautious about this approach. 

Dr. Heaton developed GIS maps for threats and recovery actions recommended for each DWMA in 

the 1994 Recovery Plan. The maps show where recovery actions are being implemented, were 

partially implemented or have not been implemented. The data sources were the “Summary of 

Desert Tortoise Recovery Actions” for each recovery unit. The documents describe agency 

management actions occurring since the 1994 Recovery Plan recommendations. These documents 

were a good starting point; however, there are many more management actions, which were not 

discussed. The maps, which highlight DWMA and recovery units, could be sent to agencies to 

address inconsistencies between implementation and recommendations. 

Within California unit there are different management units (planning areas), which implement 

actions in different ways and each unit has different strengths and weaknesses. Future maps could 

separate out management units. There was a discussion of grazing allotments and the difficult 

political climate in CA. There is only one grazing allotment (Gene Dry Lake) in NV which is not in 

a DWMA. The discussion pointed out inconsistencies between map data and actual management 

practices. There are similar problems with feral equids data. There was a recommendation made 

develop a different questionnaire and to break up maps by planning area, agency, and geographic 

locations. 

There appears to be discrepancies between the Recovery Plan and the DWMA documents. The 

monitoring health of populations may have only been suggested for Fenner Valley. There will be a 

check to determine if this was recommended or if there are discrepancies. 

Maps showing tortoise habitat voids (>5,000 ft elevation and dry lake beds) and road density in 

critical habitat were presented to the group. A suggestion was made to weigh by road usage. An 

adjacent map showing road density in areas surrounding critical habitat will be helpful. 

A data sources inventory (determine data sources) and assessment (geographic area and specifics) 

will be necessary to visualize the complexity of threats, particularly in the Western Mojave. Data 

sources are listed below. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 198 

 Air quality - types of available data from AQ monitoring stations (arsenic, barium, copper, 

lead, SO2, CO2 counts for 2000) 

 Mining – all mines, not just those currently in use. Further assessment needed (potential 

sources of toxicants and dust) 

 Urban areas 

 Toxic release sites 

 Roads 

 Railroads 

 OHV/DOD areas 

 Landfills and disposal sites 

 USGS dust traps 

 CA cattle grazing 

It is possible to layer threats and determine the number of threats (perturbations) per pixel. This has 

been done previously for sage grouse. In addition, layers showing tortoise distribution and density 

estimates would be useful. This would lead to the possibility of making flow charts, showing 

changes over time. 

ACTION: Dr. Delehanty will try and track down the literature related to layering threats for the 

sage grouse. 

It was noted that there might be a danger in illustrating the high number of threats to tortoises. When 

large sacrifices produce little noticeable improvements, its leads to feelings that eliminating one 

threat can’t make any difference. Some threats are more easily eliminated than others, despite the 

smaller benefit to tortoises. Threats are not just scientific but also political and social. By targeting 

particular demographic groups with working towards elimination of particular threats (i.e. dogs in 

urban areas, target folks in urban areas), tackling threats may be more manageable. Presenting 

information on threats (flow charts) in a visual way will be very helpful. The group came to 

consensus that excluding use of habitat will make the most difference for tortoise populations and 

that the elimination of many threats as best possible is more important than eliminating one threat 

completely. 

In addition to a source of threats data inventory, specific data are needed for modeling efforts. 

 Weather stations 

 Dry lake beds 

 Elevation 

 Wind patterns 

 Other important items: geomorphology, vegetation, etc. 

Future work and data acquisition: Work is currently being done on developing fragmentation 

indices. Data are needed for grazing allotments and planning areas from NV. 

ACTION: Dr. Heaton will work with Lewis Wallenmeyer (Clark County) to acquire necessary 

data from Nevada. 

Dr. Heaton also gave a presentation on a decision support system for desert tortoise knowledge 

being developed at the University of Redlands. The goals of the project are to create system to track 

tortoise knowledge and a forum for scientific consensus building. This will be done using an 

integrated modeling tool known as an Ecosystem Management Decision Support (EMDS). This 

tool provides the ability to evaluate missing data, rank confidence in data sources, and bridge gaps 

in knowledge. Dr. Heaton explained how the knowledge base is constructed without using what 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 199 

data is available. Data will then be linked to the different components. It is possible to have a map 

for each node in the knowledge base, which would show, for example, suitable vs. non-suitable 

habitat. The system can combines habitat and threats models. The stacking of threats interactively 

could be a way to visualize threat complexity. 

The system allows evaluation based on criteria such as conservation priority, feasibility, habitat 

suitability, and management area condition. Users can perform sensitivity analyses and trade-off 

analyses, as well as, weight the importance of certain criteria. Development of this system will be 

an iterative process and must be adaptive. There was a suggestion that both population-based and 

individual-based models would be useful for different analyses. There was also a suggestion to 

make the process self-correcting, based on data already in the model. This would involve neural 

networking. 

Responses to draft text and maps: Dr. Heaton would like reaction and direction on the threats 

section text. In addition, she would like to know if there are there other data sources to fill in the 

gaps to the data inventory. Dr. Heaton would like thoughts on threat prioritization (five-ten core 

threats, spatially associated with points on the ground) to perform overlay analysis. There was a 

suggestion to focus on threats that seem independent (i.e. fire, roads, water, human population 

density, exotics), but may be influencing each other and the final result. 

Suggestions for the Threats Section included: 

 Provide a map showing a buffer around urban areas that shows less associated threats as you 

move farther from the center. 

 Give examples in report of the types of threats analysis and highlight what is missing to 

analyze fully the interaction/complexity of threats. 

 Give an example using a smaller geographic area, and provide a visual analysis of all
 

threats.
 

 Provide as much scientific analysis as possible. 

 Hypothesize on the characterization of individual threats and the interactions among threats. 

This will be the set up for future experimentation and monitoring to test hypotheses. 

 Highlight issues of spatial and temporal importance 

Determine writing assignments and an update 

Information is accumulating concerning recommendations that the team will make for a revised 

recovery plan. There was a suggestion to arrange a framework for the end product and begin 

sending around iterations via email. The Distinct Population Segments (DPS) section is coming 

together well; however, the components that extend beyond genetics still needs to be fleshed out. A 

suggestion was made to propose a hypothesis for further dividing certain suggested DPS units 

based on ecological components, such as rainfall. By providing an hypothesis and listing pros and 

cons, this may prevent vital gaps from being lost in the future. Some ecological/behavioral 

differences may lead to divergence on different evolutionary tracts over time. 

ACTION ITEMS: 

1)	 UNR will make three separate databases containing the recovery actions in the DWMA 

document, Appendix F of the recovery plan, and pgs 45-60 of the recovery plan. Then make 

comparisons to determine if there are inconsistencies. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 200 

2)	 Roy Averill-Murray will review Dr. Heaton’s translation of the recovery action documents for 

each recovery unit into maps. (Using these categories: no implementation, partial 

implementation, ongoing implementation, no data) 

3)	 For 20 recommended actions not answered in the “Summary of Recovery Actions” documents 

(listed below), Roy Averill-Murray and Phil Medica will determine if there is data concerning 

implementation and put together a database. 

Distribution and density surveys Eliminate unauthorized bombings 

Health of populations - Law Enforcement 

Landfill Management Install RR culverts 

Stop mining Evaluate Raven use 

Install Road Culverts Restore habitat 

Install Urban Barriers Monitor health of populations 

Remove surface chemicals Establish visitor center 

Establish research natural area Install RR tortoise fencing 

DWMA management area Administration 

Establish breeding programs Install aquaduct barrier 

4) Dr. Heaton will continue writing the Threats section text and working on GIS maps. 

5) Dr. Lovich will review Dr. Heaton’s Threats section. [Tracy will assume this responsibility] 

6) Bridgette Hagerty and Ken Nussear will continue to work on population data and will send the 

final products to Dr. Heaton. 

7) Dr. Tracy will compose the first iteration of a framework for a final product and send this 

around via email. 

Preparation for July DTRPAC meeting 

Summary size/age class and density data are accumulated for NV, AZ, UT, and CA pre-1991.
 

There was discussion on collapsing from 7 size classes to 4 size classes. This will be done to allow
 

comparison of all data; however, all uncollapsed data will also be archived.
 

The question was raised, “Is there a null hypothesis for what a size/age class distribution should
 

look like?” There is a size class distribution hypothesis in the 1994 recovery plan.
 

There are three levels of data to review for the July meetings:
 

 Capture/recapture data 

 Density estimates (>180 and all) 

 Size class distribution – tortoises observed (presented in histograms) 

Meeting participants: 

C. Richard Tracy, UNR 

Ken Nussear, UNR 

Jill Heaton, U. Redlands 

Earl McCoy, USF 

David Morafka, Cal. Academy of Sciences 

David Delehanty, ISU 

Phil Medica, USFWS 

Roy Averill-Murray, AFG 

Mary Brown, UF 

Elliott Jacobson, UF 

David Thawley, UNR 

David Rostal, GSU 

Lewis Wallenmeyer, Clark County, NV 

Bridgette Hagerty, UNR 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 201 

Desert Tortoise Recovery Plan Assessment Committee Meeting

July 31 – August 1, 2003 

North Tahoe Conference Center 

Kings Beach, CA 

Announcements: The West Mojave Plan is currently out for review. Comments are welcome and 

are due by September 18th. There is also a contract out for a pathologist, as an outcome of the 

disease workshop. 

Presentations on tortoise population status in CA, NV, UT, and AZ 

Arizona and Utah data – Roy Averill-Murray, AFGD 

Ann McLuckie presented size class data from Arizona and Utah plots. Lincoln Peterson 

density estimates were presented, where available. All plots are 1 sq.mile in area and are surveyed 

for an effort of 60 person days, in two successive 30-day sweeps. During the first 30-day sweep, 

tortoises are marked, and tortoises are recaptured during the second. In some cases, more than one 

person worked a particular plot, thus lowering the amount of days necessary to complete 60 person 

days worth of effort. Consistently, there were 45 days where one person work alone surveying a 

plot. There may have been a 15-day period where a second person is working. The 60-person day 

effort was held constant. 

The graphs provided showed the number of live animals captured on each plot per year. 

Where data on sex were not given or if tortoises were not sexed due to lack of reliability, tortoise 

numbers were split in half for this exercise. Murray also provided data on the percent dead at each 

plot. Percent dead was number of carcasses removed from the plot divided by the number of live 

tortoises found plus the number dead. Tortoise carcasses are being removed during every survey 

year. In AZ, all plots will show survey technique improvements in mid-90s, thus improving the 

number of tortoises found. 

Notes associated with general plot data: 

 There is an assumption that the number of tortoises entering the plot is equal to the number 

leaving the plot. In addition, there is a higher likelihood that tortoises around the periphery 

will move off the plot than those in the center. Tortoises appear to have anchored home 

ranges, so large moves seem unlikely. 

 Juveniles and subadults in the West Mojave show great deal of movement prior to
 

reproduction (Boarman and Morafka, pers. comm.).
 

 If there have been changes in impacts (management, recreation, etc.) over time, they are 

important to note for all plots. 

 Occasionally desert tortoises have been known to die in burrows. 

 There was a suggestion to provide a rangewide estimate of growth rate, which would then 

be broken down by areas of the Mojave. 

 The dead counts and the size class of dead tortoises may vary in reliability depending on 

the experience of the crew. Preservation of the carcass, shell, scutes, etc. depends heavily 

on how the tortoise died and where the carcass is left (in moist vegetation or not). (Berry, 

pers comm.). 

 It is important to remember that some plots may be sinks while others are sources. Thus, 

one cannot assume every plot should expect good numbers of tortoises. 

 In the future, it would be helpful to include plot workers in data spreadsheets. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 202 

Beaver Dam Slope (BDS) Exclosure (AZ): The BDS Exclosure plot is less than 1 sq. mile, closer 

to 500 acres, and is located on the AZ/UT border. Caliche caves are found throughout this plot, 

which may reduce the ability to detect tortoises. This site was surveyed in 1989, 1996, and 2001. 

This site is scheduled to be surveyed in 2005, however, the survey could be done in spring 2004, 

funding permitting. 

Littlefield (AZ): This plot was surveyed in 1987, 1993, 1998, and 2002. 

Pakoon Basin (AZ): This plot is located south of the Virgin Mountains, and was only surveyed in 

1991. 

Virgin Slope (AZ): This plot was surveyed in 1992, 1997, and 2003. 

Summary of Arizona data: Plot data from Arizona suggests that there is enough evidence to be 

concerned about tortoise populations, however, there is no conclusive evidence of decline. More 

data are necessary. 

Beaver Dam Slope (UT). The BDS site was surveyed once in 1991. 

City Creek (UT): This plot was surveyed in 1988 and 1994. Line distance sampling has been the 

method used more recently in this area, and has shown constant density estimates. 

Woodbury – Hardy (UT): This plot was surveyed in 1981, 1986, 1992, and 1998. This plot is 

located in the northern edge of the tortoises range. A male biased sex ratio may be the result of prebreeding dispersal movement in males. 

Nevada data – Phil Medica, USFWS 

Phil Medica presented size class data from Nevada plots. Lincoln Peterson density 

estimates were presented, where available. Data for dead tortoise counts were not included in the 

presentation. All plots were surveyed with 60-day person effort. Most of the surveys were done 

with two people for a 15-day capture period and a 15-day recapture period. All surveys occurred 

between early April and May. Where appropriate, tortoise density estimates were provided. After 

1995, there were no plots sampled in Nevada, except at Lake Mead. 

Christmas Tree Pass (NV): This plot was surveyed in 1985, 1991, and 1994. The plot is located 

between a highway and a power line with a moderate level of disturbance. Population estimates at 

this plot are fairly stable for the years surveyed. 

Piute Valley (NV): This plot was surveyed in 1979, 1983, 1989, and 1994. In 1987 there were 

problems with the survey. The entire plot was not worked, the time of year was incorrect, and there 

were problems with data collection. For these reasons the 1987 data set was not used. Confidence 

limits for population estimates for years surveyed overlap, suggesting that the population has not 

decreased significantly. 

Coyote Springs (NV): This plot approaches the northern edge of the desert tortoises range, located 

in Lincoln County. The plot was surveyed in 1986, 1992, and 1995. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 203 

Sand Hollow (NV): This plot is the most northern plot in the NV tortoise’s range, located in 

Lincoln county. The plot does not contain good tortoise habitat for burrow construction. The site is 

east of highway 93 and west of I-15. No density estimates were provided due to low tortoise counts. 

Mormon Mesa (NV): This plot contains a caliche underpan and is located 4 miles west of I-15. 

The plot was surveyed in 1989 and 1994, and data show no significant differences in density 

estimates. 

Gold Butte (NV): This plot is located in a remote area, southeast of Mesquite near the Lake Mead 

National Recreation Area. This plot was surveyed in 1986, 1990, and 1994. Density estimates for 

this plot were stable. 

Trout Canyon (NV): This plot is located west of Las Vegas and is three miles north of a new 

highway. The plot was surveyed in 1987 and 1992. 

Sheep Mountain (NV): This plot is located south of Las Vegas and east of I-15. The plot was 

surveyed in 1979, 1984, 1992, and 1995. 

Last Chance (NV): This plot was surveyed once in 1980. 

Lake Mead National Recreation Area (NRA): Two plots (Grapevine and Cottonwood) were 

surveyed extensively in this area. Several plots were sampled sparsely since 1995. 

Grapevine Canyon (NV): This plot was surveyed for population estimate data from 1992-1995. 

These data are useful for making year-to-year comparisons. After these surveys were done, animals 

were fitted with transmitters and followed to determine survivorship. The plots were not 

systematically sampled. The data from this study were published in the June or July issue of the 

Journal of Herpetology. This plot is located northwest of Laughlin, Nevada and is not comparable 

to other plots. 

Cottonwood (NV): This plot was sampled similarly to Grapevine from 1992 to 1994 for population 

estimates. 

River Mountain (NV): This plot was sampled from 1995 – 2002. 

Summary of Nevada data: Until 1994 there was no statistical variation from survey year to survey 

year, although mortality was observed. Populations in Nevada plots appear to be stable. Although 

there is not enough data to warrant concern, follow up data for plots in recent years would be 

valuable. 

California data – Dr. Kristin Berry, USGS 

Dr. Berry initially presented preliminary results from a tortoise color study that may affect 

DTRPAC’s discussion of distinct population segments. Since 1992, color data for shells and limbs 

were taken, using the Munsell soil color chart. Initial results show statistically significant 

differences among all age classes and among larger tortoises from different regions. Juveniles also 

show statistical differences between West and East Mojave. Regional color differences seem to 

reflect original recovery units. In addition, soil color is always lighter than tortoises, and juveniles 

appear to have more variety than adults. There is a possibility that color differences have a genetic 

component if the influence of diet, etc. is eliminated. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 204 

Status and trends in CA 

Dr. Berry provided some history on the choice of long-term permanent plots. In the early 

1970s, plots with tortoise counts that too low to perform demography/trends studies were 

eliminated. Study sites were chosen after mountainous areas, pinyon/juniper areas, and other poor 

desert habitat were eliminated. Sites were chosen in all valleys in California that contained tortoise 

habitat. The plots were located in critical habitat and represent five of the six recovery units. These 

plots were not only used for demography data collection, but also for tortoise health profiles. All 

data shown were from 60-day effort surveys per 1 sq. mile during which time population data was 

collected. All shell and skeletal remains were collected for analysis including time since death, size, 

sex, relative age, and cause of death. In addition, scat from predators was analyzed. Changes in 

disturbance, such as increases in use, in plots were also assessed. In addition to demography 

surveys and health profiles, necropsies of ill, dying, recently dead tortoises were conducted and 

NOAA precipitation data were analyzed to determine if there is a relationship between drought 

conditions and die offs. 

West Mojave 

Fremont Valley (CA): This plot was surveyed in 1981, 1987, 1991 and 2001. Major threats near 

this plot include domestic dogs, recreational vehicles, a major road, ravens, and invasive species. 

Desert Tortoise Natural Area (DTNA) Interior (CA): This plot was sampled in 1979, 1982, 

1988, 1992, 1996, and 2002. The plot has an increase in shrub cover and less evidence of invasive 

species; however, outside degradation has increased. 

DTNA Interpretive Center (CA): This site was surveyed in 1979, 1985, 1989, 1993, 1997, and 

2002. This site has shown an increase in development that is evident throughout California. 

Tortoises at this plot have elevated levels of mercury in their livers (Jacobson et al 1991). 

Kramer Hills (CA): This plot was surveyed in 1980, 1982, 1987, 1991, and 1995. 

Summary of West Mojave region: With the exception of Kramer Hills, all plots in the West Mojave 

show a terrific downward trend. 

Southern Mojave 

Stoddard Valley (CA): This plot was sampled in 1981, 1987, and 1991; however, there was doubt 

raised that the data is reliable. 

Lucern Valley (CA): This plot was surveyed in 1980, 1986, 1990, and 1994. 

Johnson Valley (CA): This plot was surveyed in 1980, 1986, 1990, and 1994. 

Northeast and East Mojave region 

Shadow Valley (CA): This is a remotely located plot that is cattle grazing intensive. This plot was 

surveyed in 1978, 1988, 1992, and 2002. 

Ivanpah Valley (CA): This plot is located in the Mojave National Preserve. This plot was surveyed 

in 1979, 1986, 1990, 1994, and 2002. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 205 

Goffs (CA): This plot is located in the Mojave National Preserve; however, there is still evidence 

of cattle grazing. The plot was surveyed in 1980, 1983, 1984, 1985, 1986, 1990, 1994, and 2000. 

Data from the 2000 survey are located in a published report. Management issues at Goffs include, 

road kills, the addition of more railroad tracks, disease, and invasive plant species such as the 

Moroccan Mustard. 

Summary of the Northeast and East Mojave region: All plots in this region show a recent 

downward trajectory. 

North Colorado 

Ward Valley (CA): This plot is long and narrow and located along an elevation gradient. It was 

surveyed in 1980, 1987, 1991, 1995, and 2002. 

Chemehuevi Valley (CA): This is a 1.8 sq. mile plot that was surveyed in 1979, 1982, 1988, 1992, 

and 1999. Crude assignments of causes of death were given to shell and skeletal remains. Causes 

were mammalian predation (high number of coyotes), combination vehicle/mammalian predation, 

vehicles, avian predation, disease, and unknown. A high number of deaths were associated with 

roads. An estimation of Brassica tournefortii density suggests that higher densities are located near 

edge of road, but the species had penetrated to at least 1 mile into the plot. 

Eastern Colorado Desert 

Chuckwalla Bench (CA): This plot was surveyed in 1979, 1982, 1988, 1990, 1992, and 1996. 

Initially, this plot had the largest reported density of tortoises (225 torts/km) of all CA plots 

surveyed. Density estimates were published in the New York Turtle and Tortoise Society 

Proceedings. 

Summary on the North and East Colorado Desert: These plots generally showed downward 

trends. 

Summary on CA threats: Direct sources of tortoise mortality are raven predation, vandalism, 

poaching, road deaths, and canine predation. Examples of these sources of mortality occur at 

Lucerne Valley, DTNA, Fremont Valley, and Goffs. Indirect sources of tortoise mortality include 

habitat fragmentation, unauthorized ORV use, increased human access, and invasive plants. Most 

importantly, current inability to measure cumulative impacts to desert habitat is a serious threat. 

Comments on CA presentation: 

A discussion about the differences and similarities between Piute Valley (NV) and Chemehuevi 

(CA) followed the presentation on California data. Difference in nutrition available at sites, as well 

as, between year variations may cause differences in rebounding from a large die off. A question 

was raised that if there is a healthy source population, can a tortoise population that experiences at 

die off, rebound more quickly? 

Currently, there is a working hypothesis that ground disturbance (e.g. road construction) is causing 

free-floating toxicants to be blown onto plants, etc. This is one mechanism for finding high 

concentrations of toxicants in tortoises. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 206 

The DTRPAC will recognize that CA post-1996 data exists, and will continue with work with 

sources on how to characterize this information. New data can be handled by using dialogue and 

annotation so that the team can provide recommendations. 

Friday, August 1 

A comment was made that although plot information is critical to analysis, it is difficult to use a 

single plot to make inferences about an entire DPS unit. Scrutiny of individual plot information is 

important to determine how useful it will be to make inferences. The following question was posed, 

“How should plot information be combined to do statistical analysis of trends in each DPS?” A 

suggestion was made to use regression analysis to look at all plots in a particular area over time and 

in order to make an inference about each DPS unit. 

There was further discussion on how to use information on possible declines in the Eastern Mojave 

in order to make recommendations in the report. A suggestion was made to use Goffs (CA) and 

Piute (NV) as an example to describe the volatility of the data and explain reservations on what plot 

data suggest. 

Reservations were expressed about reporting numeric declines in any area using only density 

estimates from all size classes combined. Discussion of what is occurring in each large scale DPA 

area is critically important to make recommendations. A suggestion was made to use the following 

verbage: with available data there is no downward trend, however, a scientist gave the opinion that 

there are samples showing lower numbers in certain plots which raises concern. 

In order to clearly determine trends, there needs to be a change in infrastructure. Data collection 

should be programmatic. There is current difficulty with the disjointed nature of scientific data 

collection under USFWS permitting. 

Several suggestions were made on how to discuss the topic status in the final DTRPAC report, and 

in what units should be used. Suggestions are listed below: 

 Use original recovery units. 

 Use preliminary DPS designations. 

 Use data with all possible hypotheses for different DPS units 

 Revisit concepts of DPS units in light of status data presented earlier. 

Update on previous writing assignments 

Dr. Morafka gave an update on the Distinct Population Segments (DPS) section. 

To designate a DPS, evidence must be given to show distinctness, ecological and behavioral 

significance, and conservation status. Evidence for distinctness should be recognized as the 

prerequisite. In addition, these designations will be used sparingly, as stated by Congress. The 

USFWS definition is less strict than those in current schools of scientific thought. Genetic evidence 

should be used as an eyewitness. However, if genetic evidence is not clear, morphology can be used 

as a possible clue that genetic differences may be present. Health status (disease) may also be used 

as a lower tier criterion to make a population distinct. Therefore, threats can be used to designate 

management areas, and may result in better management recommendations, and thus recovery of 

the species. 

The second criterion is significance, both ecological and behavioral, which also has two tiers. First, 

different life history strategies may suggest that two populations may be on two different 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 207 

evolutionary trajectories. Demographics beyond life history strategies, such as responses to disease, 

weather, and environmental factors that over time may affect life histories, can be used. 

The third criterion is conservation status. This should be used a justification in addition to 

significance. A population may be considered significant to the conservation of a species if an 

international boundary is crossed, if there is threat of disease, or if a population sustains gene flow 

by serving as a bridge between other DPS units. 

Britten et al. (1997) does not provide definitive evidence to designate DPS units, however, their 

data is the best available and therefore, can be used as a justification for a recommendation for DPS 

units. Using Britten et al. data, Nevada would be divided into two units (North of Las Vegas and 

South of Las Vegas). Therefore, 4 DPS units are designated as a genetic starting point (Upper 

Virgin, North Las Vegas, South Las Vegas, and Western Mojave). 

A suggestion was made to make further divisions using hierarchical justifications. For example, 

differences in pre-adult predation or differences in summer flora (Western Mojave) may qualify as 

justification. In addition, different management needs in the far West Mojave, if they can be related 

to tortoise biology, could also be used as justification. 

Although there is no genetic evidence to separate the far West Mojave from the Colorado and 

Eastern Mojave, shape coupled with a progenetic or habitat component, or reproductive differences 

may send a population off on another evolutionary trajectory. 

The following status models were suggested to perform statistical analysis on plot data: 

 Original recovery units 

 Genetic DPS 

 Third alternative that takes into account all possibilities, resulting in five units: East Las 

Vegas, West Las Vegas, Upper Virgin, East Mojave - Colorado, West Mojave 

Description of statistical analysis: 

 Used normalized data using highest value recorded and strike plot variable. 

 Run scale to see blanks (gaps in data) 

How can line distance sampling data be used to determine status? 

 Presence/absence 

 Show the drawbacks of plots to pinpoint trends 

 Support or not for trends in plots 

o	 If plots do not show full range of variability, then line distance can point out if 

plots are in poor tortoise populations to use as representative areas. 

 Density dependent effects 

o	 Grid analysis (1 sq. mi for example) 

o	 First tally each grid unit; then randomly grab units. 

 Compare plots that were dropped in the early 70s using current LDS data. 

 To determine if LDS data provide further information on status, a regression analysis will 

be performed on LDS density estimates after G0 data is added to 2003. 

Summary of Line Distance Sampling 

Phil Medica presented a summary on line distance sampling (LDS) for 2001 – 2003. Transects were 

400 m on a side and in the shape of a bow tie or figure 8. Random point criteria were used once the 

following criteria were used. Transects included critical habitat, < 1250 m elevation, < 30% slope, 

and excluded private land and non-habitat areas (e.g. playas). Density estimates using LSD appear 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 208 

to underestimate tortoise density compared to plot density estimates. A suggestion was made to 

attempt to increase the area that could be sampled by increasing slope. Poor resolution of data 

available may give an inaccurate slope calculation. Possible area able to be sampled decreased 

mainly by changing to bowtie shape transects that could not overlap. 

Total corrected sign (TSC) data: Further discussion of TCS data will occur at the DTRPAC 

meeting that covers monitoring. 

Threats in relation to population status 

There was a discussion concerning the relation of threats in relation to downward trends. Is the 

occurrence of threats and population declines synchronous? Or are differences in management also 

responsible? Many threats have a temporal component that must be included in the analysis. In the 

West Mojave, where there have been precipitous declines, there are no unique threats, except 

perhaps poaching for food. However, there are increased threats of raven predation, human 

predation, habitat fragmentation, canine predation, releasing of sick pets, air pollution, and ground 

disturbing activities (roads, tanks, more legal and illegal OHV, open areas). Dr. Heaton brought 

forth data sets that may show some of these threats numerically. A suggestion was made to compare 

threats in areas where populations that are stable to those in declining areas. There are available 

data that would be useful for region wide comparisons. 

Determine writing assignments and action items 

ACTION: Dr. Boarman will provide a set of demography data for a highway 158 plot in the West
 

Mojave to Dr. Heaton and Ken Nussear.
 

ACTION: Ken Nussear will run statistical analysis of plot data using different DPS models.
 

ACTION: Dave Delehanty will perform a regression analysis on LDS density estimates after G0
 

data is added to 2003 data.
 

ACTION: Rich Inman will deliver G0 data for 2003.
 

ACTION: Dr. Boarman will send around draft writing on total corrected sign data for review.
 

ACTION: Dr. Heaton will produce a map with long-term plots and then with random plots to
 

determine if long-term plots are representative of a region.
 

ACTION: Dr. Heaton and Dr. Boarman will produce a threats index
 

ACTION: Dr. Heaton and Phil Medica will provide references that give history of tortoise 

sampling methods.
 

Writing Assignments: 

 Current draft of DPS section – Dr. Tracy will review the draft by Dr. Morafka and Dr. 

McCoy 

 Appreciation of Desert – Dr. Morafka is working on a draft of this section 

 Introduction to the report: Dr. Tracy and Dr. Morafka will write a draft of this section 

 Population Status Section: Dr. Tracy will write a draft of this section. 

Preparation for September 4-5 DTRPAC meeting (MONITORING in the broad sense and 

Delisting Criteria) 

 Meeting schedule: 

o	 Delisting criteria will be introduced on the morning of Sept. 4 

o	 Monitoring of threats and habitat will be discussed in the afternoon of Sept. 4 

(Guests: Mary Cable, landscape level theoretician, Dr. White) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 209 

o	 Monitoring tortoise populations will be discussed in the morning of Sept. 5. 

(Speakers: Stephen Corn, Dr. Tracy, Dr. Boarman) 

o	 Return to delisting criteria in the afternoon of Sept. 5 

o	 The DPS discussion will be revisited to incorporate new analyses. 

 To be discussed at the September meeting: 

o	 Efficacy of current methods for monitoring tortoises 

o	 Are plots valuable indicators? 

o	 How to evaluate trends in reference to the animals (relative vs. absolute) 

 Focused list of questions to pose to guests (not in any particular order) 

o	 Preamble: To instill a complete monitoring scheme, there are several components: 1) 

monitoring for focal animal, either true density estimate or indicators of trends, 2) 

monitoring of habitat, and 3) monitoring of threats (improving or worsening). 

o	 How is it possible to know if we are satisfying the given delisting criteria? 

o	 What other delisting criteria could work instead of 25-year upward or stable trend? 

o	 What are cost effective mechanisms that people are using to monitor vast expanses of 

habitat? 

o	 What are the different types of approaches to monitor habitat? Please provide a costbenefit analysis as well as the need for technical know-how? Are experts required for 

particular approaches? 

o	 What features of the environment should be monitored? (i.e What variables can 

feasibly be looked at over time?) 

o	 If you were hired as an outside consultant, and you were asked to design a scheme to 

determine if habitat has changed over time, what would you do? 

o	 How can statistical power issues be dealt with? How can habitat be measured with 

enough power to perform an analysis? 

o	 If a certain amount of habitat is being converted for use, how can that be measured? 

Remaining habitat may or may not be good tortoise habitat. How can you distinguish 

between the two? 

o	 What needs to be known about tortoise biology to design habitat monitoring? (i.e. 

movement, life history strategies etc.) 

o	 Is it feasible to track individual threats as well as measure cumulative threats? How 

can you recognize a threat? 

 Invitations for speakers (two days): 

o	 Steve Corn: Line distance sampling 

o	 Mary Cable: change detection from remote sensing 

o	 Outside evaluation (non-tortoise) – possibly Gary White or Jim Sedinger 

o	 Protocols for threats and habitat monitoring (in a general sense - theoretical) - Chuck 

Peterson (Idaho State) 

o	 Threats monitoring - Fran James or Michael Reed 

Meeting participants: 

C. Richard Tracy, UNR 

Bridgette Hagerty, UNR 

Earl McCoy, USF 

David Morafka, Cal Academy 

Phil Medica, USFWS 

Roy Averill-Murray, AFG 

Bob Williams, USFWS 

Kristin Berry, USGS 

Becky Jones, CFG 

Karen Phillips, USGS 

John Hamill, DOI 

Clarence Everly, DOD 

Bill Boarman, USGS 

Dave Delehanty, UI 

Ken Nussear, UNR 

Jill Heaton, U. Redlands 

Rich Inman, Redlands 

Lewis Wallenmeyer, Clark County 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 210 

Desert Tortoise Recovery Plan Assessment Committee Meeting

September 4 - 5, 2003 

Casa Munras Garden Hotel 

Monterey, CA 

Announcements: The Management Oversight Group is having a meeting on Wednesday, 

September 24 (10am – 3pm) at the Sun Coast in Las Vegas, NV to receive an update on DTRPAC 

progress. 

Presentation on Multi-dimensional monitoring of desert tortoise: what are the goals and 

problems associated with monitoring? 

Dr. Tracy presented information on the current status of multi-dimensional monitoring for the 

desert tortoise. The keystone delisting criterion is to demonstrate a statistically significant upward 

trend in the size of desert tortoise Mojave population over a period of 25 years. This criterion was 

used instead of a more common criterion specifying a target population size for delisting (At the 

time when the desert tortoise was listed by USFWS, there was a downward trend in population 

size). The other four delisting criteria for desert tortoise relate to conservation initiatives after an 

upward trend has been demonstrated. 

Modern monitoring requires documenting changes in three elements: 1) size of populations 

(including density and aerial extent of population), 2) habitat of the species, and 3) threats to the 

population. In addition, some monitoring should be hypothesis-based. For example, hypothesisbased monitoring could be used to determine the effects of management actions such as highway 

fencing or removing grazing. Using presence/absence data, we could identify areas which could be 

targeted for repatriation experiments or other research needed for assessing the efficacy of 

management. 

Using the data from transects conducted for distance sampling, a Kernel analysis was performed to 

predict the presence and absence of live animals and carcasses within DWMAs and recovery units. 

In some areas that were formerly in the range of desert tortoise, there appears to be no discernable 

populations. For example, the Desert Tortoise Natural Area (DTNA) has become a fragment of 

habitat that no longer appears to represent adequate tortoise habitat. The same result obtains in 

Eldorado Valley of Nevada. 

Monitoring trends 

With little variation in data, statistically determining population growth is a simple task. However, 

variance in population density estimates for desert tortoise makes determining a trend very difficult 

(or impossible). Life history characters make seeing trends difficult over a short time. This type of 

problem has been previously demonstrated for bald eagle populations. 

Sites for permanent monitoring plots were initiated to study the biology of individual tortoises 

including population ecology questions. When the 1994 recovery plan was written, there were 

population declines in the Western Mojave. This downward trend still continues. There is now a 

new concern for populations in the East Mojave, particularly due to a single data point at the Goffs 

site. This concern has highlighted the need for more data. In these areas, tortoises appear to be 

affected by various combinations of cumulative threats, not one particular threat. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 211 

There are many problems with using permanent plots to determine population trends: 

 Plots cover a small percentage of tortoise habitat, though plots are separated far enough that 

tortoises from one plot cannot move to another. 

 Plots are not randomly placed in critical habitat. 

 Replication of plots within years in inadequate for comparison. 

 Sample sizes of census years are largely inadequate to yield enough statistical power to 

perform a regression of trends in any particular plot. 

 Several plots were abandoned early in the process because they had low tortoise counts. 

 Data from plots violate assumptions in mark-recapture techniques and detectability of 

tortoises was not evaluated as part of the analyses. 

Transect Methods for Density Estimates 

During a 1995 workshop on tortoise monitoring in Reno, tortoise biologists, statisticians, and 

monitoring experts reviewed previous methods used to monitor tortoise populations and possible 

methods to use in the future. From this workshop, a decision was made to use distance sampling 

techniques to monitor tortoise populations, although the efficacy of the technique for the species 

was debated. Distance sampling requires measuring the distance perpendicular to a transect to each 

tortoise in order to calculate the detectability of animals. 

Typical density calculations are multiplied by two factors, Pa and G0. Pa is the probability that 

tortoises can be seen by the person walking a transect (detectability). G0 is the probability that 

tortoises are active and able to be sampled (either on the ground surface or visible in a burrow). 

Tortoises that are located farther from the transect line are more difficult to see. All data are 

normalized under the assumption that all tortoises on the transect line are seen. The rule of thumb 

used is that a sample size of 60 tortoises is large enough to estimate detectability. In better years, a 

person must walk more than 400 km to see 60 tortoises. More than 1 field crew contributes to the 

transect data from each site, as a result of the long distances necessary to find 60 tortoises. In some 

circumstances (temporally or spatially), distances exceeding 1000 km are necessary to find 60 

tortoises. 

More recently, measurements of each team’s ability to detect tortoises have allowed us to 

enumerate the role of the team for Pa. Two sizes of styrofoam tortoises used to train crews. Each 

tortoise is numbered and the distance to each tortoise found is measured. Currently, only one 

density of tortoises (410 tortoises per 1 km2) is used. These tests have shown that distance sampling 

is inaccurate because crews appear unable to see tortoises on the line. This violates a critical 

assumption of distance sampling as a method. Furthermore, data from different crews are fused 

together to produce transects producing 60 tortoises. The detectability estimate resulting from those 

data are irretrievably incorrect as they bias Pa to the better crews in ways that cannot be corrected. 

G0 changes among sites, during the day, throughout the season, and among years. However, data 

from the entire range are currently lumped to calculate a single G0 to estimate densities of tortoises 

for the entire range. G0 is calculated using a number of focal tortoises that are monitored to find the 

amount of time they are active. Another possible source of error is that tortoises that can be seen in 

their burrow are counted the same as tortoises found walking in the open to make one G0 estimate. 

Power analysis of distance sampling 

A power analysis was performed to detect trends in population size as a function of annual percent 

population growth rate. For a gentle growth rate, the coefficient of variation would have to be much 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 212 

lower to detect a trend statistically. A reasonable optimistic population growth rate for tortoises 

would be 3/10 % growth per year. Currently, those working on distance sampling are trying to 

reduce variance in Pa and G0, but it may be impossible to reduce variance enough to be able to 

detect an upward trend. It was noted that no time lag due to age structure was included in the 

analysis, which may make detection even more difficult. Therefore, transect methods require 

modifications to increase precision of population estimates to the point where they can be useful for 

analyses needed for delisting. 

With knowledge of what is being done to monitor tortoise populations, there was a suggestion for 

multi-dimensional monitoring program. This would include monitoring the efficacy of our 

management actions, changes in habitat, and changes in threats with time, in addition to estimating 

tortoise density adequately. 

Further discussion of distance sampling 

Steve Corn (USGS) presented additional information on the distance sampling (DS) method 

currently being used to estimate tortoise densities. Methods for distance sampling are as follows: A 

pair of field workers (leader and follower) make three passes over 100m segments. The first 

observer makes a first pass holding a measuring tape. Then, a second observer follows behind along 

the centerline. A third pass involves the observers moving in a zigzag pattern. 

In 2003, the goal for DS was to walk 4 km per day along transects that bent back upon themselves 

in a bow tie configuration, and do this in 3-5 hrs. Using the composite detection function from 

Program Distance produced comparable results among years. Transect criteria changed between 

2001 and 2002. The buffers used were different and the bow-tie configuration vs. straight line 

transects restricted number of areas available to be used as random samples. As a result, there was a 

lack of re-randomization among years because the probability of reselecting areas among years was 

much higher. The restrictions on randomly choosing a transect included: sites had to be below 4200 

ft elevation, less than 30 % (2001) and 30 degree slope (2002), not on playas, not on private land, 

not on any roads in the GIS data set (buffered 25 m on either side), and in 2002 a 25 m buffer was 

placed on all criteria for exclusion. For 2004, no buffers will be used, dirt roads will not be 

excluded, and slope exclusions will be much steeper. 

There was a suggestion that re-randomization is not always useful in reducing variation. One 

suggestion was to select random sites for sampling initially, and then continue to use the same sites 

annually. Another suggestion was to use a mixture of re-randomizing and revisiting sites to look at 

temporal differences. 

There was a discussion on the number of data points vs. the precision of data points and the 

resulting power to determine trends. A suggestion was made that there is the possibility of finding 

the optimal pooling. This would be a balance between the number of points to use, power of 

analysis, and variation in data. However, Nussear and Tracy reported that pooling invariably 

reduced power as the balance of reducing variance was offset by a reduction in degrees of freedom. 

Although tortoise densities should be easy to calculate using DS methods because of the properties 

of tortoises (i.e., tortoises are diurnal, they are found in open habitat, and their activity is linked to 

drought severity index) it is not always the case that tortoises are easy to enumerate. Tortoise 

positions that are cited while sampling are burrow (visible), deep (not visible), open, under 

vegetation, hidden, tortoise in the open but near burrow. For each recovery unit focal animals (5-

18) are repeatedly measured. The mean of observations during when observations are being taken is 

calculated. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 213 

Unfortunately, Program Distance currently only takes one G0 measurement, and this is a serious 

limitation. If a satisfactory model for G0 were developed, this would eliminate the need for focal 

animals and it would require different software. A suggestion was made to use a weighted or 

harmonic average if G0 estimates are lumped. Currently there is a developing effort to model G0 (by 

BRRC and U. of Redlands) and this may be more accurate than measuring focal animals. 

A serious bias of inability to detect tortoises on the transect line does exist, but this failure can be 

estimated in relation to effort. One way would be to use the removal factor from the second 

observer as a correction factor. A suggestion was made to change the DS technique and remove the 

third pass from the methods. There would be one pass with a leader and a follower would provide 

data for a correction factor. By not doing the zigzag pass, burrow detection may be lost. 

Someone suggested creating a combined estimator of G0. For example use burrow density, 

probability of burrow occupation, and tortoise sightings to model the probability of activity. 

A suggestion was made that human behavior affects the detection rate of Styrofoam tortoises. 

Detection of styrotorts may be different from live tortoises because they are sedentary and may be 

camouflaged by differences in habitat. 

A proposal was made that transects should be run a different way. In particular, a team would walk 

until a tortoise was found, and then a density estimate could be made for each transect using Pa 

from the training classes. Currently transects are a fixed length (whether tortoises found or not) and 

many transects produce no tortoises. Each transect would be done the same way so that variance 

would still exist, but not be ignored as is currently. This would be a logistical problem because 

sometimes great distances are required to find one tortoise. 

A rebuttal to this proposal was that the focus was on bias, and to detect trend bias is not crucial. The 

suggestion was to use training as a covariate in analysis. Fuse data within teams and then adjust for 

team variation with each team Pa. If only 1 pass were done per transect, more transects could be 

done per team. 

Long-term Study Plots 

Argument for stopping the use permanent plots for population estimation: 

o	 Choice of plots was not hypothesis driven and not random. 

o	 There is a mixed bag for temporal spacing of plot sampling, and possibly not enough 

sensitivity to detect changes 

Argument to retain permanent plots to use for population estimation: 

o	 Long- term capture/recapture data from plots has the tremendous potential for looking 

mechanisms of trends and asking size-class survivorship questions. 

o	 A suggestion was made for gridding plots and parsing out data from individual grids for 

analysis. There would be more power to determine which threats are causing. The raw data 

would be necessary for this type of analysis 

A time-trend analysis of plot data was done by Nussear to determine if plots show trends over time. 

Different DPS scenarios that have been discussed were used. After controlling for site and looking 

for a year affect, trends were only noticeable in the West Mojave using the current recovery unit 

scenario, the genetic hypothesis scenario, and the genetic and ecological scenarios. 

Status of current monitoring for desert tortoises 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 214 

Experiments to test pre and post management actions have not been done. There was an eight-year 

study on the effect of road management, which found that fencing did decrease the occurrence of 

tortoise road kill along highways. However, there are many actions, both active and nonintervention, that need to be assessed. 

Some habitat and threats data are available to extend the scope of current analysis. Although 

temporal differences in vegetation data may cause trouble, those data are collected in the same year 

of tortoise data. 

Advice and observations about population monitoring (density) from invited experts 

• There is value in a top-down organization to monitoring to have a formalized process for data 

collection. Standardized data collection and data sharing allows collaboration so that metaanalyses can be done. All parties involved should have an agreement for data sharing/pooling. 

There should be external peer review by an independent panel of experts that is hired to analyze 

and error check data. This type of process is being used with the CA spotted owl. 

• There is value in permanent study plots if you can use the data more fully. However this value is 

based on the availability of raw plot data. 

• Without the ability to pool data from all areas, plot data are not useful. It is difficult to justify 

amount of money spent on data collection from plots without having open access to the full 

data set. 

• There was a suggestion to force inter-agency coordination to acquire all necessary data for
 

analyses.
 

• Work on modifications to DS to get most precise estimates possible. This includes using
 

different detection rates and different groups of covariates in models of population density.
 

• Determine the maximum growth or decline potential for which there is enough power to detect 

the trend. Given the best of all worlds, is there power to detect a certain level of decline? 

• Perhaps try the % area occupied method discussed in MacKenzie et al. 2002. 

• Use a suite of methods to detect change at different scales. 

• One possibility is to choose five or so key permanent plots to sample annually and abandon the 

sampling of all other plots. 

• Assuming DS cannot be done well enough (lack of power) to track an increase, put effort into 

detecting decrease by tracking carcass and track die-offs for management purposes. The 

downside to this suggestion is that by the time a decline may be noticed, it may be too late. 

Points on which there was consensus for population monitoring 

o	 Continue to model and analyze what the maximum likely growth rate of the population is 

and that given the variance in data; there is enough power to detect it. The same applies to a 

downward trend. All possibilities have not been exhausted. There is need to determine how 

subtle of a decline can be distinguished past zero. In essence, what is the minimum target 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 215 

resolution we think is important to aim for to achieve power? Based on natural variation, 

when should there be an alarm? 

o	 If density cannot be measured, determine what methods can be used to detect an alternative 

measure, such as population contractions, food availability, or increasing or decreasing 

threats. 

o	 Need a central repository for data and a formalized process for collaboration of data 

collection. This includes sharing costs among agencies, having a means to certify the 

efficacy of data, providing a means by which all can access data, and that there be a means 

by which USFWS can depend upon multiple approaches to data analysis so that they are 

always aware of the status and trends of tortoise populations. 

Habitat monitoring 

Remote sensing and the Desert Tortoise 

Mary Cablk (DRI) presented information on using remote sensing to monitor changes in habitat and 

threats. Aerial photography, digital airborne data, and satellite data are all possible technologies to 

fill the remote sensing components of monitoring habitat. Mary described the data requirements 

necessary for remote sensing, as well as the necessary components for each type of technology. 

Mary emphasized the need for habitat monitoring experts to be working in the decision making 

process. The types of habitat features that could be measured using remote sensing include 

vegetation association, slope, elevation, micro-conditions, elevation limits, geomorphology, and 

urban/agricultural land. Once tortoise experts have determined the features that are important to 

measure, the features must be linked to data and the spatial, spectral, and temporal resolution 

should be determined. Using these steps, it would be more likely to capture what habitat really is 

and how to best measure it. Change detection and analysis would be used to determine seasonal or 

annual differences. Once habitat monitoring is established, links can be made between habitat and 

tortoise biology. 

Habitat monitoring for Snake River Plain reptiles and Yellowstone Amphibians 

Dr. Chuck Peterson presented new techniques in environmental mapping/modeling and habitat 

modeling/ mapping. If key features can be identified, there is a possibility to model habitat. To look 

at an environmental gradient, students in Dr. Peterson’s lab used important environmental 

characteristics (e.g. temperature and moisture) to examine an environmental gradient using 

probability monitoring logistic regression, or a combination of both. 

Another possible method for modeling and mapping habitat is to examine changes and variation in 

the body condition of individuals. This could be a possible strategy for desert tortoise monitoring. 

Additionally, one can study the changes in occurrence, as well as temporal changes in spatial 

distribution. 

A comprehensive monitoring program allows biologists and managers to understand the dynamics 

of a species fully. This type of program would include asking different questions on many different 

scales, including the level of individual using an index of condition and the populations level. 

Measuring the condition of individuals is not separate from monitoring population size. A condition 

index may provide evidence for mechanisms behind changes in population size. For example, a 

measure of condition could potentially link the risk of mortality to individual covariates. That risk 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 216 

could help contrast between a stable and declining population. Using a more formalized monitoring 

structures allows some pressure to be taken off density monitoring (i.e. density measurements are 

not relied upon to answer all questions about a population). Each scale would have different 

objectives and a coordinated effort for addressing each. For example, following individuals 

(“sentinels”) could be used to determine extent of certain threats, but not to answer exhaustive 

questions. 

Friday, September 5 

Continued discussion on population status from the August DTRPAC meeting 

Ken Nussear presented an analysis on population density using data from permanent study plots 

within habitat and in protected areas. There is a noticeable loss of tortoises within West Mojave. 

The aerial extent of habitat is changing as a result of a range wide loss of habitat. The DTRPAC is 

aiming towards a statement of concern over entire range, but heightened concern in West Mojave. 

This may lead to a change in listing from threatened to endangered in some areas due to dramatic 

density declines and loss of habitat. The recommendations still require additional steps, such as 

continued discussion of DPS designations. 

Summary of monitoring discussion 

With respect to density, there needs to be a more assertive attempt to develop a centralized 

program, which would include using an outside panel of analysts with expertise to determine how 

data should be collected and used. There was an explicit agreement that a density assessment is not 

useful if it is not a centralized program that provides USFWS with all the information needed to 

make informed decision. The program should be rigorous and formal, possibly having agencies 

contribute to one sum of money that would be distributed after there is consensus on monitoring, 

data standards, etc. Lack of coordination is currently a limiting factor; however, it will be difficult 

to have everyone agree if DPS designations are agreed upon. There was a suggestion to have 

communal funding be designated by DPS, but data collection be standardized. 

ACTION ITEM: Ask Barry Noon for documentation on the structure of the California 

spotted owl data collection program and other collaborative efforts. This information will 

help the DTRPAC to make a recommendation based on the documented successes of 

another program. List successes of this type of collaborative program and how the success 

translated into the recovery of the species. Provide examples of benefits of the collaborative 

effort for the agencies, scientists, and species. 

There has been a lack of implementation of the 1994 Recovery Plan and a collaborative program 

may remedy that problem. There was a suggestion that the DTRPAC’s goal should be an outline for 

an integrative, collaborative, rangewide program (i.e. comprehensive multi-scale approach to a 

monitoring program, including the aerial extent of population, density of populations within aerial 

extent, qualitative and quantitative gain/loss habitat, quantitative direction of threats, and a 

condition index of individuals as an indicator of the population). 

Dr. Sedinger advised the team to refine distance sampling and continue collecting data using the 

same technique (e.g., other potentially important information could be taken as part of the protocols 

by technicians conducting distance sampling transects). Currently, observers are not monitoring 

rainfall, vegetation, etc. Habitat monitoring was not described in the 1994 Recovery Plan. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 217 

There was a suggestion for DTRPAC to assess current monitoring techniques, and make 

recommendations on how to improve current monitoring, including the use of new techniques and 

approaches as well as monitoring more different things. 

A suggestion was made to regard density estimates as a “density indicator” instead of working to 

improve distance sampling to improve the accuracy density estimates which may have limitations. 

By calibrating technicians using styrotorts to calculate detectability, Pa could be modeled, and the 

focus could focus on improvements in monitoring. 

There was a discussion on the potential goals of the multi-scale monitoring program. The following 

was a possible list of goals: 

o	 Monitor to accumulate indicators of ability to delist 

o	 Monitor to inform adaptive management (failure/success) 

o	 Monitor the success of management actions (i.e. hypothesis-based monitoring) 

Approach monitoring in a hierarchical fashion 

There was a question about the usefulness of developing a bodily condition index for individual 

desert tortoises. A condition index might help biologists to mechanism contributing to population 

dynamics. In snakes, there is a correlation for body condition and reproductive fitness. 

ACTION ITEM: Bridgette Hagerty will work with Dr. Peterson to provide references on 

examples of measuring body condition. 

What are the possible goals for monitoring? 

6.	 To have viable wild populations distributed in each DPS (protect natural processes) and to 

preserve the diversity (genetic, ecological, behavioral, morphological) of the Mojave 

population 

a.	 Are there enough tortoises necessary to be self-sustaining currently? 

b.	 Is 50% for 500 years the best way to reach this goal? Do we use the existing PVA or 

make a more definitive statement? 

c.	 Increase tortoise populations in each DPS to reasonable levels to avoid an Allee effect. 

Tortoise was listed because of downward trends due to threats, not as a result of low 

population numbers. 

7.	 Determine why tortoise populations are threatened. 

a.	 Loss of quality and or quantity of habitat 

b.	 Direct threats creating mortality 

8.	 Measure the success or failure of management actions 

There was a discussion on no-net-loss or fragmentation of habitat. If you increase new breeding 

populations that are isolated, that is technically increasing fragmentation, though it can be perceived 

as a good thing. Would no net loss of individuals or habitat be enough in each DPS? Currently, this 

would not be considered enough to delist a DPS. 

Is it necessary to generate a new hypothesis because the old delisting criteria are unable to be 

measured? The original prescription was to have a 1,000 square mile reserve protected and have at 

least 10 tortoises per square mile within that reserve. If populations dropped below these numbers, 

there was a dangerous probability of an Allee effect and a resulting extinction vortex. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 218 

Discussion of the original delisting criteria 

The recovery objective is the recovery and delisting of Mojave population of desert tortoise. To 

consider the population recovered, all criteria must be met. 

Criterion 1. As determined by a scientifically credible monitoring plan, the population within a 

recovery unit must exhibit a statistically significant upward trend or remain stationary for at

least 25 years (one desert tortoise generation). 

Possible changes to this criterion 

o	 The terminology remain stationary does not work well for most of the DPS. 

o	 The criterion needs refinement because wording only refers to population size and not to 

habitat and threats. 

o	 Include (a) monitoring of habitat, (b) threats, (c) aerial extent 

o	 Revise Appendix A 

o	 Consider multiple scales (population, landscape, individual content) 

o	 Provide examples. These are the types of things to consider (e.g. body condition 

index) 

o	 Presence/absence of individuals in critical habitat (ability to determine suitability of 

habitat; spatial framework) 

o	 Define relationships between components 

o	 Include power and statistical analysis (evaluate the probability of both type 1 and 

type 2 errors) 

o	 Include language such as a “High powered test that fails to detect decline, or a statistical 

test that detects an increase.” In those areas having lower densities, it will be easier to see 

an increase statistically. Areas with very low densities will require intense management to 

increase population size and should produce a noticeable increase. 

o	 Use experimental management to test management actions. 

Criterion 2. Enough habitat must be protected within a recovery unit, or the habitat and the 

desert tortoise populations must be managed intensively enough, to ensure long-term 

population viability. 

o	 Perhaps there are more ways to use available data. 

Criterion 3. Provisions must be made for population management at each DWMA so that

population lambdas are maintained at or above 1.0 into the future. 

o	 Long-term population management is needed 

Criterion 4. Regulatory mechanisms or land management commitments have been 

implemented that provide for adequate long-term protection of desert tortoises and their habitat 

Criterion 5. The population in the recovery unit is unlikely to need protection under the

Endangered Species Act in the foreseeable future. Detailed analyses of the likelihood that a

population will remain stable or increase must be carried out before determining whether it is

recovered. (a) fluctuations in abundance, fecundity, and survivorship; (b) movements of desert

tortoises within the area and to or from surrounding areas; (c) changes in habitat, including

catastrophic events; (d) loss of genetic diversity; and (e) any other threats to the population

which might be significant. 

o	 Wording in this criterion needs to be revised. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 219 

Possible changes to Delisting criteria: 

o	 Make recommendations to have specific criteria for each DPS 

o	 Have headings for criteria (i.e. MANAGEMENT) 

o	 Perhaps use a different criterion for density (e.g., not trends in population size) 

Recommendations for monitoring 

o	 Change DISTANCE software to incorporate differences in G0 – this might require writing 

our own software 

o	 Continue to use transects sampling as these data are extremely valuable 

o	 Data collection for habitat monitoring should occur simultaneously with population 

monitoring or in parallel. 

o	 Condition measurements of individual tortoises need to be developed. The condition index 

of Nagy is not considered to be reliable insofar as that index can be biased by amount of 

water in the bladder which can amount to nearly 50% of body mass. 

o	 Assess the extent to which presence/absence data could be useful to the goals for 

monitoring.
 

o	 Perform research to reduce variation in different types of population estimates from 

transect data (may or may not be distance sampling). 

o	 Have tortoise trackers perform ground truthing of habitat variables, if remote sensing is 

used in monitoring. 

o	 Habitat monitoring should measure rainfall, vegetation, etc. 

o	 Assemble a workshop to discuss habitat monitoring (experts on tortoise habitat, image 

analysts, GIS analysts, ground truthing) 

o	 Threat monitoring needs to be hypothesis driven to measure success of management 

actions. 

Comments from stakeholder visitors 

There was a comment concerning future scenarios of cultural changes that will be occurring in 

tortoise habitat over the next 25 years. This should be considered when designing reserves and 

managing DWMAs. Changes include increase in the human population and climate change. 

There was a concern expressed that using buffers around features in the environment as criteria for 

selecting points for distance sampling transects reduces the amount of information that could be 

collected (e.g. effects of roads). 

Preparation for the October 2-3 meeting in Tucson, AZ 

October 2 

DPS designation wrap up, (morning session)
 

There will be a discussion to finalize recommendations for DPS designations.
 

ACTION ITEM: Dr. McCoy, Dr. Morafka, Dr. Delehanty, and Dr. Tracy will provide 

appropriate references for discussion prior to the meeting.
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 220 

Research needs, (afternoon session) 

This has been discussed at previous meetings. The team will revisit areas of lack of knowledge and
 

make a new list of research for the next five years.
 

ACTION ITEM: Each team member should come with suggestions for new research
 

needs or emphasis on old research needs that have not been done (i.e. gaps in knowledge).
 

ACTION ITEM: Dr. Boarman will do an analysis of what kinds of research have been
 

done since the recovery plan using desert tortoise council symposia and publications.
 

October 3 

Conservation planning, (morning session)
 

Representatives who are familiar different conservation plans (Larry Foreman, Lewis Wallenmeyer,
 

Ray Bransfield, Ann McLuckie, Becky Jones) will be invited to discuss the status of 

implementation of the recovery plan (pg 55). They will be asked to report on the number of 

management issues that have been addressed in each conservation plan.
 

Dr. Heaton will present what management actions have been done so far for each management unit,
 

using the spreadsheet put together by Roy Averill-Murray. Inconsistencies in the wording of the
 

recovery plan for management actions will be addressed. Revisit to make recommendations on how
 

to deal with this problem of diverting attention to one threat.
 

Managers will have time to react to what the team has discovered thus far.
 

John Hamill will make a presentation on the DMG recovery proposal.
 

ACTION ITEM: DTRPAC should read the conservation-planning section of the recovery
 

plan and be prepared to make recommendations for plan (adaptive management).
 

Preparation for DTRPAC presentation to the MOG on September 24th 

A task described for the DTRPAC was to update the Desert Management Group and the 

Management Oversight Group on the process and progress of the committee. There will be a 

meeting of the MOG for this specific purpose on Wednesday, September 24 from 10am to 3pm in 

the Sun Coast Casino in Las Vegas, NV. In addition, there will be a presentation on the Disease 

workshop. There will be a presentation on how members of the DTRPAC were chosen and how is 

the team approaching the assessment. All stakeholders are invited and will be asked to bring 

information and will be permitted to ask questions. There was also a suggestion to have 

presentations from stakeholders that have been regular observers of the meetings to provide a 

different perspective to the group. 

The script: 

Dr.Tracy: Introduction, Overview, and Summary of DPS discussion 

Dr. Heaton: Importance of spatially explicit modeling in the process up to this point. How GIS 

has been used in committee processes and how it can be used in future recovery efforts (e.g. 

looking at threats in a quantitative way) 

Dr. Boarman: Threats overview 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 221 

Averill-Murray: Involvement by a state agency (UT/AZ involvement) and the importance of 

process to states represented, importance of data sharing and standardized data collection 

Tracy, Medica, and Nussear – Data collection, historical data, and analyses being done to use 

historical data (plots, distance sampling, total corrected sign), Improvements in distance 

sampling 

Meeting participants 

C. Richard Tracy, UNR 

Earl McCoy, USF 

Phil Medica, USFWS 

Roy Averill-Murray, AFG 

Bob Williams, USFWS 

Ken Nussear, UNR 

Bill Boarman, USGS 

Dave Delehanty, UI 

Jill Heaton, U. Redlands 

Bridgette Hagerty, UNR 

Rich Inman, U. Redlands 

John Hamill, DOI 

Clarence Everly, DOD 

Jim Sedinger, UNR 

Steve Corn, USGS 

Barry Noon, CSU 

Chuck Peterson, ISU 

J. Michael Reed, Tufts U. 

Mary Cablk, DRI 

Lewis Wallenmeyer, Clark County 

John Willoughby, BLM 

Ron Marlow, UNR 

Ann McLuckie, Utah DOW 

Becky Jones, CFG 

Bryan Manley, representing Quad State 

Coalition 

Ray Bransfield, USFWS 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 222 

Desert Tortoise Recovery Plan Assessment Committee Meeting

October 2-3, 2003 

Inn Suites Hotel 

Tucson, AZ 

Thursday, October 2 

Briefly discuss outcome of September 24th MOG meeting 

Bob Williams (USFWS) provided some feedback on the DTRPAC presentation at the Management 

Oversight Committee on Wednesday, September 24th. The following were presentations given by 

DTRPAC members: 

 Dr. Tracy introduced the DTRPAC process, including team members, expert guests, and 

meeting topics. 

 Roy Averill-Murray discussed the importance to state agencies in the process and the 

importance of data sharing. 

 Dr. Boarman explained the DTRPAC approach to threats and emphasized interactive 

threats. 

 Dr. Heaton highlighted the use of new technologies and its importance to the DTRPAC 

process. 

 Phil Medica presented distance sampling data and methods. 

 Ken Nussear provided some preliminary results, including downward trends in the Western 

Mojave, using new analyses. Ken highlighted the team’s effort to use all available data 

including plot data and distance sampling data in new ways to make recommendations. 

After the presentations, the DTRPAC members present formed a panel to answer any questions. 

Stakeholders and agency representatives offered both compliments and constructive criticism to the 

DTPRAC process and preliminary results. A summary of the presentations given at the MOG 

meeting will be made available on line. 

Dr. Heaton gave an overview of the analyses that were presented at the MOG meeting. A kernel 

analysis was rerun using a combination of total corrected sign (TCS) and distance sampling (DS) 

data (1998-2003) to better represent areas where it is known that there are live animals. With both 

data sets, there is a suggestion that the DTNA is no longer attached to the remainder of the 

Fremont-Kramer DWMA. This area is void of evidence of tortoises, but does contain carcasses. If 

this small area of DTNA has been fragmented, it poses conservation biology concerns. These 

results are dependent on the size of the areas used for the analysis. Using smaller sampling areas for 

the analysis makes the results more conservative. In addition, a cluster analysis was done using the 

same combined data sets. The results suggest that there is a problem where there only appears to be 

clusters of carcasses, but not live animal clusters. 

A question was raised about how to include cumulative and synergistic effects in the writing of a 

recovery. There was a suggestion that there should be a focus on practical considerations. The 

DTRPAC should make recommendations that translate expertise and data into possible priorities 

for management actions. For example, although there are many connected threats, roads are a threat 

that is associated with many other threats. If the DTPRAC were to identify correlative effects, they 

could create groupings of effects that would work as a whole. A goal of the DTPRAC should be to 

identify isolated and correlated threats. One possible mechanism for doing this would be a risk 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 223 

analysis using best available information. The result would be a correlation matrix or network. The 

correlation matrix could be used to support recommendations for management actions. 

Unfortunately it is difficult to difficult to control one threat experimentally and come up with a data 

that tests multiple threats occurring simultaneously. However, it might be possible to introduce 

healthy headstarted animals in experiments in areas were there no longer appears to be tortoises. 

If the DTRPAC can provide a framework for how threats are interrelated, including recovery unit 

specific arrays of most probable threats and most probable interaction arrays, the new recovery 

team can determine the most worthy hypotheses to test. Although there may not be homogeneity 

within DPS units, it may be possible to use experimental management units to test hypotheses. 

There was a note to reemphasize hypothesis testing in DTRPAC recommendations. 

There was a discussion about what is meant by “control access.” Although it is outside the scope of 

the DTPAC to provide all the features of a definition for this term, there is a need to be precise so 

that the new recovery team will have enough information. 

Revisit DPS designations 

A draft manuscript describing the DTRPAC DPS recommendations (written by Morafka, Murphy, 

McCoy and Tracy) was distributed to the DTRPAC for review. The take home message of the 

document is that the most supportable way to delineate DPS unit is the use of genetic information. 

In order to make designations based on ecological differences, etc. more concrete information is 

required. In the case of the Mojave population of the desert tortoise, the genetic model alone 

suggests that the Upper Virgin River is justifiably different as a DPS. The West Mojave is 

genetically similar to the Eastern and Northern Colorado units. Using mtDNA, Britten et al (1997) 

suggests that the Northeastern Recovery unit should be split between North and South of Las 

Vegas. Nuclear DNA was not used in the analysis, so further resolution is necessary. However, 

there is enough information to recommend a first separation of the Recovery Unit. The genetic DPS 

hypothesis includes four units: Upper Virgin River, West Mojave, North Las Vegas, and South Las 

Vegas. Further delineation of the West Mojave DPS is warranted based on ecological information 

(e.g. differences in rainfall east and west of the Baker sink, and in threats). This information may be 

enough to justify the West Mojave to be separated from the Eastern and Northern Colorado unit. 

Currently, there is not enough information to distinguish between the Northern and Eastern 

Colorado Units. 

Discussion to finalize recommendations for DPS designations 

The possible environmental correlates to justify DPS designations have the least justification; 

therefore, more information from the literature is necessary. For example, direct life history 

characteristics and environmental correlates have been demonstrated for similar herbivorous desert 

species (chuckwalla). There is literature that suggests tortoises have differences in body growth east 

and west of the Baker sink. Differences in reproduction in east vs. west, which can be correlated to 

rainfall, have also been demonstrated, though this data has not been published and there may be a 

similar problem with acquiring access to the necessary data. Work by Turner and Henen suggest 

that clutch size declines in drought years. Therefore, there is a current working hypothesis to split 

the West Mojave from Eastern and Northern Colorado using geographical discreteness east and 

west of the Baker sink. Currently, there is not enough information or justification to separate the 

Eastern and Northern Colorado into two DPS units. The genetic similarity in the West Mojave, 

Northern Colorado and Eastern Colorado possibly suggests that these populations were a relatively 

recent extension of the desert tortoise range. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 224 

A question was raised regarding the affect of humans moving tortoises on genetic variation. This 

has occurred on a very short time scale and with a small number of individuals, so the effect is 

probably minimal. 

Discuss listing status recommendations for DPSs 

As a result of the data analyses that have been done during the DTRPAC process, the DTRPAC is 

considering elevating the West Mojave DPS to endangered status. 

What is the difference between threatened and endangered status? 

Endangered status 

 Makes jeopardy decisions possible 

 Changes public opinion 

 No 4D rule, which concerns exemptions on take 

 Takes 30 days longer to get a permit 

The West Mojave desert tortoise DPS has all the elements of an endangered species (five criteria in 

section 4 of the ESA): 

 Loss of habitat 

 Over utilization for commercial, recreational, scientific, or educational purposes 

 Disease or predation 

 The inadequacy of existing regulatory mechanisms 

 Other natural or manmade factors 

Bob Williams suggested using the example of the delisting of the Columbian white-tailed deer as a 

way to proceed with the desert tortoise. 

Discuss required management actions and monitoring for each DPS 

What are the management issues associated with individual DPS units? 

 DPS units have cross-state boundaries. 

 In the proposed South Las Vegas DPS, there would be only one DWMA in Ivanpah 

Valley/Shadow Valley. This DWMA is approximately 1000 mi2. There would be no 

DWMA in Nevada. 

What should be measured and what should the criteria be for each DPS? 

The following were suggestions of what should be measured and what criteria should be used for 

each DPS: 

 Biologists must address population growth because ESA protection is ultimately a 

demographic issue. If researchers can monitor reproduction, mortality, age class structure 

in plots within each DPS, tentative answers for population growth can be realized in the 

long-term. If the desert tortoise is a cycling species, there may only be an average value for 

population growth over a long period of time. 

 Measure response to mitigation in threats and habitat 

 Improve upon power in analyses 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 225 

A discussion on original delisting criteria was revisited. In order to detect an upward or stationary 

trend, researchers will monitor changes in habitat and threats. Monitoring should also provide 

evidence of the efficacy of management actions in relation to threats and habitat. If individual 

condition cannot be linked to demographic population parameters, then the data do not provide 

evidence of recovery. Additionally, the population may still be declining, but condition may not be 

able to predict the downward trend. By sampling at multiple scales, it would be possible to see a 

series of indications of recovery after different amounts of time. The quantitative criterion for 

habitat protection is long-term population viability. 

Repatriation may be a valid consideration in certain DPS units. Currently there is a proposal for 

repatriation as an experiment to determine mechanisms for population decline. The design uses 

adults and juveniles as a diagnostics for determining the effects of threats. 

ACTION: Dr. Heaton will provide a copy of Dr. Morafka’s repatriation proposal to help in writing 

the report. 

What differences should there be in monitoring for each DPS? 

There was a suggestion to add plots to certain DPS units where there are not enough points. There 

should also be changes in the sampling rotation so that representative plots from each DPS are 

sampled annually. There were noted reservations about continuing to use permanent study plots for 

the same purpose as distance sampling, although plots provide other information in addition to 

density estimates. However, it was also noted that if each type of monitoring has a different flaw, 

then there is value in using both methods. It was suggested that the DTRPAC should provide 

recommendations for types of monitoring to use if there is unlimited funds, and if there are limited 

funds. 

What are the required management actions for multiple, synergistic, and cumulative threats? 

The DTRPAC should recommend that the next recovery team build a management prescription per 

DPS. The DTRPAC should plot the strategy, not provide individual recommendations. 

Review of research prescribed in 1994 recovery plan and what has been published in the 

literature 

Dr. Boarman provided a review of the research recommendations in the 1994 recovery plan as well 

as the type of research that has been presented at Desert Tortoise Council Symposia, International 

symposia, and in Chelonian Conservation and Biology. 

The following were the general research recommendations in the recovery plan: 

 Density – a recommendation to collect baseline data on density and distributions and to test 

the replicability and accuracy of density estimate methods 

o Dr. Boarman noted a disproportionate number of baseline monitoring studies 

 Demography – a recommendation to produce a model for epidemiology and population 

structure (demographic and genetic). 

o	 Dr. Boarman noted that there were more papers on population structure (genetic) or 

broad geographic patterns with morphology 

o	 There were no papers comparing mortality and epidemiology. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 226 

 Impacts – a recommendation to perform long term studies to determine demographic 

impacts of grazing, road density, barriers, human-use levels, restoration, augmentation, and 

translocation. 

o	 Dr. Boarman noted that there were more papers on translocation and grazing. 

o	 Other papers focused on fire, roads, and OHV. Most papers only provided 

inferential and correlational data. 

 Protective measures – a recommendation to determine the effectiveness of DWMAs. 

o	 Dr. Boarman cited the study comparing populations within and outside the DTNA. 

A study also determined the effectiveness of fencing. 

 Climate and Plants – a recommendation to study the spatial variability in climate and 

vegetation productivity, and how that affects demography. 

o	 Typically these studies are not tortoise literature, so a fair assessment has not been 

made. 

 Nutritional ecology – a recommendation to study nutritional ecology and how it affects 

survivorship. 

o	 Dr. Boarman noted that papers focused on tortoise diet and its effect on physiology. 

 Reproductive physiology 

o	 There have been studies on clutch size and temperature dependent sex 

determination. 

The following were non-recovery plan topics that have been studied since 1994: 

 Disease and health – mostly status, etiology and pathology, not affects on demography 

 Habitat and fire – weeds and fire ecology 

 Population and behavior – juvenile movements and home range 

 Habitat characteristics – burrow characteristics, hibernation (mostly juvenile) 

 Methodology – ELISA methods for disease, putting transmitters on tortoises 

The following are successes in terms of what has been covered that was recommended in the 

recovery plan: 

 Physiology, nutrition, and reproduction – 24% 

 Density and status – 13% 

 Impacts - 10% 

 Topics not listed in the plan (disease - 17%, and fire ecology – 8%) 

The following are failures in terms of the recovery plan: 

 Epidemiology 

 Mortality (underestimated) and no relative proportions of causes of mortality 

 Impacts including roads, barriers, human-use, restoration, augmentation 

These downfalls can be explained by failures of management and lack of publishing. 

The following are research needs to be addressed in the future: 

 Demography – age-specific survivorship (juveniles) and age-specific fecundity 

 Epidemiology 

 Impacts – particularly road densities 

 Effectiveness of actions - signal of failure of management agencies 

NOTE: There was a suggestion to evaluate the effects of road density by looking at the clustering 

of live and dead animals and its correlation to road density. This analysis could be finished by the 

end of the year. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 227 

Discuss gaps in research (on a per DWMA basis) 

The following is an evaluation of research in terms of answering questions important to the species: 

3.a. Baseline data on tortoise density both inside and outside DWMAs – 

Comments: The term baseline was used because the intention was for comparisons to be 

made inside and outside of DWMAs. The term baseline is no longer appropriate. In addition, the 

wording should be changed managed and non-managed areas. Differences between these areas 

should be assessed with hypothesis driven testing. 

3.b. Develop a comprehensive model of desert tortoise demography in the Mojave region 

and within each DWMA 

Comments: This research need has not been fulfilled due to failures of technology and the lack 

of necessary data. This model should be broken down into manageable component parts. For 

example, each component would be a different size/age class. This need should also include a 

spatial and temporal natural change component. This research need emphasizes the need for data 

sharing, appropriate statistical consultation, and accountability. 

3.b.2. Research of sources of mortality and their representation of the total mortality,
 

and including human natural predation, diminishment of required resources
 

 3.b.2a.Initiate epidemiological studies of URTD and other studies 

3.b.3 Research recruitment and survivorship of younger age classes 

Comments: Researchers should focus on understanding population structure, including the 

spatial scale of both genetic and demographic processes. In addition, studies should be done to 

determine the extent to which DWMAs and recovery units to conform to natural population 

subdivisions. 

Additional comments on the organization of 3.b.: 

 Research sources of mortality (including disease), fecundity, survivorship, recruitment, 

migration for a demographic model 

o	 Include Recruitment and mortality by stage 

o	 Include fecundity for whole system 

o	 Suggestions to use the Lefkowich model 

o	 Incorporate differences between age, stage, and size 

o	 Include possible differences between individual DPS units 

o	 Suggestion to include density in the model? 

3.c Long term research on impacts of grazing, road density, barriers, human use levels, 

restoration, augmentation, and translocation. 

Comments: This particular research need should be separated into positive and negative 

impacts (i.e. threats and effectiveness of protective measures). Therefore, restoration, augmentation, 

and translocation should be moved to 3.d. There was a suggestion to produce a new list of impacts 

to study based on the correlated clusters of threats. These research needs should also include a 

spatial and temporal component. Impacts should not be tested only comparatively (e.g. grazing/nongrazing). Research should also separate the effectiveness of a DWMA and the effectiveness of 

individual management actions. This is particularly important because management is not 

consistent within or across DWMAs. 

3.d	 Assess the effectiveness of protective measures in reducing anthropogenic impacts 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 228 

3.e Collect data on spatial variability of climate and productivity of vegetation 

Comments: The spatial component of this research need should spread to other 

recommendations. There was a suggestion of include the impacts of global climate change in this 

recommendation. Another suggestion was to improve the wording of this section by including with 

and without threats. Modeling should be included in this section as well. This research need does 

not stand alone, and should be used for appropriate modeling and assessing threats in the 

appropriate contexts. 

3.f Long-term research on the nutritional and physiological ecology of various age-size 

classes 

Comments: A good amount of research has been done in response to this research need. 

However, there should be an attempt to link this research to threats. 

3.g Conduct research on reproductive behavior and physiology, focusing on requisites for 

successful reproduction 

Comments: This research need should also be discussed in the context of understanding 

threats. 

ACTION – Dr. Tracy will develop a conceptual demographic model using ideas conveyed during 

this meeting. 

What are the recommended additions to the research needs list? 

1.	 Development of new technologies that will be important to studying tortoises in the future 

 Repair of technology challenged areas and improve survey techniques 

o	 Harmonic radar 

o	 Hyperspectral imaging 

o	 Remote sensing and GIS 

2.	 Threats to habitat and tortoises (i.e. invasion of weeds, etc.): 

 Include integration of impacts of the threat to habitat and to tortoises 

 Separate for direct and indirect threats 

3.	 Habitat monitoring: 

 Habitat modeling technology (including needed data) is a possibility to support research in 

habitat monitoring over the long term. 

 Provide specific ways to understand the mechanisms behind why tortoises exhibit changes 

in aerial extent. 

 Provide a list of what is necessary to monitor habitat. 

ACTION – Ken Nussear will draft the characteristics for habitat monitoring. 

4. Target further delineation of DPS units 

Behavior
 

Genetics (nuclear DNA)
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 229 

Friday, October 3 

Presentation on the beginning of a correlation threat matrix 

The DTRPAC used a rough draft of a correlation threat matrix, which was presented by Dr.
 

Boarman and Dr. Heaton, as an exercise to tally how often different threats occur. Without
 

statistics, it is still possible to assign correlations between threats per DPS unit. The DTRPAC 

should be able to make recommendations on how to use this matrix per DPS. There was a 

suggestion to also include environmental stressors (uncontrollable environmental effects) to the
 

matrix.
 

This matrix was presented in a flow chart format. The following is an example of how to follow the
 

flow chart:
 

Direct effects (crush, predation (ravens, coyotes, feral dogs), human removal, burning) 

anthropogenic effects that may cause these (construction, landfills, roads, non-motorized, grazing,
 

mining). Note: These anthropogenic effects are in no particular order of importance.
 

The DTRPAC discussed the difference between direct and indirect effects. A suggestion was made
 

to instead look at the factors and changes harms tortoises (mortality, malnutrition, lower 

reproductive fitness). There was a suggestion to collapse factors that have similar effects. Another
 

suggestion was to give each effect an individual box (e.g. landfill). By counting the number of
 

arrows coming from each box, and the thickness or length of arrows (to emphasize magnitude of
 

the effect), the strength and magnitude of correlation could be graphically represented. Other 

suggestions included proposing a hypothesized mechanism to better support arguments, to show
 

correlations in terms of the harm effect and spatial differences (geographically specific), and to
 

include a hierarchical component that would show the outcomes for the population at the bottom of
 

the diagram.
 

Time constraints may hinder the ability of the team to produce an entire matrix, however, the team
 

should be able to put together a protocol on how to do this process for each DPS. This matrix
 

should focus on population, rather than individual effects. There was a suggestion to use broken
 

arrows when effects of a possible threat are unknown and where hypothesis driven experiments
 

need to be done at the population level.
 

One member noted the importance of recognizing that if direct effects are removed, indirect effects
 

have not necessarily been removed in space and time.
 

This type of diagram will emphasize the concept of addressing multiple threats simultaneously.
 

These network diagrams will help tease out synergistic, cumulative effects of threats. In addition
 

the network should address within habitat effects (mortality and fecundity) and the effects of losing
 

habitat (absolute aerial extent). Providing a combination of this network and a list of threats for 

each DPS to accompany the rhetoric of the report will fortify the DTRPAC’s argument for the 

“death of several cuts.” 

ACTION – Dr. Boarman, Dr. Heaton, and Dr. Delehanty will continue to work on this network to
 

include as a recommendation in the final report.
 

Research needs that resulted from this exercise:
 

All threats need to be addressed at the population level. All explanations for this should include a
 

common sense scenario. For example, the Texas tortoise lives in a higher productivity area and
 

reaches age of reproduction earlier. Therefore, the number of individual deaths can be high, and the
 

population will rebound more easily. However, the desert tortoise does not have these same life
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 230 

history and habitat characteristics. As a result, the same amount of individual mortality may be 

having a much more noticeable effect. 

Presentations on conservation planning in CA, NV, AZ, and UT 

Clark County Multi-Species Habitat Conservation Plan (MSHCP): 

Ron Marlow presented on the Clark County MSHCP. In general, habitat conservation plans 

(HCPs), authorized under Section 10 of the ESA, allow parties to avoid prohibitions on take under 

Section 9 of the ESA. For the most part, HCPs are carried out on a small scale, and are concerned 

with private parties. Clark County’s plan proposes to mitigate take on private land by managing 

public lands. The land was broken down into levels of management intensity. Intensively managed 

areas could be enhanced via payment to federal land managers to improve prospects of tortoise 

habitat. For example, one action taken by Clark County was to purchase grazing permits, resulting 

in the elimination of most grazing. In addition, certain highways that were identified as threats to 

tortoises were fenced as an MSHCP requirement. 

In Clark County, take of desert tortoises occurs on private and public land. Funding for 

conservation is both federal and non-federal. The MSHCP has a broad base public support and 

requires science-based adaptive management. This HCP has been viewed as an experiment to 

determine if this type of process results in implementation of the recovery plan. In addition, the 

MSHCP is a test for land managers to determine if independent science and stakeholders can both 

be involved in the decision making process. 

Requirements for Clark County in the HCP: 

 Permit conservation actions – public information and education; tortoise pick up and 

holding; rehabilitation and enhancement of habitat; construction tortoise barriers; 

translocation; science based adaptive management 

 Requirements for research (tortoise only) – translocation, survivorship, density, and stress. 

 Law enforcement - ACEC protection and management, predator control, conservation 

easement management, development of site conservation management plans 

A question was posed as to whether the recovery plan should address efficacy of HCPs. A 

suggestion was made to document advantages and disadvantages of how HCPs are being 

implemented in terms of the recovery plan. 

A DTRPAC member asked how adaptive management has been working for the Clark County 

MSHCP. The process of adaptive management has just barely begun. Management is occurring on 

an action-by-action basis, and there is reluctance and resistance for cooperation between federal 

mangers and Clark County. 

Washington County HCP 

Ann McLuckie presented on the Washington County HCP. The county obtained an incidental take 

permit in 1996 for over 1,000 animals and over 40,0000 known and potential tortoise habitat. The 

Red Cliff reserve (60,000 acres) includes 38,000 acres of tortoise habitat. The reserve is divided 

into 4 different zones, which several contain human use levels, and a translocation site. The reserve 

is close to urbanized areas and is divided by a highway. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 231 

Reserve management: 

Within the Red Cliff reserve, the following management actions have been taken: 

 Grazing permits have been retired 

 Habitat acquisition 

 Majority of areas have been fenced (tortoise fencing, people-proof/dog-proof, range fence 

to prevent OHVs) 

 Public use plan has been designed (trails, signs, human use monitoring program) 

 Multi-agency law enforcement to eliminate illegal OHV use, reduce vandalism, and reduce 

illegal collection. 

 Education 

 Translocation (Zone 4) - a short term study of the efficacy of translocation found it to be a 

good management tool 

 Population monitoring – density and long term trends using distance sampling transects, in 

addition to population structure, sex ratios, and survivorship estimates 

The Washington County HCP has an adequate funding mechanism, a broad base of players, and 

a reserve design based on biology. However, the reserve currently faces multiple threats 

including, drought, utility development and maintenance, habitat degradation and trail 

proliferation, and no forum for science-based adaptive management. As a result, concerns 

include, 1) the role of the technical committee is not well defined, 2) additional 

pressure/impacts created on the other species and habitat outside the reserve, and 3) general 

challenges of managing an urban reserve. 

California Conservation Plans 

Ray Bransfield presented on three large planning efforts led by the BLM: 1) North and East Mojave 

2) North and East Colorado, and 3) West Mojave. The following chart summarizes the major 

information on each plan. 

North and East Mojave North and East 

Colorado 

West Mojave 

Status Records of decision Record of Decision EIS 

Litigation Complaints filed Complaints filed ? 

DWMA Designated (BLM DWMAs 

are not a 1000 mi^2) 

Designated Proposed 

Vehicles Access Dual sport events are allowed in DWMAs – seasonal and only on roads 

No speed events in DWMAs 

Route designation is complete and proposed in the Western Mojave 

Travel will be open in certain washes 

In CA vehicles can travel 50 ft. from the center line to park, camp 

Land Status Mostly federal Mostly federal 50% private 

(introduces level of 

complexity) 

Land fills Not allowed in DWMAs 

Agriculture Not allowed in DWMAs 

Military No habitat destructive military activities 

Grazing Willing seller – willing buyer close allotment (no sheep grazing) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 232 

Burros Management goal is zero burros 

Guns Hunting per code and target shooting ok 

Ravens Target offending birds 

Reduce and remove subsidies 

Environmental assessment in preparation 

Start next spring 

More aggressive program in the West Mojave 

Fence roads Discussion about fencing roads before projects; current FG policy is causing a 

slight problem 

The following is additional information on the West Mojave Plan: 

 The proposed DWMAs include almost all critical habitat. 

 The BLM is proposing that no ground disturbance will exceed 1% within DWMAs; 

continual restoration of habitat will reduce the level of disturbance to 1%. 

 General areas will also be protected for the Mojave ground squirrel, which will benefit 

desert tortoises. 

 Projects funds will be used to buy additional private land. 

 Tortoises will not be collected prior to development; however, there will be a hot line to 

collect tortoises during development actions. 

 The West Mojave Plan is multi-species and will span several counties. 

After the HCP presentations, the DTRPAC returned to the charge of the committee, which is to 

evaluate plan based on current knowledge of HCPs. There was a suggestion that HCPs should have 

an evaluative process by a science team. Additionally, hypothesis based research should be used to 

evaluate the successes and failures of HCP actions. The DTRPAC should highlight the need for 

constant science review and make a recommendation for independent (outside) science review. 

Science should inform the initial decision to take a management action and then also evaluate the 

effectiveness of the action. Moreover, for all large planning efforts, there should be a 

recommendation to build science review into the recovery plan for HCPs. In addition to science 

review, there should be coordination among HCPs because of the large scale of these plans. 

Although each plan may be acceptable individually (compromises made in each), a comprehensive 

review of all HCPs may reveal unsatisfactory levels of management. 

Presentation on DMG recovery proposal 

John Hamill presented on the Desert Management Group Proposed Recovery Action Program 

(RAP) and asked for a DTRPAC review of the proposal. There was concern that the 

implementation of RAP may be premature before the review of the recovery plan was complete. 

Additionally, the DMG does not want actions to be inconsistent with the new recovery plan. The 

focus of this review is to determine if the RAP is consistent with best available scientific 

information and to ask for DTRPAC recommendations to improve the RAP. 

Within CA, desert tortoise recovery is addressed by 10 plans. The geographic scope of the RAP is 

the entire CA desert, and the program will be an integrated effort with the MOG. 

The goal of the RAP is to reconcile compatible human uses and recovery of the desert tortoise. The 

RAP is based of the principles of sound science, adaptive management, and stakeholder 

involvement. The DMG, which includes all principle land and resources management agencies, and 

the Regional Executive Management Group will manage the program. These groups will sign an 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 233 

MOU, work together on policy guidance, approve a work plan, and continue to engage in active 

coordination. 

The desert tortoise management framework will include public and stakeholder involvement in the 

form of NEPA compliance. The program will be based on the following basic foundation elements: 

1) annual work planning process to increase collaboration and be more cost effective, 2) science 

support to provide adaptive management standards and guidance, 3) data management, including 

central data repository with appropriate protocols that will be coordinated with other states in the 

range, 4) desert tortoise monitoring, including a commitment to improve and continue distance 

sampling and to integrate distance sampling and study plots, and 4) education and outreach to 

promote individual responsibility for desert tortoise protection. 

The first recovery actions that will be addressed by the RAP will be those that require interagency 

coordination for effective implementation. These will include management of ravens, feral dogs, 

disease, head starting, and translocation. Each element will have identified areas of management. 

The following were DTRPAC comments and clarifications on the CA RAP: 

DTRPAC members emphasized the need for coordination both among government agencies and 

between states within the desert tortoise range. 

 Given the scope of the West Mojave plan, the RAP should work to provide coordination 

with range-wide plans. Additionally, USFWS should clarify how all plans should 

coordinate. 

 Collaboration will be necessary for head starting to avoid anecdotes dominating evaluation 

of successes or failures. 

 Coordination, data sharing, regular science oversight, and scientific assessment of 

effectiveness are all key components to the success of the RAP.
 

 Focus on interagency coordination as the reason for the actions that were chosen 

DTRPAC members also highlighted some possible changes for recovery actions. 

 Specific techniques listed for monitoring should be able to be revised in the future. 

 Disease should be studied in relation to how it will effect head starting and translocation 

 Consultation with statisticians and expert in research design will be necessary to answer 

questions for projects that have range-wide implications. 

 Short-tem and long-term evaluation should be made explicit in all sections of the RAP. 

ACTION: Dr. Heaton will present the outcome of the DTRPAC meeting at the DMG meeting on 

October 8th . 

Outline of the DTRPAC report to the USFWS: 

Introduction: 

 Sections from the 1994 recovery plan that put forth a process for reviewing the plan every 

3-5 years (Tracy) 

 Sections from the DTRPAC proposal on the process of recovery plan review (Tracy) 

 The importance of turtles to ecosystems and some natural history (Morafka) 

 The DTRPAC’s opinion of the original recovery plan and a synopsis on data collected 

since 1994 (types of data used, rate of change in publications, etc. (Boarman) 

 Explanation of what the report is not 

o	 Not a recovery plan, 

o	 Not a statement on political or social actions 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 234 

o	 Not a generation of new data, 

o	 Not generated to perform new management actions) 

 Explanation of what the report is (a strategic overview, rather than a tactical overview) 

 Acknowledgement of those who were invited speakers and experts (thank them as well) 

and non-team members who consistently came to meetings (managers, etc.), and those who 

provided data 

Distinct Population Segments (changes to listings) 

 Deemphasize old categories and emphasize new categories 

 Justifications for the West Mojave including data on annual differences east and west of the 

Baker sink (rainfall and temperatures) (Tracy figure) 

 Fortify West Mojave arguments with literature (Berry, Wallace, Germano, Weinstein) 

 Maps for the old recovery units and the new recommended DPSs (Heaton) 

 Revision of draft document by Morakfa, McCoy, and Tracy 

Status and Trends (range wide assessment) 

 Maps of all original plots, distance sampling transects, and TCS (Heaton) 

 Analyses of plot data (Nussear) 

 Kernel and cluster analyses – distance sampling and total corrected sign (refinement needed 

for the West Mojave) (Nussear and Heaton) 

 Table of Distance sampling estimates (Medica) 

 Methods section about how data were acquired and cluster analyses (Heaton) 

 Methods section on kernel and regression analyses (Nussear) 

 History of distance sampling (Medica) 

 History of permanent study plots (Murray) 

 Spatial component of data 

 Conventional status based on data and Organization of this section (Murray) 

Threats and disease: 

 Proper context of disease, modern thinking, cause and effect (McCoy) 

 What is proper data collection on the population level for these issues? Capture differences 

in effects on individuals and effects on populations (McCoy) 

 Acknowledge tactical report that will be concurrent (Disease workshop) 

 Multiple, interacting, and synergistic effects 

 Network diagram of threats (Boarman, Heaton, Delehanty) 

 Distill Boarman Threats report 

 Lead - Boarman and McCoy 

Monitoring: 

 Lead - Delehanty and Tracy 

 Multiscale monitoring approach (Peterson advice) 

 Habitat, threats, and tortoise population monitoring 

Planning and Coordination: 

 Interface of Science and Management 

 Elements that should be included in HCPs and other conservation plans (Murray) 

o	 Science based adaptive management 

o	 Hypothesis-driven experiments to assess efficacy of management actions 

 Data sharing and outside scientific review (tie in information from other sections) 

(Delehanty)
 

 Recapture recommendations from other programs (spotted owl program) (Delehanty) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report	 page 235 

 Lead – Murray 

Research: 

 Introduction to this section will be a summary of past research in relation to the recovery 

plan (Boarman) 

 Significant recommendations in the original recovery plan that have not been heeded 

(Boarman, Medica) 

 Suggestion for a master plan of research – Florida example (McCoy and Morafka) 

 Gaps in research from each section – each section writer will note research gaps for this 

section 

 Research needs from original recovery plan (DTRPAC checklist) 

 Importance of interdisciplinary approaches and coordination (Morafka) 

Summary of overarching recommendations: 

 Recommendation for a new recovery team 

 Changes in the recovery plan 

 Change in listing of the West Mojave population (endangered status) and why 

 Keep a list of recommendations from each section 

ACTION: Ken Nussear and Dr. Heaton will make sure that all maps will be put on the website for 

the group to access while writing. 

ACTION: As DTRPAC members make progress, they will email sections to all DTRPAC 

members. 

Preparation for possible November DTRPAC meeting and remaining tasks 

November 6-7th in Las Vegas, NV (Bob Williams will make meeting preparations.) 

o	 Final wrap up and reviewing all writing sections 

o	 If necessary, there will be a final DTRPAC meeting in San Francisco (Jan 12-13th). 

Meeting participants: 

C. Richard Tracy, UNR 

Bridgette Hagerty, UNR 

Ken Nussear, UNR 

David Delehanty, ISU 

Roy Averill-Murray, AFG 

Bill Boarman, USGS 

Phil Medica, USFWS 

Jill Heaton, U. Redlands 

Earl McCoy, USF 

Ann McLuckie, UFG 

Ray Bransfield, USFWS 

Dave Morafka, CA Academy of Sciences 

Brian Manly, representative for QUAD 

Clarence Everly, DOD 

Ron Marlow, UNR 

John Hamill, DOI 
 

 

 

 

 

DTRPAC Report page 236 

“It is the desire for explanations that is at once systematic and 

controllable by factual evidence that generates science; and it is the 

organization and classification of knowledge on thee basis of 

explanatory principles that is the distinctive goal of the sciences.” 

Ernest Nagel, The Structure of Science. (1961) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DTRPAC Report page 237 

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Slope trend plot. Report to Bureau of Land Management, Arizona Strip District, St. George, Utah. 

Anderson, D.R., and K.P. Burnham. 1996. A monitoring program for the desert tortoise Colorado 

Cooperative Fish and Wildlife Research unit, Colorado State University, Fort Collins, CO. 15pp. 

Anderson, D.R., K.P. Burnham, B.C. Lubow, L. Thomas, P.S. Corn, P.A. Medica, and R.W. 

Marlow. 2001. Field trials of the line distance method applied to estimation of desert tortoise 

abundance. Journal of Wildlife Management 65: 583-597. 

Allen, T.F.H. and T.W. Hoekstra. 1992. Toward a unified ecology. Columbia University Press, 

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