U.S. Department of the Interior

U.S. Fish & Wildlife Service

Region 8, California and Nevada

Ecological Services

2800 Cottage Way, W-2606

Sacramento, California 95825

http://www.fws.gov

May 2008
Draft Revised Recovery Plan 

for the Mojave Population of the 

Desert Tortoise (Gopherus agassizii)

Region 8, California and Nevada 

U.S. Fish and Wildlife Service 

Sacramento, California 

Approved: ___________________________________________ 

Region 8 Director 

U.S. Fish and Wildlife Service 

 Date: ___________________________________________ 

Disclaimer 

Recovery plans delineate reasonable actions that are believed to be required to recover 

and protect listed species. We, the U.S. Fish and Wildlife Service, publish recovery plans, 

sometimes with the assistance of recovery teams, contractors, State agencies, Tribal agencies, 

and other affected and interested parties. Objectives will be attained and any necessary funds 

made available subject to budgetary and other constraints affecting the parties involved, as well 

as the need to address other priorities. Recovery plans do not obligate other parties to undertake 

specific actions and may not represent the views nor the official positions or approval of any 

individuals or agencies involved in recovery plan formulation, other than our own. They 

represent our official position only after they have been signed by the Regional Director or 

Director as approved. Recovery plans are reviewed by the public and submitted to peer review 

before we adopt them as approved final documents. Approved recovery plans are subject to 

modification as dictated by new findings, changes in species status, and the completion of 

recovery actions. 

LITERATURE CITATION OF THIS DOCUMENT SHOULD READ AS FOLLOWS: 

U.S. Fish and Wildlife Service. 2008. Draft revised recovery plan for the Mojave population of 

the desert tortoise (Gopherus agassizii). U.S. Fish and Wildlife Service, California and 

Nevada Region, Sacramento, California. 209 pp. 

Additional copies may be obtained from: 

Field Supervisor 

Nevada Fish and Wildlife Office 

U.S. Fish and Wildlife Service 

1340 Financial Boulevard, Suite 234 

Reno, Nevada 89502 

On-line: http://www.fws.gov/endangered/recovery/index.html#plans 

i 
PLAN PREPARATION 

This Recovery Plan was prepared by the Desert Tortoise Recovery Office in coordination 

with the Desert Tortoise Science Advisory Committee and the Redlands Institute at the 

University of Redlands. 

Desert Tortoise Recovery Office 

Roy C. Averill-Murray, Jody Fraser, Kimberleigh Field, Linda Allison, Cat Darst, Sandy 

Marquez 

Science Advisory Committee

Kristin Berry, U.S. Geological Survey; Peter Hudson, Penn State University; Earl McCoy, 

University of South Florida; Katherine Ralls, Smithsonian Institution; Michael Reed, Tufts 

University; Robert Steidl, University of Arizona; C. Richard Tracy, University of Nevada-Reno. 

Redlands Institute 

Jordan Henk, Lisa Benvenuti, Paul Burgess, Monica Hally, Thomas Leuteritz, Naicong Li, Philip 

Murphy (Infoharvest), Serene Ong, Nathan Strout 

ACKNOWLEDGMENTS 

The U.S. Institute for Environmental Conflict Resolution, the Center for Collaborative 

Policy, and two Desert Tortoise Management Oversight Group recovery planning workgroups 

provided extensive assistance and input into the development of the revised recovery plan. 

U.S. Institute for Environmental Conflict Resolution 

Mike Eng, Joan Calcagno, Pat Lewis 

Center for Collaborative Policy, California State University-Sacramento 

Austin McInerny, Greg Bourne, Dale Schafer 

Arizona-Nevada-Utah Working Group 

Arizona Game and Fish Department: Cristina Jones 

Bureau of Land Management: Bob Douglas, Elroy Masters, Richard Spotts 

Clark County: Marci Henson, Sue Wainscott 

Lake Mead National Recreation Area: Ross Haley 

Mohave County: Buster Johnson 

Nevada Department of Wildlife: Polly Conrad, Cris Tomlinson 

Quadstate County Government Coalition: Bill Lamb 

University of Arizona: Rob Grumbles 

University of Nevada-Reno: Maria Ryan 

Southern Utah University: Nicole Frey 

U.S. Fish and Wildlife Service: Michael Burroughs, Renee Chi, Jeff Servoss 

U.S. Geological Survey: Phil Medica 

Utah Division of Wildlife Resources: Ann McLuckie 

ii 
Washington County: Bill Mader 

California Working Group 

Bureau of Land Management: Mark Massar, Russell Scofield 

California Department of Fish and Game: Rebecca Jones 

Joshua Tree National Park: Paul DePrey 

Mojave Desert Ecosystem Program: Clarence Everly 

Mojave National Preserve: Larry Whalon 

Quadstate County Government Coalition: Gerry Hillier 

University of California-Davis: Karl MacArthur 

U.S. Fish and Wildlife Service: Brian Croft 

U.S. Geological Survey: Kristin Berry 

U.S. Marine Corps: Brian Henen, Manual Joia 

The following individuals contributed materially to one or more Science Advisory 

Committee meetings: M. Brown, University of Florida; T. Esque, L. Gass, K. Nussear, and K. 

Phillips, U.S. Geological Survey; B. Hagerty, J. Heaton, K. Hunter, and F. Sandmeier, University 

of Nevada-Reno; and B. Murphy, Royal Ontario Museum. 

In addition to previously named individuals, the following people participated in recovery 

planning workshops, provided comments, or otherwise contributed to the Recovery Plan: 

Bureau of Indian Affairs: D. Wooten 

Bureau of Land Management: S. Borchard, R. Clementsen, S. Florence, M. Herder, L. LaPre, E. 

Lorentzen, C. Ronning, A. Styles 

California Department of Fish and Game: S. Harris, S. Juarez, B. Kinney, T. Moore, D. Racine 

California Department of Transportation: A. Manee 

California – Imperial, Kern, and San Bernardino counties: W. Leimgruber, D. Maben, J, 

McQuiston, B. Mitzelfelt, R. Scott 

Department of Defense: A. Bedlion, S. Collis, M. Hagan, T. Mull (Tybrin Corp.), D. Reinke, C. 

Rognan, B. Turner, R. Wood 

Kaibab Paiute Tribe: C. Bulletts, L. Skrzynski 

National Park Service: N. Darby, D. Hughson, A. Staley, M. Vamstad 

Nevada - Clark and Nye counties: L. Bice, M. Hamilton, P. Kiakopoulos, S. Kokos, M. Henson, 

T. Wheaton 

Smithsonian Institution: R. Fleischer, E. Latch, and the genetics discussion group 

Southern Nevada Water Authority: A. Bennett, C. Doyle 

U.S. Fish and Wildlife Service: R. Bransfield, D. Elam, M. Fris, P. Henson, J. Hohman, J. 

Krueger, J. McBride, J. Rorabaugh, A. Salveter, S. Spangle, R. Williams 

Utah - Washington County: A. Gardner 

Private individuals and non-governmental organizations: I. Anderson, L. Belenky, M. Brower, 

M. Connor, C. Doyle, T. Egan, T. Frewin, B. Haley, B. Hughes, P. Kahn, J. McDonnell, 

M. McDonnell, J. McGarvie, J. Moore, C. Oathout, K. Ostler, J. Pantuso, E. Phillips, L. 

Rivera, D. Schaffy, M. Skuja, C. Sprofera, Y. Takagi, C. Vargas, C. Wilkerson 

iii 
iv
EXECUTIVE SUMMARY

CURRENT SPECIES STATUS 

The Mojave population of the desert tortoise (Gopherus agassizii) (all tortoises north and 

west of the Colorado River in Arizona, Utah, Nevada, and California) was listed as Threatened 

on April 2, 1990. A recovery plan was published in June 1994 together with a supplement 

identifying proposed Desert Wildlife Management Areas. Critical habitat was also designated in 

1994 in all four states supporting the species. Based on information in this recovery plan, the 

recovery priority number is classified as 6C and is predicated upon a) a high degree of threat, 

which has increased since 1994; b) a low potential for recovery, based on current uncertainties 

about various threats and our ability to manage them; c) listed population below the species 

level; and d) potential conflict with development or other forms of economic activity (USFWS 

1983). We anticipate that implementation of this revised recovery plan will resolve key 

uncertainties about threats and management, thereby improving recovery potential. 

HABITAT REQUIREMENTS AND LIMITING FACTORS 

Desert tortoises occupy a variety of habitats from flats and slopes dominated by Larrea 

tridentata (creosote bush) scrub at lower elevations to rocky slopes in Coleogyne ramosissima 

(blackbrush) and Juniperus spp. (juniper) woodland ecotones at higher elevations. Desert 

tortoises occur from below sea level to an elevation of 2,225 meters (7,300 feet). Throughout 

most of the Mojave Desert, tortoises occur most commonly on gently sloping terrain with sandygravel soils and where there is sparse cover of low-growing shrubs, which allows establishment 

of herbaceous plants. Soils must be friable enough for digging of burrows, but firm enough so 

that burrows do not collapse. Typical habitat for the desert tortoise in the Mojave Desert has 

been characterized as Larrea tridentata scrub where precipitation ranges from 5 to 20 

centimeters (2 to 8 inches), the diversity of perennial plants is relatively high, and production of 

ephemerals is high. 

The vast majority of threats to the desert tortoise or its habitat are associated with human 

land uses. The threats identified in the 1994 Recovery Plan, and that formed the basis for listing 

the tortoise as a threatened species, continue to affect the species. However, despite clear 

demonstration that these threats impact individual tortoises, there are few data available to 

evaluate or quantify the effects of threats on desert tortoise populations. While current research 

results can lead to predictions about how local tortoise abundance should be affected by the 

presence of threats, quantitative estimates of the magnitude of these threats, or of their relative 

importance, have not yet been developed. Thus, a particular threat or subset of threats with 

discernable solutions that could be targeted to the exclusion of other threats has not been 

identified for the desert tortoise. In this revised recovery plan, we underscore the need to build on 

our understanding of individual threats, yet place new emphasis on understanding their multiple 

and synergistic effects due to the failure of simple threat models to inform us about tortoise 

abundance. 

v 
 

The desert tortoise requires 13-20 years to reach sexual maturity, has low reproductive 

rates during a long period of reproductive potential, and individuals experience relatively high 

mortality early in life. These factors make recovery of the species difficult. Even moderate 

downward fluctuations in adult survival rates can result in rapid population declines. Thus, 

high survivorship of adult desert tortoises is critical to the species’ persistence, and the slow 

growth rate of populations can leave them susceptible to extirpation events in areas where 

adult survivorship has been reduced. Another factor integral to desert tortoise recovery is 

maintaining the genetic and ecological variability within and among populations to allow 

tortoises to adapt to changes in the environment over time. Because desert tortoises occupy 

large home ranges, the long-term persistence of extensive, unfragmented habitats is essential 

for the survival of the species. The loss or degradation of these habitats to urbanization, habitat 

conversion from frequent wildfire, or other landscape-modifying activities place the desert 

tortoise at increased risk of extirpation. 

RECOVERY STRATEGY 

The 1994 Recovery Plan described a strategy for recovering the desert tortoise, which 

included the identification of six recovery units, recommendations for a system of Desert 

Wildlife Management Areas within the recovery units, and development and implementation of 

specific recovery actions. Maintaining high survivorship of adult desert tortoise was identified 

as the key factor in recovery. We recognize that the most significant challenge in the 

implementation of the 1994 Recovery Plan was not the number or types of actions implemented, 

but rather the coordination, description, documentation and evaluation of implementation of the 

actions. As a result, the revised strategy emphasizes partnerships to direct and maintain focus on 

implementing recovery actions and a system to track implementation and effectiveness of 

recovery actions. Strategic elements within a multi-faceted approach designed to improve the 

1994 Recovery Plan are: 

1. Develop, support, and build partnerships to facilitate recovery. 

2. Protect existing populations and habitat, instituting habitat restoration where necessary. 

3. Augment depleted populations in a strategic manner. 

4. Monitor progress toward recovery. 

5. Conduct applied research and modeling in support of recovery efforts within a strategic 

framework. 

6. Implement a formal adaptive management program. 

The Desert Tortoise Management Oversight Group will be the partnership (Element 1) 

responsible for providing “executive-level” support and direction for recovery implementation, 

thus tying the entire program together. Regional Recovery Implementation Teams will include a 

member of the Desert Tortoise Recovery Office to provide guidance and coordination to 

vi 
land/wildlife managers and stakeholders on the teams, which will be responsible for developing 

step-down recovery-action plans and implementing those actions on the ground. The adaptive 

management program (Element 6) provides a formal framework with which the partnerships can 

make better, more informed, and more explicit decisions. Through the partnership and adaptive 

management elements, habitat management (Element 2) and population augmentation (Element 

3) actions will be prioritized, implemented, and reported. Aggressive management needs to be 

applied within existing tortoise conservation areas, as defined herein, or other important areas 

identified by Recovery Implementation Teams. Monitoring (Element 4) effects of these specific 

actions, as well as progress toward overall recovery, will again feed into the adaptive 

management system and inform managers on recovery progress. Finally, applied research and 

modeling (Element 5) will help us better understand desert tortoise ecology and better define our 

expectations of management actions. 

RECOVERY GOALS, OBJECTIVES, AND CRITERIA 

The goals of the recovery plan are recovery and delisting of the desert tortoise. The 

recovery criteria represent our best assessment of the conditions that would most likely result in 

a determination that delisting of the desert tortoise is warranted. Recovery criteria should ideally 

include the management or elimination of threats, addressing the five statutory (de-)listing 

factors. However, even though a wide range of threats affect desert tortoises and their habitat, 

very little is known about their demographic impacts on tortoise populations or the relative 

contributions each threat makes to tortoise mortality. Therefore, specific and meaningful threatsbased recovery criteria cannot be identified at this time. In the meantime, we assume that threat 

mitigation will have been successful if the current recovery criteria have been met (taking into 

consideration any head-starting or translocation efforts). Specific recovery actions, including 

research, must be implemented to identify sets of threats that contribute to a greater number of 

mortality mechanisms or affect size structure or fecundity. As quantitative information on threats 

and tortoise mortality is obtained, more specific threats-based recovery criteria may be defined 

during future recovery plan review and revision. 

Recovery Objective 1 (Demography). Maintain self-sustaining populations of desert tortoises 

within each recovery unit into the future. 

Recovery Criterion 1. Rates of population change (λ) for desert tortoises are increasing 

(i.e., λ > 1) over 25 years (a single tortoise generation), as measured 

a) by extensive, range-wide monitoring across tortoise conservation areas within each 

recovery unit, and 

b) by direct monitoring and estimation of vital rates (recruitment, survival) from 

demographic study areas within each recovery unit. 

Recovery Objective 2 (Distribution). Maintain well-distributed populations of desert tortoises 

throughout each recovery unit. 

vii 
Recovery Criterion 2. Distribution of desert tortoises throughout each tortoise 

conservation area is increasing over 25 years (i.e., ψ > 0). 

Recovery Objective 3 (Habitat). Ensure that habitat within each recovery unit is protected and 

managed to support long-term viability of desert tortoise populations. 

Recovery Criterion 3. The quantity of desert tortoise habitat within all desert tortoise 

conservation areas is maintained with no net loss until tortoise population viability is 

ensured. When parameters relating habitat quality to tortoise populations are defined and 

a mechanism to track these parameters established, the condition of desert tortoise habitat 

should also be demonstrably improving. 

RECOVERY ACTIONS 

The recovery actions for each strategic element are as follows: 

1. Develop, Support, and Build Partnerships to Facilitate Recovery 

1.1. Establish regional, inter-organizational Recovery Implementation Teams to prioritize 

and coordinate implementation of recovery actions. 

2. Protect Existing Populations and Habitat 

2.1. Protect intact desert tortoise habitat. 

2.2. Reduce factors contributing to disease (particularly upper respiratory tract disease). 

2.3. Establish/continue environmental education programs. 

2.4. Increase law enforcement. 

2.5. Restrict, designate, close, and fence roads. 

2.6. Restore desert tortoise habitat. 

2.7. Install and maintain urban or other barriers. 

2.8. Sign and fence boundaries of sensitive or impacted areas. 

2.9. Secure lands/habitat for conservation. 

2.10. Restrict off-highway vehicle events within desert tortoise habitat. 

2.11. Connect functional habitat. 

2.12. Limit mining and minimize its effects. 

2.13. Limit landfills and their effects. 

2.14. Reduce excessive predation on tortoises. 

2.15. Minimize impacts from horses and burros. 

2.16. Minimize livestock grazing. 

3. Augment Depleted Populations through a Strategic Program 

3.1. Develop protocols and guidelines for the population augmentation program, including 

those specific to head-starting and translocation. 

3.2. Identify sites at which to implement population augmentation efforts. 

3.3. Secure facilities and obtain tortoises for use in augmentation efforts. 

3.4. Implement translocations in target areas to augment populations using a scientifically 

rigorous, research-based approach. 

viii 
 

4. Monitor Progress toward Recovery 

4.1. Monitor desert tortoise population growth. 

4.2. Monitor the extent of tortoise distribution in each recovery unit. 

4.3. Track changes in the quantity and quality of desert tortoise habitat. 

4.4. Quantify the presence and intensity of threats to the desert tortoise across the 

landscape. 

5. Conduct applied research and modeling in support of recovery efforts within a strategic 

framework 

5.1. Characterize stable age distributions of stable or increasing populations. 

5.2. Determine factors that influence the distribution of desert tortoises. 

5.3. Conduct research on the restoration of desert tortoise habitat. 

5.4. Improve models of threats, threat mitigation, and desert tortoise demographics. 

5.5. Conduct research on desert tortoise diseases and their effects on tortoise populations. 

5.6. Resolve population structure of the desert tortoise across its range. 

6. Implement an Adaptive Management Program 

6.1. Revise and continue development of a recovery decision support system. 

6.2. Develop/revise recovery action plans. 

6.3. Amend land use plans, habitat management plans, and other plans as needed to 

implement recovery actions. 

6.4. Incorporate scientific advice for recovery through the Science Advisory Committee. 

TOTAL ESTIMATED COST OF RECOVERY 

$159,000,000 plus additional costs that cannot be estimated at this time. 

DATE OF RECOVERY 

If recovery actions are implemented promptly and are effective, including continued 

implementation of the current monitoring program, recovery criteria could be met by 

approximately 2025. 

ix 
x
TABLE OF CONTENTS 

PLAN PREPARATION ............................................................................................................... ii 

ACKNOWLEDGEMENTS ......................................................................................................... ii 

EXECUTIVE SUMMARY .......................................................................................................... v 

BACKGROUND ........................................................................................................................... 1 

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

The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or 

Overutilization for Commercial, Recreational, Scientific, or Educational Purposes 

SPECIES DESCRIPTION AND TAXONOMY .....................................................................................4 

POPULATION TRENDS AND DISTRIBUTION ..................................................................................5 

LIFE HISTORY AND ECOLOGY .....................................................................................................9 

HABITAT CHARACTERISTICS.....................................................................................................10 

CRITICAL HABITAT ...................................................................................................................11 

REASONS FOR LISTING AND CONTINUING THREATS..................................................................13 

Range (Factor A)..........................................................................................................14 

(Factor B).....................................................................................................................15 

Disease or Predation (Factor C).........................................................................................15 

Inadequacy of Existing Regulatory Mechanisms (Factor D).............................................16 

Other Natural or Manmade Factors Affecting its Continued Existence (Factor E)...........17 

CONSERVATION EFFORTS ........................................................................................................ 18 

BIOLOGICAL CONSTRAINTS AND NEEDS .................................................................................. 30 

RECOVERY PROGRAM.......................................................................................................... 31

RECOVERY STRATEGY ............................................................................................................. 31 

RECOVERY UNITS .................................................................................................................... 38 

RECOVERY GOAL, OBJECTIVES, AND CRITERIA ....................................................................... 56 

RECOVERY ACTIONS................................................................................................................ 63 

IMPLEMENTATION SCHEDULE ......................................................................................... 87

LITERATURE CITED .............................................................................................................. 93

LIST OF FIGURES 

Figure 1. Desert tortoise critical habitat overlaid on the draft U.S. Geological Survey habitat 

model (Esque et al., in prep.)........................................................................................................ 12

Figure 2. Desert tortoise conservation areas................................................................................ 21

Figure 3. Additional land designations providing conservation benefits to the desert tortoise in 

relation to critical habitat and major highways............................................................................. 22

xi 
 

Figure 4. Schematic representation of strategic elements within the Desert Tortoise Recovery 

Program......................................................................................................................................... 37

Figure 5. Recovery units as delineated in the 1994 Recovery Plan............................................. 39

Figure 6. Ratio of rainfall in winter compared to summer in the Mojave Desert........................ 42

Figure 7. Revised recovery units for the Mojave population of the desert tortoise..................... 43

Figure 8. Upper Virgin River Recovery Unit .............................................................................. 44

Figure 9. Northeastern Mojave Recovery Unit............................................................................ 45

Figure 10. Eastern Mojave Recovery Unit .................................................................................. 47

Figure 11. Colorado Desert Recovery Unit ................................................................................. 49

Figure 12. Western Mojave Recovery Unit ................................................................................. 52

Figure 13. Example of hypothetical occupancy pattern............................................................... 61 

LIST OF TABLES 

Table 1. Summary of density estimates for each of the 1994-designated recovery units.............. 7 

Table 2. Critical habitat by state and land management .............................................................. 13 

Table 3. Climatic summary for weather stations within desert tortoise recovery units............... 54 

Table 4. Reference table connecting major recovery actions to listing factors and recovery 

objectives. ..................................................................................................................................... 84 

LIST OF APPENDICES 

Appendix A. Threats to Desert Tortoise and its Habitat since the Time of Listing .................. 109 

Appendix B. Understanding Disease in Desert Tortoise Populations: A Brief Summary of 

Appendix C. Draft Decision Support System for Desert Tortoise Recovery: A Tool for 

Knowledge and Recommendations Pertinent to Conservation................................................... 153 

Evaluating Recovery Action Effectiveness ................................................................................ 175 

Appendix D. Recommended Specifications for Desert Tortoise Exclusion Fencing................ 207 

xii 
I. BACKGROUND 

A. INTRODUCTION 

1. Listing History 

We, the United States Fish and Wildlife Service, listed the desert tortoise (Gopherus 

agassizii) on the Beaver Dam Slope in Utah as Threatened under the Endangered Species Act of 

1973, as amended, and designated critical habitat in 1980 (U.S. Fish and Wildlife Service 

[USFWS] 1980). In 1984, we were petitioned by the Defenders of Wildlife, Natural Resources 

Defense Council, and Environmental Defense Fund to list the species as Endangered. The 

following year, we determined that listing the desert tortoise as Endangered was warranted, but 

higher priorities precluded any action. 

On August 4, 1989, new information on mortality resulted in the emergency listing of 

desert tortoises north and west of the Colorado River (excluding the Beaver Dam Slope) as 

Endangered (USFWS 1989). On April 2, 1990, we listed the entire Mojave population (all 

tortoises north and west of the Colorado River in Arizona, Utah, Nevada, and California) as 

Threatened (USFWS 1990), and a recovery plan was published in June 1994 (USFWS 1994a). 

Previously, the species had a recovery priority number of 8C, which, according to the Recovery 

Priority Criteria, is based on a) moderate degree of threat, b) high potential for recovery, c) 

taxonomic classification as a species, and d) potential conflict with development or other forms 

of economic activity (USFWS 1983). Based on updated information, the recovery priority 

number has been reclassified as 6C and is predicated upon a) a high degree of threat, which has 

increased since 1994; b) a low potential for recovery, based on current uncertainties about 

various threats and our ability to manage them; c) listed population below the species level; and 

d) potential conflict with development or other forms of economic activity (USFWS 1983). With 

regard to the “low potential for recovery” as defined in the Recovery Priority Criteria, we 

anticipate that implementation of this revised recovery plan will resolve key uncertainties about 

threats and management, thereby improving recovery potential. 

The 1994 Recovery Plan described a strategy for recovering the Mojave population of the 

desert tortoise, which included the identification of six recovery units, recommendations for a 

system of Desert Wildlife Management Areas (DWMAs) within the recovery units, and 

development and implementation of specific recovery actions, especially within DWMAs. 

Establishment of recovery units and DWMAs was intended, in part, to facilitate an ecosystem 

approach to land management and desert tortoise recovery, as stipulated by section 2(b) of the 

Endangered Species Act (USFWS 1994a). 

2. Management 

The Desert Tortoise Management Oversight Group was established in 1988 to coordinate 

agency planning and management activities affecting the desert tortoise and to implement the 

management actions in the Bureau of Land Management’s Desert Tortoise Rangewide Plan. 

Charter members of the Management Oversight Group included the four Bureau of Land 

1
Management State Directors from Arizona, California, Nevada, and Utah; the four State Fish and 

Game Directors from these States; the three Fish and Wildlife Service Regional Directors that 

share tortoise management responsibilities; and a Bureau of Land Management Washington 

Office representative. Membership was subsequently expanded to include representatives of the 

National Park Service, Biological Resources Division of the U.S. Geological Survey, and 

officials of the four branches of the military (Army, Air Force, Navy, and Marine Corps) that 

have Mojave tortoise habitat. County governments within the range of the desert tortoise were 

also included in 2007. 

The original charter of the Management Oversight Group called for it to review a variety 

of topics, including a) standardize procedures for the analysis and interpretation of tortoise 

information, b) report on management actions completed for the benefit of the desert tortoise, c) 

recommend funding priorities, d) identify areas lacking sufficient information for habitat 

management, e) identify research needs to resolve management issues, f) identify threats and 

conflicts, g) complete annual status or progress reports, h) coordinate existing laws and guidance, 

and i) review ongoing research. Subsequent to the listing of the Mojave population as Threatened 

and following the publication of the recovery plan in 1994, the Management Oversight Group 

assumed a leadership role in coordinating agency activities directed toward recovery plan 

implementation. 

The California Desert Managers Group was organized to provide a forum for government 

agencies to work together to conserve and enhance the California deserts. The Desert Managers 

Group is comprised of field-level managers from agencies and county governments with land 

and resource management or regulatory responsibilities in the California deserts. It also includes 

the U.S. Geological Survey, which serves in a scientific support role to the managers. The 

Group’s 5-year plan includes several topics related to desert tortoise management. 

Like the Desert Managers Group, the Southern Nevada Agency Partnership does not 

focus specifically on desert tortoise issues, but was formed as an interagency partnership to 

address various initiatives including litter clean-up, volunteerism, resource protection, recreation, 

science and research, outdoor recreation education, law enforcement, and other issues. This 

partnership is comprised of the Bureau of Land Management, National Park Service, U.S. Fish 

and Wildlife Service, and U.S. Forest Service. 

In Arizona, both the Mojave and Sonoran populations of desert tortoise are considered 

Species of Greatest Conservation Need under Arizona’s Comprehensive Wildlife Conservation 

Strategy: 2005-2015 (Arizona Game and Fish Department 2006). Desert tortoises are also 

protected under the Arizona Revised Statutes Title 17 laws and the Reptile and Amphibian 

Regulations 2007-2008, under which it has been unlawful to collect this species since 1989. In 

California, state laws have been in place since 1939 to protect the desert tortoise. The species 

was listed as Threatened under the California Endangered Species Act in 1989 and is considered 

a Species at Risk under California’s Wildlife Action Plan (Bunn et al. 2006). The California 

Department of Fish and Game manages over 19,670 hectares (48,000 acres) of land for the 

conservation of the desert tortoise, and additional lands continue to be acquired as mitigation for 

projects that result in impacts to the species. In Nevada, the desert tortoise is protected under the 

2
Nevada Administrative Code 503.080, wherein the species is listed as a State protected reptile 

further classified as Threatened, and collection is prohibited under section 503.093. The desert 

tortoise is also considered a Species of Conservation Priority under the Nevada Wildlife Action 

Plan (Abele et al. 2006), which is being implemented by the Nevada Department of Wildlife. 

Desert tortoises are listed as State Endangered in Utah, where collection and importation are 

prohibited. Possession is controlled, meaning one must have a Certificate of Registration prior to 

possession of an individual animal. The species is protected under the Utah Division of Wildlife 

Resources Administrative Rule R657-53 and is considered a Species of Greatest Conservation 

Need under the Utah Comprehensive Wildlife Conservation Strategy: 2005-2015 (Gorrell et al. 

2005). 

3. Recovery Plan Review and Revision 

The U.S. General Accounting Office report, Endangered Species: Research Strategy and 

Long-Term Monitoring Needed for the Mojave Desert Tortoise Recovery Program (General 

Accounting Office [GAO] 2002), found that the listing decision, critical habitat designation, and 

recommendations in the recovery plan were reasonable, given the available information. 

Unfortunately, the effectiveness of actions implemented by Federal agencies and others to 

benefit desert tortoises was not monitored adequately and remains largely unknown. Because 

much was unknown about the severity of specific threats to desert tortoises at the time the plan 

was written, the recommendations were made without establishing priorities that would reflect 

differences in the seriousness of the threats. The General Accounting Office report recommended 

that we develop and implement a coordinated research strategy for linking land management 

decisions with research results. Without such a strategy, recovery of the desert tortoise would be 

left to chance rather than informed decisions based on science. In response, we initiated a review 

of the 1994 Recovery Plan. 

In March 2003, we impaneled the Desert Tortoise Recovery Plan Assessment Committee 

to conduct a thorough review of the Recovery Plan in the context of scientific and analytical 

advances made since its publication in 1994. The assessment (Tracy et al. 2004) concluded that 

the 1994 Recovery Plan was fundamentally strong but could benefit substantially from 

modification. The assessment also identified strategies that would promote a more cohesive, 

scientifically powerful recovery program. Taking recommendations of the General Accounting 

Office report and 2004 assessment, we established the Desert Tortoise Recovery Office (DTRO) 

in 2004. The DTRO’s staff focuses solely on the desert tortoise and its recovery. The DTRO 

coordinates recovery planning and implementation, research, monitoring, and recovery 

permitting, while working closely with those Service biologists focusing on regulatory issues. 

The DTRO assists in the coordination among land managers, research scientists, the interagency 

Desert Tortoise Management Oversight Group, the California Desert Managers Group, and other 

local, state, or regional working groups. To complement the DTRO, we assembled a Desert 

Tortoise Science Advisory Committee in 2005. This committee is composed of seven scientists 

from diverse yet highly relevant backgrounds (see Plan Preparation) who are charged with 

providing recommendations relative to desert tortoise recovery implementation and approach, 

such that rigorous scientific standards are met. The scope of the Science Advisory Committee’s 

3
recommendations to date has included recovery criteria, threats assessment, effectiveness 

monitoring, and key research. 

Based on recommendations in the recovery plan assessment, the Desert Tortoise 

Management Oversight Group recognized that the recovery plan should be revised with 

collaboration from scientists, managers, and stakeholders (Tracy et al. 2004), and an assessment 

of stakeholder input on recovery planning for the desert tortoise was conducted (U.S. Institute for 

Environmental Conflict Resolution and Center for Collaborative Policy 2006). To allow for 

broad participation, the Science Advisory Committee formed the base team for the scientific 

foundations, while government and non-government stakeholders were invited to participate and 

engage on management issues through various workshops, open houses, and review drafts of this 

plan. Thus, a collaborative effort resulted in this revised recovery plan for the Mojave population 

of the desert tortoise. 

B. SPECIES DESCRIPTION AND TAXONOMY 

The desert tortoise is a large, herbivorous (plant-eating) reptile that occurs in the Mojave 

and Sonoran deserts in southern California, southern Nevada, Arizona, and the southwestern tip 

of Utah in the U.S., as well as Sonora and northern Sinaloa in Mexico. The designated Mojave 

population of the desert tortoise includes those animals living north and west of the Colorado 

River in the Mojave Desert of California, Nevada, Arizona, and southwestern Utah, and in the 

Sonoran (Colorado) Desert in California (USFWS 1990; USFWS 1994a). 

The generic assignment of the desert tortoise has gone through a series of changes since 

its original description by Cooper (1863) as Xerobates agassizii. It has also been referred to in 

the literature as Scaptochelys agassizii. Currently, the accepted scientific name is Gopherus 

agassizii (Campbell 1988; Crumly 1994). Differentiation between the Mojave and Sonoran 

assemblages of the desert tortoise are supported via multiple forms of evidence, including 

morphology, ecology, and genetics (Weinstein and Berry 1987; Lamb et al. 1989; Lamb and 

Lydehard 1994; Berry et al. 2002a; Van Devender 2002a,b; Murphy et al. 2007). Although fewer 

data are available to compare Sinaloan desert tortoises to the Sonoran and Mojave assemblages, 

the Sinaloan population is considerably more isolated, and differentiation in mitochondrial DNA 

is considerable (Lamb et al. 1989; Van Devender 2002b). 

Desert tortoises reach 20 to 38 centimeters (8 to 15 inches) in carapace (upper shell) 

length and 10 to 15 centimeters (4 to 6 inches) in shell height. Hatchlings emerge from eggs at 

about 5 centimeters (2 inches) in length. Adults have a domed carapace and relatively flat, 

unhinged plastrons (lower shell). Their shells are high-domed and greenish-tan to dark brown in 

color with tan scute (horny plate on the shell) centers. Adult desert tortoises weigh 3.6 to 6.8 

kilograms (8 to 15 pounds). The forelimbs have heavy, claw-like scales and are flattened for 

digging. Hind limbs are more elephantine (Ernst et al. 1994). 

Two other tortoise species in the genus Gopherus occur in the United States, and another 

occurs in Mexico. The Texas tortoise (Gopherus berlandieri) occurs in southern Texas and 

northeastern Mexico, and the gopher tortoise (Gopherus polyphemus) occurs in southwestern 

4
South Carolina, Florida, Georgia, Alabama, Mississippi, Louisiana, and extreme southeastern 

Texas. The Mexican species is the Bolson tortoise (Gopherus flavomarginatus), which is found 

in a very small area in Chihuahua and Durango, Mexico. The desert tortoise is distinguished 

from the other three species by a combination of characters that are described in detail in the 

final listing rule and 1994 Recovery Plan (USFWS 1990; USFWS 1994a). For additional 

information regarding the morphological characteristics and distinguishing features of these 

species, refer to Ernst et al. (1994) and the references cited therein. 

Although there are significant differences genetically and ecologically, desert 

tortoises that belong to the Sonoran population could be confused visually with tortoises of 

the Mojave population. Because there are only minor visual differences between the animals 

in these populations, we determined at the time of listing that the Sonoran population also 

warranted protection as a threatened species under section 4(e) of the Endangered Species 

Act (similarity of appearance) when located outside of its natural range. This level of 

protection eliminates the need for law enforcement personnel to determine the origin of each 

individual when conducting enforcement activities under section 9 of the Endangered 

Species Act (USFWS 1990). 

C. POPULATION TRENDS AND DISTRIBUTION 

The Mojave population of the desert tortoise includes those animals living north and west 

of the Colorado River in the Mojave Desert of California, Nevada, Arizona, and southwestern 

Utah, and in the Sonoran (Colorado) Desert in California. This region was the target of most 

early research on desert tortoises (see Tracy et al. 2004). Studies during this early period focused 

on basic biology and demography and were largely centered in areas with high densities of 

tortoises. These high-density areas were used to establish permanent (long-term) study plots that 

have been studied at various intervals from 1979 through the present, while some low-density 

plots were discontinued (Berry 1984; K. Berry, U.S. Geological Survey, pers. comm. 2003, as 

reported in Tracy et al. 2004). However, historic estimates of desert tortoise density or 

abundance do not exist at the range-wide or regional level for use as a baseline. While a 

substantial body of data has been collected from long-term study plots and other survey efforts 

over the years, plot placement is generally regarded as a factor limiting demographic and trend 

conclusions only to those specific areas. Tracy et al. (2004) concluded that estimating accurate 

long-term trends of desert tortoise populations, habitat, and/or threats across the range was not 

feasible based on the combined suite of existing data and analyses. Instead, these data provide 

general insight into the range-wide status of the species and show appreciable declines at the 

local level in many areas (Luke et al. 1991; Berry 2003; Tracy et al. 2004). For example, Tracy 

et al. (2004) concluded that the apparent downward trend in desert tortoise populations in the 

western portion of the range that was identified at the time of listing is valid and ongoing. 

Results from other portions of the range were inconclusive, but recent surveys of some 

populations found too few tortoises to produce population estimates (e.g., 2000 survey of the 

Beaver Dam Slope, Arizona), suggesting that declines may have occurred more broadly. 

In an attempt to refine the long-term monitoring program for the desert tortoise, annual 

range-wide population monitoring using line distance transects began in 2001 (1999 in the Upper 

5
 

Virgin River Recovery Unit; McLuckie et al. 2002) and is the first comprehensive effort 

undertaken to date to estimate densities across the range of the species (USFWS 2006a). The 

monitoring program is designed to detect long-term population trends, so density estimates from 

any brief time period (e.g., 2001 to 2005) would be expected to detect only catastrophic declines 

or remarkable population increases. Therefore, following the first 5 years of the long-term 

monitoring project, the goal was not to document trends within this time period, but to gather 

information on baseline densities and annual and regional (between recovery unit) variability. 

This baseline information can also be used to refine the monitoring design because it includes 

estimates for transect-to-transect variability in tortoise counts as well as regional variability in 

detection functions (USFWS 2006a). 

Total length of transects surveyed ranged from 2,977 kilometers (1,850 miles) in 2001 to 

8,851 kilometers (5,500 miles) in 2005, with variation between years resulting from changes in 

survey technique and available funding. Density estimates of adult tortoises varied among 

recovery units and years. Only if this variability is associated with consistent changes between 

years will monitoring less than 25 years describe important trends. For instance, considerable 

decreases in density were reported in 2003 in the Eastern Colorado and Western Mojave 

recovery units, with no correspondingly large rebound in subsequent estimates (Table 1). Until 

the underlying variability that may affect our interpretation of these first years of data can be 

identified, inferences as to the meaning of these data should not be made. Over the first 5 years 

of monitoring, tortoises were least abundant in the Northeast Mojave Recovery Unit (1 to 3 

tortoises per kilometer2

 [2 to 8 tortoises per mile2]; USFWS 2006a), and the highest reported 

densities occurred in the Upper Virgin River Recovery Unit (17 to 30 tortoises per kilometer2

 [44 

to 78 tortoises per mile2]; McLuckie et al. 2002, 2006). 

Patterns of tortoise distribution are available from preliminary spatial analyses in Tracy et 

al. (2004). Their analyses revealed areas with higher probabilities of encountering both live and 

dead tortoises. In the western Mojave, areas with concentrations of dead tortoises without 

corresponding concentrations of live tortoises were generally the same areas where declines have 

been observed in the past, namely the northern portion of the Fremont-Kramer critical habitat 

unit and the northwestern part of the Superior-Cronese critical habitat unit. Limited data revealed 

large areas where dead tortoises, but no live tortoises, were observed in the Piute-Eldorado 

Valley and northern Coyote Springs Valley, Nevada, and the western and southern portions of 

the Ivanpah Valley, California, critical habitat unit. Most other recently sampled areas (mostly 

within critical habitat) reveal continued tortoise presence, although local population declines are 

known within some of these areas, such as the Beaver Dam Slope, Arizona. 

Collectively, these analyses, based on different combinations of data, do not suggest that 

implementation of specific management actions over time has abated declines of, or resulted in 

detectable increases in, desert tortoise populations across most of the range. The evidence of 

localized declines has not been offset elsewhere by detectable increases in numbers of 

individuals or higher densities. The life history of the species (i.e., delayed reproductive 

maturity, low reproductive rates, and relatively high mortality early in life) is such that observing 

relatively rapid increases in populations is highly unlikely, even over the 23-year monitoring 

period evaluated. In addition, threats that are difficult to manage, such as disease and invasion of 

6
7

Table 1. Summary of density estimates for each of the 1994-designated recovery units. “Adult tortoises” is the number of a(midline carapace length ≥180mm). See USFWS (2006a) for additional details. 

Recovery Unit Year No. of Transects Length (km) Adult Tortoises Encounter Rate Std Error Density (km2) Std Error Coefficient of Variation (%) 9

2001 136 254.8 9 0.035 0.012 2.32 0.786 34.0 

2002 75 293.2 3 0.010 0.006 0.84 0.476 56.6 

Northeast Mojave 2003 189 699.2 39 0.056 0.008 3.01 0.465 15.4 

2004 96 947.3 18 0.019 0.004 1.42 0.342 24.2 

2005 166 1754.4 40 0.023 0.004 2.15 0.400 18.6 

2001 224 371.6 17 0.046 0.012 3.00 0.784 26.2 

2002 284 1120.4 56 0.050 0.008 4.11 0.797 17.0 

Eastern Mojave 2003 59 215.1 11 0.051 0.016 2.76 0.874 31.7 

2004 140 1511.2 113 0.075 0.010 5.57 0.750 13.4 

2005 165 1839.5 108 0.059 0.006 5.54 0.656 11.8 

2001 205 328.0 54 0.165 0.025 10.80 1.712 15.9 

2002 104 416.7 42 0.101 0.019 8.28 1.670 20.2 

Eastern Colorado 2003 108 431.7 32 0.074 0.014 4.00 0.774 19.3 

2004 132 1414.0 102 0.072 0.009 5.38 0.684 12.7 

2005 91 1094.3 74 0.068 0.011 6.38 1.062 16.6 

2001 201 321.6 39 0.121 0.020 7.95 1.390 17.5 

2002 – – – – – – – – 

Northern Colorado 2003 112 445.2 54 0.121 0.020 6.55 1.122 17.1 

2004 76 835.9 79 0.095 0.014 7.04 1.099 15.6 

2005 94 1128.8 94 0.083 0.010 7.86 1.005 12.8 

2001 865 1384.0 160 0.116 0.010 7.58 0.710 9.4 

2002 547 2176.8 188 0.086 0.008 7.10 0.756 10.6 

Western Mojave 2003 522 2083.2 218 0.105 0.008 5.65 0.499 8.8 

2004 166 1867.9 133 0.071 0.008 5.31 0.663 12.5 

2005 229 2746.6 173 0.063 0.006 5.95 0.612 10.3 
Table 1. Continued. 

Recovery Unit Upper Virgin River1 

Year 

1999 2000 2001 2002 2003 2004 2005 

Transects 

158 153 

159 

– 

157 

– 

155 

Length 

(km) 

306.5 302.0 

313.8 

– 

309.1 

– 

304.5 

Adult 

Tortoises 

150 162 

168 

– 

96 

– 

136 

Encounter 

Rate 

0.49 0.54 

0.535 

– 

0.311 

– 

0.45 

Std 

Error 

0.07 0.07 

0.069 

– 

0.038 

– 

0.05 

Density 

(km2) 

27 30 

30.11 

– 

16.88 

– 

21.77 

Std 

Error 

3.92 4.36 4.16 

– 

2.17 

– 

3.17 

Coefficient of 9

Variation (%) 

14.5 14.5 13.8 

– 

12.8 

– 

14.6 

1Data from McLuckie et al. (2002, 2006). 

8 
habitats by non-native invasive species, probably have large negative effects on populations, and 

desert ecosystems require long periods of time for natural recovery once impacts are removed. 

Please refer to the Desert Tortoise Recovery Plan Assessment (Tracy et al. 2004) for a 

detailed description of the population trend and distribution analyses described above. In 

addition, Range-wide Monitoring of the Mojave Population of the Desert Tortoise: 2001-2005 

(USFWS 2006a) provides information regarding the current monitoring effort. 

D. LIFE HISTORY AND ECOLOGY 

Desert tortoises are well adapted to living in a highly variable and often harsh desert 

environment. They spend much of their lives in burrows, even during their seasons of activity. 

In late winter or early spring, they emerge from over-wintering burrows and typically remain 

active through fall. Activity does decrease in summer, but tortoises often emerge after summer 

rain storms. Mating occurs both during spring and fall (Black 1976; Rostal et al. 1994). During 

activity periods, desert tortoises eat a wide variety of herbaceous vegetation, particularly 

grasses and the flowers of annual plants (Berry 1974; Luckenbach 1982; Esque 1994). During 

periods of inactivity, they reduce their metabolism and water loss and consume very little food. 

Adult desert tortoises lose water at such a slow rate that they can survive for more than a year 

without access to free water of any kind and can apparently tolerate large imbalances in their 

water and energy budgets (Nagy and Medica 1986; Peterson 1996a,b; Henen et al. 1998). 

The size of desert tortoise home ranges varies with respect to location and year (Berry 

1986) and also serves as an indicator of resource availability and opportunity for reproduction 

and social interactions (O’Connor et al. 1994). Females have long-term home ranges that are 

approximately half that of the average male, which range from 10 to 80 hectares (25 to 200 

acres) (Burge 1977; Berry 1986). Over its lifetime, each desert tortoise may use more than 3.9 

square kilometers (1.5 square miles) of habitat and may make periodic forays of more than 11 

kilometers (7 miles) at a time (Berry 1986). 

In drought years, the ability of tortoises to drink while surface water is available 

following rains may be crucial for survival (Nagy and Medica 1986). During unfavorable 

periods, desert tortoises decrease surface activity and remain mostly inactive or dormant 

underground (Duda et al. 1999), which reduces water loss and minimizes energy expenditures 

(Nagy and Medica 1986). Duda et al. (1999) showed that home range size, number of different 

burrows used, average distances traveled per day, and levels of surface activity were 

significantly reduced during drought years. 

Tortoises are long-lived and grow slowly, requiring 13 to 20 years to reach sexual 

maturity, and have low reproductive rates during a long period of reproductive potential (Turner 

et al. 1984; Bury 1987; Germano 1994). The number of eggs as well as the number of clutches 

(set of eggs laid at a single time) that a female desert tortoise can produce in a season is 

dependent on a variety of factors including environment, habitat, availability of forage and 

drinking water, and physiological condition (Turner et al. 1986, 1987; Henen 1997; McLuckie 

and Fridell 2002). Success rate of clutches has proven difficult to measure, but predation appears 

to play an important role in clutch failure (Germano 1994). Bjurlin and Bissonette (2004) found 

9
 

that nest predation was highly variable. They surmised that the regular presence of researchers 

may facilitate predator detection of desert tortoises and that systematic studies should be 

undertaken to better understand predator behavior as it relates to research activities (Bjurlin and 

Bissonette 2004). 

The most complete account of the biology, ecology, and natural history of a population 

of desert tortoises is that of Woodbury and Hardy (1948), wherein details regarding 

reproduction, growth and development, longevity, food habits, behavior, movement patterns, and 

general adaptations to desert conditions are provided for a population on the Beaver Dam Slope 

of Utah. These characteristics of tortoises do vary with changes in habitat and environment, and 

further information on the range, biology, and ecology of the desert tortoise is available in Bury 

and Germano (1994), Ernst et al. (1994), Luckenbach (1982), Van Devender (2002c), and 

collected papers in Chelonian Conservation and Biology (2002, Vol. 4, No. 2). 

E. HABITAT CHARACTERISTICS 

The desert tortoise occurs in the broadest latitudinal range, climatic regimes, habitats, and 

biotic regions of any North American tortoise species (Auffenberg and Franz 1978; Bury 1982; 

Patterson 1982; Bury et al. 1994; Germano 1994). The species occupies a variety of habitats 

from flats and slopes dominated by Larrea tridentata (creosote bush) scrub at lower elevations to 

rocky slopes in Coleogyne ramosissima (blackbrush) and Juniperus spp. (juniper) woodland 

ecotones (transition zone) at higher elevations (Germano et al. 1994). Records of desert tortoises 

range from below sea level to an elevation of 2,225 meters (7,300 feet) (Luckenbach 1982). 

Luckenbach (1982) also states that the most favorable habitat occurs at elevations of 

approximately 305 to 914 meters (1,000 to 3,000 feet); however, based on current information 

and data from recent range-wide monitoring efforts, the species has consistently been 

documented above 914 meters (3,000 feet) (USFWS 2006a; USFWS unpublished data). In fact, 

surveys at the Nevada Test Site revealed that tortoise sign (e.g., scat, burrows, tracks, shells) was 

more abundant on the upper alluvial fans and low mountain slopes than on the valley bottom 

(Rautenstrauch and O’Farrell 1998). Current rangewide monitoring strategies do account for the 

possibility of tortoises occurring in mountainous habitats. 

Throughout most of the Mojave Desert, tortoises occur most commonly on gently sloping 

terrain with sandy-gravel soils and where there is sparse cover of low-growing shrubs, which 

allows establishment of herbaceous (non-woody) plants (Germano et al. 1994; USFWS 1994a). 

Soils must be friable (easily crumbled) enough for digging burrows, but firm enough so that 

burrows do not collapse (USFWS 1994a). During the winter, tortoises will opportunistically use 

burrows of various lengths, deep caves, rock and caliche crevices, or overhangs for cover (Bury 

et al. 1994). Typical habitat for the desert tortoise in the Mojave Desert has been characterized as 

creosote bush scrub in which precipitation ranges from 5 to 20 centimeters (2 to 8 inches), where 

a diversity of perennial plants is relatively high, and production of ephemerals is high 

(Luckenbach 1982; Turner 1982; Turner and Brown 1982; Germano et al. 1994). 

The Mojave Desert is relatively rich in winter annuals, which serve as an important food 

source for the desert tortoise. Tortoises will also forage on perennial grasses, woody perennials, 

and cacti as well as non-native species such as Bromus rubens (red brome) and Erodium 

10
 

cicutarium (red-stem filaree). Ninety percent of the precipitation that facilitates germination of 

important forage species for desert tortoise occurs in winter and sometimes in the form of snow 

(Germano et al. 1994). Tortoises in the eastern Mojave Desert are more likely to be subjected to 

freezing winter temperatures and prolonged drought than tortoises in the Sonoran Desert and 

Sinaloan region where freezing temperatures are rare and rainfall is more predictable (Germano 

1994). 

The U.S. Geological Survey has developed a draft habitat model for most of the Mojave 

Desert north and west of the Colorado River using 16 environmental variables such as 

precipitation, geology, vegetation, and slope (Figure 1) (Esque et al., in prep.). The model is 

based on desert tortoise occurrence data from sources spanning more than 80 years, especially 

including data from the 2001 to 2005 range-wide monitoring surveys (USFWS 2006a), using 

3,753 tortoise presence points to develop the model and 938 points to test the model. The final 

model is expected to be available soon and will contribute substantially to management by 

providing a range-wide quantification of desert tortoise habitat that can help direct where 

management actions should be implemented, as well as providing a basis for documenting trends 

in habitat impacts or loss. 

The desert tortoise’s range, outside the listed Mojave population, extends into the 

Sonoran Desert, where tortoises occur in the lower Colorado River valley, Arizona uplands, 

plains of Sonora, and the central Gulf Coast; the species has not been documented in 

northeastern Baja California (Germano et al. 1994). As in the Mojave Desert, Larrea tridentata 

is a dominant species in areas occupied by tortoises, although this dominance is tempered by the 

relatively high abundance of several tree species (Turner and Brown 1982; Germano et al. 1994). 

In the Sonoran Desert, tortoises tend to inhabit bajadas (slope at the base of a mountain) and 

steep, rocky slopes and are not common in the valleys (Germano 1994; Averill-Murray and 

Averill-Murray 2005). Desert tortoises are also found in the Sinaloan thornscrub, which is a 

transitional habitat between the Sonoran Desert and Sinaloan deciduous forest where the 

vegetation is dominated by drought-resistant shrubs and deciduous trees. The Sinaloan deciduous 

forests are differentiated from the thornscrub by taller plants with larger leaves and fewer thorny 

or succulent species (Germano et al. 1994; Fritts and Jennings 1994). 

F. CRITICAL HABITAT 

Under section 3 of the Endangered Species Act, critical habitat is defined as the specific 

areas supporting those physical and biological features that are essential for the conservation of 

the species and that may require special management considerations or protection (Box 1). The 

1994 Recovery Plan identified general areas as proposed Desert Wildlife Management Areas 

where recovery efforts for the desert tortoise would be focused (Brussard et al. 1994; USFWS 

1994a; Box 1). Based on the draft recovery plan, we designated critical habitat in February 1994, 

encompassing over 2,428,114 hectares (6,000,000 acres) in portions of the Mojave and Colorado 

deserts (Figure 1; Table 2). This designation includes primarily Federal lands in southwestern 

Utah, northwestern Arizona, southern Nevada, and southern California (USFWS 1994b). 

Primary constituent elements for the desert tortoise are those physical and biological 

attributes that are necessary for the long-term survival of the species. These elements were 

11
identified as sufficient space to support viable populations within each of the six recovery units 

and to provide for movement, dispersal, and gene flow; sufficient quantity and quality of forage 

species and the proper soil conditions to provide for the growth of such species; suitable 

substrates for burrowing, nesting, and overwintering; burrows, caliche (hard layer of subsoil 

typically containing calcium carbonate) caves, and other shelter sites; sufficient vegetation for 

shelter from temperature extremes and predators; and habitat protected from disturbance and 

human-caused mortality (USFWS 1994b). 

Figure 1. Desert tortoise critical habitat overlaid on the draft U.S. Geological Survey habitat model 

(Esque et al., in prep.). Areas not included in the habitat model are shown as desert tortoise distribution 

from Bury et al. (1994). 

12
 

 

 

Box 1. Glossary of terminology relating to desert tortoise habitat: 

Desert Wildlife Management Areas (DWMA) - General areas recommended by the 1994 Recovery 

Plan within which recovery efforts for the desert tortoise would be concentrated. DWMAs had no 

specific legal boundaries in the 1994 Recovery Plan. The Bureau of Land Management formalized the 

general DWMAs from the 1994 Recovery Plan through its planning process and administers them as 

Areas of Critical Environmental Concern (see below). 

Critical Habitat – Specific, legally defined areas that are essential for the conservation of the desert 

tortoise, that support physical and biological features essential for desert tortoise survival, and that 

may require special management considerations or protection. Critical habitat for the desert tortoise 

was designated in 1994, largely based on proposed DWMAs in the draft Recovery Plan. 

Area of Critical Environmental Concern (ACEC) – Specific, legally defined, Bureau of Land 

Management designation where special management is needed to protect and prevent irreparable 

damage to important historical, cultural, scenic values, fish and wildlife, and natural resources (in this 

case, the desert tortoise) or to protect life and safety from natural hazards. Designated critical habitat 

and ACEC boundaries generally, but not always, coincide along legal boundaries. 

Table 2. Critical habitat by state and land management in hectares (1 hectare=2.47 acres) (Brannon 2000). 

State 

Management 

Arizona California Nevada Utah 

Total 

Bureau of Land Management 116,691 1,024,356 451,146 35,521 1,627,714 

National Park Service 17,241 360,931 39,453 0 417,625 

Bureau of Reclamation 71 0 1,519 0 1,590 

Forest Service 0 0 0 18 18 

Department of Defense 0 156,347 168 0 156,515 

Tribal Land 0 0 0 797 797 

State Land 0 4,133 0 1,574 5,707 

Fish and Game 3,067 19,677 13 8,383 31,140 

Private Land 940 290,063 1,509 5,789 298,301 

Water 117 0 310 0 427 

Total 138,127 1,855,507 494,118 52,082 2,539,834 

G. REASONS FOR LISTING AND CONTINUING THREATS 

In determining whether to list, delist, or reclassify (change from endangered to threatened 

status, or vice versa) a taxon under the Endangered Species Act, we evaluate the role of five 

factors potentially affecting the species. These factors are: 

A) The present or threatened destruction, modification, or curtailment of its habitat or 

range; 

B) overutilization for commercial, recreational, scientific, or educational purposes; 

13
C) disease or predation; 

D) the inadequacy of existing regulatory mechanisms; and 

E) other natural or manmade factors affecting its continued existence. 

Documented threats to the Mojave population of the desert tortoise were described in the 

final listing rule in 1990 as they pertain to the five listing factors (USFWS 1990) and in the 1994 

Recovery Plan (USFWS 1994a). The threats identified in the 1994 Recovery Plan, and that 

formed the basis for listing the tortoise as a threatened species (GAO 2002), continue to affect 

the species. Extensive research shows that all of these individual threats directly kill or indirectly 

affect tortoises. Research has also clarified many mechanisms by which these threats act on 

tortoises. However, despite the clear demonstration that these threats impact individual tortoises, 

there are few data available to evaluate or quantify the effects of threats on desert tortoise 

populations (Boarman 2002). While current research results can lead to predictions about how 

local tortoise abundance should be affected by the presence of threats, quantitative estimates of 

the magnitude of these threats, or of their relative importance, have not yet been developed. 

Thus, a particular threat or subset of threats with discernable solutions that could be targeted to 

the exclusion of other threats has not been identified for the desert tortoise. 

The assessment of the 1994 Recovery Plan emphasized the need for a greater 

appreciation of the implications of multiple, simultaneous threats facing tortoise populations and 

a better understanding of the relative contribution of multiple threats on demographic factors 

(i.e., birth rate, survivorship, fecundity, and death rate; Tracy et al. 2004). The approach of 

focusing on individual threats may not have produced expected gains toward desert tortoise 

recovery since 1994 because multiple threats act simultaneously to suppress tortoise populations 

at any given location within the species’ range. In this revised recovery plan, we underscore the 

need to build on our understanding of individual threats, yet place new emphasis on 

understanding their multiple and synergistic effects (interacting so that the combined effect is 

greater than the sum of individual effects) due to the failure of simple threat models to inform us 

about tortoise abundance. The following narrative provides a brief overview of the threats to the 

desert tortoise and its habitat as categorized by the five listing factors. A more detailed 

discussion of these threats is contained in Appendix A. 

1. The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or 

Range (Factor A) 

Since the 1800s, portions of the desert southwest occupied by desert tortoises have been 

subject to a variety of impacts that cause habitat loss, fragmentation, and degradation, thereby 

threatening the long-term survival of the species (USFWS 1994a). Some of the most apparent 

threats are those that result in mortality and permanent habitat loss across large areas, such as 

urbanization, and those that fragment and degrade habitats, such as proliferation of roads and 

highways, off-highway vehicle activity, grazing, and habitat invasion by non-native invasive 

species (Berry et al. 1996; Boarman and Sazaki 2006; Avery 1997; Jennings 1997; Boarman 

2002). Indirect impacts to desert tortoise populations and habitat are also known to occur in 

14
areas that interface with intense human activity (Berry and Burge 1984; Berry and Nicholson 

1984). 

Another threat that has come to the forefront is the increased frequency of wildfire due to 

the invasion of desert habitats by non-native plant species (USFWS 1994a; Brooks 1998). 

Changes in plant communities caused by non-native plants and recurrent fire can negatively 

affect the desert tortoise by altering habitat structure and species available as food plants (Brooks 

and Esque 2002). Off-highway vehicle activity, roads, grazing, agricultural uses, and other 

activities contribute to the spread of non-native species and the direct loss and degradation of 

habitats (Brooks 1995; Avery 1998). 

Landfills and other waste disposal facilities potentially affect desert tortoises and their 

habitat through fragmentation and permanent loss of habitat, spread of garbage, introduction of 

toxic chemicals, increased road kill of tortoises on access roads, and increased predator 

populations (Boarman et al. 1995; Kristan and Boarman 2001). Military operations have taken 

place in the Mojave Desert since 1859 and can affect tortoises and their habitats similarly to 

other large human settlements (i.e., illegal collection of tortoises, trash dumping, increased raven 

(Corvus corax) populations, domestic predators, off-highway vehicle use, increased exposure to 

disease, and increased mortality) (USFWS 1994a; Krzysik 1998; Boarman 2002). 

2. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes 

(Factor B) 

Despite legal protection under Federal and State laws, deliberate maiming or killing of 

tortoises (previously referred to as vandalism) and collection of desert tortoises by humans for 

food or as pets were cited as potential threats to the species (USFWS 1994a). Data and anecdotal 

observations indicate that collection for personal or commercial purposes was justifiably 

considered significant in the past (USFWS 1994a). While illegal collection of desert tortoises 

still occurs and such collection could possibly impact local populations, there is no quantitative 

estimate of the magnitude of this threat (Berry et al. 1996; Boarman 2002). 

Research projects that may provide information to guide management and recovery of the 

desert tortoise may result in injury or loss of individuals. These activities are permitted under 

section 10 of the Endangered Species Act. Permits include terms and conditions to minimize 

injury and mortality of individuals. 

3. Disease or Predation (Factor C) 

Two diseases have been implicated in negatively affecting desert tortoise populations: 

upper respiratory tract disease (Jacobson et al. 1991) and cutaneous dyskeratosis or shell disease 

(Jacobson et al. 1994). Other diseases or infections have also been identified in tortoises 

including herpesvirus, shell necrosis, bacterial and fungal infections, and urolithiasis (bladder 

stones) (Homer et al. 1998; Berry et al. 2002b; Origgi et al. 2002), but little information is 

available regarding the distribution of these maladies or the magnitude of their effect within or 

among desert tortoise populations (Boarman 2002). Additional research is needed to clarify the 

role of disease in desert tortoise population dynamics relative to other threats. 

15
The role of environmental contaminants in directly inducing toxicosis-related diseases 

(i.e. liver diseases) and increasing susceptibility to infectious diseases has recently been 

suggested as a significant source of mortality, but further investigation is required to confirm that 

hypothesis (Homer et al. 1994, 1996; Berry 1997; Boarman 2002). Illegal dumping of hazardous 

wastes in the California deserts may expose tortoises to increased levels and possible 

consumption of toxic substances and affect populations on a localized level where these 

activities are concentrated (Boarman 2002). 

Desert tortoises, particularly hatchlings and juveniles, are preyed upon by several native 

species of mammals, reptiles, and birds. The common raven has been the most highly visible 

predator of small tortoises, while coyotes have been commonly implicated in the deaths of adult 

tortoises. The population-level effects of these or any of the other predators are unknown. Except 

for extreme predation events brought on by unusual circumstances, predation by native predators 

alone would not be expected to cause dramatic population declines. This reiterates the 

importance of combined and synergistic effects of threats. For example, predation pressure by 

ravens is increased through elevated raven populations as a result of resource subsidies 

associated with human activities. Ravens obtain food in the form of organic garbage from 

landfills and trash containers, water from sewage ponds and municipal areas, and nesting 

substrates on billboards, utility towers, bridges, and buildings (Boarman et al. 2006). 

Other avian predators of the desert tortoise include red-tailed hawks (Buteo jamaicensis), 

golden eagles (Aquila chrysaetos), loggerhead shrikes (Lanius ludovicianus), American kestrels 

(Falco sparvarius), burrowing owls (Athene cunicularia), and greater roadrunners (Geococcyx 

californianus) (Boarman 1993). Coyotes (Canis latrans), kit foxes (Vulpes macrotis), mountain 

lions (Felis concolor), ground squirrels (Spermophilus spp.), and free-roaming dogs are some of 

the known mammalian predators (Bjurlin and Bissonette 2001; Boarman 2002; M. McDermott, 

Southern Nevada Environmental, Inc., pers. comm. 2006, K. Nagy, University of California-Los 

Angeles, pers. comm. 2006). Invertebrate predators of eggs and hatchling tortoises include native 

fire ants (Nagy et al. 2007). 

4. Inadequacy of Existing Regulatory Mechanisms (Factor D) 

The final listing rule acknowledged that all four states within the range of the Mojave 

population of the desert tortoise have laws in place to protect the species. In addition, a great deal 

of effort has been dedicated to planning by the various land management agencies whose 

jurisdictions include desert tortoise habitat. Many of the existing plans include language specific 

to protection of the species, such as limiting off-highway vehicle use and competitive/organized 

events, grazing, vegetation harvest, and collection of desert tortoises. However, the multiple-use 

mandates under which the agencies function require a complex balance between conservation 

and use of public lands, and management agencies frequently do not have sufficient funding to 

enforce their regulations. Also, state wildlife/endangered species permitting requirements do not 

specifically address impacts to habitat, making mitigation of impacts to potentially unoccupied 

but suitable habitat difficult. 

16
Land exchanges and transfers may result in loss of desert tortoise habitat, increased 

fragmentation, and displacement of resident desert tortoises, because habitat that is exchanged 

out of Federal ownership into the private sector is at greater risk of urban development (Sievers 

et al. 1988; but see Conservation Efforts, Land Acquisitions and Habitat Conservation Plans, 

below). Energy and mineral development and extraction also pose a significant threat to desert 

tortoises through habitat loss and fragmentation (Luke et al. 1991; Lovich and Bainbridge 1999; 

LaRue and Dougherty 1999). In the California Desert, applications for solar energy facilities in 

2007 total nearly 202,343 hectares (500,000 acres) because of an emphasis on advancing 

alternative energy sources. In Nevada, habitat lost through energy development is also a potential 

threat, where various energy development projects have been proposed and applications have 

been submitted for solar power facility right-of-ways on over 53,800 hectares (133,000 acres) of 

potential desert tortoise habitat. 

5. Other Natural or Manmade Factors Affecting its Continued Existence (Factor E) 

Global climate change and drought are potentially important long-term considerations 

with respect to recovery of the desert tortoise. There is now sufficient evidence that recent 

climatic changes have affected a broad range of organisms with diverse geographical 

distributions (Walther et al. 2002). While little is known regarding specific direct effects of 

climate change on the desert tortoise or its habitat, predictions can be made about how global and 

regional precipitation regimes may be altered and the consequences of these changes (Weltzin et 

al. 2003; Seager et al. 2007). 

The Intergovernmental Panel on Climate Change has suggested that increasingly reliable 

regional climate change projections are now available as the result of improved modeling 

capabilities and advanced understanding of climate systems (Christensen et al. 2007). Twentyone Atmosphere-Ocean General Circulation Models were run to predict regional temperature and 

precipitation in 2080 through 2099 as changed from conditions that occurred between 1980 and 

1999. Generally, predictions for the geographic range of the desert tortoise’s listed population 

suggest a 3.5 to 4.0o C (6.3 to 7.2o F) increase in annual mean temperature, with the greatest 

increases occurring in summer (June-July-August mean up to 5o C (9o F) increase) (Christensen 

et al. 2007). Precipitation will likely decrease by 5 to 15 percent annually in the region, with 

winter precipitation decreasing in the range of 5 to 20 percent (Christensen et al. 2007). Because 

germination of the tortoise’s food plants is highly dependent on cool season rains, the forage 

base could be reduced due to increasing temperatures and decreasing precipitation in winter. 

Further predictions need to be developed specifically for the desert tortoise to help inform 

recovery efforts. 

Other activities that may impact the species include non-motorized recreation such as 

camping, hunting, target shooting, rock collecting, hiking, horseback riding, biking, and sightseeing. These activities bring with them threats associated with increased human presence, such 

as loss of habitat from development of recreational facilities, handling and disturbance of 

tortoises, increased road kill and deliberate maiming or killing of tortoises, increased raven 

predation, degradation of vegetation, and soil compaction (USFWS 1994a; Averill-Murray 

2002). Desert habitats are also disturbed by construction and maintenance of linear utility 

17
corridors and ancillary facilities and to some degree by vandalism and harvest of vegetation for 

personal or economic purposes (LaRue and Dougherty 1999; Olson 1996). 

Another potential threat facing the desert tortoise is the unauthorized breeding of pet 

tortoises, which can lead to pressures on wild tortoise populations as well as management 

agencies. Wolff and Seal (1993) noted that disease spread by the release of captive-bred animals 

and relocation of wild animals is a major concern in conservation biology. Captive releases have 

the potential to introduce disease into wild populations of desert tortoises and may also result in 

genetic contamination. 

Please refer to Appendix A for a more detailed discussion of the threats to the desert 

tortoise and its habitat briefly described above. 

H. CONSERVATION EFFORTS 

While precise correlations between the multitude of threats and desert tortoise 

populations have not been clearly shown, a great deal of effort has been put forth by research 

scientists and land managers to actively conserve the species. For instance, substantive datasets 

pertaining to disease, non-native invasive plant species, and fire have been assembled over the 

years that will be used to inform decisions relative to recovery of the desert tortoise and its 

habitats. On-the-ground conservation actions such as land acquisitions, installing protective 

fencing, retiring grazing allotments, limiting off-highway vehicle access, and implementing 

restoration projects have been important recovery and management efforts based on what we do 

know about threats to the desert tortoise at this time (see GAO 2002). The following are 

examples of existing guidance and strategies to further resource conservation. 

1. Wildlife Conservation Strategies 

In 2000, Congress enacted the State Wildlife Grants Program to fund activities that 

benefit species of concern and their habitats. To receive funding under this program, state 

wildlife agencies needed to complete a Service approved wildlife action plan (or comprehensive 

wildlife conservation strategy). All four states where the Mojave population of the desert tortoise 

occurs are currently implementing these strategies to guide species and habitat management 

through 2015 (Gorrell et al. 2005; Abele et al. 2006; Arizona Game and Fish Department 2006; 

Bunn et al. 2006). 

Each state has identified conservation priorities and recommendations that are both 

species and habitat specific. Some of these actions include, but are not limited to, the following: 

• improve stewardship on federally managed lands to protect wildlife diversity; 

• work cooperatively with landowners/permittees by providing financial and technical 

assistance (through incentive programs) for conservation projects; 

• work with city and county planners to incorporate wildlife values in urban/rural 

development plans; 

• promote design and construction of overpasses, underpasses, or culverts to increase 

permeability of existing or planned roads; 

18
• identify and protect key wildlife corridors for landscape connectivity; 

• reduce off-highway vehicle damage to wildlife habitats; 

• encourage revegetation and restoration of existing unauthorized roads and trails; 

• improve efforts and partnerships for controlling existing occurrences of invasive species 

and prevent new introductions; 

• rehabilitate burned and disturbed areas with native plants; 

• pursue projects to limit spread of disease to sensitive wildlife populations; 

• use fencing and/or increased law enforcement presence to reduce unauthorized use and 

access to sensitive habitats; and, 

• implement a statistically robust range-wide monitoring program and adaptive 

management framework that captures population trends and impacts to the species. 

2. Federal Land Management Plans 

Land use management plans provide guidance and establish a mechanism by which 

Federal agencies implement actions on lands under their purview. Throughout the range of the 

desert tortoise, multiple Federal agencies are involved in the long-term management and 

conservation of the species as part of their respective missions. These include the Bureau of Land 

Management, National Park Service, Bureau of Indian Affairs, U.S. Fish and Wildlife Service, 

Bureau of Reclamation, U.S. Forest Service, Department of Defense, and Department of Energy. 

In addition to Federal land use plans, counties and local jurisdictions draft general plans to guide 

their activities. 

Within the range of the desert tortoise, the following programmatic level documents are 

currently in place or in preparation. Many of the respective plans include language specific to the 

protection and conservation of natural resources including desert tortoises and their habitats. 

These are often supplemented by more specific guiding documents, such as habitat management 

plans or wilderness management plans: 

Bureau of Land Management: 

• Arizona Strip Resource Management Plan Revision, Grand Canyon-Parashant National 

Monument Management Plan (jointly managed with the National Park Service), and 

Vermilion Cliffs National Monument Management Plan; Proposed Resource 

Management Plan/Final Environmental Impact Statement (BLM and National Park 

Service [NPS] 2007a) 

• California Desert Conservation Plan of 1980 as amended (BLM 1999a) 

• Northern and Eastern Mojave Desert Management Plan (BLM 2002a) 

• Northern and Eastern Colorado Desert Coordinated Management Plan (BLM 2002b) 

• West Mojave Plan (BLM et al. 2005) 

• Tonopah Resource Management Plan (BLM 1997) 

• Las Vegas Resource Management Plan (BLM 1998a) 

• Red Rock Canyon National Conservation Area Resource Management Plan (BLM 2001) 

• Sloan Canyon National Conservation Area Resource Management Plan (BLM 2006) 

• Nevada Test and Training Range Resource Management Plan (BLM 2004) 

• Caliente Management Framework Plan (BLM 2000) 

19
• St. George Resource Management Plan (BLM 1999b) 

Fish and Wildlife Service: 

• Desert National Wildlife Refuge Comprehensive Conservation Plan (USFWS in 

preparation)

National Park Service: 

• Joshua Tree National Park General Management Plan, as amended (NPS 2000a) 

• Death Valley National Park General Management Plan (NPS 2002a) 

• Mojave National Preserve General Management Plan (NPS 2002b) 

• Lake Mead National Recreation Area, Arizona and California, Strategic Plan Fiscal Year 

2001-2005 (NPS 2000b) 

U.S. Forest Service: 

• General Management Plan for the Spring Mountains National Recreation Area, An 

Amendment to the Land and Resource Management Plan (U.S. Forest Service 1996) 

Department of Defense: 

• National Training Center at Fort Irwin Integrated Natural Resources Management Plan 

(U.S. Army 2006) 

• Edwards Air Force Base Integrated Natural Resources Management Plan (U.S. Air Force 

2001) 

• Marine Corps Logistics Base, Barstow, Integrated Natural Resources Management Plan 

(Tierra Data, Inc. 2005) 

• Marine Corps Air Ground Combat Center, Twentynine Palms, Integrated Natural 

Resources Management Plan, Fiscal Years 2007-2011 (U.S. Marine Corps 2006) 

• Naval Air Weapons Station, China Lake, Comprehensive Land Use Management Plan 

and Integrated Natural Resources Management Plan (Naval Air Weapons Station, China 

Lake and BLM 2004) 

• Yuma Training Range Complex, Arizona and California (U.S. Navy 2001) 

• Draft Nellis AFB and Nevada Test and Training Range Integrated Natural Resources 

Management Plan (U.S. Air Force 2007) 

Among the most important recovery actions implemented pursuant to the 1994 Recovery 

Plan has been formalizing Desert Wildlife Management Areas (DWMAs; Box 1) through 

Federal land use planning processes (Figure 2). Particularly on Bureau of Land Management 

lands, DWMAs are administered and designated as Areas of Critical Environmental Concern 

(ACEC; Box 1; BLM 1998a, 1999b, 2000, 2002a, 2002b, BLM et al. 2005, BLM and NPS 

2007). These ACECs define specific management areas based on the general recommendations 

for DWMAs in the 1994 Recovery Plan. Boundaries of the ACECs were refined slightly from 

the critical habitat designation based on various management and biological considerations. The 

Bureau of Land Management DWMAs/ACECs, together with National Park Service lands, 

designated wilderness areas, other lands allocated for resource conservation, as well as restrictedaccess military lands provide an extensive network of habitats that are managed either directly or 

indirectly (e.g., wilderness areas outside desert tortoise ACECs) for desert tortoise conservation 

(Figures 2 and 3). 

20
Figure 2. Desert tortoise conservation areas (see Box 2). DWMA = Desert Wildlife Management Area; 

ACEC = Areas of Critical Environmental Concern; DTCC = Desert Tortoise Conservation Center. 

21
Figure 3. Additional land designations providing conservation benefits to the desert tortoise in relation to 

critical habitat and major highways. Conservation areas for other species not shown (e.g., Mohave ground 

squirrel [Spermophilus mohavensis], Mimulus mohavensis [Mojave monkeyflower]) may also provide 

benefit to the desert tortoise. DFG = Department of Fish and Game; DPR = Department of Parks and 

Recreation. 

22
The most recent example of landscape-scale conservation was the Bureau of Land 

Management’s designation of ACECs and wildlife habitat areas under the Arizona Strip 

Resource Management Plan Revision and Grand Canyon-Parashant National Monument 

Management Plan (BLM and NPS 2007). On the Arizona Strip, lands managed to maintain 

wilderness characteristics were proposed on 87,100 hectares (215,345 acres) within the Grand 

Canyon-Parashant National Monument and on 14,120 hectares (34,900 acres) within the Arizona 

Strip field office’s area of responsibility. Nearly 68,800 hectares (170,000 acres) are designated 

as ACECs on the Arizona Strip, which directly benefits the desert tortoise and its habitat. The 

Resource Management Plan contains the following goals: 

• The Mojave population of desert tortoise would be recovered and delisted. 

• There would be no net loss in the quality or quantity of desert tortoise habitat within the 

ACECs or wildlife habitat areas. 

• Desert tortoise populations within the ACECs and DWMAs would be healthy and selfsustaining. Populations would be stable or increasing. Population declines would be 

halted. 

• Desert tortoise populations outside of the ACECs and wildlife habitat areas would be 

healthy and stable. Declines in the wildlife habitat areas would be minimized to the 

extent possible through mitigation. 

• Desert tortoise habitat would provide sufficient forage and cover attributes to support 

thriving populations of the species. 

• Habitat connectivity would be maintained, providing sufficiently frequent contact 

between tortoises to maintain genetic diversity.

One of the most extensive land and resource management plans currently in place was 

developed for the 10,117,141-hectare (25,000,000-acre) California Desert Conservation Area. In 

1976, Congress passed the Federal Land Policy Management Act to direct the management of 

the public lands of the United States. Under that law, the California Desert Conservation Area 

was established and includes 4,856,228 hectares (12,000,000 acres) of public lands administered 

by the Bureau of Land Management. The California Desert Conservation Area Plan of 1980 as 

amended provides guidance relative to the use of the public lands and resources of the California 

Desert Conservation Area, including economic, educational, scientific, and recreational uses, in a 

manner that enhances wherever possible, and does not diminish the environmental, cultural, and 

aesthetic values of the desert and its productivity. Under the California Desert Conservation Area 

Plan, all state and federally listed species and their habitats are to be managed so that the 

continued existence of each is not jeopardized. Consultation for federally listed species would be 

conducted as appropriate (BLM 1999a). 

The California Desert Conservation Area Plan was subsequently amended by region, 

which generally corresponded to the recovery units delineated in the 1994 Recovery Plan. The 

Northern and Eastern Mojave Desert Management Plan (BLM 2002a), the West Mojave Plan 

(BLM et al. 2005), and the Northern and Eastern Colorado Desert Coordinated Management 

Plan (BLM 2002b) all designated DWMAs and included new management measures for desert 

tortoise conservation. 

23
PECI 

AL DESIGNATIONS –

The California Desert Conservation Area also encompasses the 10,117-hectare (25,000­

acre) Desert Tortoise Natural Area, which was established in the western Mojave Desert in 1972. 

The Mojave National Preserve was created under the California Desert Protection Act in 1994 

for which a general management plan was drafted in 2002 (NPS 2002b). The California Desert 

Protection Act also expanded the boundaries of both Death Valley and Joshua Tree National 

Parks and designated millions of acres of wilderness, which eliminated vehicle access to these 

areas. 

Many of the actions recommended in the 1994 Recovery Plan have been incorporated 

into the land and resource management plans identified above, particularly within 

DWMAs/ACECs. Tracy et al. (2004) summarized the level of implementation of the 

management recommendations by reviewing land and wildlife managers’ responses to surveys 

asking what recovery actions had been implemented. However, the survey responses were not 

explicit enough to quantify the level of implementation for each specific recovery action; 

therefore, the results only speak to whether or not some action had been taken. In addition, 

research and monitoring have not been targeted to evaluate the effectiveness of these actions 

(Boarman and Kristan 2006), and ongoing population monitoring has been performed at a 

regional scale rather than a local implementation scale. The main conclusion was that improved 

reporting and quantification of recovery actions is necessary to more accurately assess the 

progress of desert tortoise recovery (Tracy et al. 2004). 

3. Grazing Removal and Limitations 

A specific example of landscape-scale conservation of desert tortoise habitat was the 

removal of grazing and the implementation of seasonal grazing restrictions on several allotments 

within designated critical habitat on public lands. This was identified in the 1994 Recovery Plan 

as an important component in the recovery of the species. For example, in 1995 the Desert 

Tortoise Preserve Committee and The Wildlands Conservancy bought the 550-hectare (1,360­

acre) Blackwater Well Ranch in northwestern San Bernardino County and gained control (and is 

seeking retirement) of grazing on the 19,830-hectare (49,000-acre) Pilot Knob cattle grazing 

allotment. Together with the Bureau of Land Management, we initiated various planning efforts 

in California that resulted in the removal of grazing on nearly 1,214,000 hectares (3,000,000 

acres) within the California portions of the Mojave and Sonoran deserts (BLM 2002a,b; BLM et 

al. 2005; USFWS 2005, 2006b). In addition, national Bureau of Land Management grazing 

administration regulations became effective in 1996, which provided direction for states to 

develop Standards for Rangeland Health and Guidelines for Grazing Management on Bureau of 

Land Management Lands (BLM 1996). All of the states within the range of the desert tortoise 

have incorporated standards and guidelines into their management plans. 

Under the West Mojave Plan (BLM et al. 2005), grazing has been retired on several 

allotments mostly within designated critical habitat or DWMAs. Additional restrictions such as 

season of use and forage type (ephemeral or perennial) have also been instituted on some 

allotments within the plan area. Fort Irwin, which lies within the West Mojave Plan area, 

purchased fee lands within three cattle allotments in the Western Mojave Recovery Unit to 

partially offset the effects of its base expansion, and the Bureau of Land Management 

subsequently retired these allotments. The Bureau of Land Management has removed grazing 

24
from at least four other allotments in the plan area. Collectively, over 307,560 hectares (760,000 

acres) in the West Mojave Plan area have been retired from grazing (USFWS 2006b). 

Where grazing will continue within the West Mojave Plan area, the Bureau of Land 

Management has identified a number of conservation prescriptions to be implemented within 

cattle and sheep allotments, which include existing Regional Public Land Health Standards and 

Guidelines for Grazing Management, utilization restrictions, guidelines for grazing both within 

and outside of desert tortoise habitats and DWMAs, terms and conditions of existing Fish and 

Wildlife Service biological opinions, and new management prescriptions contained in the plan 

(BLM et al. 2005; USFWS 2006b). 

The Northern and Eastern Mojave Desert Management Plan (BLM 2002a) removed or 

restricted grazing on approximately 126,260 hectares (312,000 acres) within DWMAs in the 

Northeastern and Eastern Mojave recovery units, which constitutes all but about 5,261 hectares 

(13,000 acres) of critical habitat in the Shadow Valley and Ivanpah Valley DWMAs. One 

relatively small allotment within the Ivanpah Valley DWMA will remain open with some 

utilization restrictions, and all ephemeral allotments within DWMAs will be terminated (USFWS 

2005). 

The Northern and Eastern Colorado Desert Coordinated Management Plan (BLM 2002b) 

established two DWMAs that encompass over 647,500 hectares (1,600,000 acres). Only one 

allotment remains within designated critical habitat or a DWMA. Approximately 8,090 hectares 

(20,000 acres) of this active allotment was closed to grazing due to high tortoise densities, and in 

other portions of the allotment, utilization restrictions and season of use requirements will be 

implemented (USFWS 2005). 

Under the Mojave National Preserve General Management Plan (NPS 2002b), grazing 

has been removed on nine allotments and remains active on another two (D. Hughson, NPS, 

pers. comm. 2007). The overall management goal is to completely remove grazing on the entire 

Preserve through voluntary relinquishment by lessees or acquisition of grazing permits and water 

rights by conservation organizations. As the acquisition process moves forward, and for permit 

holders unwilling to sell, grazing will continue. These activities will be managed according to 

Bureau of Land Management allotment management plans and National Park Service grazing 

management plans, together with additional restrictions designed to give resource protection 

priority over grazing (NPS 2002b). 

Since 1994, the Bureau of Land Management and U.S. Forest Service have closed 70 

ephemeral grazing allotments in Clark and southern Nye counties totaling over 2,023,400 

hectares (5,000,000 acres). Approximately 22,600 hectares (56,000 acres) currently remain 

available for grazing in 5 allotments in Clark and southern Nye counties (E. Masters, BLM, pers. 

comm. 2007). According to the Las Vegas Resource Management Plan, no legal grazing occurs 

within Areas of Critical Environmental Concern in Clark County and southern Nye County 

(ACECs; BLM 1998a). Under the Clark County Multiple Species Habitat Conservation Plan 

(MSHCP) and its predecessor (see discussion below), which lies within the Las Vegas District of 

the Bureau of Land Management, the County has been actively purchasing the rights to 

25
permanently remove grazing from over 809,370 hectares (2,000,000 acres) of public lands within 

and outside of DWMAs (J. Bair, USFWS, pers. comm. 2007). 

Under the Caliente Management Framework Plan Amendment (Lincoln County, 

Nevada), all allotments or portions of allotments within ACECs were closed to livestock grazing 

(85,996 hectares [212,500 acres]). Outside ACECs, season of use on all perennial allotments was 

established through allotment evaluation and multiple-use decision processes. It was determined 

for areas outside ACECs, livestock use could occur between March 15 and October 15 provided 

forage utilization does not exceed 40 percent for key perennial grasses, forbs, and shrubs (BLM 

2000). 

Allotment closures and restrictions were also instituted on the Bureau of Land 

Management Arizona Strip District within ACECs and within the National Monuments (BLM 

1998b; BLM 2007a). However, livestock grazing is authorized on portions of 11 allotments that 

support desert tortoise habitat. Grazing activities will be limited in these areas through utilization 

restrictions and season-of-use requirements; grazing use is limited to October 15 through March 

15, generally coinciding with desert tortoise inactivity. Ecological site inventory (basic inventory 

of present and potential vegetation on BLM rangelands) data are expected to serve as the 

baseline for range conditions and utilization is not to exceed 45 percent of the current year’s 

growth. Overall, conditions must meet the Bureau of Land Management’s Standards for 

Rangeland Health and National Park Service’s Vital Sign Standards (BLM 2007a). 

4. Land Acquisitions and Habitat Conservation Plans (HCPs) 

Land acquisitions and transfers may negatively impact desert tortoises and their habitats 

when the lands are targeted for urban development. On the other hand, these transactions may 

result in conservation benefits. For instance, since 1986, California Department of Fish and 

Game has acquired over 19,670 hectares (48,000 acres) of desert tortoise habitat within critical 

habitat, and additional lands with endowment fees have been and continue to be acquired 

through mitigation for projects that impact tortoise habitats. To ensure management of these 

lands, endowment fees are collected for each parcel acquired (Steele and Jones 2006). In 

addition, under the Southern Nevada Public Lands Management Act (see Appendix A: Land 

Acquisitions, Exchanges, and Transfers), approximately 1,500 hectares (3,725 acres) within 

occupied or suitable desert tortoise habitat have been purchased since 2000 through the land 

acquisition program for environmentally sensitive lands (BLM 2007b). 

In 1999, The Wildlands Conservancy facilitated the purchase of nearly 242,810 hectares 

(600,000 acres) under their California Desert Land Acquisition Project. It also funded land 

exchanges that resulted in the addition of over 14,160 hectares (35,000 acres) into six Bureau of 

Land Management wilderness areas and gifted an additional 11,330 hectares (28,000 acres) of 

acquired lands to Joshua Tree National Park. The acquisition of these lands will ensure 

landscape-level conservation into the future and will provide habitat connectivity and reduce the 

potential for fragmentation (The Wildlands Conservancy 2007). 

The Department of the Army purchased approximately 40,100 hectares (99,100 acres) of 

lands formerly owned by the Catellus Development Corporation and fee lands within three cattle 

26
allotments in the Western Mojave Recovery Unit to partially offset the effects of the National 

Training Center expansion; the Bureau of Land Management subsequently retired these 

allotments. This mitigation resulted in the relinquishment of grazing on over 129,500 hectares 

(320,000 acres) (R. Bransfield, U.S. Fish and Wildlife Service, pers. comm. 2007). 

Several HCPs have been developed for private lands within desert tortoise habitat that 

include provisions for acquisitions and transfers that would meet the objectives of the HCP as 

well as secure conservation lands for tortoises. However, land acquisition is an expensive, timeconsuming task. For example, 61 separate actions were necessary to acquire just over 3,760 

hectares (9,300 acres) within the 25,090-hectare (62,000-acre) Red Cliffs Desert Reserve, which 

was established to provide protection for the desert tortoise and its habitat under the 1996 

Washington County HCP in Utah. Approximately 2,995 hectares (7,400 acres) remain to be 

acquired within the present boundaries of the Reserve. The approximate value of the lands 

acquired stands at $87,073,000 (not adjusted for present value) (J. Crisp, BLM, pers. comm. 

2007). 

In southern Nevada, the Clark County Multiple Species Habitat Conservation Plan 

(MSHCP) was completed in 2000. The Clark County MSHCP superseded the Desert 

Conservation Plan, which was prepared in response to the Federal listing of the desert tortoise as 

a threatened species. The MSHCP plan area encompasses a total of 169,160 hectares (418,000 

acres) (all of Clark County and, for the Nevada Department of Transportation, portions of Nye, 

Lincoln, Mineral, and Esmeralda counties, Nevada) (RECON 2000). The underlying purpose of 

the MSHCP is to achieve a balance between the long-term conservation of listed species and 

natural resources that are an important part of the natural heritage of Clark County and the 

economic development of Clark County (USFWS 2000a). As additional mitigation under the 

MSHCP, Clark County purchased a 34,800-hectare (86,000-acre), long-term conservation 

easement (50 years) from Boulder City. 

Under the Clark County MSHCP, site-specific conservation management strategies were 

required for each of the DWMAs within the county; these include Coyote Springs, Gold Butte, 

Mormon Mesa, and Piute-Eldorado (Clark County 2007a,b,c,d, respectively). The purpose of 

each conservation management strategy is to guide species and habitat management using a 

coordinated, adaptively managed approach. Each strategy identifies management actions, 

protective measures, restoration efforts, public outreach and education, inventory and monitoring 

actions, applied research actions, and impact mitigation measures that will direct conservation of 

tortoises and their habitats. 

Habitat conservation plans are also being developed for other parts of southern Nevada. 

The Southeastern Lincoln County HCP is in the final planning stages. The plan area totals 

720,400 hectares (1,780,140 acres), of which 311,365 hectares (769,400 acres) is desert tortoise 

habitat. Approximately 9,090 hectares (20,000 acres) of the tortoise habitat within the plan area 

will be developed over a 30-year time frame. The focus of this plan is to provide a mechanism to 

allow orderly growth and development north of Mesquite and urban expansion in the Alamo area 

in Lincoln County (J. Brown, USFWS, pers. comm. 2007). Efforts to develop a HCP for the 

Coyote Springs Valley in Lincoln County are also in the final planning stages. This plan includes 

allowing development of 8,680 hectares (21,454 acres) over 40 years while setting aside a 5,570­

27
hectare (13,767-acre) reserve for the desert tortoise and other sensitive species. In addition, 

mitigation fees paid by the applicant for the loss of desert tortoise habitat would be used to fund 

management of the reserve and desert tortoise research. A short-term HCP is also being 

developed for activities around the town of Pahrump in Nye County. As in Clark County, this 

plan will be superseded by a long-term HCP that will address the portions of the county within 

the range of the tortoise, including Pahrump. 

The Coachella Valley MSHCP in Riverside County, California would establish 

conservation areas and a reserve system for species and natural communities covered under the 

plan, including the desert tortoise. These lands constitute approximately 301,855 hectares 

(745,900 acres) within the 485,620-hectare (1,200,000-acre) plan area boundary. About 206,790 

hectares (511,000 acres) of desert tortoise habitat lies within the areas identified for conservation 

under the Coachella Valley MSHCP, with about 65,150 hectares (161,000 acres) not yet secured 

for these purposes. The conserved lands include the 9,090-hectare (20,000-acre) Coachella 

Valley Preserve that was established in 1986 for Coachella Valley fringe-toed lizard (Uma 

inornata). Over 26,300 hectares (65,000 acres) (12 percent of all habitat and 28 percent of nonFederal land within the plan area) are subject to disturbance under the plan. This constitutes 

about 4,450 hectares (11,000 acres) of what is considered “core” habitat for various species as 

described in the Coachella Valley MSHCP. This plan is currently in the final planning stages 

(Coachella Valley Association of Governments 2007). 

The California Desert Conservation Area Plan Amendment for the Coachella Valley 

specifically commits the Bureau of Land Management to conserving at least 99 percent of 

vegetation community types on the lands it administers within the MSHCP reserve system. In the 

portion of the MSHCP area where the Northern and Eastern Colorado Desert Coordinated 

Management Plan applies to federal land, new surface disturbance is cumulatively limited to 1 

percent of the federal portion of each critical habitat unit, which is consistent with the other large 

regional plans (Coachella Valley Association of Governments 2007; BLM 2002c). 

Within the region covered by the West Mojave Plan (BLM et al. 2005), a MSHCP is 

currently being drafted for development on approximately 1,214,000 hectares (3,000,000 acres) 

of private lands. This plan may cover as many as 15 species, including the desert tortoise. The 

MSHCP is still in the planning stages and the specific goals and objectives have yet to be 

determined. 

Unfortunately, while desert tortoise population monitoring has occurred in association 

with the Washington County HCP and Clark County MSHCP, in particular, the duration of 

monitoring efforts has been insufficient to date to observe detectable, large-scale increases in 

tortoise populations or habitat condition (see Population Trends and Distribution). Continued 

management and focused monitoring, similar to the recovery strategy outlined below, are 

required to determine whether the HCPs are meeting their objectives. 

5. Other Activities 

Over 404,685 hectares (1,000,000 acres) of Mojave Desert vegetation burned in wildfires 

in 2005 and 2006, fueled largely by invasive, non-native grasses. About half of the areas burned 

28
supports desert tortoise habitat, and if this trend continues, native plant communities and much of 

the diversity of the Mojave Desert ecosystem may eventually be lost. Because of this recent 

devastating fire activity in the Mojave Desert, research scientists, land managers, and agency 

biologists in Arizona, Nevada, and Utah have come together to develop an initiative designed to 

protect intact, functional habitats and restore key areas that have burned. This initiative is a 

collaborative effort among Federal, state, and local jurisdictions and will focus on fire 

management and habitat protection and restoration. 

During the summer of 2005, wildfires burned approximately 36,180 hectares (89,400 

acres) within the Pakoon Basin of the Grand Canyon Parashant National Monument; about 

14,570 hectares (36,000 acres) are located within the Gold Butte-Pakoon critical habitat unit for 

the desert tortoise. As a result, the Arizona Strip District of the Bureau of Land Management 

initiated soil stabilization and revegetation efforts of desert tortoise habitats using a variety of 

treatments, including aerial seed application, mechanical seed incorporation, and grazing 

exclusion (fencing). Rehabilitation objectives and success criteria will be developed, and 

invasive species establishment will be controlled. Treatments within each area affected by the 

fires will be monitored at either existing or new monitoring sites through 2009 (USFWS 2006c). 

In addition, we issued a memo to the Desert Tortoise Management Oversight Group in May 2006 

recommending that when feasible, implementing fire suppression techniques that minimize 

impacts to the habitat is desirable; however, reduction of total acreage lost to fire, especially in 

critical habitat, through the use of mobile attack with engines, fireline construction with 

bulldozers, aerial fire retardant, or other necessary techniques should be prioritized. 

We are currently undertaking efforts to reduce human subsidies of food, water, and nest 

sites to the common raven in the California desert. Activities designed to reduce raven predation 

on desert tortoises include reducing trash availability at landfills, removing illegal dumps, 

fencing along highways to reduce road-kills, and removing or modifying nesting and roost sites. 

The program also provides immediate protection to hatchling and juvenile desert tortoises by 

identifying and removing ravens that have preyed or attempted to prey on desert tortoises. The 

environmental assessment we recently released provides a full description of the proposed 

activities (USFWS et al. 2008). 

In addition, Bureau of Land Management’s West Mojave Plan includes a series of 

recommendations to reduce raven predation on the desert tortoise including, but not limited to, 

controlling solid and organic wastes and standing water at and outside of sanitary landfills; 

encouraging livestock operators to reduce availability of food sources for ravens; limiting 

availability of nesting and perch substrates, especially in the urban interface; selectively 

removing problem ravens especially within the Desert Tortoise Natural Area, critical habitat 

units, and head-starting sites; conducting additional research on raven life history, behavior, and 

efficacy of control methods; and implementing adaptive management and public education 

programs (BLM et al. 2005). 

The California Desert Managers Group oversees a program to develop and implement an 

information and education campaign about the desert tortoise to build public support for, and 

involvement in, its recovery. The Clark County (Nevada) Desert Conservation Program also 

includes an education component that targets communities in southern Nevada and extends into 

29
portions of Arizona. The outreach efforts attempt to inform the public about desert tortoise 

conservation issues through brochures, surveys and feedback, and educational materials for 

schools. 

I. BIOLOGICAL CONSTRAINTS AND NEEDS 

The biological constraints that were identified in the 1994 Recovery Plan (i.e., life history 

and reproductive characteristics and maintenance of genetic and ecological variability) remain 

important considerations in current and future recovery planning and implementation. Desert 

tortoises possess a combination of life history and reproductive characteristics that affect the 

ability of populations to survive external threats. For instance, this long-lived species requires 13 

to 20 years to reach sexual maturity and has low reproductive rates during a long period of 

reproductive potential (Turner et al. 1984; Bury 1987; Germano 1994). Also, similar to other 

turtles, desert tortoises experience relatively high mortality early in life. These factors make 

recovery of the desert tortoise more difficult, and 1 or 2 good years of reproductive success do 

not signal a trend toward recovery any more than several poor ones signal inevitable 

extirpation (USFWS 1994a). Delayed but prolonged reproduction is advantageous where 

availability of resources is unpredictable and juvenile survival rates are highly variable, but 

even moderate downward fluctuations in adult survival rates can result in rapid population 

declines. Thus, high survivorship of adult desert tortoises is critical to the species’ persistence, 

and the slow growth rate of populations can leave them susceptible to extirpation events in 

areas where adult survivorship has been reduced (USFWS 1994a). 

Another factor integral to desert tortoise recovery is maintaining the genetic and 

ecological variability known to exist within and among populations. This variation is necessary 

to allow tortoises to adapt to changes in the environment over time (USFWS 1994a). Finally, 

because desert tortoises occupy large home ranges, the long-term persistence of extensive, 

unfragmented habitats is essential for the survival of the species (USFWS 1994a). Contiguous 

native vegetation communities provide shrubs for cover and annuals for forage. The loss or 

degradation of these habitats to urbanization, habitat conversion from frequent wildfire, or 

other landscape-modifying activities place the desert tortoise at increased risk of extirpation. 

30
 

II. RECOVERY PROGRAM 

A. RECOVERY STRATEGY 

Recovery of the desert tortoise has been and will continue to be complex and challenging 

in part because tortoise populations face a wide range of threats. Because desert tortoises require 

over a decade to reach sexual maturity, have temporally variable reproduction, and juveniles 

have variable but low survival rates, tortoise populations will be naturally slow to increase in 

response to strategies designed to ameliorate anthropogenic impacts. These life history 

characteristics, combined with reduced populations and extended time periods for recovery of 

desert ecosystems, also make it difficult to assess relative impacts of individual threats. 

The 1994 Recovery Plan described a strategy for recovering the desert tortoise, which 

included the identification of six recovery units, recommendations for a system of Desert 

Wildlife Management Areas (DWMAs) within the recovery units, and development and 

implementation of specific recovery actions focused within the DWMAs. Maintaining high 

survivorship of adult desert tortoise was identified as the key factor in recovery. We recognize 

that the most significant challenge in the implementation of the 1994 Recovery Plan was not the 

number or types of actions implemented, but rather the coordination, description, documentation, 

and evaluation of implementation of the actions (Tracy et al., 2004). As a result, the revised 

strategy described herein emphasizes partnerships to direct and maintain focus on implementing 

recovery actions and a system to track implementation and effectiveness of recovery actions. 

Strategic elements within a multi-faceted approach designed to improve the 1994 Recovery Plan 

are: 

1. Develop, support, and build partnerships to facilitate recovery; 

2. Protect existing populations and habitat, instituting habitat restoration where necessary; 

3. Augment depleted populations in a strategic manner; 

4. Monitor progress toward recovery; 

5. Conduct applied research and modeling in support of recovery efforts within a strategic 

framework; and 

6. Implement a formal adaptive management program through which information gained 

while implementing the above strategic elements is used to revise and improve the 

recovery plan and recommend management actions on a regular basis. 

Each strategic element is described more fully below, but the recovery program does not provide 

a “cookbook” of prescriptions that will ensure recovery of the desert tortoise. Instead, this 

program establishes a process by which recovery can be achieved. 

31
1. Strategic Element 1: Develop, Support, and Build Partnerships to Facilitate Recovery 

Implementing a recovery plan for a species with a wide distribution and facing such 

complex challenges requires many cooperators and diverse partnerships. As noted above, we 

believe the most significant challenge in the implementation of the 1994 Recovery Plan was not 

the number or types of actions implemented, but rather the coordination, description, 

documentation and evaluation of implementation of the actions. The revised recovery plan 

emphasizes partnering across jurisdictional boundaries through standing Recovery 

Implementation Teams to maintain focus on implementing and tracking recovery actions. 

Therefore, this element relies on the successful establishment of regional, long-term Recovery 

Implementation Teams comprised of land managers, stakeholders, and scientists that will work 

together to develop recovery-action plans, prioritize recovery actions on the ground, secure 

necessary resources, and compile results into a range-wide database and decision support system 

that can be applied at the local level (Element 6). The Recovery Implementation Teams will also 

facilitate education and outreach activities to build support for, understanding of, and compliance 

with the recovery program. Organization of Recovery Implementation Teams will likely be 

based on recovery units, but it may vary depending on logistical practicalities among the 

representatives. Our Desert Tortoise Recovery Office will serve as the focal point for 

coordinating Recovery Implementation Teams in cooperation with the Desert Tortoise 

Management Oversight Group. 

2. Strategic Element 2: Protect Existing Populations and Habitat 

Since 1994, desert tortoise habitat has continued to be lost or severely degraded (e.g., by 

urbanization, fire, invasive plants; see Appendix A), keeping tortoise populations in a precarious 

state, including those that may not be currently in decline. As a result, protecting existing 

populations and habitat is paramount. The recommended actions in the 1994 Recovery Plan 

formed a logical basis for recovery (GAO 2002), and little information since 1994 contradicts 

these recommendations (Boarman and Kristan 2006). In fact, due to slow growth rates of 

individuals and populations, insufficient time has elapsed over which detectable increases in 

desert tortoise populations could be realistically expected. In any case, applying uniform, highly 

restrictive regulations across the entire Mojave population is not feasible, even if we knew the 

precise mechanisms affecting population declines at each site. Therefore, aggressive 

management as generally recommended in the 1994 Recovery Plan needs to be applied within 

existing tortoise conservation areas (Box 2) or other important areas identified by Recovery 

Implementation Teams (Element 1) to ensure 

that populations remain distributed throughout Box 2. “Tortoise conservation areas,” 

the species’ range. Tortoise conservation areas collectively depicted in Figure 2, include desert 

capture the diversity of the Mojave population tortoise habitat within critical habitat, Desert 

of the desert tortoise within each recovery unit, Wildlife Management Areas, Areas of Critical 

Environmental Concern, Grand Canyon­ conserving the genetic breadth of the species Parashant National Monument, Desert National and providing a margin of safety for the species Wildlife Range, National Park Service lands, to withstand catastrophic events. Especially Red Cliffs Desert Reserve, and other given uncertainties related to the effects of conservation areas or easements managed for climate change on desert tortoise populations desert tortoises.

and distribution, we consider tortoise 

32
conservation areas to be the minimum baseline within which to focus our recovery efforts. Much 

of the land contained within existing tortoise conservation areas is managed under multiple-use 

directives. It must also be recognized that activities occurring on lands beyond the boundaries of 

existing tortoise conservation areas can affect tortoise populations and the effectiveness of 

conservation actions occurring within the conservation area boundaries. Agencies must work 

within the context of their respective land use plans to determine how to effectively implement 

recovery actions contained within this plan. 

Recovery Implementation Teams should use the decision support system (Element 6) to 

guide management both inside and outside tortoise conservation areas, according to different 

opportunities or constraints within different areas and jurisdictions. While recovery efforts may 

be prioritized within existing desert tortoise conservation areas, populations, habitats, and actions 

outside of these areas may also contribute to (or hamper) recovery of the species, and their 

importance is in no way diminished (other local, State, or Federal regulations may apply to 

actions potentially impacting tortoises and habitat outside tortoise conservation areas). For 

example, Department of Defense lands are subject to more dramatic changes in management or 

use than other Federal lands depending on the changing national security situation. However, the 

value of military lands to conservation has long been recognized. Similarly, wilderness 

designation on public lands entails restrictions on the types of activities that may be conducted 

there, precluding or otherwise limiting several forms of active management activities. Military 

lands, wilderness areas, and other land designations with conservation objectives include a great 

deal of desert tortoise habitat outside of and contiguous with tortoise conservation areas (see 

Figure 3), making them valuable components of the recovery landscape. In addition to habitat 

management recommendations, specific recommendations for managing desert tortoise 

populations relative to disease have been developed by the Science Advisory Committee 

(Appendix B) and are incorporated herein. 

3. Strategic Element 3: Augment Depleted Populations through a Strategic Program 

Because of the intractable nature of discriminating specific effects of threats on desert 

tortoise populations, we are placing an emphasis on proactively bolstering populations where 

possible. Augmentation will be approached experimentally, in terms of both the continued 

development and evaluation of techniques and the use of augmentation to help us assess specific 

threats and recovery actions (Tracy et al. 2004; Armstrong and Seddon 2007). Population 

augmentation in conjunction with threats management and restoration activities (Element 2) and 

research (Element 5) designed to investigate the effectiveness of these actions is a means to both 

gain insights into causes of declines and to increase the rate at which depleted populations could 

be revived. It is important to realize that if the causes of tortoise population declines are not 

addressed, simply increasing population numbers in the wild through augmentation will not 

result in recovery. Augmentation will not be a long-term strategy for conservation of the desert 

tortoise, but rather a short-term strategy to increase populations more rapidly than possible 

through natural processes. 

An augmentation strategy will be developed that identifies locally depleted or extirpated 

populations, particularly within desert tortoise conservation areas. Translocation and headstarting (described below) will be used to augment (or re-establish) these populations in 

33
 

conjunction with elevated threat management and/or habitat restoration (Element 2) or directed 

research on the factors affecting success of the augmentation strategy (Element 5). 

Head-starting and translocation are fundamental aspects of the augmentation program. 

Both must account for factors such as genetics and disease. Head-starting is raising of young in 

captivity to allow them to reach sizes at which they are less vulnerable to certain threats, such as 

predation by ravens, before translocation to the wild. Currently, experiments in head-starting are 

taking place at several locations in California. Research at the National Training Center’s Fort 

Irwin Study Sites (FISS 1 and FISS 2), Edwards Air Force Base, and the Marine Corps Air 

Ground Combat Center at Twentynine Palms has laid a strong foundation on which to build (see 

Morafka et al. 1997; Dickson et al. 2006; Henen et al. 2007), and facilities at these sites will 

likely be important in a collaborative head-starting effort. Head-starting facilities are lacking in 

Arizona, Nevada, and Utah, but proposals are being developed to use the Desert Tortoise 

Conservation Center in Las Vegas as the site for new facilities servicing several surrounding 

recovery units. The Desert Tortoise Recovery Office will coordinate development of guidelines 

and protocols for the head-starting of desert tortoises range-wide in accordance with our 

controlled propagation policy (USFWS 2000b). 

Augmentation also involves translocation of tortoises to pre-selected sites. The efficacy 

of translocation itself has been questioned over the years. Early studies did not provide sufficient 

evidence to support or refute translocation as a conservation strategy (see Berry 1974; Cook et 

al. 1978; Cook 1983). More recent studies have shown initial success in translocation to be high 

(Field et al. 2000; Nussear 2004; Field et al. 2007). Again, the Desert Tortoise Recovery Office 

will coordinate the development of translocation guidelines and protocols to be implemented 

range-wide, taking into account guidelines for addressing disease issues in translocation 

developed by the Science Advisory Committee (Appendix B). 

4. Strategic Element 4: Monitor Progress toward Recovery 

Monitoring is a fundamental requirement for adaptive management (Element 6). It is one 

process by which information is updated and the success of recovery actions can be evaluated. 

This information can be used adaptively, to refine management during the course of recovery, to 

evaluate progress toward achieving recovery criteria, and to help evaluate whether delisting the 

species may be appropriate. While the 1994 Recovery Plan focused exclusively on monitoring 

desert tortoise populations, a multi-dimensional monitoring program is necessary to assess the 

status of tortoise populations, habitat, and threats (Tracy et al. 2004). Monitoring activities 

described in this plan are therefore tied directly to individual recovery criteria related to these the 

status of populations, habitat, and threats. Recovery progress will be measured by monitoring 

trends in tortoise distribution, abundance, and population growth. The quantity and quality of 

habitat and the distribution of threats across the landscape also will require monitoring over time. 

The protracted life history and longevity of the desert tortoise, as well as the long time 

frame necessary for habitat restoration in the desert, require long-term monitoring to measure 

success. However, evaluations at 5-year intervals will identify potential trends, will feed into 5­

year status reviews, and will provide an opportunity to adjust management based on any 

observed trends. Effectiveness monitoring of specific management actions is also needed 

34
(Boarman and Kristan 2006) and is discussed below as applied research.(Element 5). It is also 

important that monitoring be conducted as an integrated effort, coordinated through the Desert 

Tortoise Recovery Office, to ensure that efficiency of the recovery program and review of its 

progress are maximized. Consistent agency reporting through the decision support system 

(Elements 1 and 6) will help identify correlations between management efforts or threat 

reduction and tortoise populations, which can signify successful management. 

5. Strategic Element 5: Conduct Applied Research and Modeling in Support of Recovery 

Efforts within a Strategic Framework 

In this plan we update the research recommendations from the 1994 Recovery Plan with 

new priorities. Although scientists have studied desert tortoises for over 3 decades, many 

important questions remain unanswered. In particular, we have a relatively poor understanding of 

how some human activities interact with ecological factors to affect tortoise populations and 

what threat-abatement measures might counteract those effects. As mentioned above, the desert 

tortoise’s life history makes it difficult to tease apart relative impacts of individual threats 

(although some impacts, such as habitat loss, are fairly straightforward in that they eliminate 

populations completely). As a result, studying most individual threats/management actions in 

isolation from other possible threats/actions is impractical. However, such topics should be 

studied experimentally whenever possible. Given the difficulties surrounding applied ecological 

research on the desert tortoise, ecological models should be co-developed with management 

actions to make and test predictions about tortoise population responses to threats or 

management actions. These models then can be modified as new information becomes available 

(Element 6). Finally, similar to the coordination required of the monitoring program (Element 4), 

research should be coordinated through the Desert Tortoise Recovery Office (with advice from 

the Science Advisory Committee and input from the Recovery Implementation Teams) to ensure 

that the highest priority questions are addressed first and that the entire recovery program can be 

leveraged from timely research results. 

6. Strategic Element 6: Implement a Formal Adaptive Management Program 

Integrating the results of recovery actions into a formal adaptive management program is 

critical to recovering the desert tortoise and serves as the foundation of an effective recovery 

plan if successfully implemented. Even though the 1994 Recovery Plan called for regular 

updates based on new information, a formal process for accomplishing this task was not 

established. Using research and monitoring to revise management efforts on an ad hoc basis is 

inefficient and has contributed to slow progress in the recovery of desert tortoise since 1994. The 

Department of Interior technical guide on adaptive management provides an operating definition 

adopted from the National Research Council: 

Adaptive management [is a decision process that] promotes flexible decision making that 

can be adjusted in the face of uncertainties as outcomes from management actions and 

other events become better understood. Careful monitoring of these outcomes both 

advances scientific understanding and helps adjust policies or operations as part of an 

iterative learning process. Adaptive management also recognizes the importance of 

natural variability in contributing to ecological resilience and productivity. It is not a 

35
‘trial and error’ process, but rather emphasizes learning while doing. Adaptive 

management does not represent an end in itself, but rather a means to more effective 

decisions and enhanced benefits. Its true measure is in how well it helps meet 

environmental, social, and economic goals, increases scientific knowledge, and reduces 

tensions among stakeholders (Williams et al. 2007). 

Adaptive management is a structured approach (implementation-monitoring-evaluationadjustment) that emphasizes accountability and explicitness in decision making (Williams et al. 

2007). Critical to successful adaptive management is the development of conceptual models that 

link management actions to predicted responses by desert tortoise populations or their habitat. 

Implementing a formal adaptive management program, integrated among agencies as much as 

possible, will enable us to continually update and improve models and the accuracy of 

predictions regarding the effects of management actions. Realistic expectations of adaptive 

management should recognize, however, that the life history of desert tortoises and the complex 

interactions among tortoise populations, habitat, and threats will typically result in extended 

learning cycles over which improvements in understanding and management will occur. 

Therefore, we should not expect rapid cycles of implementation-monitoring-evaluationadjustment. In many cases, intermediate or indirect benchmarks may be needed to measure 

progress. 

Given the complexities of desert tortoise recovery described above, fully active adaptive 

management that vigorously pursues learning through management under structured 

experimental designs (Williams et al. 2007) will not always be possible. In these cases, passive 

adaptive management can be used to focus monitoring on resource status and other system 

attributes (Schwarz 1998; Williams et al. 2007). An assessment of the monitoring results can 

then be applied to on-the-ground management actions as we continue to learn and better 

understand the recovery needs of the species. In either case, the use of structured decision 

making and a decision support system will facilitate the adaptive management process (Ralls and 

Starfield 1995; Rauscher 1999; Williams et al. 2007). A decision support system is an interactive 

system that computes the output of a set of models (e.g., effects of a threat on a tortoise 

population) based on underlying databases (e.g., the spatial extent of the threat, tortoise 

population, and management actions). In fact, a decision support system will provide a vehicle 

for implementing adaptive management (Starfield and Bleloch 1991). The recovery decision 

support system will incorporate a range-wide, geospatial database of current management 

activities, threats, and tortoise populations, providing managers a better framework for 

recognizing and implementing successful recovery actions. Through the use of conceptual 

models and research and monitoring results (Element 5), the decision support system will 

provide an explicit, well-documented process for making decisions. 

Importantly, adaptive management requires an ongoing commitment of executive 

leadership, including management involvement and funding throughout the life of the recovery 

effort (Williams et al. 2007). It will also require effective communication among the various 

groups. Therefore, the Desert Tortoise Recovery Office will serve as the focal point for 

coordinating among agencies and researchers, through Recovery Implementation Teams 

(Element 1), to maintain and improve the decision support system. Finally, the Desert Tortoise 

Recovery Office will continue to coordinate with the Science Advisory Committee, which serves 

36
in an advisory role to us, to the interagency Desert Tortoise Management Oversight Group, and 

to the Recovery Implementation Teams to ensure that recovery action plans, recovery action 

effectiveness, research and monitoring, and recovery plan revision meet rigorous scientific 

standards. 

7. Synthesis and Implementation 

As indicated in the narrative above, these strategic elements are not independent of each 

other, but each is inter-connected with the others (Figure 4). The Desert Tortoise Management 

Oversight Group will be the partnership (Element 1) responsible for providing “executive-level” 

support and direction for recovery implementation, thus tying the entire program together. 

Regional Recovery Implementation Teams will include a member of the Desert Tortoise 

Recovery Office to provide guidance and coordination to land/wildlife managers and 

stakeholders on the teams, which will be responsible for developing step-down recovery-action 

plans and implementing those actions on the ground. The Recovery Implementation Teams may 

leverage existing management partnerships such as the California Desert Managers Group or the 

Southern Nevada Agency Partnership. The Management Oversight Group will review the 

recovery-action plans, and the Recovery Implementation Teams will report back to the 

Management Oversight Group on an annual basis to review progress. The Desert Tortoise 

Recovery Office will provide linkages between the Management Oversight Group, Recovery 

Implementation Teams, and Science Advisory Committee. 

Adaptive Management 

Figure 4. Schematic representation of strategic elements within the Desert Tortoise Recovery Program. 

The adaptive management program (including a decision support system; Element 6) 

provides a formal framework with which the partnerships can make better, more informed, and 

more explicit decisions. Through the partnership and adaptive management elements, habitat 

management (Element 2) and population augmentation (Element 3) actions will be prioritized, 

implemented, and reported. Monitoring (Element 4) effects of these specific actions, as well as 

progress toward overall recovery, will again feed into the adaptive management system and 

37
inform managers on recovery progress. Finally, applied research and modeling (Element 5) will 

help us better understand desert tortoise ecology and better define our expectations of 

management actions. The Desert Tortoise Recovery Office is responsible for reviewing Federal 

recovery/research permits and for ensuring that permitted research addresses priorities identified 

by the Recovery Implementation Teams and Science Advisory Committee. 

Implementation of recovery actions within each strategic element will result in more 

visible progress toward recovery of the desert tortoise. Likewise, mitigation of activities harmful 

to desert tortoises should draw on the suite of opportunities provided by these elements, with the 

flexibility to apply an action most appropriate to the situation. Communication between Fish and 

Wildlife field offices, the Desert Tortoise Recovery Office, Recovery Implementation Teams, 

and other agency staff through section 7 and 10 activities will ensure that these activities are 

consistent with the Recovery Implementation Teams’ recovery-action plans and this recovery 

program. 

B. RECOVERY UNITS 

Recovery of the desert tortoise will follow a geographic approach, similar to the 1994 

Recovery Plan. The desert tortoise is a wideranging species inhabiting a large geographic 

area, so recovery actions will be tailored to 

regional ecological and socio-political conditions 

within recovery units (Box 3). Recovery units 

should not be confused with “distinct population 

segments” (DPSs). Vertebrate populations that are 

“discrete” and “significant” under the Service’s 

DPS policy (USFWS 1996) and designated as 

DPSs can be considered for listing or delisting. At 

this time, we have not determined whether 

specific areas within the Mojave population of 

desert tortoise might constitute separate DPSs. 

Designation of DPSs can only be done through a 

formal rule-making process. Recovery plans do 

not designate DPSs. If recovery and delisting by 

DPS (or any other “significant portion of the 

range” as specified under the Endangered Species 

Act) is deemed desirable in the future, 

information provided in our recovery unit 

descriptions and elsewhere in this plan may help 

define appropriate areas for a potential delisting 

rule. 

1. Background 

Box 3. Recovery units for the desert tortoise 

are special units that are geographically 

identifiable and are essential to the recovery 

of the entire listed population, i.e., recovery 

units are individually necessary to conserve 

the genetic, behavioral, morphological, and 

ecological diversity necessary for long-term 

sustainability of the entire listed population. 

Recovery criteria (described below) must be 

evaluated for each individual recovery unit 

for the entire listed population of the desert 

tortoise to be considered for delisting. 

Recovery units collectively cover the entire 

range of the species. Critical habitat and 

other management designations included 

within “tortoise conservation areas” are focal 

areas for recovery within each recovery unit. 

As a result, evaluation of recovery criteria 

and implementation of most recovery actions 

will be focused within tortoise conservation 

areas as defined in Box 2 and Figure 2. 

The 1994 Recovery Plan identified six recovery units: Upper Virgin River, Northeastern 

Mojave, Eastern Mojave, Eastern Colorado, Northern Colorado, and Western Mojave (Figure 5). 

38
Figure 5. Recovery units as delineated in the 1994 Recovery Plan (outlined in purple). 

When the recovery units were delineated initially, genetic, morphological, ecological, and 

behavioral differences were identified at a species-wide scale (e.g., 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). Within the Mojave population, 

finer-scale genetic, morphological, ecological, and behavioral differentiation was acknowledged 

in the 1994 Recovery Plan (USFWS 1994a). Three closely related demes were identified in the 

Mojave population using a parsimony approach to compare the relative mitochondrial DNA 

(mtDNA) differences in restriction fragment length polymorphisms exhibited by the North 

American tortoise species (Lamb et al. 1989). Additional variation in habitat type and ecosystem 

interactions (including those influenced by humans), life history characteristics, and physiology, 

39
morphology, and behavior contributed to the identification of the original six recovery units. 

Further genetic resolution has since been recommended to enhance the best available data to 

delineate recovery units (Tracy et al. 2004). Two population genetic assessments have recently 

been completed and are in the process of being published (Hagerty and Tracy 2007; Murphy et 

al. 2007). In delineating recovery units for this plan, we considered genetic and ecological 

variation across the range of the species, as described below. 

2. Assessment of Revised Recovery Units 

(a) Genetic variation. Gene flow is the result of dispersal accompanied by successful 

reproduction and incorporation of genes in a population. Ultimately, gene flow governs the 

amount of genetic connectivity among populations. A lack of gene flow will allow populations to 

differentiate over time by means of genetic drift and natural selection. Desert tortoises possess 

characteristics that potentially allow for high levels of gene flow among populations. For 

example, individuals have the ability to move long distances (Berry 1986; Edwards et al. 2004a). 

The capability for long-distance dispersal, combined with longevity and opportunities to 

reproduce annually throughout adulthood, indicates high potential for gene exchange outside of 

local areas. Free genetic exchange will be constrained, however, by the large distributional range 

of the tortoise given the relatively much smaller home range size and dispersal ability (isolationby-distance phenomenon; see Allendorf and Luikart 2007:209). Topographic features (e.g., 

mountain ranges) and other potential barriers (e.g., impassable habitat types, extreme climate 

conditions) can structure regional populations and lead to variable exchange of migrants among 

populations. 

All recent genetic studies of the desert tortoise have suggested that its population 

structure is characterized by isolation-by-distance (Britten et al. 1997; Edwards et al. 2004b; 

Hagerty and Tracy 2007; Murphy et al. 2007). That is, populations at the farthest extremes of the 

distribution are the most differentiated, but a gradient of genetic differentiation occurs between 

those populations, across the range of the species. Historically, levels of gene flow among 

subpopulations were likely high, corresponding to high levels of connectivity among habitat 

types (Murphy et al. 2007). Historically high levels of gene flow are further supported by the fact 

that multidimensional scaling analysis of DNA microsatellite data depicts a continuous gradient 

of genetic difference across the range of the desert tortoise (Hagerty and Tracy 2007), and 

analysis of molecular variance revealed that over 93 percent of the variation occurs within, not 

among, populations (Hagerty and Tracy 2007; Murphy et al. 2007). In addition, with the 

exception of the Upper Virgin River Recovery Unit, assignment tests incorrectly placed 11 to 45 

percent of individuals (Murphy et al. 2007), a seemingly high level of immigration between 

regions to be explained by human-mediated translocations alone, especially given the general 

failure of such early translocations (Berry 1986). In contrast, greater than 90 percent of gopher 

tortoises were assigned to the correct genetic assemblage from where they were sampled in 

Georgia and Florida, where relocations of tortoises have been extensive (Schwartz and Karl 

2005). 

Based on the distribution of habitat occupied by the Mojave population of the desert 

tortoise, especially relative to that occupied by the Sonoran population (Figure 1; Germano et al. 

1994), genetic differentiation within the Mojave population is consistent with isolation by 

40
distance in a continuous-distribution model of gene flow. The continuous-distribution model of 

gene flow describes a situation in which populations of a particular neighborhood size could be 

identified anywhere (such as the sample sites of Murphy et al. 2007), and individuals inside 

those neighborhoods would represent a panmictic (randomly mating) group (Allendorf and 

Luikart 2007:209-211). To describe genetic relationships within species, methods require 

analysis of many individuals sampled across relatively evenly spaced locations. In a more-or-less 

continuous population, we risk wrongly inferring genetic discontinuities between sampling 

locations if clusters of individuals are sampled from locations far apart (Allendorf and Luikart 

2007:400). As a result of the apparent pattern of gene flow among desert tortoise populations, we 

use genetic information to validate or reinforce other ecological or topographic boundaries, 

rather than as the primary means of identifying recovery units. 

(b) Ecological variation. Similar to the gradient of genetic differentiation across the 

desert tortoise’s range, the Mojave Desert is itself a transitional vegetation type wedged between 

the Great Basin and Sonoran deserts (Rowlands et al. 1982; Turner 1982; MacMahon 1990). 

Furthermore, physiographic and biological subdivisions of the Mojave Desert do not coincide 

(MacMahon 1990). The Colorado Desert (a subdivision of the Sonoran Desert) lies in the 

southeastern-most part of California and the Mojave population of the desert tortoise’s range, 

and it is recognized as a distinct biome with a different climate relative to the Mojave Desert 

(Brown 1982). However, separation of the Mojave Desert along its boundary with Sonoran 

(Colorado) desertscrub is commonly blurred because distinct coincidental breaks in indicator 

species’ ranges are lacking (Turner 1982). In addition, climate variables vary linearly across the 

range of the desert tortoise (e.g., winter:summer rainfall; Figure 6; Table 4). The central Mojave 

is topographically and climatically transitional between the southwestern and eastern Mojave 

desert. The south-central Mojave is a transitional region to the Colorado Desert, and the southern 

half of this region is similar climatically and floristically to the eastern Mojave. Much of the 

differences in vegetation can be explained by differences in climate (Rowlands 1995). Given the 

broad or incongruent transitions between identified subdivisions of the Mojave and Sonoran 

deserts, we minimize the use of these transitions in identifying recovery units where other 

supporting data are absent. 

(c) Recovery unit delineation. Given the generally continuous variation in genetics and 

biomes across the Mojave desert tortoise’s range, our approach in delineating revised recovery 

units stressed identification of geographic discontinuities or barriers that coincide with any 

observed variation among tortoise populations. We use these geographic features to define 

boundaries between units. Several potential barriers are evident from topographic maps and the 

draft U.S. Geological Survey habitat model (Figure 1). We used differences in genetic, 

ecological, and physiological characteristics to help highlight boundaries or other differences 

between units, which is consistent with the argument that demographic, ecological, and 

behavioral considerations should often be of greater importance than genetic issues alone in the 

formulation of conservation plans for threatened or endangered species (Avise 2004:486-487). 

41
Figure 6. Ratio of rainfall in winter compared to summer in the Mojave Desert. Graph reprinted from 

Tracy et al. (2004). 

With the aid of modern GIS tools we are able to map boundaries of each recovery unit 

(Figure 7) much more precisely than in 1994, although as indicated above, transitions between 

recovery units are not always as precise on the ground as depicted by lines on a map. We have 

reduced the number of recovery units from six to five and have changed some boundaries of the 

1994 recovery units, as described below. Note that the peripheral boundaries, other than the 

Colorado River, are more or less arbitrarily depicted in Figure 7 with the intention of 

encapsulating the entirety of the desert tortoise’s current range. Descriptions of vegetation 

communities and complexes and related desert tortoise ecology are as generally described by 

Rowlands et al. (1982) and USFWS (1994a) except where otherwise noted. Finally, we also note 

that variation in genetics, behavior, morphology, ecology, or other evidence within recovery 

units emphasizes the need, when evaluating management actions (particularly head-starting and 

translocation), to consider whether the environmental conditions or habitat type of different 

populations has been different for many generations. If they have been, this could lead to 

adaptations even in the face of high gene flow that are important for the long-term persistence of 

the species (Allendorf and Luikart 2007:415; Murphy et al. 2007). 

(i) Upper Virgin River Recovery Unit. This recovery unit is equivalent to the 

original Upper Virgin River Recovery Unit and encompasses all desert tortoise habitat in 

Washington County, Utah, east of the Beaver Dam Mountains (Figure 8). 

The recovery unit includes the Upper Virgin River critical habitat unit and Washington 

County’s Red Cliffs Desert Reserve. Modeled tortoise habitat depicted directly south of 

the Red Cliffs Reserve and extending into Arizona has either been lost to urbanization or 

is not known to have ever been occupied (Bury et al. 1994). 

Recent DNA microsatellite evidence (Hagerty and Tracy 2007) suggests that there is little 

genetic differentiation between the Upper Virgin River and the neighboring recovery 

unit, which agrees with earlier evidence from allozyme (protein) and mtDNA markers 

(Lamb et al. 1989; Britten et al. 1997), although assignment tests correctly identified this 

42
recovery unit for greater than 95 percent of individuals sampled here (Murphy et al. 

2007). However, unique habitat characteristics and tortoise behavior in this region justify 

separating the most northern extreme of the tortoise’s range, east of the Beaver Dam 

Mountains, into a separate recovery unit. 

Figure 7. Revised recovery units for the Mojave population of the desert tortoise. Yellow ovals are 

general sampling areas from Murphy et al. (2007). Green dots are sample points from Hagerty and Tracy 

(2007). Recovery units encompass the entire range of the listed species, so the only “hard” peripheral 

edge is along the Colorado River; the northern, western, and southern boundaries are defined by the actual 

distributional limits of the desert tortoise. 

43
Figure 8. Upper Virgin River Recovery Unit. 

The tortoise population in the area of St. George, Utah, is at the extreme northeastern 

edge of the species’ range and experiences long, cold winters (about 100 freezing days) 

and mild summers (Table 4), during which the tortoises are continually active. Here the 

animals live in a complex topography consisting of canyons, mesas, sand dunes, and 

sandstone outcrops where the vegetation is a transitional mixture of sagebrush (Artemisia 

spp.) scrub, creosote bush scrub, blackbrush scrub, and a psammophytic (sandy-soil) 

community. Desert tortoises often use sandstone and lava caves instead of burrows, travel 

to sand dunes for egg laying, and use still other habitats for foraging. In contrast to 

populations at more distant parts of the range, two or more desert tortoises often use the 

same burrow. 

(ii) Northeastern Mojave Recovery Unit. The Northeastern Mojave Recovery Unit 

is equivalent to the original Northeastern Mojave Recovery Unit, extending into extreme 

southwestern Utah, northwestern Arizona, and into California’s Ivanpah Valley (Figure 

9). The east end of the unit extends south from the Beaver Dam Mountains, across the 

north end of the Virgin Mountains, down to the Colorado River. From the Colorado River 

at approximately Cottonwood Cove, the southern boundary extends west through 

Searchlight, down the New York Mountains, curving around to the south end of the 

44
Ivanpah Mountains, up to Mountain Pass. From here, the western boundary extends 

north-northeast up the spines of the Clark and Spring mountains before hooking back to 

the northeast through the Specter and Spotted ranges. 

Figure 9. Northeastern Mojave Recovery Unit. DWMA = Desert Wildlife Management Area; ACEC = 

Areas of Critical Environmental Concern; DTCC = Desert Tortoise Conservation Center. 

45
This recovery unit includes the Beaver Dam Slope, Gold Butte-Pakoon, and Mormon 

Mesa critical habitat units, as well as the Ivanpah Valley portion of the Ivanpah and the 

Eldorado Valley portion of the Piute-Eldorado critical habitat units (Figure 9). It also 

includes Lake Mead National Recreation Area south to Cottonwood Cove, Grand 

Canyon-Parashant National Monument on the Arizona Strip, the Mojave National 

Preserve (in Ivanpah Valley), and the Desert National Wildlife Range. 

DNA microsatellite data indicate that this unit is genetically similar to the Upper Virgin 

River Recovery Unit, but the Northeastern Mojave Recovery Unit does contain distinct 

microsatellite differences compared to the remainder of the range (Hagerty and Tracy 

2007). Some variation may occur to the south and west from the Mormon Mesa, but 

genetic breaks appear to be ambiguous relative to at least semi-permeable topographic 

barriers to gene flow, such as the Muddy Mountains (Hagerty and Tracy 2007). In the 

Las Vegas Valley, an allozyme cluster at one locus from populations in the Mormon 

Mesa critical habitat unit overlaps another cluster identified from populations in Piute 

Valley (Britten et al. 1997). Microsatellite and mtDNA analyses suggest that Searchlight 

Pass (part of the Highland Range extending into the Newberry Mountains) acts as a 

barrier between Eldorado and Piute Valleys (Lamb et al., 1989; Hagerty and Tracy 2007). 

Mountain Pass, which is comprised of the Ivanpah and Clark mountain ranges, appears to 

act as a semi-permeable barrier between Shadow Valley and Ivanpah Valley. The New 

York Mountains isolate Ivanpah Valley from Eldorado Valley. The Spring Mountains 

and the Spotted and Specter ranges act as a barrier for the western portion of this unit. A 

distinct shell phenotype also occurs in the Beaver Dam Slope region (USFWS 1994a; 

Britten et al. 1997), but these tortoises are not genetically isolated from adjacent 

populations (Bury et al. 1994). 

Desert tortoises in this recovery unit are generally found in creosote bush scrub 

communities of flats, valley bottoms, alluvial fans, and bajadas, but they occasionally use 

other habitats such as rocky slopes and blackbrush scrub. Average daily winter 

temperatures usually fluctuate above freezing, and summer temperatures are typically a 

few degrees cooler than the recovery units to the south and west. About 30 to 40 percent 

of annual rainfall occurs in summer (Table 4). Two or more desert tortoises often den 

together in caliche caves in bajadas and washes or caves in sandstone rock outcrops, and 

they typically eat summer and winter annuals, cacti, and perennial grasses. 

(iii) Eastern Mojave Recovery Unit. The Eastern Mojave Recovery Unit is 

approximately equivalent to the original Eastern Mojave Recovery Unit, spanning the 

Nevada-California border, including Oasis Valley, Amargosa Desert, Pahrump Valley, 

and extending south into Shadow Valley (Figure 10). From its border with the 

Northeastern Mojave Recovery Unit down the Spotted, Specter, and Spring mountain 

ranges to Mountain Pass and the south end of the New York Mountains, the eastern 

boundary extends down the Providence Mountains to the Granite Mountains. From there 

the western boundary extends north through the Bristol Mountains, Soda Lake, and 

Silurian and Death valleys. 

46
The recovery unit includes the east side of Death Valley National Park and much of 

Mojave National Preserve, as well as the Nevada Test Site and the southwestern end of 

the Nellis Air Force Range. It also includes most of the Ivanpah Valley critical habitat 

unit (Figure 10). 

Figure 10. Eastern Mojave Recovery Unit. DWMA = Desert Wildlife Management Area; ACEC = Areas 

of Critical Environmental Concern. 

47
A majority of this unit had not been sampled previously; however, recent microsatellite 

data reflect unique nuclear allele frequencies, indicating that this area is isolated from 

other recovery units (Hagerty and Tracy 2007). Allele frequencies from tortoises at 

Amargosa Desert and Pahrump Valley sites also form a homogeneous cluster different 

from other Nevada sites (Britten et al. 1997). The Spring Mountains and the Spotted and 

Specter ranges appear to form a barrier to tortoise movement between the eastern side of 

the recovery unit and the Northeastern Mojave Recovery Unit. Mountain Pass appears to 

act as a semi-permeable barrier between Shadow Valley and Ivanpah Valley. The 

Providence Mountains divide this recovery unit from Fenner Valley and the Colorado 

Desert Recovery Unit to the east. Saline Valley and Death Valley extending south into 

Silurian Valley and Soda Dry Lake act as a barrier between this recovery unit and the 

Western Mojave Recovery Unit. Although gene flow likely occurred intermittently 

during favorable conditions across this western edge of the recovery unit, this area 

contains a portion of the Baker Sink, a low-elevation, extremely hot and arid strip that 

extends from Death Valley to Bristol Dry Lake. This area is generally inhospitable for 

desert tortoises. 

In this section of the Mojave Desert, desert tortoises are often active in late summer and 

early fall, in addition to spring, reflecting the fact that this region receives up to about 25 

percent of its annual rainfall in summer (Table 4) and supports two distinct annual floras 

on which tortoises can feed. Winter temperatures rarely drop to freezing, except in the 

higher elevations (Table 4). These desert tortoises occupy a variety of vegetation types 

and feed on summer and winter annuals, cacti, perennial grasses, and herbaceous 

perennials. Tortoises den singly in caliche caves, bajadas, and washes, or caves in 

sandstone rock outcrops. Tortoises at the Nevada Test Site produce fewer eggs than 

similarly sized tortoises near Goffs in the Colorado Desert Recovery Unit (Mueller et al. 

1998). Tortoises at the Nevada Test Site grow to the largest reported size (21 centimeter 

[8.2 inch] carapace length) before reproducing compared to populations in other recovery 

units (Mueller et al. 1998). 

(iv) Colorado Desert Recovery Unit. This recovery unit combines the original 

Eastern Colorado and Northern Colorado recovery units, as well as a portion of the 

Eastern Mojave Recovery Unit in Piute and Fenner valleys. It is primarily found in 

California, though it extends into Piute Valley, Nevada, in the northern corner (Figure 

11). Piute Valley spans the northern border of the northern Colorado Desert and southern 

edge of the eastern Mojave Desert. The recovery unit shares its north and west 

boundaries with the Northeastern Mojave and Eastern Mojave recovery units: west from 

Cottonwood Cove Road, through Searchlight, down the New York and Providence 

mountains, to the Granite Mountains. From the Granite Mountains, the boundary extends 

through the Old Dad and Bristol mountains, southeast through Bristol Lake and Cadiz 

Valley, to the southern end of the Calumet Mountains. From there, the boundary drops 

down to and extends west along California State Highway 62 all the way to the San 

Bernardino Mountains, including the Morongo Basin. The southern boundary 

circumscribes the tortoise’s range east to the Colorado River. 

48
Figure 11. Colorado Desert Recovery Unit. DWMA = Desert Wildlife Management Area; ACEC = Areas 

of Critical Environmental Concern. 

The recovery unit includes the Piute-Eldorado critical habitat unit (south of Eldorado 

Valley) and the Chemehuevi, Pinto Mountain, and Chocolate Mountain critical habitat 

units. This unit encompasses the eastern end of Mojave National Preserve, the 

49
southernmost limits of Lake Mead National Recreation Area, Joshua Tree National Park, 

and the Chocolate Mountains Gunnery Range. 

Desert tortoises in this recovery unit share mtDNA haplotypes with the Western Mojave 

Recovery Unit (Lamb et al. 1989; Murphy et al. 2007) and possess the California shell 

type (USFWS 1994a). They are differentiated from desert tortoises in the Northeastern 

Mojave and Western Mojave recovery units at several allozyme loci (Rainboth et al. 

1989; Britten et al. 1997). Microsatellite data also support the boundary between the 

Colorado Desert Recovery Unit and the Northeastern Mojave and Eastern Mojave 

recovery units (Hagerty and Tracy 2007; Murphy et al. 2007), but less so with the 

Western Mojave Recovery Unit (Hagerty and Tracy 2007). Inclusion of the Fenner and 

Piute valleys in this recovery unit, rather than in the Eastern Mojave Recovery Unit as in 

1994, is justified by the contiguous habitat and the failure to reliably assign sampled 

tortoises to the correct site between Fenner and Chemehuevi valleys (Murphy et al. 

2007). 

The prominent Providence and New York mountain ranges, which transect Mojave 

National Preserve, isolate this recovery unit from the recovery units to the northwest. 

Searchlight Pass is the northern boundary, which separates Eldorado and Piute valleys. 

The north half of this recovery unit is separated from the Western Mojave Recovery Unit 

by the Baker Sink, a low-elevation, extremely hot and arid strip that extends from Death 

Valley to Bristol Dry Lake and Cadiz Valley. To the south, the transition between the 

Colorado and Mojave deserts is more subtle. However, urban development along 

California State Highway 62 now largely separates the two recovery units. While the 

Baker Sink almost divides this recovery unit in half, as generally reflected in the 1994 

Northern and Eastern Colorado recovery units (Figure 5), the Colorado Desert is a 

distinct biome that encompasses a continuum of climatic and floristic characteristics 

(Turner 1982) and only subtle differences were originally noted in these recovery unit 

descriptions (USFWS 1994a). Furthermore, minimal genetic variation is now recognized 

within the entire Colorado Desert biome (Hagerty and Tracy 2007; Murphy et al. 2007). 

What little genetic variation that has been observed between former Northern and Eastern 

Colorado recovery units is likely due to an absence of sampling from populations in the 

central part of the combined unit, south of Highway 62 and east of Highway 177 (cf. 

Allendorf and Luikart 2007:400; Figures 7 and 11). Patchy habitat southeast of the Cadiz 

Valley appears to provide some linkage between the northern and southern halves of this 

recovery unit (Figure 11). As a result, we merged these two recovery units. 

In the Colorado Desert Recovery Unit, desert tortoises are found in the valleys, on 

bajadas, desert pavements, rocky slopes, and in the broad, well-developed washes 

(especially to the south). Vegetation is characterized by relatively species-rich succulent 

scrub, creosote bush scrub, and blue paloverde (Parkinsonia florida)-ironwood (Olneya 

tesota)-smoke tree (Psorothamnus spinosus) communities. Tortoises feed on both 

summer and winter annuals, because this region receives about 1/3 of its annual rainfall 

in summer (Table 3) and supports two distinct annual floras on which they can feed. 

Tortoises den singly in burrows under shrubs, in inter-shrub spaces, and washes. Farther 

north, tortoises are more likely to burrow in caliche caves and washes. The climate is 

somewhat warmer than in other recovery units, with very few freezing days per year 

50
(Table 3). Tortoises within this recovery unit near Goffs produce relatively smaller eggs, 

produce more eggs overall, lay their second clutches earlier, and are smaller overall than 

tortoises in the Desert Tortoise Research Natural Area in the Western Mojave Recovery 

Unit (Wallis et al. 1999). They also produce more eggs than similarly sized females at the 

Nevada Test Site in the Eastern Mojave Recovery Unit (Mueller et al. 1998). 

(v) Western Mojave Recovery Unit. This recovery unit is generally equivalent to 

the original Western Mojave Recovery Unit and is found entirely in California (Figure 

12). It includes the central, southwestern, south-central, and part of the northern Mojave 

regions described by Rowlands et al. (1982). The eastern boundary, which it shares with 

the Eastern Mojave Recovery Unit, extends down Death and Saline valleys, through Soda 

Lake and the Bristol Mountains, to the Granite Mountains. The eastern boundary 

continues down the low-lying Baker sink and Cadiz Valley, separating it from the 

Colorado Desert Recovery Unit. The boundary extends west along California State 

Highway 62 to the San Bernardino Mountains. 

The recovery unit includes the Fremont-Kramer, Superior-Cronese, and Ord-Rodman 

critical habitat units. The recovery unit also includes the western half of Death Valley 

National Park, Marine Corps Air Ground Combat Center, Fort Irwin National Training 

Center, China Lake Naval Weapons Center, and Edwards Air Force Base. 

There is conflicting microsatellite evidence concerning the degree of differentiation 

between the Western Mojave and Colorado Desert recovery units, although genetic 

differentiation is generally low (Hagerty and Tracy 2007; Murphy et al. 2007). However, 

the Western Mojave Recovery Unit is genetically differentiated from the adjacent Eastern 

Mojave Recovery Unit (Hagerty and Tracy 2007; Murphy et al. 2007). Morphological 

characteristics and mtDNA from populations in the Western Mojave overlap those in the 

Colorado Desert Recovery Unit (Lamb et al. 1989; USFWS 1994a; Murphy et al. 2007). 

Tortoises in the west Mojave from the Kramer Hills region are differentiated from desert 

tortoises at in the Chemehuevi Valley in the Colorado Desert Recovery Unit at several 

allozyme loci (Rainboth et al. 1989). There also may be some sub-structuring within the 

Western Mojave Recovery Unit (Murphy et al. 2007), which may be an artifact of 

discrete sampling within generally continuous habitat (Allendorf and Luikart 2007:400). 

In addition, up to 40 percent of individuals were incorrectly assigned to the appropriate 

subpopulation in assignment tests; habitat in California was well connected prior to 

human development, allowing gene flow to occur over long geographic distances and 

multiple vegetation types (Murphy et al. 2007). The north half of this recovery unit 

borders the Eastern Mojave Recovery Unit along the Baker Sink, a low-elevation, 

extremely hot and arid strip that extends from Death Valley to Bristol Dry Lake and 

Cadiz Valley. To the south, the transition between the Colorado and Mojave deserts is 

more subtle. However, urban development along California State Highway 62 now 

largely separates the Western Mojave and Colorado Desert recovery units. 

51
Figure 12. Western Mojave Recovery Unit. DWMA = Desert Wildlife Management Area; ACEC = 

Areas of Critical Environmental Concern. 

A pronounced difference between the Western Mojave and other recovery units, 

including the closely allied Colorado Desert Recovery Unit, is in timing of rainfall and 

the resulting vegetation. Most rainfall occurs in fall and winter (Table 3) and produces 

winter annuals, which are the primary food source of tortoises. The Western Mojave 

Recovery Unit contains a unique combination of vegetation types, including the Mojave 

saltbush (Atriplex spp.)-allscale (A. polycarpa) scrub complex, blackbrush scrub, 

cheesebush (Hymenoclea salsola) scrub, iodinebush (Allenrolfea occidentalis)-alkali 

scrub complex, desert needlegrass (Achnatherum speciosum) scrub steppe, big galleta 

(Pleuraphis rigida) scrub steppe, and the Indian ricegrass (Achnatherum hymenoides) 

scrub-steppe complex, extending slightly into the southwestern Colorado Desert (USFWS 

1994a). Above-ground activity occurs primarily (but not exclusively) in spring, 

associated with winter annual production. Thus, tortoises are adapted to a regime of 

winter rains and rare summer storms. Here, desert tortoises occur primarily in valleys, on 

alluvial fans, bajadas, and rolling hills. The extreme differences in precipitation and food 

availability relative to the other recovery units correspond to different foraging and 

52
activity patterns, as well as life history characteristics. Tortoises dig deep burrows 

(usually located under shrubs on bajadas) for winter hibernation and summer estivation 

due to generally warm summers and cold winters (Table 3). These desert tortoises 

generally den singly. Tortoises in the Desert Tortoise Research Natural Area within this 

recovery unit produce relatively larger eggs, produce fewer eggs overall, lay their second 

clutches later, and are larger overall than tortoises near Goffs in the Colorado Desert 

Recovery Unit (Wallis et al. 1999). Tortoises in the western Mojave Desert have the 

smallest reported minimum size at first reproduction (less than 18 centimeters [7 inches]) 

compared to populations in other recovery units (Germano 1994). Behaviorally, western 

Mojave tortoises are much less active during summer than are tortoises in other recovery 

units. 

53
5

4

Table 3. Climatic summary for weather stations within desert tortoise recovery units. %J-S = percent of precipitation fallin

number of winter and summer days with 2.5 mm precipitation. Some stations are listed more than once where they occur nmultiple recovery units. Superscripts are initials of recovery units which particular stations border. Table modified from Ta(1994a). 

Temperature (oC) Precipitation (mm) 

Mean Ann Mean July No. Days 

Station Elev (m) Min Mean Jan Max Freeze Mean Ann %J-S 

Upper Virgin River Recovery Unit St. George 823 15.6 -5.3 38.4 96 209.6 29.2 

Northeastern Mojave Recovery Unit Littlefield 567 18.2 -1.1 40.3 74 157.5 23.8 

Las Vegas WPAP 659 18.9 -0.1 40.1 46 99.1 40.0 

Boulder City 770 19.4 3.3 38.4 13 137.2 33.4 

Desert NWR 890 16.8 

-1.5 

38.2 127 103.9 27.1 

SearchlightCD 

1070 

17.5 1.7 36.1 34 208.7 37.3 

Mountain PassEM 1442 --- -2.0 34.8 --- 173.0 31.2 

Eastern Mojave Recovery Unit Cow Creek -38 25.1 4.9 46.7 3 49.5 17.4 

Greenland -51 22.4 3.1 46.6 8 41.4 18.4 

BakerWM 319 --- 0.9 42.9 --- 75.2 20.7 

Beatty 1010 15.3 -2.4 37.5 88 118.0 14.9 Mountain PassNM 1442 --- -2.0 34.8 --- 173.0 31.2 

Colorado Desert Recovery Unit Thermal -37 22.8 3.9 41.8 12 70.1 21.4 Indio 3 22.9 3.4 41.6 15 79.8 19.7 Blythe 81 22.2 2.0 42.2 12 100.3 32.7 Palm Springs 128 22.3 4.4 42.2 12 138.9 11.2 Parker Res 225 23.3 5.3 42.3 1 129.3 32.8 

Needles 278 22.5 4.7 42.3 6 111.8 33.9 

Iron Mtn 281 23.0 5.6 42.1 2 79.5 20.1 

Eagle Mtn 297 23.0 5.6 41.0 1 82.8 36.5 

Hayfield 418 21.1 3.4 40.5 15 95.6 31.9 Twentynine PalmsWM 602 19.7 1.6 37.2 29 104.4 36.3 

Joshua TreeWM 838 --- --- --- --- 123.7 23.4 

SearchlightNM 1070 17.5 1.7 36.1 34 208.7 37.3 
Table 3. Continued. 

55

Temperature (oC) Precipitation (mm) 

Mean Ann Mean July No. Days 

Station Elev (m) Min Mean Jan Max Freeze Mean Ann %J-S 

Western Mojave Recovery Unit BakerEM 319 --- 0.9 42.9 --- 75.2 20.7 

Trona 517 18.9 -0.6 41.3 47 82.0 8.4 Twentynine PalmsCD 602 19.7 1.6 37.2 29 104.4 36.3 

Barstow 653 17.7 -0.4 39.1 57 108.5 27.2 Lancaster 717 16.1 -1.9 37.4 80 124.2 2.9 

Inyokern 744 17.6 -1.1 39.4 65 90.7 5.6 Palmdale AP 767 15.8 -1.6 36.7 81 139.2 3.2 Buckus Ranch 806 16.6 -1.2 37.0 67 162.9 5.5 

Palmdale 809 16.5 -2.7 36.6 60 130.8 3.7 

Joshua TreeCD 838 --- --- --- --- 123.7 23.4 

Mojave 846 --- -0.7 37.4 --- 128.5 8.1 

Victorville 871 15.3 -2.7 35.4 84 135.7 5.6 

Lucerne Valley 919 15.8 -2.4 38.9 104 108.2 18.1 

Fairmont 933 15.7 2.2 32.6 29 376.7 2.3 

Hesperia 974 --- --- --- --- 157.7 6.3 

Randsberg 1076 17.2 1.6 36.7 33 149.6 9.9 

Valyermo 1129 13.9 -2.5 40.3 103 263.3 7.6 Llano 1164 16.1 0.9 34.5 44 174.8 7.9 Haiwee 1166 15.5 -1.3 37.0 73 150.6 9.6 

Wildrose RS 1250 --- -1.6 35.1 --- 185.2 19.8 

Kee Ranch 1318 --- --- --- --- 167.6 9.2 
C. RECOVERY GOAL, OBJECTIVES, AND CRITERIA 

Downlisting or delisting is warranted when a listed species no longer meets the definition 

of threatened or endangered under the Endangered Species Act. We set recovery criteria to serve 

as objective, measurable guidelines to assist us in determining when a species has recovered to 

the point that the protections afforded by the Endangered Species Act are no longer necessary. 

However, the actual change in listing status is not 

solely dependent upon achieving the recovery Box 4. Definitions according to section 3 of 

criteria set forth in a recovery plan; it requires a the Endangered Species Act. 

formal rule-making process based upon an 

Endangered Species – Any species that is in analysis of the same five factors considered in the danger of extinction throughout all or a listing of a species (Reasons for Listing and significant portion of its range. Continuing Threats). The recovery criteria 

presented in this recovery plan thus represent our Threatened Species – Any species that is best assessment of the conditions that would most likely to become endangered within the likely result in a determination that delisting of foreseeable future throughout all or a the desert tortoise is warranted as the outcome of significant portion of its range. 

a formal five-factor analysis in a subsequent 

regulatory rule-making. 

The recovery criteria can be viewed as the targets (rather than strict rules) by which 

progress toward achievement of recovery objectives can be measured. The revised criteria 

address a) representation (conserving the breadth of the genetic makeup of the species to 

conserve its adaptive capabilities), b) resiliency (ensuring that each population is sufficiently 

large to withstand stochastic events), and c) redundancy (ensuring a sufficient number of 

populations to provide a margin of safety for the species to withstand catastrophic events). 

Recovery criteria must be measurable and objective, but they need not all be quantitative. 

Importantly, recovery criteria should also include the management or elimination of 

threats, addressing the five statutory (de-)listing factors. However, even though a wide range of 

threats affect desert tortoises and their habitat (and some such as disease and fire have attracted 

much recent attention), very little is known about their demographic impacts on tortoise 

populations or the relative contributions each threat makes to tortoise mortality (Boarman 2002; 

Tracy et al. 2004). As described previously, the facts that desert tortoises require over a decade 

to reach maturity, they have temporally variable reproduction, and juveniles have low survival 

rates, make it difficult to tease apart relative impacts of individual threats (although some 

impacts, such as habitat loss, are fairly straightforward in that they eliminate populations 

completely). Therefore, specific and meaningful threats-based recovery criteria cannot be 

identified at this time. For example, we lack quantitative data on the specific contribution of 

raven predation, disease, or other individual threats on tortoise population declines. A specific 

criterion to reduce raven predation by a specified amount may ultimately be unnecessary as we 

learn more about, and better manage, other particular threats. 

In the meantime, threats are addressed in the recovery actions outlined in the next section, 

and we assume that threat mitigation will have been successful if the current recovery criteria 

have been met (taking into consideration any head-starting or translocation efforts). While it is 

56
important to understand as much as possible about the direct links between threats and tortoise 

population response (i.e., cause and effect), the number of potential threats affecting desert 

tortoises and the nature of the species’ life history (especially long generation time) may make it 

impractical to reach this level of understanding completely. However, evaluating the extent and 

intensity of threats across the landscape over time will allow recovery efforts to be better tailored 

to specific areas in conjunction with information gained through research (see Recovery Action 

4.4). Specific recovery actions, including research, must be implemented to identify sets of 

threats that contribute to a greater number of mortality mechanisms or affect size structure or 

fecundity. Experimental (or, in some cases, observational) studies should be applied to specific 

plots or areas to better understand the relationship of threats, management actions, and tortoise 

populations (Recovery Actions 3.4, 5.4, 5.5). 

The relative strengths of postulated connections between threats and mortality must also 

be evaluated (some individual linkages may be more important than multiple linkages from other 

threats). This assessment should be based on data from research designed specifically to 

elucidate relationships between threats and mortality. As quantitative information on threats and 

tortoise mortality is obtained, more specific threats-based recovery criteria may be defined 

during future recovery plan review and revision, and effective management actions can be 

identified, prioritized, and implemented through land use plans, cooperative agreements, or other 

recovery management agreements. In fact, given the list of – and uncertainty surrounding the 

relative importance of – threats to the desert tortoise, the desert tortoise may well fit within the 

concept of a conservation-reliant species, requiring ongoing, concerted management efforts even 

after our recovery criteria have been achieved (Scott et al. 2005). 

1. Recovery Goal 

The goal of the recovery plan is recovery and delisting of the desert tortoise. 

2. Recovery Objectives and Criteria 

Recovery objectives and criteria are outlined below, followed by more detailed 

explanation and rationale. Note that the recovery criteria generally will be measured within 

tortoise conservation areas or other areas identified by Recovery Implementation Teams (see 

Recovery Action 1), and they are not independent of each other but must be evaluated 

collectively. Recovery does not depend on absolute numbers of tortoises or comparisons to prelisting estimates of tortoise populations, but rather the reversal of downward population trends 

and elimination or reduction of threats that initiated the listing. 

(a) Recovery Objective 1 (Demography). Maintain self-sustaining populations of 

desert tortoises within each recovery unit into the future. 

Recovery Criterion 1. Rates of population change (λ) for desert tortoises are 

increasing (i.e., λ > 1) over 25 years (a single tortoise generation), as measured 

a) by extensive, range-wide monitoring across tortoise conservation areas within each 

recovery unit, and 

57
b) by direct monitoring and estimation of vital rates (recruitment, survival) from 

demographic study areas within each recovery unit. 

(b) Recovery Objective 2 (Distribution). Maintain well-distributed populations of 

desert tortoises throughout each recovery unit. 

Recovery Criterion 2. Distribution of desert tortoises throughout each tortoise 

conservation area is increasing over 25 years (i.e., ψ > 0). 

(c) Recovery Objective 3 (Habitat). Ensure that habitat within each recovery unit is 

protected and managed to support long-term viability of desert tortoise populations. 

Recovery Criterion 3. The quantity of desert tortoise habitat within all desert tortoise 

conservation areas is maintained with no net loss until tortoise population viability is 

ensured. When parameters relating habitat quality to tortoise populations are defined 

and a mechanism to track these parameters established, the condition of desert 

tortoise habitat should also be demonstrably improving. 

3. Rationale 

(a) Recovery Objective/Criterion 1 (Demography). This objective and associated 

criteria emphasize the need to increase desert tortoise populations across tortoise conservation 

areas in each recovery unit over 25 years (a tortoise generation). Achievement of these criteria 

will indicate that all listing factors (A-E) will have successfully been addressed. 

The original listing of the desert tortoise was based on documented downward trends in a 

number of populations rather than on absolute numbers of tortoises being below a threshold level 

(USFWS 1990). In addition, while we have some historical information on desert tortoise 

densities within some localized areas, no historical (pre-listing) information exists on regional 

population levels. Therefore, evidence that the ecological processes maintaining tortoise 

populations have been sufficiently restored to warrant consideration for delisting will be based 

on observation of a positive population trend over 25 years. Basing the criteria on trends has an 

advantage over setting specific target numbers (e.g., 40 tortoises per kilometer2 [104 tortoises per 

mile2

]), because absolute tortoise numbers may show considerable variation between regions as a 

result of ecological differences or other factors, but a positive population trend is a clear 

indication that mechanisms leading to recovery are in place and that recovery is occurring. For 

example, there is evidence that historic natural population densities differed between the Upper 

Virgin River and Colorado Desert recovery units (USFWS 2006a), but the reason for different 

population densities is not known. There is no reason to think that a single target density should 

be applied to all recovery units, yet attempting to set unique targets for each recovery unit would 

not be prudent given the lack of data on both historic population numbers and what numbers 

would constitute sustainable populations in the current environment. However, if all areas 

demonstrate a positive population trend regardless of actual population counts, the interpretation 

will be that recovery is occurring. 

58
The way ecologists estimate whether a population is increasing or decreasing is by using 

a variable called lambda (λ), which indicates population change. When λ is greater than one, the 

population is considered to be increasing and when it is less than one, the population is 

decreasing. Several kinds of data (e.g., counts of individuals, recruitment and survival rates) can 

be used to derive estimates of λ. This is reflected in our use of two recovery criteria here. 

Recovery Criterion 1a is based on data that are relatively easy to gather over large areas using 

range-wide monitoring with counts of individuals (i.e., line distance sampling), while Recovery 

Criterion 1b is based on data that are more difficult to gather but that may give us a more precise 

indication of population change using vital rates such as recruitment and survival from 

demography study areas, as described more fully below. 

Natural variability in population size and inherent measurement error make it extremely 

difficult to detect realistic natural increases (i.e., less than 2 percent per year) in desert tortoise 

populations in as few as 25 years (USFWS 2006a). For this and other reasons, the Science 

Advisory Committee recommended the recovery criteria rely on a suite of measures instead of 

relying primarily on a single quantitative estimate that is difficult to measure in a species with a 

low intrinsic growth rate and is difficult to detect. At the same time, the Science Advisory 

Committee proposed using a 90 percent confidence band (α = 0.10) to describe population 

trends. For an increasing trend, the lower 90 percent confidence limit for each estimate of λ

should exceed 1. This precision level makes it possible to distinguish a small (less than 2 percent 

per year) trend from a non-growth trend, but is still fairly conservative. Although a convention 

exists to use 95 percent confidence intervals (α = 0.05) for many statistical tests, setting α = 0.10 

has the conservative effect of guarding against incorrectly concluding a decline in tortoise 

density has not occurred at the expense of a slightly increased possibility that an increasing or 

declining trend is “detected” when, in fact, the population is stable (Shrader-Frechette and 

McCoy, 1993). Anderson and Burnham (1996), proposed α = 0.15 for this monitoring program at 

the time they proposed the design. The Science Advisory Committee also noted that combined 

use of independent measures of recovery (population trends, habitat quantity and quality, threat 

abatement) provides additional assurance that detected trends are meaningful. 

Range-wide monitoring (Criterion 1a). The number of tortoises in each recovery unit is 

related to the density of tortoises estimated by line distance sampling techniques (USFWS 

2006a). It can also be related to the extent of the habitat occupied by tortoises and how that 

extent expands or contracts over time (e.g., Royle et al. 2005; see Recovery Criterion 2). Either 

approach can relate changes in an index (density or occupancy) to changes in time to estimate the 

population growth rate, λ. Either density or occupancy will focus on particular size classes, often 

neglecting the smallest size class, for instance. This approach therefore assumes that if the focal 

size class is increasing, this is because it is recruited from and contributing to the neighboring 

size classes, which must also be increasing. When evaluating an endangered species, however, 

this assumption should be validated by independent evidence that the other size classes are 

recruiting as well, hence we will also validate the recovery-unit-wide estimates through more 

intensive study of the underlying recruitment and survival rates on smaller scales within recovery 

units (Criterion 1b). 

Vital rates (Criterion 1b). Validating that vital rates are at increasing levels will be 

important to ensure that populations are able to maintain their size or trajectory upon delisting. 

59
Demographic (vital) rates describe the proportion of each size class, for instance, that grows into 

the next size class and/or produces offspring in a given time period. These rates also include 

mortality rates, estimating the proportion of each size class that dies during that time interval. 

These rates allow us to describe how a population changes from one time period to the next. 

Because the total number of tortoises changes from one time period to the next, dynamic models 

should be used to provide an independent estimate of the population growth rate, λ. 

However, measuring recruitment and survival across the entire range of the tortoise is 

logistically difficult and prohibitively expensive. Therefore, the concept of “demographic study 

areas” is introduced to focus sampling efforts at a scale at which statistically defensible trends of 

the desired population parameters can be measured (see Recovery Actions 4.1, 5.1). The number, 

size, and sampling frequency of demographic study areas remain to be defined in coordination 

with the Science Advisory Committee and Recovery Implementation Teams, but they should be 

small relative to the size of each recovery unit, and they should be representative of each 

recovery unit. Existing permanent study plots may be incorporated into the set of demographic 

study areas within each recovery unit, if appropriate. Measuring recruitment and survivorship 

rates within demographic study areas within each recovery unit addresses the recovery concepts 

of representation and resiliency. 

(b) Recovery Objective/Criterion 2 (Distribution). This objective and associated 

criterion emphasize increasing the distribution of desert tortoises (within tortoise conservation 

areas) over 25 years. As such, it applies to Listing Factor A, the present or threatened 

destruction, modification, or curtailment of the tortoise’s habitat or range. 

Recovery Criterion 1 focuses on population growth. Recovery Criterion 2 focuses on the 

distribution of tortoises across the landscape. The 1994 Recovery Plan only indirectly addressed 

this issue by recommending enough habitat be conserved to ensure viable tortoise populations, 

but it did not directly address population processes acting across the spatial scale of entire 

recovery units. The purpose of Criterion 2 is to prevent range contraction of the desert tortoise. 

To detect changes in desert tortoise distribution, we will monitor the ratio of sampling points at 

which tortoises are detected across tortoise conservation areas within each recovery unit (Figure 

13). The probability that randomly sampled sites are occupied by the desert tortoise is referred to 

as occupancy (indicated by ψ; MacKenzie et al. 2006). Similar to λ in Recovery Criterion 1, we 

specify that the lower 90 percent confidence limit be used to evaluate the slope of ψ within each 

recovery unit (which must exceed 0). An average increase in tortoise density in a recovery unit 

reflected by growth only in highly localized areas, while tortoises in other areas are extirpated, 

would not reflect recovery. 

This recovery objective provides for representative, resilient, and redundant populations. 

Although habitat is explicitly addressed by Recovery Objective 3, implicit in Objective 2 is the 

maintenance of sufficient habitat to sustain tortoises on the landscape. That is, increasing tortoise 

distributions, even if augmented by translocation or head-starting, can only be achieved by 

managing habitat appropriately. Establishing a precise geographic baseline across all lands 

within tortoise conservation areas will help ensure that habitat loss does not result in a 

comparison of similar relative measures of tortoise occupancy across smaller absolute areas in 

the future. 

60
(c) Recovery Objective/Criterion 3 (Habitat). This objective and associated criterion 

emphasize maintaining desert tortoise habitat within desert tortoise conservation areas, but are 

not meant to diminish the importance of populations and habitat outside the conservation areas. 

Therefore, they directly apply to Listing Factor A, the present or threatened destruction, 

modification, or curtailment of the tortoise’s habitat or range. 

Habitat is the suite of resources (food, shelter) and environmental conditions (abiotic 

variables such as temperature and biotic variables such as competitors and predators) that 

determine the presence, survival, and reproduction of a population (Caughley and Sinclair 1994). 

Quality of habitat can affect reproductive success and survival of individuals occupying the 

habitat (Pulliam 1996), and declining or extirpated populations typically require intensive habitat 

management to stabilize and reverse trends. Much is known about what constitutes desert 

tortoise habitat, and a range-wide model of habitat for the Mojave population of the desert 

tortoise is nearing completion (T. Esque, U.S. Geological Survey, pers. comm. 2007). 

Figure 13. Example of hypothetical occupancy pattern. Stippled green polygons = tortoise conservation 

areas; filled circles = samples with at least 1 tortoise observation; open circles = samples with no tortoise 

observations; yellow boxes = hypothetical demographic study areas. Recovery Criterion 2 stipulates that 

tortoise occupancy increases (not necessarily the same samples, just the overall level). 

Criterion 3 establishes a target for no net loss (Box 5) of current habitat within tortoise 

conservation areas. The geographic baseline over which trends in habitat quantity will be 

61
 

monitored includes all potential desert 

tortoise habitat (Box 5) within tortoise 

conservation areas at the time of 

publication of the final, revised recovery 

plan (see Recovery Action 4.3). This 

baseline will be “memorialized” in a 

range-wide recovery database (managed 

by the Desert Tortoise Recovery Office) 

by applying the final U.S. Geological 

Survey habitat model to habitat data at 

the time the recovery plan is published, 

in coordination with Recovery 

Implementation Teams (see Recovery 

Action 6.1). Habitat degradation or 

loss in some areas should be balanced 

with habitat acquisition or restoration of 

degraded habitat in other areas, as 

specified in the West Mojave Plan for 

example (BLM et al. 2005), thus 

achieving the no-net-loss standard and 

maintaining tortoise occupancy through 

maintenance of (quality) available 

habitat. However, the target for no net 

loss established by Recovery Criterion 3 

may be relaxed on a limited, case-bycase basis, if we determine that greater 

recovery benefits can be achieved 

through other means than replacing 

every acre of lost habitat with another 

acre elsewhere. Given that tortoise 

conservation areas include both 

designated critical habitat and BLM’s Desert Wildlife Management Areas and Areas of Critical 

Environmental Concern, which do not always coincide, the Recovery Implementation Teams 

will refine and recommend the geographic baseline for measuring no net loss of habitat, using 

available tortoise data in coordination with and approval by the Desert Tortoise Recovery Office. 

Given the vast amount of desert tortoise habitat already under Federal management, 

Criterion 3 does not apply generally to private lands. However, private or other non-Federal 

lands under conservation management for desert tortoises are included in tortoise conservation 

areas (see Box 2, page 32) and can contribute substantially to this recovery objective. In addition, 

habitat loss and degradation elsewhere must be minimized and mitigated, while not appreciably 

reducing the likelihood of survival and recovery of the tortoise, pursuant to section 10(a)(2) of 

the Endangered Species Act. 

In order to manage desert tortoise habitat well enough to meet Objectives 1 and 2, we 

would also benefit from statistical models linking habitat data to tortoise demographic data (see 

Box 5. Terms related to monitoring habitat. 

“Habitat loss” (evaluated under Recovery Criterion 3) 

is considered here as acreage subject to the complete or 

absolute removal of elements necessary for desert 

tortoise occupation (i.e., grading or paving of the 

landscape so that no food or shelter resources are 

available) or other identified thresholds of habitat 

quality fall below that which can support desert 

tortoises. 

"No net loss" of desert tortoise habitat refers to 

balancing acreage of habitat loss on public lands within 

tortoise conservation areas with new, restored, or 

enhanced acreage of habitat, such that at least the 

minimum conditions for desert tortoise occupation are 

met. No net loss of habitat may be relaxed under 

special circumstances in which we determine greater 

recovery benefits can be achieved through other means, 

and it will be evaluated over the expected 25-year 

recovery period. 

“Habitat degradation” involves impacts to desert 

tortoise habitat, short of absolute habitat loss, that 

compromise its ability to support desert tortoises (e.g., 

invasion of fire-adapted, non-native vegetation or 

increased incidence of unauthorized off-highway 

vehicle trails). 

“Potential desert tortoise habitat” as defined here is 

based on the forthcoming U.S. Geological Survey 

habitat model, regardless of current occupancy by 

desert tortoises. 

62
Recovery Action 5.2). Information from this type of model would allow us to identify minimum 

habitat conditions for potential tortoise occupancy and, therefore, to analyze occupancy as a 

function of habitat characteristics. We ultimately need to define specific parameters that relate to 

the quality of desert tortoise habitat (see Recovery Action 5.2) and to develop and implement a 

system for tracking habitat quality over time. In particular, we need to identify thresholds below 

which habitat degradation is so severe that the habitat fails to provide the minimum conditions 

for potential occupancy, due to fires for example. Measures related to habitat quality could 

include miles of roads and trails or the number and size of habitat fragment polygons created by 

roads. Incorporating a GIS “ledger” of habitat status into the range-wide recovery database, 

accounting for restored areas on the positive side and degraded or lost areas on the negative side, 

will enable managers to quantitatively measure the amount of occupied habitat, the amount of 

newly available (restored) habitat for tortoises to disperse into, the rate that restored habitat is 

occupied, and effectiveness of the restoration (e.g., BLM 2002b: Appendix G). Through the 

Recovery Implementation Teams, management agencies should report habitat status (particularly 

habitat loss/gains) on their lands (Recovery Action 1.1). 

Land management agencies must work within the context of their respective land use 

plans, including the provisions of adaptive management such as Recovery Actions 6.2-6.3 

contained within this recovery plan, to determine measures to assure no net loss and to improve 

quality of existing desert tortoise habitat. Until better population/habitat viability models are 

developed (see Recovery Action 5.2), land managers should also strive to limit the loss of desert 

tortoise habitat outside conservation areas as much as possible, although we reiterate that the 

most aggressive recovery efforts are targeted toward tortoise conservation areas. A variety of 

means are available to improve existing desert tortoise habitat both within and outside 

conservation areas. Re-establishment of native vegetation on burned landscapes may increase 

desert tortoise populations (see Recovery Action 2.6, especially for associated research needs). 

Closure of unnecessary or illegal routes of travel can create larger unfragmented blocks of 

habitat. Additional mitigation for habitat impacts outside conservation areas could include 

options such as habitat acquisition or restoration of degraded habitat in other areas or recovery 

units, contributions to research, or facilitating population augmentation programs within 

conservation areas, depending on current needs, priorities, and opportunities. 

Actions or projects occurring outside tortoise conservation areas, which will be reviewed 

under existing State laws and the Federal section 7 and 10 processes, should seek to minimize (1) 

negative impacts in adjacent areas and (2) creation of edge effects (impacts within an area from 

projects or activities outside that area) within the conservation areas. This approach recognizes 

the need for large natural areas to accommodate stochastic events (i.e., resiliency). Tortoise 

conservation areas should be as undisturbed as possible and include intensive restoration or other 

management (e.g., weed management), as necessary. Modeling should help better quantify what 

proportion of the habitat needs to be occupied or is available to be occupied for population 

sustainability. 

D. RECOVERY ACTIONS 

As noted previously, the recommended actions in the 1994 Recovery Plan formed a 

logical basis for recovery (GAO 2002), little information since 1994 contradicts these 

63
recommendations (Boarman and Kristan 2006), and insufficient time has elapsed over which 

detectable increases in desert tortoise populations or natural recovery of habitat could be 

realistically expected. Therefore, many of the specific recommendations listed below, especially 

under Strategic Element 2, are adapted from the 1994 Recovery Plan. However, the revised plan 

places a greater emphasis on solidifying partnerships across jurisdictional boundaries to maintain 

focus on implementing the recommended actions and conducting applied research, modeling, 

and effectiveness monitoring to evaluate actions in a formal adaptive management context. Table 

4 identifies the listing factors and recovery objectives addressed by each major recovery action. 

1. Develop, Support, and Build Partnerships to Facilitate Recovery 

1.1. Establish regional, inter-organizational Recovery Implementation Teams to 

prioritize and coordinate implementation of recovery actions. Implementation of 

this recovery plan throughout the four-state range of the desert tortoise is a daunting 

prospect. However, if approached from a regional or local level, recovery becomes 

much more feasible. Therefore, regional Recovery Implementation Teams (which are 

exempted from the Federal Advisory Committee Act by section 4[f][2] of the 

Endangered Species Act) need to be established within 6 months of publication of the 

recovery plan to develop step-down plans and maintain focus on implementing 

recovery actions in coordination with the Desert Tortoise Recovery Office. The 

Desert Tortoise Recovery Office will work with interested managers and stakeholders 

to form the Recovery Implementation Teams in coordination with the Desert Tortoise 

Management Oversight Group. Recovery Implementation Teams could be formed as 

new independent teams or may be working groups within existing organizations such 

as the California Desert Managers Group or Southern Nevada Agency Partnership. In 

any case, Recovery Implementation Teams should have broad representation by 

communities and the public in the recovery effort. Both technical experts and 

stakeholders should be represented. 

Recovery Implementation Teams are the fundamental partnerships tying the adaptive 

management process together (Strategic Element 6; Figure 4). As a result, it is 

important that their regional/local efforts are productive and contribute to the rangewide effort. In order to ensure timely performance of tasks and cooperation between 

groups with disparate views, we recommend the following procedures: 

 Each Recovery Implementation Team should have a chair to facilitate each 

meeting, and the Desert Tortoise Recovery Office should help organize activities 

through its regional recovery coordination staff. Independent facilitation should 

be secured, if necessary. 

 Once the Recovery Implementation Team is constituted, the minimum list of 

participants to go forward with any meeting will be set. Unless decisions are 

adopted by all relevant parties, the Recovery Implementation Team is not making 

progress. 

64
 The Recovery Implementation Team chair will alert participants to deadlines and 

ensure that all parties are aware of the need and schedule for moving the process 

forward. 

 Recovery Implementation Teams should report annually to the Management 

Oversight Group and Science Advisory Committee to review progress on 

recovery implementation and provide any new recommendations for management 

or research. 

Specific tasks of the Recovery Implementation Teams are described under Recovery 

Action 6 within the context of implementing the adaptive management program, but 

generally the teams should tier off the recovery plan by developing 5-year action 

plans and budget needs with priorities for management based on an updated decision 

support system (scaled to the level of local or jurisdictional levels). Priorities for 

studying the effectiveness of management actions (5.4) should be included in these 

action plans. Recovery Implementation Teams should also identify areas not included 

within existing tortoise conservation areas that may warrant focused management 

efforts to ensure recovery of the desert tortoise within their respective recovery units. 

Throughout recovery implementation, the Desert Tortoise Recovery Office and 

Recovery Implementation Teams should emphasize the collation of up-to-date 

information on threats and recovery action implementation into the decision support 

system and range-wide recovery database. 

2. Protect Existing Populations and Habitat 

A prototype decision support system (Strategic Element 6, Appendix C), using 

information provided by managers during recovery planning workshops, produced preliminary 

recovery action priorities relative to protecting desert tortoise populations and habitat for each 

recovery unit (Appendix C-7). Actions 2.1 and 2.2 below are general actions that are not 

included in the current decision support system. While general priorities for each recovery unit 

are included in the descriptions of the remaining actions below and specific rankings are listed in 

Appendix C-7, relative priorities for each action may change as additional information is 

integrated into the decision support system at local levels within each recovery unit or as new 

information is gained through research and monitoring. Most of the actions described below have 

been implemented to a greater or lesser extent in various parts of the desert tortoise’s range. 

Inclusion in the revised plan reflects an emphasis on maintaining these actions where 

implemented, although general priorities may be lessened for actions that have been more 

broadly implemented (e.g., minimize livestock grazing) and effectiveness generally needs to be 

more specifically evaluated. Note that other State or Federal agency policies and regulations may 

impose specific measures or processes to determine appropriate compensation or mitigation both 

within and outside of tortoise conservation areas. 

At this stage, the following actions serve as guidelines, especially within tortoise 

conservation areas as defined in Box 2, that management agencies should implement according 

to their respective land-use or similar plans. For example, specific measures designed to 

minimize or mitigate habitat loss (i.e., maintain the “no net loss” standard of Recovery Criterion 

65
3) or habitat degradation should be implemented by each land management agency in 

coordination with their respective Recovery Implementation Teams according to the local 

situation (e.g., short-term or long-term impact, effect to high-quality or low-quality habitat) and 

governing authorities. Deviations from the following actions may be appropriate in some cases, 

but they should be supported by scientific rationale or justification as to how they can contribute 

to recovery. Again, quantifying the effectiveness of these or modified recovery actions is 

important, as specified under Action 5.4. 

2.1. Protect intact desert tortoise habitat. Land disturbances should be precluded within 

tortoise conservation areas. In particular, fires should be suppressed aggressively 

throughout the Mojave and Colorado deserts to contain the grass-fire cycle. 

Minimizing the size and intensity of fires will ease subsequent restoration efforts 

(2.6), even in previously burned areas. Fire suppression would also minimize direct 

and indirect effects on individual tortoises. Identifying and mapping priority areas and 

developing a fire plan for habitat protection, fire-crew access, and the use of natural 

or created fuel breaks could help limit response time and fire spread. 

Development of alternative energy sources has also recently come to the forefront as 

a necessary and congressionally mandated use of public lands that could have largescale impacts to desert tortoise habitat. Pursuant to the Bureau of Land Management 

land use plans, solar project facilities will be sited outside Desert Wildlife 

Management Areas and Areas of Critical Environmental Concern. Current proposals 

for energy projects within these land allocations should be relocated so that impacts 

to these areas are avoided. A cumulative impacts assessment should be conducted and 

appropriate areas and mitigation measures for this type of activity should be 

identified. 

2.2. Reduce factors contributing to disease (particularly upper respiratory tract 

disease). Strategies for managing natural populations depend on the disease status of 

the population, deemed broadly as a) uninfected, b) recently infected with infection 

spread, or c) infection status endemic. An endemic-status population is defined as one 

where the proportion that is seropositive is above zero and remains stable over time. 

Specific recommendations are listed below, and additional background and details 

can be found in Appendix B. 

 All tortoises found in the wild that may be released captives without a health 

check should be removed from the wild and used for breeding, adoption, or 

research programs unless they are determined to be uninfected and are genetically 

acceptable for that population. 

 No action should be taken to remove infectious or seropositive individuals from 

natural populations, particularly where data indicate the disease status of that 

population is endemic. 

 In populations known to be uninfected, individual tortoises exhibiting clinical 

signs of acute infection should be removed for further testing, but should be 

returned to the point of capture if diagnostic tests confirm they are uninfected. 

66
Uninfected populations that have recently become infected should be carefully 

monitored with the removal of all individuals exhibiting acute infections. Acute 

infections are defined as those exhibiting a nasal or ocular discharge at an 

inappropriate time of year. 

2.3. Establish/continue environmental education programs. Environmental education, 

identified as a high priority in all recovery units, is a preventative action that can be 

used to reduce stakeholder conflict before it happens. Aggressive and widespread 

efforts in schools (such as the Mojave Max program in Clark County, Nevada), 

museums, hunting clubs, and in Bureau of Land Management and National Park 

Service visitor centers and interpretive sites are needed to inform the public about the 

status of the desert tortoise and its recovery needs. 

Interpretive kiosks or visitor centers should be used to disseminate information about 

the desert tortoise and the need for regulated access and use of habitat. The Desert 

Tortoise Conservation Center in Las Vegas should be developed into a regional 

education and research facility for these purposes. Education programs should include 

such subjects as husbandry and adoption programs for captive tortoises, the 

importance of discouraging unauthorized breeding of desert tortoises in captivity, and 

the illegality under State laws of releasing captive tortoises into wildlands. Education 

efforts should be focused on groups that use the desert on a regular basis, such as 

rock-hounds and off-highway vehicle enthusiasts. A permit system for access to 

sensitive areas would offer one way to educate desert recreationists. Additional 

educational tools include public service announcements, news releases, informational 

videos, brochures and newsletters, websites, and volunteer opportunities. 

2.4. Increase law enforcement. People may conduct illegal activities either because they 

are unaware of the laws, they do not realize the consequence of their behavior, or they 

enjoy some personal benefit that outweighs the risk of being caught. Increased law 

enforcement presence is a relatively high priority in all recovery units (especially 

Upper Virgin River) and includes enforcing regulations pertinent to the specific 

recommendations to protect tortoises or their habitat listed below. This action also 

includes using existing officers to ensure law enforcement presence during peak 

recreational use periods such as weekends and holidays on a rotational basis so 

enforcement activity is not lost on casual users during standard work week hours. 

Increasing fines and establishing agreements between offices of adjacent management 

authorities to enforce regulations across jurisdictional lines would also improve the 

effectiveness of law enforcement efforts. 

An increased law enforcement presence need not be restricted to commissioned peace 

officers, but could also include “rangers” or other personnel with a physical presence 

in the field who would make contact with public land users, communicate with law 

enforcement officers, and conduct other activities, as necessary (e.g., minor 

restoration or trash removal). Such personnel should be coordinated with the 

appropriate agencies to focus on particular issues in their respective areas. Brochures 

identifying and encouraging reporting of problem illegal activities could be developed 

67
and distributed to management agencies for further distribution to recreationists or 

others. The following is a list of illegal activities known to negatively affect the desert 

tortoise and warrant increased enforcement. 

 Unauthorized off-road vehicle travel. Across all recovery units, this aspect of law 

enforcement is the most important. Impacts from off-highway vehicle use include 

mortality of desert tortoises on the surface and below ground; collapsing of desert 

tortoise burrows; damage or destruction of plants used for food, water, and 

thermoregulation; damage or destruction of the mosaic of cover provided by 

vegetation; damage or destruction of soil crusts; soil erosion; proliferation of 

weeds; and increases in numbers and locations of wildfires. Unauthorized offhighway vehicle use also results in increased human access and associated 

impacts such as deliberate maiming and killing of tortoises. 

 Deliberate maiming and killing of tortoises. Formerly referred to as vandalism 

(Luke et al. 1991), specific examples include shooting, crushing, driving over, 

flipping over, and decapitating tortoises. Shooting (also called “plinking”), by far, 

is the most prevalent method (Boarman 2002). Preventing the discharge of 

firearms, except for hunting authorized by state game and fish departments, in 

problem or other sensitive areas could help minimize this threat. 

 Unauthorized breeding and release of captive tortoises. Captive release of 

tortoises (not limited to desert tortoises) poses numerous problems to wild host 

populations. Examples include genetic pollution, hybridization between 

populations and possibly other tortoise species, the potential for introducing or 

spreading disease (e.g., upper respiratory tract disease), and disturbance to the 

social structure of the host population. Unauthorized breeding, particularly in 

Nevada (breeding and possession of desert tortoises is prohibited in California 

and Washington County, Utah, respectively), and release of pet desert tortoises 

particularly contributes to genetic pollution and disease spread. Placement of 

excess tortoises in adoption or translocation programs places a large burden (e.g., 

cost of pick-up services, health testing, placement efforts) on resources that would 

otherwise be available for more productive recovery efforts. New state or local 

regulations may be necessary to prohibit unauthorized breeding of desert 

tortoises, and (increased) fines may be warranted for the release of captive 

tortoises into the wild. 

 Uncontrolled dogs. Domestic and feral free-roaming dogs are documented threats 

to captive and wild tortoises (Bjurlin and Bissonette 2001; see Boarman 2002). 

With the growing number and sizes of cities, towns, and settlements in the desert, 

this type of threat is increasing and will be difficult to control. Dogs singly, and in 

packs, may roam miles from home, dig up, and injure desert tortoises. This action 

entails implementing measures to control off-leash dogs (domestic dogs should at 

least be within sight and voice control), live-trapping free-ranging dogs, and 

developing free-ranging dog management plans. 

68
 Dumping and littering. Dumping and littering provide subsidies to predators, thus 

elevating their populations and predation pressure on tortoise populations. It can 

also introduce toxic chemicals or hazardous materials to the environment. 

2.5. Restrict, designate, close, and fence roads. Paved highways, unpaved and paved 

roads, trails, and tracks have significant impacts on desert tortoise populations and 

habitat. In addition to providing many opportunities for accidental mortality, they also 

provide access to remote areas for collectors, vandals, poachers, and people who do 

not follow vehicle-use regulations. Substantial numbers of desert tortoises are killed 

on paved roads. Roads also fragment habitat and facilitate invasion of non-native 

vegetation. Collectively, the actions described below are of relatively high priority in 

all recovery units. 

 Establishment of new roads should be avoided to the extent practicable within 

desert tortoise habitat on public lands, especially within tortoise conservation 

areas. Tortoise conservation areas should have a minimum goal of “no net gain” 

of roads. 

 Existing roads should be designated as open, closed, or limited. This action is 

especially pertinent for closed or limited designations, which can help mitigate 

impacts mentioned above. Maintenance of route designation signs may also be 

required due to vandalism. Route designation is a particularly high priority in all 

recovery units except Upper Virgin River (moderate priority). 

 Non-essential or redundant routes should be closed, especially within tortoise 

conservation areas. Emergency closures of dirt roads and routes may also be 

needed to reduce human access and disturbance in areas where human-caused 

mortality of desert tortoises is a problem. Road closures are a particularly high 

priority in all recovery units except Upper Virgin River (moderate priority). 

 Tortoise-barrier fencing should be installed, according to specifications provided 

in Appendix D, and maintained along highways in desert tortoise habitat. 

“Hot-spots” of road mortality should be identified and prioritized, but fencing 

roads is a particularly high priority in the Upper Virgin River Recovery Unit. 

Other areas in California in need of fencing include parts of US-395, I-40, and 

SR-247 in the Western Mojave Recovery Unit and US-95, I-10, I-15, I-40, 

redundant roads within Mojave National Preserve and Joshua Tree National Park, 

and the Union Pacific rail line in the Eastern Mojave and Colorado Desert 

recovery units. Many roads have already been fenced in Clark County, Nevada, 

but remaining areas include US-93 from I-15 to Pahranagat, SR-75 (Valley of 

Fire Road) from I-15 to State Park Boundary, SR-168 from I-15 to US-93, CalNev-Ari (tie in fencing to US-95), and Cottonwood Cove Road. 

Alternatives to fencing may be investigated in areas of high-maintenance (e.g., 

subject to flash flooding) or viewshed concern. Culverts and underpasses should 

69
be incorporated into road-fencing projects to minimize the fragmenting effects of 

the road (2.11). 

 While graded roads typically need not be fenced, berms should be maintained 

such that tortoises do not get trapped in the roadbed. This is a particular issue in 

the Colorado Desert Recovery Unit, as well as throughout the Mojave National 

Preserve. 

2.6. Restore desert tortoise habitat. Habitat restoration is a countermeasure to many of 

the impacts discussed above, such as grazing, military operations, off-highway 

vehicle use, roads and trails, construction, mining, horses and burros, invasive 

species, fire, environmental contaminants, and utility corridors. As such, this action is 

highly prioritized within the Eastern Mojave, Western Mojave, and Colorado Desert 

recovery units and moderately prioritized within the Northeastern Mojave and Upper 

Virgin River recovery units. The specific restoration activities may vary by recovery 

unit and management agency. 

A first step in restoration is assessing habitat status and desired conditions, then 

targeting restoration (or protection) efforts to meet those conditions. Natural recovery 

of severely degraded desert scrub is expected to occur over centuries, not decades, so 

active restoration efforts will be required in such areas. A great deal of research has 

been conducted on restoration and rehabilitation of habitats in arid and semi-arid 

ecosystems with varied results (see Roundy et al. 1995; Bainbridge 2007). Previous 

and ongoing studies should be used to inform implementation of restoration activities 

in desert tortoise habitats. 

In general, because of the uncertainties and costs associated with revegetation and the 

long periods required for natural recovery, the first priorities in habitat conservation 

should be to preclude land disturbance in the first place and protect remaining, intact 

habitats (2.1). Even so, incentive programs to restore habitat through habitat 

rehabilitation credits or mitigation banking could be used to encourage persons or 

entities to rehabilitate degraded habitat (BLM et al. 2005). Several restoration 

activities warrant specific attention below, although methods for successful 

implementation for most need to be developed or refined. 

 Eradicate or suppress invasive weeds. Methods for weed suppression or 

eradication on large scales are currently unavailable, but the use of herbicides or 

other measures may be particularly appropriate on smaller scales in tortoise 

conservation areas. 

 Revegetate degraded areas with native plants of high nutritive quality to desert 

tortoises, as well as shrubs needed for cover. Given the vast scales of recent 

wildfires, post-fire rehabilitation should be approached strategically toward areas 

determined to have a higher likelihood of successful restoration, considering fire 

severity, soil types, biological connectivity of native source plants, etc. This 

action may also be appropriate for smaller-scale applications such as obscuring 

closed roads and mitigating utility corridor disturbances. 

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 Remove toxicants and unexploded ordnance. Areas with elevated levels of 

elemental toxicants associated with mining, other industrial operations, 

unexploded ordnance, and unauthorized dump sites should be identified and 

remediated where possible. 

2.7. Install and maintain urban or other barriers. Urban development indirectly affects 

desert tortoise populations through spillover of human impacts, such as unauthorized 

off-highway vehicle use and free-roaming dogs, into the surrounding habitat. 

This action entails installing and maintaining appropriate barriers at the urbanwildland interface or adjacent to other uses incompatible with desert tortoise 

populations, particularly adjacent to tortoise conservation areas. Depending on the 

particular impacts of interest, the actual type of barrier may differ. For example, 

tortoise-proof fencing (Appendix D) may be sufficient adjacent to aqueducts or offhighway vehicle areas, but larger fences or block walls may be necessary adjacent to 

urban development to limit off-highway vehicle use and free-roaming dogs. Priority 

areas for this action include: 

 around the Red Cliffs Desert Reserve in the Upper Virgin River Recovery Unit 

and 

 around new developments (e.g., Coyote Springs Valley) and the edges of the Las 

Vegas metropolitan area in the Northeastern Mojave Recovery Unit. 

 Barriers around the Desert Tortoise Natural Area, Helendale, Barstow/Daggett, 

Yucca Valley, Joshua Tree, and Twentynine Palms, as well as adjacent to the 

Johnson Valley Open Area, in the Western Mojave Recovery Unit, and 

 around the town of Goffs in the Colorado Desert Recovery Unit ranked as midlevel priorities in the decision support system (Appendix C). 

2.8. Sign and fence boundaries of sensitive or impacted areas. This action (relatively 

high priority in the Upper Virgin River Recovery Unit and moderate priority 

elsewhere) entails marking boundaries of particularly sensitive or heavily impacted 

areas with signs and fencing to regulate authorized use and to discourage 

unauthorized use. This can include marking boundaries of protected areas, research 

sites, off-highway vehicle routes, roads, military lands, and parks. Signs or kiosks 

may also be used to for educational purposes and to raise awareness. 

2.9. Secure lands/habitat for conservation. This action is of moderate priority in all 

recovery units. It counters habitat loss and protects tortoises, provided secured lands 

are suitable habitat (see Action 2.1) or can serve as corridors or buffers. However, 

given the vast amount of desert tortoise habitat already under Federal management or 

primary conservation use, this action should focus on particularly sensitive areas that 

would connect functional habitat or improve management capability of the 

71
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surrounding area. Land acquisitions should include surface and subsurface mineral 

rights whenever possible. Conservation agreements and other private-landowner 

incentives could also be developed to protect desert tortoise habitat in such areas. 

Land managers should coordinate with the Department of Defense on efforts such as 

the Readiness and Environmental Preparedness Initiative and the Army Compatibility 

Use Buffer program to acquire lands that would serve a dual purpose of preventing 

encroachment on military installations and conserving desert tortoise habitat. 

Areas of particular emphasis noted by managers for this recovery action include the 

Western Mojave Recovery Unit and inholdings within National Parks. In addition, 

consolidating private lands within the Red Cliffs Desert Reserve is important for 

habitat connectivity. 

The following actions typically ranked as mid- to lower-level priorities in the decision 

support system (Appendix C) and should be addressed as higher priority actions are 

implemented, as part of elevated management within tortoise conservation areas, or as other 

opportunities or needs arise. 

2.10. Restrict off-highway vehicle events within desert tortoise habitat. This action 

refers to large- or small-scale competitive races or non-competitive events involving 

up to thousands of motorcycles and other off-highway vehicles. Prior to the 

implementation of current permitting and management practices (see for example 

BLM 1998a), competitive off-highway vehicle events led to the widening of old 

routes, creation of new routes, camping and staging by race participants and observers 

in unauthorized areas, littering, and inability of race monitors to prevent unauthorized 

activities. 

This action entails prohibiting or demonstrably minimizing the effects of such events 

within tortoise habitat; limiting the number of events per year, limiting events to the 

winter season, and limiting the number of participants per event; and ensuring all 

participants stay on designated roads. Event planning should avoid existing tortoise 

conservation areas to the extent practicable. 

2.11. Connect functional habitat. Connecting fragmented habitat helps to maintain gene 

flow between isolated populations. This action improves species fitness (ability to 

maintain or increase its numbers in succeeding generations) by maintaining diversity, 

allowing populations to interbreed, and providing access to larger habitats (Forman et 

al. 2003). Roads and urban areas form barriers to movement and tend to create small, 

local populations which are much more susceptible to extinction than large, 

connected populations (Wilcox and Murphy 1985). 

This action is of consistently moderate priority among recovery units. It entails 

connecting isolated blocks of desert tortoise habitat, particularly through corridors of 

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natural habitat for large-scale connectivity, as well as culverts for smaller-scale 

connectivity across fenced roads and railroads. 

2.12. Limit mining and minimize its effects. Impacts from mining can include habitat 

destruction and direct mortality from off-road exploratory travel; habitat loss to road 

and development construction, sand and gravel extraction, leachate ponds, tailings, 

and trash; introduction of toxins; fugitive dust and soil erosion; development of 

ancillary facilities to support large mining operations; temporary (short- or long-term 

oil and gas leases) use of public lands; refuse of stakes and wire from seismic testing; 

creation of disturbance zones for invasive plant species to establish. 

Mining should be withdrawn (if feasible) from, or otherwise limited through mining 

plans of operations, within tortoise conservation areas or where indirect effects from 

adjacent areas would affect these areas. 

2.13. Limit landfills and their effects. Landfills impact tortoise populations by removing 

habitat, spreading garbage, introducing toxic chemicals, increasing road kills by 

vehicles going to and from the landfill, and facilitating proliferation of predators. 

Predator proliferation is considered the most significant of these impacts with 

landfills providing food subsidies for ravens and coyotes, leading to more young that 

move into adjacent areas in the spring to prey upon tortoises (Boarman 2002). Proper 

landfill management (including dumps and sewage ponds) can help reduce several 

threats to tortoises, but especially from ravens (Boarman and Kristan 2006). 

This action entails reducing or eliminating the use of authorized landfills by tortoise 

predators, siting new landfills outside of desert tortoise habitat, and/or precluding new 

landfills within 8 kilometers (5 miles) of existing tortoise conservation area 

boundaries. 

2.14. Reduce excessive predation on tortoises. Predation by the common raven is focused 

on younger age classes of the desert tortoise. During the first 5 to 7 years of life, the 

tortoise shell is incompletely ossified; it is soft and easy to puncture and open. 

Coyotes have been seen to prey upon numerous adult desert tortoises within local 

areas, especially in times of drought. 

Several other recovery actions (2.4, 2.5, 2.13) address raven population management 

by limiting human subsidies (e.g., food obtained at landfills and from roadkills). This 

action emphasizes direct predator-control programs to reduce predation on tortoises 

where specific problem areas are identified. Control methods can include targeted 

removal of known tortoise predators by shooting or trapping (live or lethal), as well 

as nest removal, directed at specific problem areas within tortoise conservation areas 

or where predation is affecting specific recovery-related research. We do not consider 

general, widespread predator control to be an appropriate recovery action. 

2.15. Minimize impacts from horses and burros. Wild horses and burros alter desert 

tortoise habitat through soil compaction and vegetation change (Boarman 2002). 

73
Tortoises and horses and burros may also compete for the same food. The California 

Desert Managers Group has been coordinating among member agencies since 1998 to 

substantially remove horses and burros from outside herd management areas. Herds 

have been eliminated in most critical habitat, and efforts are continuing to reduce 

their numbers. Within the Las Vegas District of the Bureau of Land Management, all 

herd management areas are at appropriate management levels, and herds outside of 

herd management areas have been eliminated. 

This action entails continued exclusion of horses and burros from desert tortoise 

conservation areas by fencing and/or removal. Managing for zero population levels 

and gathering animals to maintain this goal inside desert tortoise conservation areas is 

consistent with existing land use plans and the Wild Free Roaming Horses and Burros 

Act of 1971. 

2.16. Minimize livestock grazing. Grazing by livestock (cattle and sheep) affects desert 

tortoises through crushing animals or their burrows, destroying or altering vegetation 

(which may introduce weeds and change the fire regime), altering soil, and competing 

for food (Boarman 2002). 

While many cattle and sheep allotments have already been retired within desert 

tortoise habitat, this action entails continued exclusion of livestock grazing by 

fencing, removing trespass cattle, retiring allotments, and prohibiting supplemental 

feeding, especially where it still occurs within tortoise conservation areas. More 

flexible grazing practices, such as allowing or reducing grazing during specific times 

of the year (e.g., after ephemeral forage is gone or winter only) or under certain 

environmental conditions (e.g., following a specified minimum amount of winter 

rain), would be most appropriate outside conservation areas, but should be used 

experimentally to investigate the compatibility of grazing with desert tortoise 

populations. 

3. Augment Depleted Populations through a Strategic Program 

3.1. Develop protocols and guidelines for the population augmentation program, 

including those specific to head-starting and translocation. Specific guidelines and 

protocols should be developed with other permitting agencies and experts, drawing 

from knowledge gained through recent research into head-starting and translocation. 

Protocols and guidelines should also draw upon recommendations by the Science 

Advisory Committee relative to controlling disease (Appendix B). 

3.2. Identify sites at which to implement population augmentation efforts. Populations 

to be augmented should be identified based upon knowledge of population trends and 

threats in the area, unique opportunities to learn about augmentation techniques or 

threats through a research-based program, and feasibility. Data from previous 

population monitoring efforts, including a spatial analysis (Nussear in prep.), and 

recent advances in genetics will facilitate selection of the target areas. 

74
 

3.3. Secure facilities and obtain tortoises for use in augmentation efforts. 

 Secure facilities for head-starting tortoises. Several groups in California have 

begun research into head-starting techniques. Currently, facilities exist at the 

National Training Center’s Fort Irwin Study Sites (FISS 1 and FISS 2), Edwards 

Air Force Base, and Marine Corps Air Ground Combat Center at Twentynine 

Palms. These facilities may be used and additional facilities will need to be 

constructed. For example, the addition of facilities in the Las Vegas area could 

serve several surrounding recovery units. The existing Desert Tortoise 

Conservation Center could be renovated to house such facilities in a secure 

location. See also Science Advisory Committee recommendations related to 

desert tortoise holding facilities and the control of disease (Appendix B). 

 Obtain adult tortoises for generation of progeny. Tortoises used in the headstarting program will be of known origin and of the genotype (genetic makeup) 

that inhabits the specific areas to be augmented. Depending on several factors, 

breeding colonies may be maintained in captivity, or wild females may be 

periodically captured and released after collection of eggs. 

 Head-start progeny. Maintain progeny in captivity as specified in guidelines 

developed under 3.1. 

 Obtain adult tortoises for translocation. Some adult tortoises removed from 

construction sites or other disturbed areas may be suitable for translocation to 

target areas. Refer to guidelines developed under 3.1. 

3.4. Implement translocations in target areas to augment populations using a 

scientifically rigorous, research-based approach. Translocation and head-starting 

efforts should be implemented in conjunction with directed research on the factors 

affecting success of the augmentation, including methodological factors, but 

especially including factors related to management of habitat and threats. Refer to 

guidelines developed under 3.1 for information on target areas. 

4. Monitor Progress toward Recovery 

The ability to describe range-wide trends depends on reliable, adequate, and consistent 

funding. A key recommendation of the General Accounting Office’s audit of the desert tortoise 

recovery program was that the Departments of the Interior and Defense work with other agencies 

and organizations “to identify and assess options for securing continued funding for range-wide 

population monitoring” (GAO 2002). Rather than developing monitoring based on individualagency annual budgeting considerations, the Desert Tortoise Management Oversight Group 

should implement the GAO’s recommendation (for example, through 5-year time frames) to 

allow effective planning, contracting, and hiring to be implemented under a long-term study 

plan. The following recovery actions parallel the recovery criteria described earlier, helping 

ensure that progress toward recovery is measured effectively. 

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4.1. Monitor desert tortoise population growth. Trends in tortoise populations can be 

assessed either by directly enumerating the number of tortoises, or by estimating the 

rate of births, deaths, and related recruitment into each age or size class so that the 

resulting trend in population growth can be determined. 

 Monitor the number of tortoises in each recovery unit. We will estimate 

population change (λ) on a recovery-unit-wide scale through measures of 

population size, density, and/or occupancy. Refinement of range-wide monitoring 

techniques should continue, as recommended by USFWS (2006a). 

 Use demographic rates in key areas of each recovery unit (i.e., demographic study 

areas) to independently estimate population growth in each recovery unit. 

Dynamic vital-rate models should be used to provide an independent estimate of 

the population growth rate, λ. Some existing or prior study plots may be 

appropriate for inclusion in the set of demographic study areas to make use of 

long-term datasets. 

4.2. Monitor the extent of tortoise distribution in each recovery unit. Monitoring 

changes in desert tortoise distribution by estimating occupancy of tortoises entails 

investigating the most feasible scale at which occupancy would be evaluated, as well 

as the number of visits to a given site that would be needed to estimate detection 

probability if tortoises are present. Taken together and repeated over the years of the 

recovery program, occupancy estimation would provide a description of the rates at 

which tortoises are being locally extirpated from occupied habitat as well as 

recolonizing currently unoccupied habitat across the range. Occupancy estimation, if 

feasible, would also provide another estimate of population growth rate, λ. In 

addition, historical study-plot and sign-count data should be compared with current 

patterns of live and dead tortoise concentrations to provide insights into recent larger 

scale declines relative to those reported from some plots (USFWS 2006a). 

4.3. Track changes in the quantity and quality of desert tortoise habitat. A baseline 

for tracking habitat quantity across each recovery unit will exist with the habitat 

model specified in this revised recovery plan (5.2). Trends in habitat quality over time 

should be integrated into the recovery database/decision support system (6.1) as 

conditions affecting habitat quality are identified (5.2). Remote sensing and GIS data, 

validated by ground truthing as necessary, can be used to quantify the loss or 

restoration of habitat against the baseline (for instance, habitat completely lost to 

urbanization, degraded by wildfires, or authorized for use as rights-of-way or energy 

projects; the number and average size of habitat fragment polygons created by roaded 

boundaries). 

4.4. Quantify the presence and intensity of threats to the desert tortoise across the 

landscape. Remote sensing, GIS data, ground truthing, and other surveys should be 

used to update and refine information on threats presented in the background of this 

recovery plan and used in the initial decision support system (6.1, Appendix C), 

including disease and other threats that may be related to habitat quality discussed 

76
above. This information will allow recovery efforts to be better tailored to specific 

areas while being incorporated with additional information gained through research 

and monitoring. 

5. Conduct applied research and modeling in support of recovery efforts within a strategic 

framework 

5.1. Characterize stable age distributions of stable or increasing populations. 

Research on demographic study areas should document age distributions sufficiently 

to characterize the stable age distribution (the age distribution of a population under 

constant survivorship and recruitment) that distinguishes a stable or increasing 

population from a decreasing one, especially including the proportion of juveniles 

represented. 

5.2. Determine factors that influence the distribution of desert tortoises. 

 Validate and refine the desert tortoise habitat model. The draft U.S. Geological 

Survey desert tortoise habitat model should be completed within the first year of 

publication of the final revised recovery plan. Data collected from the range-wide 

monitoring program or other surveys, especially those outside currently 

designated critical habitat, should be used to refine the model. 

 Determine characteristics that contribute to the relative condition (e.g., high, 

medium, or low quality) of desert tortoise habitat. Variation in desert tortoise 

habitat quality likely contributes to habitat-specific demographic rates (e.g., 

higher recruitment in habitats with nutritious forage and few ravens; see Pulliam 

1996) and occupancy. Some environmental factors, such as water available from 

rainfall, may be beyond the scope of management, but identifying specific, 

measurable characteristics of habitat that contribute to high rates of survival, 

reproduction, and recruitment is important to inform effective recovery efforts. 

Information from this recovery action is essential to meeting Recovery Criterion 3 

relative to ensuring that habitat quality increases over the next 25 years. Research 

in this area should identify: 

• landscape attributes, if any, that cause clumping of desert tortoises; and 

• minimum conditions for potential desert tortoise occupancy. 

 Model desert tortoise demography relative to habitat condition to determine the 

proportion of habitat that needs to be occupied (or is available to be occupied) for 

recovery. As habitat-specific demography is clarified, population models should 

be developed to refine estimates of habitat quantity and tortoise occupancy 

necessary to sustain populations into the future. Models should incorporate 

predicted effects of climate change on desert tortoise demography, as well as on 

the current composition of tortoise habitat. Information from this recovery action 

is essential to refining Recovery Criterion 3a relative to the amount of habitat 

needed to meet the conditions for delisting. 

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5.3. Conduct research on the restoration of desert tortoise habitat. 

 Evaluate the effectiveness of different restoration methods. The science of 

restoration and revegetation of desert ecosystems is in its infancy, and more work 

is necessary to identify effective restoration methods in order to successfully 

implement Recovery Action 2.6. 

 Identify methods to eradicate non-native, invasive plants within desert tortoise 

habitat. Invasive plants are a significant threat to desert tortoise habitat and 

populations across the species’ range. Research is needed to identify methods for 

weed suppression or eradication in order to successfully implement Recovery 

Action 2.6. 

 Correlate habitat restoration with desert tortoise population status. The response 

of tortoise populations to restoration efforts should be evaluated, especially as 

habitat-specific demography is clarified (5.2). This action may also be 

implemented in coordination with population augmentation (3.1-3.4) and 

monitoring demographic study areas (4.1). 

5.4. Improve models of threats, threat mitigation, and desert tortoise demographics. 

The decision support system (6.1) requires information on how threats affect desert 

tortoise populations and how management actions abate those threats. This 

information has currently been incorporated in the decision support system in a very 

rudimentary way. 

 Develop conceptual and quantitative models of threats. Models of desert tortoise 

threats are needed to clarify interactive relationships between threats and to 

identify critical synergies that contribute to population declines. In addition, the 

demographic effects of individual threats and suites of threats on desert tortoise 

populations should be determined experimentally whenever possible. 

 Develop and test models of the effectiveness of management actions. The 

corollary of modeling and experimentally investigating threats is determining the 

effectiveness of threat mitigation by specific management actions. Recovery 

Implementation Teams should identify and secure funding for applied research on 

the effectiveness of recovery actions based on local priorities. Conceptual models 

should be developed for all recovery actions, and these models should be 

quantified with new research and monitoring information, as it becomes available. 

5.5. Conduct research on desert tortoise diseases and their effects on tortoise 

populations. While the precise role of disease in desert tortoise population declines 

relative to other threats is unclear, disease has been a high-profile and controversial 

78
topic. Therefore, we provide specific recommendations to better understand the 

nature and relative importance of disease to desert tortoise populations. The first three 

recommendations below arise from the working hypothesis that mycoplasmosisinduced die-offs are initiated by environmental stressors (see Appendix B for more 

information). 

 Determine whether population declines through environmental stress are less 

severe when Mycoplasma is absent. 

 Determine if desert tortoises exposed to simulated drought conditions become 

more susceptible to infection and more infectious. 

 Determine whether diets high in non-native plants increase susceptibility to 

disease, as well as infectiousness. 

 Identify the virulent and less virulent strains of Mycoplasma circulating in wild 

and captive populations and monitor temporal and spatial change in prevalence in 

relation to host genetic status and environmental stressors. Identification of genes 

expressing toxin production and the circumstances when these genes are 

expressed could be a fruitful area of research. Studies examining the level of cross 

immunity between strains and variation in resistance in relation to the plane of 

nutrition and availability of water would be of great assistance. This research aims 

to examine the presence and variation in Mycoplasma strains with the aim of 

containing virulent strains. 

 Identify which individual tortoises are shedding, how they shed (i.e., transmit), 

when they shed and, for how long they shed infectious Mycoplasma particles. 

Identify whether individuals removed from drought-stressed areas or areas with 

severely deteriorated habitats continue to shed Mycoplasma and for how long. 

This research will identify in more detail seasonal forces of infection, the period 

of infectiousness, and how infectiousness varies under different circumstances. 

 Undertake trials to determine if it is possible to cure individuals with Mycoplasma 

infections, even if only feasible in captive individuals. Preliminary veterinary 

trials with mixed antibiotics and anti-inflammatory steroids have met with some 

success and could be extended. 

 Examine the behavior of infectious tortoises in comparison to uninfected tortoises 

in the wild. Obtain estimates of contact rate according to sex, age, and season. 

This research will help us understand the most critical epidemiological parameters 

associated with transmission and, with other data, allow us to produce a predictive 

model of outbreak. 

 Examine the implications of releasing sick tortoises into uninfected populations. 

Such studies should occur within enclosures at captive holding facilities. 

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 Create a comprehensive disease-tortoise population model that incorporates the 

above information. A disease-tortoise population model could be used to 

anticipate outbreaks and patterns of spread. 

 Evaluate other known or emerging diseases for effects on desert tortoise 

populations. Less is known about other diseases that have been identified in the 

desert tortoise (e.g., herpesvirus, cutaneous dyskeratosis). Continued study of 

Mycoplasma will help to form a model that will facilitate investigations of other 

diseases. In the meantime, surveys or pathological study of other diseases should 

be conducted within the context of other threats (e.g., 5.4). 

5.6. Resolve population structure of the desert tortoise across its range. Additional 

research is needed to refine understanding of desert tortoise population structure and 

the extent to which recovery units conform to natural population subdivisions, as well 

as the importance of corridors and physical barriers to gene flow. 

 Determine the importance of corridors and physical barriers to desert tortoise 

distribution and gene flow. Determining the importance of corridors and barriers 

will allow population models to be made spatially explicit relative to current land 

management (e.g., population and habitat fragmentation due to roads and 

urbanization; clarification of recovery unit boundaries) and potential distributional 

shifts resulting from climate change. 

6. Implement an Adaptive Management Program 

Recovery Implementation Teams (established under Strategic Element 1; Partnerships in 

Figure 4) will be the driving force, in coordination with the Desert Tortoise Recovery Office, 

behind the implementation of the adaptive management program. Here, we describe the specific 

steps that the Recovery Implementation Teams and Desert Tortoise Recovery Office must apply 

in order to fully implement the program. We refer to these steps, depicted in Figure 4, with 

italicized labels in the text below. 

6.1. Revise and continue development of a recovery decision support system. The 

Recovery Implementation Teams begin the adaptive management process by 

Assessing the Problem. Toward that end, a preliminary decision support system has 

been developed (Appendix C) to identify and prioritize recovery actions relative to 

managing desert tortoise populations and habitat (see Protect Existing Populations 

and Habitat, above). Due to the lack of data on the effects of individual threats on 

tortoise demography, the initial decision support system is based largely on 

information collected from workgroups convened during the recovery planning 

process or other sources, simple preliminary models, and the expert opinion of 

approximately 20 individuals from the tortoise science and management community 

(see Appendix C). In addition, the data input into the decision support system are only 

partially complete, and virtually no spatially explicit synthesis of recovery actions 

that have been implemented pursuant to the 1994 Recovery Plan has been completed. 

Thus, the current outputs of the decision support system are very preliminary and 

cannot be regarded as absolutes. However, the objective of applying the decision 

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support system at this time is not an attempt to represent certainties about the 

relationship between tortoise populations, habitat, threats, and management, but 

instead to establish a “rapid prototype” that will identify key assumptions and allow 

evaluation of the relative importance of different assumptions, components, or gaps in 

the model (Starfield 1997; Nicolson et al. 2002). 

The models contained within this rapid-prototype decision support system, including 

any new monitoring or research results, should be regularly Evaluated (at least 

biennially) by independent reviewers including the Science Advisory Committee. The 

decision support system should be then be Adjusted to achieve goals that a) ensure the 

overall decision support system is clearly partitioned into a suite of models with clear 

purposes, b) ensure all models or components are transparent and comprehensible, 

and c) the sensitivity of model output to different parameter values and assumptions 

is adequately tested. It is especially critical to continue to update the underlying data 

in the decision support system with a range-wide, geospatial database of current 

management activities, landscape information on threats, habitat quality and quantity, 

and tortoise populations. In addition to contributing to models, maintaining an up-todate database will facilitate reporting of implementation progress. 

One of the challenges in developing the prototype decision support system was 

making the list of recovery actions more operational. Several actions listed in the 

1994 Recovery Plan overlap with one another, and it was clear from the recovery 

planning workshops that various actions meant different things to different people. 

Not all actions are mutually exclusive of one another. Several are complementary and 

can be implemented in tandem. Refinement of the decision support system should 

also continue to clarify and operationalize recovery action terminology. 

Specific tasks and timelines relative to this action include: 

 Within the first year after publication of the final, revised recovery plan, the 

Recovery Implementation Teams, Desert Tortoise Recovery Office, and other 

partners, should update the underlying data in the decision support system for at 

least two recovery units, including data on threats and current recovery-action 

implementation. This stage should be completed for the remaining recovery units 

within the second year, and regular updates to all recovery units should occur on 

an ongoing basis thereafter. 

 Within the second year after publication of the revised recovery plan, the Desert 

Tortoise Recovery Office, Science Advisory Committee, and other independent 

reviewers should evaluate the underlying models in the decision supports system. 

Re-evaluation should occur at least biennially, although it is likely that different 

models will be in different stages of evaluation or revision within each biennium. 

6.2. Develop/revise recovery action plans. Recovery Implementation Teams should use 

the decision support system to tier off the recovery plan by developing 5-year action 

plans and budget needs with priorities for management scaled down to local or 

jurisdictional levels. Five-year action plans should be coordinated with the 

81
Management Oversight Group and completed within the first year of publication of 

the revised recovery plan. Initial application of the decision support system for 

prioritizing actions at the local or regional level will vary among recovery units 

according to the timeline for updating the system, as described above. 

 The first step in each adaptive-management iteration includes prioritizing general 

actions, followed by identification of spatially and temporally explicit actions, 

specific enough that the action plans can be reviewed, critiqued, and adopted 

without confusion in relevant planning documents of the participating land 

management agencies. For instance, if “roads” are identified as a priority threat in 

a particular Recovery Implementation Team area, the general action 

recommended might be “road closures.” The Recovery Implementation Team 

would then proceed to recommend specific roads for closure, so that the 

appropriateness of this action can be evaluated, and the action agencies have clear 

understanding of the Recovery Implementation Teams’ recommendations. 

 In conjunction with prioritizing recovery actions, the Recovery Implementation 

Teams must prioritize needs for effectiveness Monitoring or other Research. In 

order to rank monitoring priorities, a further step from the decision support 

system is required. Recovery Implementation Teams will need to describe 

conceptual models that link each threat to each of the pathways that impact 

tortoise health, survival, movement, population structure, recruitment, or 

fecundity. These models are part of Assessing the Problem and are the first step in 

describing the linkages that will be affected by management activities, so they 

also point to the type of Monitoring or Research that will capture the 

effectiveness of these activities in breaking the links. Population augmentation in 

conjunction with other land management, effectiveness monitoring, or research 

activities may also be recommended through the procedures described under 

Recovery Action 3. These 4 elements (Strategic Elements 2-5) will be reviewed 

by the Desert Tortoise Recovery Office and placed within the larger range-wide 

strategy. 

 Once the recovery action plans, including prioritized actions, monitoring, and 

research, have been developed by the Recovery Implementation Teams and 

Desert Tortoise Recovery Office and approved by the Management Oversight 

Group, the relevant land management agencies will use their own processes to 

Design and Implement actions. By Design, we mean that the necessary planning 

processes will be engaged to formalize each agency’s commitments to the 

adopted actions. Because all Recovery Implementation Team members should 

remain fully engaged, it is important that all represented land management 

agencies have clear tasks for each Recovery Implementation Team cycle. 

 The Recovery Implementation Teams and Desert Tortoise Recovery Office 

should report progress on recovery implementation to the Management Oversight 

Group on an annual basis and revise the recovery action plans accordingly. 

82
6.3. Amend land use plans, habitat management plans, and other plans as needed to 

implement recovery actions. Federal, State, County, and City land managers should 

Adjust recovery efforts based on outcomes of the processes described above by 

amending planning documents as needed. Broad land-use plans, such as Bureau of 

Land Management resource management plans, may not need revision, as they often 

include language stipulating that agencies will strive to implement recovery for 

federally listed species. Program-level or area-specific plans, such as habitat 

management plans, wilderness plans, and Area of Critical Environmental Concern 

plans, are an opportunity to work with stakeholders to build in detailed planning at 

local levels. 

6.4. Incorporate scientific advice for recovery through the Science Advisory 

Committee. The Desert Tortoise Recovery Office should continue to work directly 

with the Science Advisory Committee and other independent experts, meeting at least 

annually to Evaluate progress in Research and Monitoring and other recovery plan 

accomplishments. The Science Advisory Committee should make new 

recommendations, as needed, based on progress in implementing the recovery plan. A 

particular need exists for vigilance in focusing on large-scale, range-wide tortoise 

recovery, maintaining connection to Recovery Criteria in the 25-year horizon, 

through at least 5-year evaluations of the range-wide monitoring program. Annual 

Science Advisory Committee meetings should include an opportunity for stakeholder 

and manager interaction, potentially in association with Management Oversight 

Group meetings, to provide direct feedback and information exchange. 

83
Table 4. Reference table connecting major recovery actions to listing factors and recovery objectives. 

Recovery actions are categorized according to each strategic element of the recovery program. Subactions 

for each major recovery action are not listed (see the recovery narrative). 

Recovery Action Listing 

Factor 

Recovery 

Objective 

1. 

1.1 

Develop, support, and build partnerships to facilitate recovery 

Establish regional, inter-organizational Recovery Implementation 

Teams to prioritize and coordinate implementation of recovery actions. 

All All 

2. 

2.1 

2.2 

2.3

2.4 

2.5 

2.6 

2.7 

2.8 

2.9 

2.10 

2.11 

2.12 

2.13 

2.14 

2.15 

2.16 

Protect existing populations and habitat 

Protect intact desert tortoise habitat. 

Reduce factors contributing to disease. 

 Establish/continue environmental education programs. 

Increase law enforcement. 

Restrict, designate, close, and fence roads. 

Restore desert tortoise habitat. 

Install and maintain urban or other barriers. 

Sign and fence boundaries of sensitive or impacted areas. 

Secure lands/habitat for conservation. 

Restrict off-highway vehicle events within desert tortoise habitat. 

Connect functional habitat. 

Limit mining and minimize its effects. 

Limit landfills and their effects. 

Reduce excessive predation on tortoises. 

Minimize impacts from horses and horses. 

Minimize livestock grazing. 

A,E 

C 

All 

A-D 

A-D 

A,E 

A-C 

A,B 

A 

A,B 

A 

A,C 

A,C 

C 

A 

A 

3 

1,2 

All 

All 

All 

3 

All 

3 

3 

All 

2 

All 

1,3 

1 

3 

3 

3. 

3.1 

3.2 

3.3 

3.4 

Augment depleted populations through a strategic program 

Develop protocols and guidelines for the augmentation program. 

Identify sites at which to implement population augmentation efforts. 

Secure facilities and obtain tortoises for use in augmentation efforts. 

Implement translocations in target areas to augment populations. 

All 

All 

All 

All 

1-2 

1-2 

1-2 

All 

4. 

4.1 

4.2 

4.3 

Monitor progress toward recovery 

Monitor desert tortoise population growth. 

Monitor the extent of tortoise distribution in each recovery unit. 

Track changes in the quantity and quality of desert tortoise habitat. 

All 

All 

A,D,E 

1 

2 

3 

84
 

 

Table 4. Continued. 

Recovery Action Listing 

Factor 

Recovery 

Objective 

4.4 Quantify the presence and intensity of threats to the desert tortoise 

across the landscape. 

All All 

5. 

5.1 

5.2 

5.3 

5.4 

5.5 

5.6 

Conduct applied research and modeling in support of recovery efforts within a 

strategic framework 

Characterize stable age distributions of stable or increasing populations. All 1 

Determine factors that influence the distribution of desert tortoises. All 2,3 

Conduct research on the restoration of desert tortoise habitat. A,E 3 

Improve models of threats, threat mitigation, and desert tortoise 

demographics. 

All 1,3 

Conduct research on desert tortoise diseases and their effects on tortoise 

populations. 

C 1,2 

Resolve population structure of the desert tortoise across its range. All 1,2 

6. 

6.1 

6.2 

6.3 

6.4 

Implement an adaptive management program 

Revise and continue development of a recovery decision support system. All All 

Develop/revise recovery action plans. All All 

Amend land use plans, habitat management plans, and other plans as 

needed to implement recovery actions. 

All All 

Incorporate scientific advice for recovery through the Science Advisory 

Committee. 

All All 

Listing Factors: 

A. The present or threatened destruction, modification, or curtailment of its habitat or range 

B. Overutilization for commercial, recreational, scientific, or educational purposes 

C. Disease or predation 

D. The inadequacy of existing regulatory mechanisms 

E. Other natural or manmade factors affecting its continued existence 

Recovery Objectives: 

1. Maintain self-sustaining populations of desert tortoises within each recovery unit into the future. 

2. Maintain well-distributed populations of desert tortoises throughout each recovery unit. 

3. Ensure that habitat within each recovery unit is protected and managed to support long-term viability of desert 

tortoise populations. 

85
86
III. IMPLEMENTATION SCHEDULE 

The implementation schedule outlines the tasks discussed in Part II and indicates task 

numbers, priorities, durations, estimated costs, and partners that may be involved in 

implementing the task. When accomplished, these tasks would enable the desert tortoise to be 

delisted. The costs for each task are rough estimates, and actual budgets will have to be 

determined when each task is undertaken (TBD = to be determined). Cost estimates are 

unavailable for several actions, such as research, due to uncertainties in the scope and magnitude 

of the specific action. Recovery plans are non-regulatory documents, and as such, identified 

partners are not obligated to implement recovery tasks. Cost estimates do not commit funding by 

any agency. 

Action priorities in the implementation schedule are assigned as follows: 

Priority 1: An action that must be taken to prevent extinction or to prevent the species from 

declining irreversibly in the foreseeable future. Note that no recovery actions have been assigned 

at the Priority 1 level based on the judgment that the desert tortoise is not on the verge of 

extinction or declining irreversibly at this time (reflected by its status as Threatened, rather than 

Endangered). Furthermore, many actions are already being implemented, so an urgent need 

does not exist for implementation to prevent extinction. Most actions are assigned at the Priority 

2 level, described below. 

Priority 2: An action that must be taken to prevent a significant decline in species population 

numbers or habitat quality or some other significant negative impact short of extinction. 

Priority 3: All other actions necessary to provide for full recovery of the species. 

We have attempted to provide an overall priority for each recovery action that applies 

across recovery units. However, threats, and therefore the importance of recovery actions that 

ameliorate those threats, vary by recovery unit. A preliminary assessment of threats by recovery 

unit is presented in the decision support system description in Appendix C. Recovery 

Implementation Teams need to be established upon publication of the final revised recovery plan 

(Recovery Action 1.1), and they should guide recovery action priorities and develop updated 

budget projections within each recovery unit through the use of an updated/improved decision 

support system (6.1-6.2). 

Task duration in Column 4 indicates the number of years estimated to complete the task. 

A Continuing task will continue to be conducted once implemented. Many tasks are listed as 

Ongoing; these are already being conducted and should continue. The Responsible Party 

indicates the lead agency or agencies identified for a particular task and includes the full suite of 

local, state, and Federal land and wildlife management agencies within the desert tortoise’s range 

(= Land Managers). Other stakeholders or organizations (included in “All”) may also contribute 

to particular recovery actions. However, other parties may also have significant roles in different 

tasks, and (as mentioned above) the listing of a party does not require the identified party to 

implement the action(s) or to secure funding for implementing the action(s). 

87
Abbreviations of the responsible parties identified in the Implementation Table are 

defined as follows: 

BLM – Bureau of Land Management 

CC MSHCP – Clark County, Nevada, MSHCP 

CS MSHCP – Coyote Springs, Nevada, MSHCP 

DOD – Department of Defense 

MNP – Mojave National Preserve 

NPS – National Park Service 

USFWS – U.S. Fish and Wildlife Service 

USGS – U.S. Geological Survey 

WC HCP – Washington County, Utah, HCP 

88
8

9

Implementation Schedule Costs (tho

Duration Responsible 

Recovery Action Priority (years) Party FY 1 FY 2 FY 

1. Develop, support, and build partnerships to facilitate recovery 

1.1 Establish regional, inter-organizational RITs to coordinate 2 Continuing USFWS (All) 500 500 5

implementation activities of recovery actions. 

2. Protect and manage existing populations and habitat 2.1 Protect intact desert tortoise habitat. 2 Ongoing Land Managers TBD TBD TB

2.2 Reduce factors contributing to disease. 2 Continuing All 10 10 1

2.3 Establish/continue environmental education programs. 2 Ongoing All 100 100 1

2.4 Increase law enforcement. 2 Ongoing Land Managers 1000 1000 102.5 Restrict, designate, close, and fence roads. 2 Ongoing BLM, NPS 1000 1000 102.6 Restore desert tortoise habitat. 2 Continuing Land Managers TBD TBD TB

2.7 Install and maintain urban or other barriers. 

Upper Virgin River Recovery Unit 2 2 WC HCP 0 0 

Northeastern Mojave Recovery Unit 2 5 CC MSHCP CS MSHCP 0 0 Western Mojave Recovery Unit 2 5 Land Managers 200 200 2

Remainder of desert tortoise range 3 5 Land Managers 500 500 5

2.8 Sign and fence boundaries of sensitive or impacted areas. 

Upper Virgin River Recovery Unit 2 2 WC HCP 0 0 

Remainder of desert tortoise range 3 Ongoing Land Managers 600 600 6

2.9 Secure lands/habitat for conservation. 

Upper Virgin River, Eastern Colorado, and Western Mojave 2 Ongoing Land Managers TBD TBD TBrecovery units Remainder of desert tortoise range 3 Ongoing Land Managers TBD TBD TB

2.10 Restrict off-highway vehicle events within desert tortoise habitat. 3 Ongoing BLM 50 50 5

2.11 Connect functional habitat. 3 Ongoing Land Managers TBD TBD TB
9

0

Implementation Schedule Continued Costs (tho

Recovery Action Priority 

Duration 

(years) 

Responsible 

Party FY 1 FY 2 FY 

2.12 Limit mining and minimize its effects. 3 Ongoing BLM 100 100 1

2.13 Limit landfills and their effects. 3 Ongoing Counties 100 100 1

2.14 Reduce excessive predation on tortoises. 3 10 Land Managers 100 100 1

2.15 Minimize impacts from horses and horses. 3 Ongoing BLM, NPS 500 500 52.16 Minimize livestock grazing. 3 Ongoing BLM, MNP 100 100 1

3. Augment depleted populations through a strategic program 3.1 Develop protocols and guidelines for the augmentation program. 2 1 USFWS 50 

3.2 Identify sites at which to implement population augmentation 

efforts. 

2 1 USFWS 50 

3.3 Secure facilities and obtain tortoises for use in augmentation efforts. 2 10 USFWS, DOD, 

MNP 

500 500 5

3.4 Implement translocations in target areas to augment populations 

using a scientifically rigorous, research-based approach. 

2 15 USFWS, Land 

Managers 

TB

4. Monitor progress toward recovery 4.1 Monitor desert tortoise population growth. 3 Ongoing USFWS (All) 1,500 1,500 1,54.2 Monitor the extent of tortoise distribution in each recovery unit. 3 Continuing USFWS (All) 1,500 1,500 1,54.3 Track changes in the quantity and quality of desert tortoise habitat. 3 Continuing USFWS (All) TBD TBD TB

4.4 Quantify the presence and intensity of threats to the desert tortoise 

across the landscape. 

3 Continuing USFWS (All) TBD TBD TB

5. Conduct applied research and modeling in support of recovery efforts within a strategic framework 5.1 Characterize stable age distributions of stable or increasing 

populations. 

3 TBD USFWS 

(research 

institutions) 

TBD TBD TB

5.2 Determine factors that influence the distribution of desert tortoises. 3 TBD USFWS, USGS 

(other research 

institutions) 

TBD TBD TB
9

1

Implementation Schedule Continued Costs (tho

Recovery Action Priority 

Duration 

(years) 

Responsible 

Party FY 1 FY 2 FY 

5.3 Conduct research on the restoration of desert tortoise habitat. 3 TBD All, research 

institutions 

TBD TBD TB

5.4 Improve models of threats, threat mitigation, and desert tortoise 

demographics. 

3 TBD USFWS (All; 

research 

institutions) 

TBD TBD TB

5.5 Conduct research on desert tortoise diseases and their effects on 

tortoise populations. 

3 TBD USFWS 

(research 

institutions) 

TBD TBD TB

5.6 Resolve population structure of the desert tortoise across its range. 3 3 Research 

institutions 

TBD TBD TB

6. Implement an adaptive management program 6.1 Revise and continue development of a recovery decision support 

system. 

2 Ongoing USFWS (All) 50 10 

6.2 Develop/revise recovery action plans. 2 Continuing All TBD TBD TB

6.3 Amend land use plans, habitat management plans, and other plans as 

needed to implement recovery actions. 

3 Continuing Land Managers TBD TBD TB

6.4 Incorporate scientific advice for recovery through the Science 

Advisory Committee. 

3 Ongoing USFWS (All) 5 5 

FY Totals (These totals are minimum cost estimates that do not include TBD costs.) 8615 8475 84

1Costs for minimizing mortality and Habitat Conservation Plan activities are not included because these costs are typically required by regulatory proc

proactive recovery actions. 

Total cost of recovery through 2025: $159,000,000 plus additional costs that cannot be estimated at this time. 
92
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desert tortoises (Gopherus agassizii): the importance of food abundance, body size, and 

date of egg shelling. Journal of Herpetology 33:394-408. 

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Hoegh-Guldberg, and F. Bairlein. 2002. Ecological responses to recent climate change. 

Nature 416:389-395. 

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Weinstein, M.N., and K.H. Berry. 1987. Morphometric analysis of desert tortoise populations. 

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Smith, D.T. Tissue, and J.C. Zak. 2003. Assessing the Response of Terrestrial 

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Hughson, Debra. 2007. National Park Service, Mojave National Preserve. Barstow, California. 

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APPENDIX A 

THREATS TO DESERT TORTOISE AND ITS HABITAT 

SINCE THE TIME OF LISTING

Below is a synopsis of the threats that formed the basis for listing the tortoise as a 

threatened species (USFWS 1990), were further discussed in the 1994 Recovery Plan (USFWS 

1994), and continue to affect the species. A substantive body of data has been accumulated since 

1994 for some of the threats, but others remain relatively unstudied. New information is provided 

where available, and all of the threats warrant continued attention and data collection that will 

inform management actions and recovery implementation through the use of a range-wide 

database and decision support system. 

The vast majority of threats to the desert tortoise or its habitat are associated with human 

land uses. Extensive research shows that all of these individual threats directly kill or indirectly 

affect tortoises. Research has also clarified many mechanisms by which these threats act on 

tortoises. However, despite the clear demonstration that these threats impact individual tortoises, 

there are few data available to evaluate or quantify the effects of threats on desert tortoise 

populations (Boarman 2002; Tracy et al. 2004). While current research results can lead to 

predictions about how local tortoise abundance should be affected by the presence of threats, 

quantitative estimates of the magnitude of these threats, or of their relative importance, have not 

yet been developed. Thus, a particular threat or subset of threats with discernable solutions that 

could be targeted to the exclusion of other threats has not been identified for the desert tortoise. 

The assessment of the 1994 Recovery Plan emphasized the need for a greater 

appreciation of the implications of multiple, simultaneous threats facing tortoise populations and 

a better understanding of the relative contribution of multiple threats on demographic factors 

(i.e., birth rate, survivorship, fecundity, and death rate; Tracy et al. 2004). The approach of 

focusing on individual threats may not have produced expected gains toward desert tortoise 

recovery since 1994 because multiple threats act simultaneously to suppress tortoise populations 

at any given location within the species’ range. Therefore, this revised recovery plan focuses on 

expanding our knowledge of individual threats and places emphasis on understanding their 

multiple and combined effects on tortoise populations. 

A. The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or 

Range 

1. Urbanization 

Urban development directly affects desert tortoise populations through fragmentation 

and permanent loss of habitat. Areas of the desert southwest occupied by desert tortoises have 

been subject to episodic human settlements and associated impacts since the mid to late 1800s 

(USFWS 1994). Urbanization within desert ecosystems continues to take place at a rapid pace 

(Table A-1), and currently more than 30 million people live in close proximity to the desert, 

which is popular with recreationists (Berry et al. 2006). Between the years 2000 and 2005, the 

West experienced an 8.1 percent change in population, compared to 7.3 percent in the South, 2.4 

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percent in the Midwest, and 2.0 percent in the Northeast (U.S. Census Bureau 2005). During this 

same time period, Nevada saw a 20.8 percent increase, Arizona a 15.8 percent increase, Utah a 

10.6 increase, and California a 6.7 percent increase in population growth (U.S. Census Bureau 

2005). 

Table A-1. Human population growth in the states and counties 

within the range of the Mojave population of the desert tortoise 

between 1994 (when the Recovery Plan was published) and 2006. 

State/Counties 1994 Population 

Estimate1 

2006 Population 

Estimate2 

Percent 

Change 

Arizona 4,147,561 6,166,318 48.7 

 Mohave 116,320 193,035 66.03 

California 31,317,179 36,457,549 16.4

 Imperial 136,248 160,301 17.7 

 Inyo 18,450 17,980 -2.5

 Kern 608,858 780,117 28.1 

 Los Angeles 9,048,129 9,948,081 9.9 

 Riverside 1,354,966 2,026,803 49.6 

 San Bernardino 1,553,732 1,999,332 28.7 

Nevada 1,456,388 2,495,529 71.4 

 Clark 938,611 1,777,539 89.4 

 Esmeralda 1143 790 -30.9 

 Lincoln 3849 4738 23.1 

Nye 21,648 42,693 97.2 

Utah 1,930,436 2,550,063 32.1 

Washington 65,520 126,312 92.8 1

 Byerly and Deardorff 1995 

2

 U.S. Census Bureau 2007b 

3

 Most population increase has been outside the Arizona Strip and the range of the Mojave population of 

the desert tortoise. 

Population growth and urban development in the desert region of the Southwest continue 

to expand into previously undisturbed areas, putting intense pressures on the natural resources. 

St. George, Utah, was the fastest-growing metropolitan area in the U.S. between 2000 and 2006, 

with growth of 39.8 percent. Las Vegas, Nevada, grew 29.2 percent, making it one of the top five 

fastest-growing areas during this time period (U.S. Census Bureau 2007a). In fact, the population 

of the Las Vegas metropolitan area nearly doubled between 1995 and 2005, as more than 5,000 

newcomers continue to move to the Las Vegas area every month. If the current growth trends 

continue, the metropolitan area will have 2,058,000 residents by 2010. The growth rate is 

projected to slow to approximately 7 percent per year in the longer term (2020 through 2025) as 

the economy matures and fewer new hotels are added (Clark County Department of Aviation 

2006). 

Rapid growth is not limited to metropolitan areas. Mohave County, Arizona, grew 66 

percent between 1994 and 2006, and Nye County, Nevada, grew 97 percent during the same time 

period (Table A-1). The Beaver Dam/Littlefield community (within the Virgin River Basin) on 

the Arizona Strip supported some 1,580 persons in 2000. This area saw more than 200 percent 

110
 

 

growth between 1990 and 2000. Given this rapid growth rate, the population for the basin will be 

between 3,000 and 4,000 persons in 2010 (S. Donahue, Mohave County, pers. comm. 2007). 

Increasing human populations result in corresponding increases in impacts to desert 

tortoise habitat not only through direct habitat loss, but also through associated human activities 

as more people recreate in the desert and greater infrastructure is needed to support growing 

communities. Lovich and Bainbridge (1999) identified various types of anthropogenic impacts 

from which desert ecosystems may take 50 to 300 years to recover to pre-disturbance plant cover 

levels. However, areas that have experienced permanent, direct habitat loss due to intense 

urbanization will never be restored or recovered. In addition, urban environments have indirect 

impacts on desert tortoise populations and habitat at their interface with the desert (Berry and 

Burge 1984; Berry and Nicholson 1984). Unconfined pets may kill or wound tortoises (see 

section C(3), Predation), and unauthorized collecting of desert tortoises may affect populations 

(see section B(1), Collection by Humans). Indiscriminate use of firearms and off-highway 

vehicles, dumping of trash, and removal of vegetation or unimproved road proliferation are 

activities that occur in and beyond the urban-desert interface that may result in injury and 

mortality to tortoises and degradation of their habitats (see section E, Other Natural or Manmade 

Factors). Habitat fragmentation resulting from infrastructure associated with urbanization such as 

residential fencing, roads, and railroad tracks, can greatly inhibit desert tortoise movements 

(Edwards et al. 2004; Brooks and Lair 2005). These barriers to movement and population 

connectivity have implications to exchange of genetic material, which can lead to inbreeding, 

and may result in mortality of individuals (Boarman and Sazaki 1996) (see section A(2), Roads). 

2. Paved and Unpaved Roads, Routes, Trails, and Railroads. 

Vehicular roads, routes, and trails are the most common type of human disturbance 

observed in desert ecosystems, and much emphasis has been placed on understanding the 

impacts these linear features have on arid environments (Brooks and Lair 2005). Brooks and Lair 

(2005) cite vehicular routes as one of the biggest challenges to land managers in the desert 

southwest, especially as they relate to the conservation status of the desert tortoise. 

Direct and indirect impacts of roads and railroads on desert tortoise populations are well 

documented and include habitat and population fragmentation and degradation as well as mortality of 

individual tortoises (USFWS 1994, Boarman 2002). Paved and unpaved roads serve as corridors for 

urbanization and dispersal of invasive species and provide access to recreation; railroads also 

facilitate urbanization and the spread of non-native plants. Roads and railroads also act as barriers to 

movement. Railroads are similar to roads as sources of mortality for desert tortoises, as they can 

become caught between the tracks causing them to overheat and die or be crushed by trains (U.S. 

Ecology 1989). 

Direct effects to desert tortoise habitat from roads, routes, trails, and railroads also occur 

during initial stages of construction or off-highway vehicle route/trail establishment when 

vegetation and soils are lost or severely degraded. Construction of these features can result in 

physical and chemical changes to soils within unpaved roadways as well as in adjacent areas 

(Brooks and Lair 2005). In addition, roadside vegetation is often more robust and diverse 

because water that becomes concentrated along roadside berms promotes germination, which 

attracts tortoises and puts them at higher risk of mortality as road-kill (Boarman et al. 1997). 

111
Hoff and Marlow (2002) demonstrated that there is a detectable impact on the abundance 

of desert tortoise sign adjacent to roads and highways with traffic levels from 220 to over 5,000 

vehicles per day. That is, the extent of the detectable impact was positively correlated with the 

measured traffic level; the higher the traffic counts, the greater the distance from the road 

reduced tortoise sign was observed (Hoff and Marlow 2002). This supports LaRue (1993) and 

Boarman et al. (1997), wherein depauperate desert tortoise populations were observed along 

highways. Subsequent research shows that populations may be depressed in a zone at least as far 

as 0.4 kilometers (0.25 miles) from the roadway (Boarman and Sazaki 2006). Hoff and Marlow 

(2002) also surmised that unpaved access roads with lower traffic levels may have significant 

effects on tortoises. Desert tortoise populations may also be indirectly affected by road corridors 

that fragment habitat and limit an animal’s ability to migrate and disperse (Boarman et al. 1997). 

Subsequently, populations may become isolated and at higher risk of localized extirpation from 

stochastic events or from inbreeding depression (Boarman et al. 1997; Boarman and Sazaki 

2006). 

 Boarman et al. (1997) attempted to discern the utility of fences and culverts in reducing 

desert tortoise mortality along highways and whether or not the animals would use culverts for 

crossing linear corridors. Data suggest fences may reduce mortality of desert tortoises as well as 

other wildlife species; however, population fragmentation may only be exacerbated by fences 

especially if the tortoises do not readily utilize culverts for crossing the road (Boarman et al. 

1997). 

(a) Spread of Invasive Plants. Construction and maintenance of roadways facilitates 

changes in plant species composition and diversity. Non-native, invasive species and edgeassociated species often become dominant along these linear features, which serve as corridors 

for weed dispersal (Boarman and Sazaki 2006). Vegetation removal and manipulation and 

addition of soils in preparation for road construction, as well as grading of unpaved roads, create 

areas of disturbance that allow weedy species to become established and proliferate (Gelbard and 

Belnap 2003). Vehicles serve as a major vector in dispersal of non-native species along 

roadways (Brooks and Lair 2005). 

Near Canyonlands National Park in Utah, cover of the non-native grass Bromus tectorum 

(cheatgrass) was three times greater along paved roads than four-wheel-drive tracks, and richness 

(a measure of species diversity) and cover of non-native species were more than 50 percent 

greater and native species richness 30 percent lower at interior sites along paved roads than fourwheel-drive tracks. There appears to be a correlation between the level of road improvement 

(i.e., paved, improved, unpaved) and the level of invasion by non-natives (Gelbard and Belnap 

2003). As previous studies show (LaRue 1993; Boarman et al. 1997; Hoff and Marlow 2002; 

Boarman and Sazaki 2006), the greater the distance from the road, the more desert tortoise sign 

is observed. Similarly, the cover and richness of non-native species decreases as distance from 

the road increases (Boarman and Sazaki 2006). 

As natural areas are impacted by linear features such as roads, routes, trails, and railroads, 

previously intact, contiguous habitats become degraded and fragmented, and non-native invasive 

species play a more dominant role in ecosystem dynamics. For instance, increases in plant cover 

112
due to the proliferation of non-natives have altered fire regimes throughout the Mojave Desert 

region (Brooks 1999; Brooks and Esque 2002; Esque et al. 2003; Brooks et al. 2004) (see 

sections A(4)(b) and A(5) on Invasive Species and Increasing Fuel Load and Fire). 

(b) Predator Subsidies. In the desert southwest, common raven populations have 

increased over the past 25 years (greater than 1000 percent), probably in response to increased 

human populations and anthropogenic changes to the landscape, including roads, utility 

corridors, landfills, and sewage ponds (Knight and Kawashima 1993; Boarman and Berry 1995; 

Boarman et al. 1995; Knight et al. 1999; Boarman et al. 2006). See section C(3), Predation, for a 

detailed description of the effects of predator subsidies on the desert tortoise. 

3. Off-Highway Vehicles 

Off-highway vehicle activities take many forms, from organized events, small- or largescale competitive races involving up to thousands of motorcycles (e.g., the Barstow to Las Vegas 

motorcycle competition), to casual family activities. Organized events and off-highway vehicle 

tours are now reviewed and permitted by land managers. Generally, an education component and 

speed limitations are requirements of the permit. Nonetheless, unauthorized off-highway vehicle 

use continues to be of concern, for instance south of Interstate 10 in the Colorado Desert and 

adjacent to the Johnson Valley Open Area in the Western Mojave Recovery Unit, and present a 

variety of threats to the desert tortoise. 

Impacts from off-highway vehicle use include mortality of tortoises on the surface and 

below ground, collapsing of desert tortoise burrows, damage or destruction of annual and 

perennial plants and soil crusts, soil erosion, proliferation of weeds, and increases in numbers 

and locations of wildfires. Despite the many observations that have been documented and 

reported, statistical correlation between off-highway vehicle impacts and reduced desert tortoise 

densities continues to be lacking (Boarman 2002). However, it is evident that off-highway 

vehicle activities remain an important source of habitat degradation and could result in 

reductions in desert tortoise densities (Boarman 2002). Damage to or destruction of shrubs and 

burrows can lead to disruption of desert tortoises’ water balance, thermoregulation, and energy 

requirements and the loss of annual plants reduces the availability of food (USFWS 1994). One 

of the most significant ecological implications of off-highway vehicle routes is the exacerbation 

of erosion and changes in drainage patterns (Brooks and Lair 2005). 

Bury and Luckenbach (2002) compared habitat, abundance, and life history features of 

desert tortoises on one unused, natural area and a nearby area used heavily by off-highway 

vehicles. The unused, natural area had 1.7 times the number of live plants, 3.9 times the plant 

cover, 3.9 times the number of desert tortoises, and 4 times the number of active tortoise burrows 

than the area used by off-highway vehicles. The two largest tortoises in the off-highway vehicle 

use area weighed less than would be expected based on what is known about season-to-season 

fluctuations. Despite the lack of pre-disturbance data for the off-highway vehicle area and the 

patchy distribution of tortoises, the areas furthest from concentrated off-highway vehicle activity 

(pit areas) still reflected the least amount of habitat impact and supported more tortoises (Bury 

and Lukenbach 2002). 

113
Jennings (1997) found that desert tortoises are vulnerable to negative effects from offhighway vehicles because of their habitat preferences. Tortoises in a study at the Desert Tortoise 

Natural Area spent significantly more time traveling and foraging in hills and washes than on the 

flats. Tortoises use washes for travel, excavation of burrows, and foraging, and at least 25 

percent of their forage plants were found to occur within washes. Hills and washes are also 

favored by users of motorcycles, trail bikes, all-terrain vehicles, and other four-wheel vehicles. 

Because tortoises prefer washes and hills, they are more vulnerable to direct mortality from offhighway vehicles. Additionally, off-highway vehicle use in these habitats causes degradation of 

vegetation and loss of forage species important in the desert tortoise diet (Jennings 1997). 

Surface disturbance from off-highway vehicle activity can cause erosion and large 

amounts of dust to be discharged into the air. Recent studies on surface dust impacts on gas 

exchanges in Mojave Desert shrubs showed that plants encrusted by dust have reduced 

photosynthesis and decreased water-use efficiency, which may decrease primary production 

during seasons when photosynthesis occurs (Sharifi et al. 1997). Sharifi et al. (1997) also showed 

reduction in maximum leaf conductance, transpiration, and water-use efficiency due to dust. Leaf and 

stem temperatures were also shown to be higher in plants with leaf-surface dust. These effects may 

also impact desert annuals, an important food source for tortoises. 

Off-highway vehicle activity can also disturb fragile cyanobacterial-lichen soil crusts, a 

dominant source of nitrogen in desert ecosystems (Belnap 1996). Belnap (1996) showed that 

anthropogenic surface disturbances may have serious implications for nitrogen budgets in colddesert ecosystems, and this may also hold true for the hot deserts that tortoises occupy. Soil 

crusts also appear to be an important source of water for plants, as crusts were shown to have 53 

percent greater volumetric water content than bare soils during the late fall when winter annuals 

are becoming established (DeFalco et al. 2001). DeFalco et al. (2001) found that non-native 

plant species comprised greater shoot biomass on crusted soils than native species, which 

demonstrates their ability to exploit available nutrient and water resources. Once the soil crusts 

are disturbed, non-native plants may colonize, become established, and out-compete native 

perennial and annual plant species (DeFalco et al. 2001; D’Antonio and Vitousek 1992). 

Invasion of non-native plants can affect the quality and quantity of plant foods available to desert 

tortoises (see section A(4)(a), Invasive Plants and Nutrition). Increased presence of invasive 

plants can also contribute to increased fire frequency (see sections A(4)(b) and A(5), Increasing 

Fuel Load and Fire). 

4. Invasive Plants 

Proliferation of invasive plants is increasing in the Mojave and Sonoran deserts and is 

recognized as a significant threat to desert tortoise habitat. Many species of non-native plants 

from Europe and Asia have become common to abundant in some areas, particularly where 

disturbance has occurred and is ongoing. As non-native plant species become established, native 

perennial and annual plant species may decrease, diminish, or die out (D’Antonio and Vitousek 

1992). 

Land managers and field scientists identified 116 species of non-native plants in the 

Mojave and Colorado deserts (Brooks and Esque 2002). Some of the more common non-native 

114
or native weedy species found within the Mojave region include: Erodium cicutarium (redstem 

filaree), Bassia hyssopifolia (bassia), Ambrosia acanthicarpa (sand bur), Ambrosia psilostachya 

var. californica (western ragweed), Hemizonia pungens (common spikeweed), Matricaria 

matricarioides (pineapple weed), Amsinckia intermedia (fiddleneck), A. tessellata (bristly 

fiddleneck), Descurania sophia (flixweed), Sisymbrium altissimum (tumble mustard), S. irio 

(London rocket), Salsola iberica (Russian thistle), Eremocarpus setigerus (turkey mullein), and 

Marrubium vulgare (horehound) (Tierra Madre Consultants, Inc.1991; BLM files 2006). Annual 

grasses include: Bromus rubens (red brome), B. tectorum, Hordeum glaucum (smooth barley), H. 

jubatum (foxtail barley), H. leporinum (hare barley), Schismus barbatus (split grass), and S. 

arabicus (Arab grass). Brassica tournefortii (Sahara mustard) and Hirschfeldia incana 

(Mediterranean mustard) are rapidly spreading, non-native winter annuals invading the desert 

southwest, especially in sandy soils (LaBerteaux 2006). 

Increased levels of atmospheric pollution and nitrogen deposition related to increased 

human presence and combustion of fossil fuels can cause increased levels of soil nitrogen, which 

in turn may result in significant changes in plant communities (Aber et al. 1989). Many of the 

non-native annual plant taxa in the Mojave region evolved in more fertile Mediterranean regions 

and benefit from increased levels of soil nitrogen, which gives them a competitive edge over 

native annuals. Studies at three sites within the central, southern, and western Mojave Desert 

indicated that increased levels of soil nitrogen can increase the dominance of non-native annual 

plants and promote the invasion of new species in desert regions. Furthermore, increased 

dominance by non-native annuals may decrease the diversity of native annual plants, and 

increased biomass of non-native annual grasses may increase fire frequency (Brooks 2003). 

(a) Nutrition. Nutritional intake affects growth rates in juvenile desert tortoises (Medica 

et al. 1975) and female reproductive output (Turner et al. 1986, 1987; Henen 1992). Invasion of 

non-native plants can affect the quality and quantity of plant foods available to desert tortoises, 

and thereby affect nutritional intake. Desert tortoises are generally quite selective in their choices 

of foods (Burge 1977; Nagy and Medica 1986; Turner et al. 1987; Avery 1992; Henen 1992; 

Jennings 1992, 1993; Esque 1992, 1994), and in some areas the preferences are clearly for native 

plants over the weedy non-natives. 

As native plants are displaced by non-native invasive species in some areas of the Mojave 

Desert, non-native plants can be a necessary food source for some desert tortoises. However, 

non-native plants may not be as nutritious as native plants. Recent studies have shown that 

calcium and phosphorus availability are higher in forbs than in grasses and that desert tortoises 

lose phosphorus when feeding on grasses but gain phosphorus when eating forbs (Hazard et al. 

2002). Nagy et al. (1998), in a comparative study on the nutritional qualities of native vs. nonnative grasses and forbs commonly consumed by desert tortoises (Achnatherum hymenoides 

[Indian ricegrass] vs. Schismus barbatus; Malacothrix spp. [desert dandelion] vs. Erodium 

cicutarium), found that the nutritional value of the two grasses was similar, but both grasses had 

much lower nutritional value than the forbs. This suggests that the proliferation of non-native 

grasses such as Schismus to the exclusion of native forbs and other plants (D’Antonio and 

Vitousek 1992) places desert tortoises at a nutritional disadvantage. Furthermore, if tortoises 

consume just enough food to satisfy their energy needs (as commonly noted in other vertebrate 

115
groups), then the native forbs provide significantly more nitrogen and water than the non-native 

forbs (Nagy et al. 1998). 

Changes in the abundance and distribution of native plants also may affect desert 

tortoises in more subtle ways. In the Mojave Desert, many food plants are high in potassium 

(Minnich 1979), which is difficult for desert tortoises to excrete due to the lack of salt glands that 

are found in other reptilian herbivores such as chuckwallas (Sauromalus obesus) and desert 

iguanas (Dipsosaurus dorsalis) (Minnich 1970; Nagy 1972). Reptiles are also unable to produce 

osmotically concentrated urine, which further complicates the ability for desert tortoises to expel 

excess potassium (Oftedal and Allen 1996). Oftedal (2002) suggested that desert tortoises may 

be vulnerable to upper respiratory tract or other disease due to their need to obtain sufficient 

water and nitrogen from food plants to counteract the negative effects of dietary potassium. Only 

high quality food plants (as expressed by the Potassium Excretion Potential, or PEP, index) allow 

substantial storage of protein (nitrogen) that is used for growth and reproduction, or to sustain the 

animals during drought. Non-native, annual grasses have lower PEP indices than most native 

forbs (Oftedal 2002; Oftedal et al. 2002). Foraging studies have demonstrated that juvenile 

Mojave tortoises are highly selective while foraging, selecting both the plant species and plant 

parts that are have the highest PEP value. Impacts to vegetation (such as livestock grazing, 

invasion of non-native plants, and soil disturbance) that reduce the abundance and distribution of 

high PEP plants may result in additional challenges for foraging desert tortoises (Oftedal et al. 

2002). 

Tracy et al. (2006) also quantified the rates of passage of digesta (food in the stomach) in 

young desert tortoises in relation to body size and diet quality. They observed that, compared to 

adults, young, growing tortoises need higher rates of nutrient assimilation to support their higher 

metabolic rates. Juvenile desert tortoises also forage selectively by consuming plant species and 

plant parts of higher quality (Oftedal et al. 2002) and pass food through the gut more quickly 

(Tracy et al. 2006). Hence, these findings of differential passage rates suggest that it is beneficial 

for young tortoises to specialize on low-fiber diets, as this would allow for more efficient uptake 

of nutrients. In addition, habitat disturbances (e.g., invasion of annual grasses) that favor species 

with little nutritional value and preclude access to low-fiber foods may negatively impact the 

physiological and behavioral ecology of young desert tortoises. Adults, on the other hand, may 

be better adapted to tolerate low-quality foods for a longer period of time because of their lower 

metabolism, more voluminous guts compared to subadults, and consequent longer retention 

times (Tracy et al. 2006). 

(b) Increasing Fuel Load. The proliferation of non-native plant species has contributed 

to an increase in fire frequency in tortoise habitat by providing sufficient fuel to carry fires, 

especially in the inter-shrub spaces that are mostly devoid of native vegetation (Brown and 

Minnich 1986; USFWS 1994; Brooks 1998; Brooks and Esque 2002). Invasive, non-native 

annual grasses and forbs increasingly spread over the desert floor, resist decomposition, and 

provide flash fuel for fires. Brooks (1999) found that non-native annual grasses contributed most 

to the continuity and biomass of dead annual plants and to the spread of summer fires compared 

to native forbs. Red brome in particular has contributed to significant increases in fire frequency 

since the 1970s (Kemp and Brooks 1998; Brooks et al. 2003; Brooks and Berry 2006). Once 

fires occur, opportunities for invasion and proliferation of non natives increase because they 

116
 

regenerate on burned areas more quickly than native plants (Brown and Minnich 1986). Changes 

in plant communities caused by non-native plants and recurrent fire negatively affect the desert 

tortoise by altering habitat structure and species composition of their food plants (Brooks and 

Esque 2002) (see also section A(5), Fire). 

Brooks and Berry (2006) found that while non-native plant species comprised only a 

small fraction of the total annual plant flora, they were the dominant component of the annual 

plant community biomass. For instance, in 1995, a high rainfall year in the Mojave Desert, nonnative annuals accounted for 6 percent of the flora and 66 percent of the biomass; in 1999, a low 

rainfall year, non-natives comprised 27 percent of the flora and 91 percent of the biomass. 

Annual species dominate the non-native flora, with Bromus rubens, Schismus barbatus, and 

Erodium cicutarium being the most widespread and abundant, representing up to 99 percent of 

the non-native biomass (Brooks and Berry 2006). 

Evidence of disturbance was a more reliable indicator of non-native dominance than was 

native plant diversity or primary productivity (Brooks and Berry 2006). Brooks and Berry (2006) 

also found that there were strong environmental correlations between dirt road densities and 

richness and biomass of Erodium cicutarium, as well as correlations between the size and 

frequency of fires and biomass of Bromus rubens. An altered fire regime in the desert Southwest 

resulting from changes in species composition has tremendous implications for the quality and 

quantity of desert tortoise habitat across the species’ range (see section A(5), Fire). 

5. Fire 

Fire has the potential to be an important force governing habitat quality and persistence 

of desert tortoises. Tortoises can be killed or seriously injured by burning and smoke inhalation 

during fire events. The extent of the direct impacts experienced by tortoises is influenced by 

tortoise activity at the time of fire (whether inside or outside burrow), depth of burrow (to afford 

protection), fire intensity (amount of heat generated), speed of fire (how quickly it moves 

through an area), and patchiness (extent of an area burned) (Esque et al. 2003). Early-season 

fires may be more threatening than summer fires because desert tortoises are active above ground 

and more vulnerable to direct effects of fire at that time. Fire can also compromise the quality of 

tortoise habitat by reducing the vegetation that provides shelter, cover, and nutrition (key forage 

plants) for tortoises (Brooks and Esque 2002; Esque et al. 2003). 

Natural fire regimes have been altered due to profuse invasions of non-native grasses 

throughout much of the range of the desert tortoise. The biomass of weedy species has increased 

remarkably in the desert Southwest as a result of disturbance from vehicles, grazing, agriculture, 

urbanization, and other human land uses (Brooks and Berry 1999; Brooks and Esque 2002; 

Brooks et al. 2003; Brooks and Berry 2006; Brooks and Matchett 2006). Fuel loads that consist of 

dense annual grasses rather than sparse cover of native species make it more likely for fire to become 

hot enough to damage native shrubs, which are poorly adapted to survive and/or regenerate quickly 

after fire and are poor colonizers (Tratz and Vogl 1977; Tratz 1978). Ultimately, recurrent fire can 

result in conversion of shrublands to annual grasslands, which can be devastating for desert tortoises 

that depend upon shrubs for cover (Brooks and Esque 2002). Conversion to grassland also tends to 

create a self-perpetuating grass/fire cycle as fuels continuously reestablish in burned areas 

(D’Antonio and Vitousek 1992). 

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Years of high rainfall promote the growth of invasive annuals that increase the fine fuel 

loads, but high rainfall also increases food and water availability for desert tortoises. Desert 

tortoise reproduction also increases in high rainfall years. Small hatchlings are more vulnerable 

to fire than larger tortoises, and tortoises in general are more vulnerable to fire when they are 

above ground foraging. Thus, the high rainfall episodes that are important to maintaining healthy 

desert tortoise populations may also create the highest fire risk (Brooks and Esque 2002). 

Plant litter produced by non-native annual grasses decomposes more slowly than native 

annuals and accumulates during successive years, thus providing an excess of fine fuels that 

sustains and spreads fires throughout the desert ecosystem (Brooks 1999). Historical fire 

intervals of 30 to greater than 100 years have been shortened to an average of 5 years in some 

areas of the Mojave Desert, due to the invasion of non-native grasses. Additionally, fires can 

increase the frequency and cover of non-native annual grasses within 3 to 5 years of a fire event, 

thus promoting the continuity of this grass/fire cycle that shortens the fire interval (Brooks et al. 

1999; Brooks and Esque 2002; Brooks and Minnich 2006). Increased levels of surface-disturbing 

activities, rainfall, and atmospheric nitrogen and carbon dioxide may also increase the 

dominance of non-native plants and frequency of fires in the future (Brooks and Esque 2002; 

Brooks et al. 2003). 

The most striking changes in fire frequency in the Mojave Desert have been observed in 

the middle elevations dominated by Larrea tridentata (creosote bush), Yucca brevifolia (Joshua 

tree), and Coleogyne ramosissima (blackbrush), at the upper limits of desert tortoise distribution, 

where most of the fires occurred between 1980 and 2004 (Brooks and Matchett 2006). The 

combination of enough cover of native vegetation to carry a fire and the accumulation of fuels 

from non-native annual grasses following years of above average rainfall may result in 

significantly larger fires at shorter return intervals than normally expected in this zone. Lower 

elevations are less susceptible to larger fires because of the natural lack of native plant cover, 

whereas upper elevations may experience larger fires as they generally support enough native 

fuels to carry large fires (Brooks and Matchett 2006). Brooks and Matchett (2006) advise, 

however, that additional research is necessary to confirm their results due to a limited dataset, 

and that longitude, elevation, and regional climatic conditions may cause substantial variation in 

observations. 

According to Bureau of Land Management files (2006), a particularly bad fire year in the 

Mojave Desert was in 2005, when numerous wildfires burned over 202,343 hectares (500,000 

acres) of habitat across the range of the desert tortoise, 55,442 hectares (137,000 acres) of which 

are designated critical habitat (2.1 percent of all designated critical habitat). The fires affected 

three of the six desert tortoise recovery units (the Upper Virgin Recovery Unit, the Northeastern 

Mojave Recovery Unit, and the Eastern Mojave Recovery Unit) (Table A-2). Within the Upper 

Virgin Recovery Unit, approximately 1,700 hectares (4,200 acres) of the Upper Virgin River 

critical habitat unit was burned. Within the Northeastern Mojave Recovery Unit, three critical 

habitat units were impacted: 18,922 hectares (46,757 acres) (23 percent) of the Beaver Dam 

Slope critical habitat unit, 25,279 hectares (62,466 acres) (13 percent) of the Gold Butte-Pakoon 

critical habitat unit, and 6,297 hectares (15,559 acres) (4 percent) of the Mormon Mesa critical 

habitat unit. Within the Eastern Mojave Recovery Unit, 62 hectares (154 acres) (less than 1 

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percent) in the Piute-Eldorado and 431 hectares (1,065 acres) (less than 1 percent) in the Ivanpah 

critical habitat units burned. Although it is likely that tortoises were burned and killed in the 

fires, tortoise mortality estimates are not available. In 2006, about 20,234 hectares (50,000 acres) 

of desert tortoise habitat burned, which includes less than 8,094 hectares (20,000 acres) of desert 

tortoise critical habitat. 

Table A-2. Approximate area of desert tortoise habitat burned in each recovery unit during 

2005 (does not encompass all of the critical habitat units; 1 hectare=2.47 acres) (BLM 2006). 

Recovery Unit Habitat Burned 

(hectares) 

Percent 

Habitat 

Burned 

CH* Burned 

(acres) 

Percent CH 

Burned 

Upper Virgin River** 4,227 < 19 4,227 19 

Northeastern Mojave*** 202,343 10 50,497 11 

Eastern Mojave 2,428 < 1 493 <1 

Western Mojave 0 0 0 0 

Northern Colorado 0 0 0 0 

Eastern Colorado 0 0 0 0 

Total 208,998 - 55,217 -

*CH = critical habitat 

**Estimates only for Upper Virgin River; GIS data analysis needed 

***Potential habitat was mapped and calculated as Mojave Desert less than 4,200 feet in elevation minus 

playas, open water, and developed and agricultural lands. 

Studies were conducted in five burned areas within the range of the desert tortoise to 

determine immediate effects of the fire and fire suppression tactics, and to monitor the recovery 

of habitats (Esque et al. 1994, 2003). Between 16 to 81 hectares (40 and 200 acres) were 

surveyed for wildlife remains on each fire via walking transects 9 to 15 meters (30 to 50 feet) 

apart. Desert tortoise mortality was documented at 0 to 7 per transect, but live tortoises were also 

observed. There were statistically significant losses of perennial cover, but some fires left 

unburned patches of vegetation that can serve as refugia for tortoises and plants. These refugia 

may be important to the long-term recovery of burned desert ecosystems. No destroyed burrows 

or desert tortoise mortalities were observed in surveys of routes used for off-road fire 

suppression activities in Utah, indicating that carefully planned and monitored fire suppression 

maneuvers can help stop the spread of damaging wildfires while reducing immediate and longterm tortoise mortality (Esque et al. 1994, 2003). 

In general, as fire becomes more prevalent throughout the range of the desert tortoise, the 

threats to the species from mortality or injury by burning and smoke inhalation during fire events 

and impacts to desert habitats will also increase. Changes in habitat structure from shrubdominated communities to non-native annual grasslands would limit the availability of cover 

sites for tortoises as well as alter species composition of food plants. 

6. Grazing 

Impacts of grazing on arid lands are well documented (Fleischner 1994; Jones 2000). 

Recovery from these impacts is variable, but can take decades, will likely require significant 

management effort beyond excluding livestock, and will be affected by other factors such as 

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drought (GAO 1991; Friedel 1991; Laycock 1991). Livestock grazing (sheep and cattle as well as 

horses and burros) is known to have direct and indirect impacts on desert tortoises and their habitats 

through trampling that results in direct mortality either while above ground or in burrows, and 

degradation of vegetation and soils (Boarman 2002). The magnitude of the threat on desert tortoise 

populations remains unclear, and the degree of impact depends on a number of factors including, but 

not limited to, resiliency of soil and vegetation types, type of livestock, stocking rates, season of use, 

and years of use with and without rest (USFWS 1994). Other factors that interact with livestock 

grazing and can affect the degree and extent of impacts to desert tortoises include introduction and 

spread of weeds, previous grazing-induced changes in vegetation, fire, drought, and other land uses 

(USFWS 1994). 

Oldemeyer (1994) suggests that the primary evidence that grazing adversely affects 

desert tortoises relates to an overlap in food habits of livestock and tortoises. Grazing is thought 

to reduce cover of shrubs and annual forbs. Studies in the eastern Mojave Desert on foraging 

behavior and food preferences of range cattle and desert tortoises showed that a dietary overlap 

(spatial and temporal) exists and that this overlap is greatest in the spring when fresh annual 

plants preferred by both desert tortoise and livestock are at their peak biomass and densities. 

Competition for these food plants is expected to be greatest when annual plants start to dry in the 

spring, before cattle and tortoises switch to other forage plants (Avery and Neibergs 1997). 

Avery and Neibergs (1997) observed direct and indirect interactions between cattle and 

tortoises. Their study indicates that grazing during winter may destroy a large percentage of 

active tortoise burrows. They noted that tortoises outside an ungrazed cattle exclosure spent more 

nights outside of burrows than tortoises within the exclusion area, because more burrows were 

destroyed in the grazed area than in the ungrazed area. In a study on translocated tortoises in the 

northwest Mojave Desert, one tortoise was found alive in its hibernation burrow even though the 

burrow had been crushed by cattle. It had skin lesions and had been parasitized by fly larvae. The 

tortoise was removed from the study because it was assumed that it would have died if it had 

been left in the crushed burrow (Nussear 2004). Tortoises with home ranges located in areas of 

heavy cattle grazing may experience increased risk of mortality, increased energetic costs, and 

changes in activity time budgets (caused by additional time and effort required to build new 

burrows). 

Comparative studies of historically grazed and never-grazed grasslands in southeast Utah 

(Neff et al. 2005) showed that grazing can continue to impact soil biogeochemical characteristics 

three decades after grazing had been removed. Reduced soil nutrient levels in the historically 

grazed site compared to the never-grazed site were attributed to erosion of nutrient-rich fine soil 

materials due to disturbance caused by grazing practices. Soil organic matter, carbon and 

nitrogen content, and microbial biomass were also lower in the grazed site. The decline of 

organic matter content may be attributed to the destruction of biological soil crusts or long-term 

changes in vegetation cover/composition resulting from grazing. This study illustrates the 

sensitivity of arid land biogeochemical processes to land use change and the need for a better 

understanding of potential long-term impacts from grazing practices in the southwestern United 

States. Furthermore, wind erosion may contribute significantly to loss of soil nutrient content and 

should be considered in management of arid land ecosystems (Neff et al. 2005). 

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Studies at the Desert Tortoise Natural Area also showed that both abundance and 

diversity of native plants and animals is higher inside than outside of the protected desert tortoise 

habitat (Brooks 2000). It should be noted that the Desert Tortoise Natural Area has received 

limited protection since 1973, but has been effectively protected from sheep grazing and offhighway vehicle use through the installation of exclusion fencing for the last 10 years (Brooks 

2000). Similarly, grazing (and simulated grazing treatments) negatively impacted native plant 

species, while non-native species were unaffected and demonstrated superior competitive 

abilities, at Carrizo Plain National Monument, California (Kimball and Schiffman 2003). 

7. Agriculture 

Lands in the Mojave Desert have been used for agricultural purposes since the early 

nineteenth century when peoples of the Mohave Tribe planted crops within the floodplain of the 

Colorado River to sustain their populations (Mojave Desert.net 2007). The 1994 Recovery Plan 

stated that the most significant effect agriculture has on desert tortoises is loss of habitat. Since 

the 1950s, losses of tortoise populations have been attributed to urbanization and agriculture in 

the western Mojave Desert in the Indian Wells, Antelope, Victor, Apple, Lucerne, and Johnson 

valleys (Berry and Nicholson 1984). Once converted to agricultural fields, the habitat becomes 

unsuitable to tortoises for foraging or burrowing. Agricultural activities may also result in 

drawdown of the water table, introduction of invasive plants, production of fugitive dust, and 

possible introduction of toxic chemicals (Koehler 1977; Wilshire 1980; Berry and Nicholson 

1984). Additionally, agricultural fields can support ravens, which prey upon juvenile tortoises 

(Knowles et al. 1989a,b; Camp et al. 1993; Knight et al. 1999). Old agricultural fields are often 

invaded by non-native, invasive species, which compete with native plants for resources and may 

reduce the abundance and diversity of the native species that provide shelter and food for desert 

tortoises (Hobbs 1989; USFWS 1994). 

8. Energy and Mineral Development 

Exploration for and development of energy and mineral resources, as well as sand and 

gravel extraction, result in habitat fragmentation and permanent habitat loss due to haul roads, 

development of facilities necessary to support large mining operations, ancillary facilities, leachate 

ponds, and mine tailings. Additional impacts to the desert tortoise may result from fugitive dust and 

soil erosion, establishment of invasive plant species in disturbance zones, and introduction of toxins 

(see section C(1), Disease). Tortoises may be killed during exploration, construction and ongoing 

operations, and maintenance activities (USFWS 1994; Boarman 2002). 

At the time the 1994 Recovery Plan was approved, it was estimated that 41 percent of highdensity tortoise habitat throughout the species’ range was leased or partially leased for oil or gas, 

and 2 percent was directly impacted by mining operations or leased for geothermal development 

(Luke et al. 1991; USFWS 1994). The extent of impacts to desert tortoise habitat and effects to 

tortoise populations from energy and mineral development are still not well documented. 

Cumulative habitat loss from mining-related disturbances combined with increased development 

to support those operations may pose the most significant impact resulting from mining (Lovich 

and Bainbridge 1999; Boarman 2002). 

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In the California Desert, no oil and gas development has yet occurred, but applications 

for solar and wind energy facilities total nearly 202,343 hectares (500,000 acres) because of 

recent public emphasis on advancing alternative energy sources. Dozens of project sites have 

been proposed, and the Bureau of Land Management in California has committed to excluding 

these projects from designated critical habitat for the desert tortoise and Desert Wildlife 

Management Areas. Habitat loss through energy development is also a potential threat in 

Nevada, where various projects have been proposed and applications have been submitted for 

solar power facility rights-of-way on over 53,800 hectares (133,000 acres) of suitable desert 

tortoise habitat. The energy development process on Bureau of Land Management lands appears 

to be constantly changing, with applicants submitting multiple requests to modify their projects 

or withdrawing their applications altogether (J. Crisp, Bureau of Land Management, pers. comm. 

2007). 

9. Landfills 

There are more than 25 authorized sanitary landfills and waste disposal facilities known 

in the California deserts, with 11 of those located in the west Mojave Desert (Boarman 2002). In 

other urban areas throughout the range of the tortoise, all communities produce solid waste that 

must be transported to appropriate facilities. Landfills and other waste disposal facilities 

potentially affect desert tortoises and their habitat through fragmentation and permanent loss of 

habitat, spread of garbage that attracts predators, introduction of toxic chemicals, increased road 

kill of tortoises on access roads, and increased predator populations (Boarman 2002) (see also 

section C(3), Disease and Predation). With the exception of raven predation, which is considered 

one of the most important consequences of landfills, negative effects on tortoises associated with 

the presence of landfills have not been quantified (Boarman 2002). 

10. Military Operations 

Military operations in the Mojave Desert have taken place since as early as 1859 

(USFWS 1994; Boarman 2002). Military activities that impact desert tortoises and their habitats 

can be categorized as: (1) construction, operation, and maintenance of bases and support 

facilities (air strips, roads, etc.); (2) development of local support communities, including urban, 

industrial, and commercial facilities; (3) field maneuvers including tank traffic, air to ground 

bombing, static testing of explosives, and abandonment of unexploded ordnance, shell casings, 

and ration cans; and (4) distribution of chemicals. These activities result in degradation and 

permanent loss of desert tortoise habitat and are often coupled with other impacts associated with 

large human settlements in the desert (i.e., collection of tortoises, trash dumping, increased raven 

populations, domestic pets as predators, off-highway vehicle use, increased exposure to disease, 

and increased road-kill mortality) (USFWS 1994). 

The military bases and test ranges in the Mojave Desert include the Nevada Test and 

Training Range, Nellis Air Force Range in Nevada, Edwards Air Force Base in California, 

Twentynine Palms Marine Corps Air Ground Combat Center in California, Barstow Marine 

Corps Logistics Bases in California (includes the Yermo Annex, Main Base at Nebo, and the 

Marine Corps Rifle Range), Fort Irwin National Training Center in California, China Lake Naval 

Air Weapons Station in California, and the Mojave B and Randsburg Wash Test Ranges (in 

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California). The Chocolate Mountains Aerial Gunnery Range in California is the primary base 

affecting desert tortoise habitat in the Colorado Desert (USFWS 1994). All of these military 

facilities encompass desert tortoise habitat. 

All of the threats associated with military activities described above continue to threaten 

desert tortoises and their habitat. The expansion of military bases and activities into previously 

unused areas occupied by desert tortoises also threatens the species. In 2004, we issued a 

biological opinion to the Department of the Army for the use of additional training lands at the 

Fort Irwin National Training Center in California. This action will result in the loss or 

degradation of approximately 76,081 hectares (188,000 acres) of desert tortoise habitat, 

including approximately 30,351 hectares (75,000 acres) within the Superior-Cronese critical 

habitat unit, and the translocation of several hundred desert tortoises from harm’s way. To date, 

the Department of the Army has purchased approximately 40,104 hectares (99,100 acres) of 

lands formerly owned by the Catellus Development Corporation and portions of cattle allotments 

in the western Mojave Desert to minimize impacts associated with the expanded training areas 

(R. Bransfield, U.S. Fish and Wildlife Service, pers. comm. 2007). The Bureau of Land 

Management subsequently retired these allotments and removed grazing on over 129,499 

hectares (320,000 acres). A plan has also been developed to guide the translocation of tortoises 

in the expansion area (Esque et al. 2005). 

11. Utility Corridors 

By 1994, most critical habitat units had one or more power lines, natural gas pipelines, 

fiber optic cables, and/or communication sites within their proposed boundaries (USFWS 1994). 

Disturbances associated with these corridors are usually linear in nature, and the zone of 

disturbance can vary in width from 15.2 to 30.5 meters (50 to 100 feet) to several hundred meters 

or yards, depending on the number of transmission lines (USFWS 1994). Impacts to desert 

tortoise habitat and individuals occur both during initial construction as well as during long-term 

maintenance activities (Boarman 2002). Additionally, utility corridors are often used by the 

public for off-highway vehicle and recreational access. LaRue and Dougherty (1999) evaluated 

results of over 230 biological opinions issued by our southern California and Nevada offices and 

found that 80 percent of the tortoises reported killed in these two states were found along utility 

corridors. Most of these mortalities resulted from a few large projects during the construction 

phases, and very few tortoises have been killed during utility maintenance projects (R. 

Bransfield, U.S. Fish and Wildlife Service, pers. comm. 2007). While tortoises may be observed 

within these corridors, continual vehicular use along access roads may alter use by tortoises both 

for foraging and movement, and may result in road-kills (Boarman 2002). Utility towers also 

provide nesting substrate and hunting perches to avian predators, such as ravens and red-tailed 

hawks. 

12. Vandalism and Harvest of Vegetation 

Vandalism and harvest of vegetation, particularly cacti and yuccas, were identified as 

potential threats to desert tortoises and their habitats in the 1994 Recovery Plan. Harvest of 

vegetation includes the removal of vegetation for personal or economic purposes (i.e., use in 

landscaping or sale for profit). Vandalism of vegetation is considered to be the deliberate destruction 

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of vegetation (i.e., shooting, crushing). While these activities may still occur on a relatively small 

scale and may pose some threat on a localized level, there is no recent documentation that 

indicates this activity poses a significant or widespread threat to tortoise populations throughout 

their range. 

B. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes 

1. Collection by Humans 

Some of the threats to the desert tortoise identified in the 1994 Recovery Plan include the 

deliberate removal of desert tortoises by humans for use as food (Berry and Nicholson 1984; 

Swingland and Klemens 1989; Schneider and Everson 1989; Ditzler 1991; BLM files 2006), and 

collection and commercial trade for pets (Berry and Nicholson 1984; St. Amant 1984; Berry and 

Burge 1984). Collection of desert tortoises by humans for food or as pets was cited as a potential 

threat to the species, and collecting for personal or commercial purposes was evidently 

significant in the past (Grant 1936; Berry and Burge 1984; Berry and Nicholson 1984; Ditzler 

1991; Berry et al. 1996; USFWS 1994). Desert tortoises are protected from collection under both 

Federal and State law in all states where it occurs; however, the legal status has not always 

served as a deterrent to this activity (Boarman 2002). For example, nine cases of illegal 

collection were documented from the Red Cliffs Desert Reserve, Washington County, Utah, 

between May 2003 and May 2006, including four cases within 5 weeks during 2006 (A. 

McLuckie, Utah Division of Wildlife Resources, pers. comm. 2006). While illegal collection of 

desert tortoises still occurs and could possibly impact local populations, little quantitative 

evidence exists to support it as a significant threat causing declines in the Mojave populations 

(Boarman 2002). Also, information specific to this threat is limited owing to the wide 

distribution of the species coupled with the need for additional law enforcement officers and 

wardens on the ground (see section D, Inadequacy of Existing Regulatory Mechanisms). 

2. Deliberate Maiming and Killing by Humans 

Little additional information regarding maiming and killing of desert tortoises has been 

obtained since the 1994 Recovery Plan. Postmortem forensic analysis determined that 14.3 

percent of 635 carcasses collected at 11 of 27 California desert sites between 1976 and 1982 

showed evidence of gunshots (Berry 1986). Evidence of gunshot was significantly higher in 

carcasses from the west Mojave than from the east Mojave or Colorado Desert (Berry 1986), 

which may be a function of the proximity of human populations in the west Mojave region 

compared to that in the east Mojave or Colorado Desert. 

3. Research Activities 

We permit various research activities that will inform management and recovery of the 

desert tortoise but may unintentionally result in infrequent injury or mortality. The following 

activities may be permitted with terms and conditions to minimize injury and potential mortality 

of individuals: 

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(a) Population monitoring, which involves pursuit, capture, and handling of free-ranging 

tortoises to determine weight, size, sex, and to mark them for recapture. 

(b) Epidemiological studies, which involve general health assessments and diseaserelated investigations (e.g., collection of blood samples and nasal lavages); moribund 

tortoises may be collected from the wild and occasionally euthanized.; 

(c) Research on recruitment and survivorship of younger age classes of desert tortoises, 

which includes marking of individuals using notching/clipping of marginal scutes, 

insertion of PIT tags (passive integrated responders); attachment of radio transmitters 

or other hardware in accordance with USFWS-approved protocol; and pursuit and 

capture of study animals during monitoring activities. 

(d) Research on impacts of grazing, road density, barriers, human-use levels, restoration, 

and augmentation and translocation on desert tortoise population dynamics, which 

may include many of the activities and associated effects described above. 

(e) Research on nutritional and physiological ecology of various age classes of desert 

tortoises, which includes many of the types of activities and associated effects 

described above. In addition, captive tortoises may be injected with labeled or 

tritiated water in association with physiological studies. 

(f) Research on reproductive behavior and physiology, which includes many of the types 

of activities and associated effects described above, and involve both free-ranging and 

captive desert tortoises. 

Potential stress to desert tortoises from handling may vary depending on the time, 

frequency, and activity involved. Invasive procedures associated with obtaining physiological 

data can cause significant stress to individuals (Berry et al. 2002a). For example, female tortoises 

that void their bladders during handling may be at a reproductive disadvantage since the loss of 

fluid may negatively affect egg production, which requires higher total body water in 

reproductive females than non-reproductive females (Averill-Murray 2002). In one study, 

tortoises that urinated during handling had lower survival than those that did not (Averill-Murray 

2002). 

Despite the inherent low-level risk associated with activities covered under recovery 

permits, incidental injury or mortality of desert tortoises is not expected. However, if injury or 

mortality should occur, the permit is suspended until the circumstances surrounding the incident 

are reviewed and appropriate procedures are in place to prevent further injury or mortality. In 

any given year, we generally issue fewer than 15 recovery permits for desert tortoise research. 

Because of the emphasis that we, through the Desert Tortoise Recovery Office, intend to place 

on recovery-related research activities pertaining to the desert tortoise, the number of permits 

issued may increase over the next few years. 

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C. Disease or Predation 

1. Disease 

Disease is a natural phenomenon within wild animal populations, and epidemic outbreaks 

can have catastrophic effects on small or declining populations. Two diseases have been 

implicated in negatively affecting desert tortoise populations: upper respiratory tract disease 

(Jacobson et al. 1991) and cutaneous dyskeratosis or shell disease (Jacobson et al. 1994). 

Herpesvirus has also been suspected of having population-level impacts, but little data are 

available to support or refute this hypothesis (Berry et al. 2002b; Origgi et al. 2002). Other 

diseases or infections have also been identified in tortoises, including shell necrosis, bacterial 

and fungal infections, and urolithiasis (bladder stones) (Homer et al. 1998), but little information 

is available regarding the distribution of these maladies in desert tortoise populations (Boarman 

2002). Likewise, only correlative studies (i.e., not based on cause and effect investigations) have 

linked upper respiratory tract disease or cutaneous dyskeratosis to population declines (Berry 

1997). Additional research is needed to clarify the role of disease in desert tortoise population 

dynamics relative to other threats, and the level of effort we should expend in disease control as 

compared to other threats. 

At least two pathogenic species of Mycoplasma have been identified (M. agassizii and M. 

testudineum) that are known to cause upper respiratory tract disease in desert and gopher 

tortoises (Brown et al. 1994, 1999, 2001, 2002; Berry 1997; Jones et al. 2005). The pathogens 

are likely transmitted by contact with an infected individual or aerosols (airborne liquid droplets 

or solid particles). Once infected, tortoises may develop lesions in the nasal cavity, excessive 

nasal discharge, swollen eyelids, sunken eyes, and ultimately lethargy and possible death 

(Jacobson et al. 1991; Schumacher et al. 1997; Homer et al. 1998; Berry and Christopher 2001). 

Boarman (2002) notes, however, that these clinical signs may also be symptomatic of other 

conditions such as dehydration or infection with herpesvirus. An enzyme-linked immunosorbent 

assay (ELISA) serological test is available to determine exposure to the pathogens (Schumacher 

et al. 1993; Wendland et al. 2007), and a polymerase chain reaction test has been developed to 

determine active infection (Brown et al. 1995); however, in-depth epidemiological study is 

necessary to more thoroughly understand the factors involved in the spread and virulence of the 

disease in the wild (Boarman 2002). 

Because the release or escape of infected captive tortoises has been implicated as a 

potential cause of outbreaks of upper respiratory tract disease in natural populations in the 

Mojave, Johnson et al. (2006) evaluated captive tortoises in Barstow, California, to determine 

pathogen exposure. Anti-Mycoplasma antibodies (indicating exposure to the pathogen) were 

present in 82.7 percent of the tortoises tested (sample size of 179), and anti-herpesvirus 

antibodies were observed in 26.6 percent of the animals (sample size of 109). A positive link was 

also established between tortoises with anti-Mycoplasma antibodies and the severity of clinical 

signs of upper respiratory tract disease, as well as with age class, with adults being more likely to 

test positive for presence of antibodies. However, this linkage was not observed with herpesvirus 

exposure. These results indicate that captive tortoises released into the wild may be a source of 

upper respiratory infection, but not herpesvirus infection, for natural populations (Johnson et al. 

2006). 

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 In contrast, Jones et al. (2005) found that captive tortoises do not appear to serve as a 

reservoir for upper respiratory tract disease when released in the Sonoran population of desert 

tortoise. They did find higher incidence of disease in suburban areas around Tucson, Arizona, 

which suggests that habitat degradation associated with urbanization may be a stressor that 

contributes to disease outbreaks. Reasons for the susceptibility of tortoises to upper respiratory 

tract disease remain speculative and require further study (Boarman 2002). Additional insights 

and recommendations relative to this disease are provided by the Science Advisory Committee in 

Appendix B. 

Little is known about the causes of cutaneous dyskeratosis, which manifests itself as 

lesions along scute sutures of the plastron, and sometimes on the carapace, which then spread to 

the scutes themselves. This disease has been associated with population declines on the 

Chuckwalla Bench in California; however, the extent to which it contributes to mortality of 

desert tortoises remains unclear (Jacobson et al. 1994). Toxins in the environment and nutritional 

deficiencies have been implicated in causing shell disease (Jacobson et al. 1994; Homer et al. 

1998); however, there are few data to support this linkage (see section C(2), Toxicants and 

Disease Susceptibility). 

2. Toxicants and Disease Susceptibility 

Illegal dumping of hazardous wastes that occurs in the California deserts may expose 

tortoises to increased levels and possible consumption of toxic substances. Garbage, litter, and 

toxic spills may affect tortoises on a localized level where these activities are concentrated 

(Boarman 2002). Toxicant load in the environment may also be a factor that induces diseases 

related to toxicosis (e.g. liver disease) and influences the susceptibility of tortoises to infectious 

diseases and mortality. For example, tortoises that died of mycoplasmosis at the Desert Tortoise 

Natural Area in 1989 through 1990 had 11 times the mercury content in their livers than tortoises 

from a control area (Jacobson et al. 1991). Some necropsies showed elevated levels of arsenic in 

scutes (Seltzer and Berry 2005). 

Fugitive dust containing toxicants that affect tortoises may be released from 

anthropogenic sites such as mines, roads, construction, and other disturbances. Chaffee and 

Berry (2006) collected soil, stream sediment, and plant samples at six tortoise habitat study areas 

in the Mojave and Colorado deserts. They analyzed samples for up to 66 different elements to 

determine their distribution and abundance at a regional and local level, to identify potential 

sources of toxicants in desert tortoise habitats. Some measurements of high concentrations of 

arsenic, mercury, and lead, were attributed to mining and vehicle exhaust. High levels of soil and 

plant arsenic extended more than 14 kilometers (9 miles) from some existing mine sites, and 

mercury was detected more than 5 kilometers (3 miles) from some mine tailings. Traces of lead 

were found more than 21 kilometers (13 miles) from a paved road and likely had been 

redistributed by vehicle exhaust, wind, and rain events. Elevated levels of these elements have 

been observed in ill tortoises found in these areas; however, additional research is necessary to 

ascertain the direct effects of elemental toxicants on desert tortoise health and their susceptibility 

to disease (Chaffee and Berry 2006). 

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3. Predation 

Desert tortoises, particularly hatchlings and juveniles, are preyed upon by several native 

species of mammals, reptiles, and birds; however, the contribution of mammalian or avian 

predation to overall desert tortoise mortality has not been quantified. Natural predation in 

undisturbed, healthy ecosystems is generally not considered a threat, but under some 

circumstances predation comes to the forefront as a management concern, especially where 

landscapes have been altered and intensive human use occurs. In addition, during times of 

drought when typical prey species are limited, food habits of predators may shift and tortoises 

become more frequent components of their diets (USFWS 1994). 

The best-documented predator of small tortoises is the common raven (Corvus corax). 

For example, Campbell (1986) found 136 carcasses of juvenile desert tortoises with evidence of 

raven predation at the base of fence posts on the perimeter of the Desert Tortoise Natural Area. 

Berry et al. (1990) reported that 30 and 45 percent, respectively, of all desert tortoise deaths at two 

study plots during a 6-year period were probably caused by raven predation; up to 75 percent of 

deaths of tortoises <103 mm (4.1 in) carapace length were attributed to raven predation at these 

plots. 

In the desert southwest, common raven populations have increased over the past 25 years 

(greater than 1000 percent), probably in response to increased human populations, associated 

food and water subsidies, and anthropogenic changes to the landscape (Boarman and Berry 1995; 

Boarman et al. 1995; Boarman et al. 2006). For instance, ravens obtain food in the form of 

organic garbage from landfills and trash containers, water from sewage ponds and municipal 

areas, and nesting substrates on billboards, utility towers, bridges, and buildings (Boarman et al. 

2006). Particularly in the west Mojave and Coachella Valley, linear features such as roads and 

utility corridors and other urban sites such as landfills and sewage ponds have been shown to 

attract common ravens, red-tailed hawks (Buteo jamaicensis), and turkey vultures (Cathartes 

aura) (Knight and Kawashima 1993; Boarman et al. 1995; Knight et al. 1999). The use of 

anthropogenic nesting substrates facilitates increased predation of juvenile tortoises, especially 

within about 0.4 kilometers (0.25 miles) of the raven nest (Boarman 2002; Kristan and Boarman 

2003). The presence of roads may encourage such opportunistic species because road-killed 

animals are a reliable food source (Camp et al. 1993; Boarman and Sazaki 2006). 

Raven numbers were shown to decrease with distance from urban sites in the west 

Mojave, placing tortoises that occur in the urban-desert interface at higher risk of predation 

(Kristan and Boarman 2003). This risk also increases with the numbers of ravens in the vicinity, 

and the distribution of breeding and non-breeding ravens is likely to influence patterns of 

predation across the landscape. Breeding ravens tend to disperse more evenly across suitable 

habitats, whereas non-breeding birds are concentrated around anthropogenic sites. This suggests 

that occupied desert tortoise habitats distant from population centers and the urban-desert 

interface experience reduced predation pressures from ravens (Boarman et al. 1993; Boarman 

2002; Kristan and Boarman 2003). 

Determining precise demographic impacts of (increased) raven predation on desert 

tortoise populations is complicated because of the difficulty of monitoring small, hard to find 

128
 

juvenile tortoises (Boarman 2002). Nevertheless, the potential impact to desert tortoise 

populations from raven predation is a conservation concern, especially where subsidized 

predators are able to persist in large numbers despite declines in their prey base. Populations of 

long-lived animals like the desert tortoise can sustain moderate levels of annual juvenile 

mortality (e.g., 25 percent), but in the face of depressed adult survival, juvenile mortality must be 

reduced to approximately 5 percent to ensure recruitment into the breeding population (Congdon 

et al. 1993). Human-subsidized predators thus put at great disadvantage any prey species such as 

the desert tortoise that is unable to rebound from predation pressures (Kristan and Boarman 

2003). 

Red-tailed hawks, golden eagles (Aquila chrysaetos), loggerhead shrikes (Lanius 

ludovicianus), American kestrels (Falco sparverius), burrowing owls (Athene cunicularia), and 

greater roadrunners (Geococcyx californianus) have also been implicated in tortoise predation, 

although available data are minimal (Boarman 1993). Coyotes (Canis latrans), kit foxes (Vulpes 

macrotis), mountain lions (Felis concolor), ground squirrels (Citellus spp., and free-roaming 

dogs are known mammalian predators of desert tortoise (Boarman 2002; M. McDermott, 

Southern Nevada Environmental, Inc., pers. comm. 2006). However, few data exist that quantify 

the impact of mammalian predation on desert tortoises. Invertebrate predators of eggs and 

hatchling tortoises include native fire ants (Nagy et al. 2007). 

D. Inadequacy of Existing Regulatory Mechanisms 

1. Law Enforcement 

The final listing rule acknowledged that all four states within the range of the Mojave 

population of the desert tortoise have laws in place to protect the species. However, State 

wildlife or endangered species permitting requirements do not specifically cover habitat and 

generally do not require mitigation of impacts to suitable, potentially occupied habitat. In 

addition, a great deal of effort has been dedicated to planning by the various Federal and State 

land management agencies whose jurisdictions include desert tortoise habitat. While many of the 

existing plans include language specific to protection of the species, such as limiting off-highway 

vehicle use and competitive/organized events, grazing, vegetation harvest, and collection of 

desert tortoises, agency multiple-use mandates require a complex balancing of tortoise 

conservation and public use of Federal and State lands. Also, land management agencies 

frequently do not have sufficient funding to enforce their land use regulations (Table A-3). The 

number of law enforcement officers or game wardens on the ground does not necessarily 

translate into protection of the species, as personnel are often spread across vast landscapes and 

have multiple resource responsibilities. As calculated from the data in Table A-3, current 

information indicates that each law enforcement officer is responsible for an average of more 

than 89,000 hectares (220,000 acres). 

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Table A-3. Law enforcement (LE) resources within desert tortoise habitat by agency. 

Responsible Agency/Unit1 Number of 

LE Officers 

Number of 

Vacancies 

(if applicable) 

Number of Acres 

(approx.) 

BLM-California Desert District2 43 4 10,400,000 

 Barstow Field Office 8 0 3,000,000 

 El Centro Field Office 12 0 1,400,000 

 Needles Field Office 6 2 3,300,000 

 Palm Springs – South Coast Field Office 9 2 1,700,000 

 Ridgecrest Field Office 8 0 1,800,000 

BLM-Arizona Strip Field Office3

 3 1 2,000,000 

BLM-NPS Grand Canyon-Parashant National Monument4 3 BLM 

2 NPS 0 1,100,000 

BLM-Las Vegas and Ely Field Offices5 14 (Vegas) 

1 (Ely) ? 3,000,000 726,000 

BLM-St. George Field Office6

 1 0 630,000 

NPS-Mojave National Preserve7

 9 4 1,400,000 

NPS-Joshua Tree National Park8

 10 4 790,000 

NPS-Death Valley National Park9

 14 ? 3,300,000 

NPS-Lake Mead National Recreation Area10 16 ? 1,500,000 

USFWS-Desert National Wildlife Refuge Complex11 5 2 1,600,000 

US Forest Service-Spring Mountains National Recreation 

Area12 3 2 317,000 

Arizona Game and Fish Department13 2 ? 

California Department of Fish and Game14 16 3 

Nevada Department of Wildlife15 16 3 

Utah Division of Wildlife Resources16 4 0 

Clark County MSHCP-Boulder City Conservation 

Easement17 1 0 86,000 

Total 163 23 >36,249,000 1

 Information provided via electronic mail or personal communication (July, August 2007) from the following: 

2

 Jim Abbott, Bureau of Land Management California State Office 

3

 Scott Florence, Bureau of Land Management Arizona Strip District 

4

 Kathleen Harcksen, Bureau of Land Management Grand Canyon-Parashant National Monument 

5

 Elroy Masters, Bureau of Land Management Nevada State Office 

6

Jim Crisp, Bureau of Land Management St. George Field Office 

7

 Debra Hughson, Kirk Gebicke, National Park Service, Mojave National Preserve 

8 Paul DePrey, Curt Sauer, National Park Service Joshua Tree National Park 9

 David Ek, National Park Service Death Valley National Park 

10 Bill Dickinson, National Park Service Lake Mead National Recreation Area 

11 Cynthia Martinez, USFWS Desert National Wildlife Refuge Complex 

12 David Leveille, USFS Humboldt-Toiyabe National Forest 13 Cristina Jones, Luke Thompson, Arizona Game and Fish Department 

14 Rebecca Jones, Mike McBride, California Department of Fish and Game 15 Polly Conrad, Fred Henson, Nevada Department of Wildlife 

16 Ann McLuckie, Utah Division of Wildlife Resources 17 Sue Wainscott, Clark County 

? Information not provided or not available. 

130
2. Land Acquisitions, Exchanges, and Transfers 

Land exchanges and transfers may result in loss of desert tortoise habitat, increased 

fragmentation, and displacement of resident desert tortoises. Tortoise habitat that is exchanged 

out of Federal ownership is at greater risk of development, resulting in loss of habitat on the new 

private holdings (Sievers et al. 1988). Transactions may also be executed in the interest of 

securing additional lands targeted for conservation of the desert tortoise and other sensitive 

species or habitats (see Conservation Efforts). 

In 1988, the Bureau of Land Management exchanged 11,758 hectares (29,055 acres) of 

public land in the Coyote Springs Valley in southern Nevada to Aerojet-General Corporation for 

private wetlands in Florida for wildlife conservation under the Nevada-Florida Land Exchange 

Authorization Act. An additional 5,571 hectares (13,767 acres), which are surrounded by the 

11,758 hectares (29,055 acres), were leased to Aerojet for an initial term of 99 years with a 99­

year extension. The Coyote Springs Investment (CSI) HCP is being developed to address urban 

development and tortoise conservation on CSI lands in Lincoln County. The plan would permit 

development over 8,682 hectares (21,454 acres) in Lincoln County, most of which is desert 

tortoise habitat (Mormon Mesa critical habitat unit). The plan would also establish a desert 

tortoise reserve on 5,571 hectares (13,767 acres) of the CSI leased. 

Under the Bureau of Land Management’s Western Mojave Land Tenure Adjustment 

Program, which provides a mechanism pursuant to the Federal Land Policy and Management Act 

of 1976 to acquire lands within and dispose of Federal lands outside of DWMAs, approximately 

21,044 hectares (52,000 acres) of land within desert tortoise critical habitat have been acquired 

and approximately 6,880 hectares (17,000 acres) outside of designated critical habitat have been 

transferred out of Federal management since 1990. The overall ratio of acquired to disposed 

habitat of the desert tortoise is expected to be approximately 2.3:1 at the completion of the 

Western Mojave Land Tenure Adjustment Program, for a net benefit to the amount of desert 

tortoise habitat protected on Federal lands (BLM 2005). 

The Southern Nevada Public Lands Management Act of 1998, as amended (Public Law 

[PL]-105-263), provides for the “disposal of certain Federal lands in Clark County, Nevada, and 

for the acquisition of environmentally sensitive lands in the State of Nevada.” The law was 

enacted partly to address the Bureau of Land Management’s extensive and complicated land 

management responsibilities for disjunct parcels that are interspersed with or adjacent to private 

land in the Las Vegas Valley and the rapid urbanization taking place in the valley. In order to 

“promote responsible and orderly development in the Las Vegas Valley, certain of those Federal 

lands should be sold by the Federal Government based on recommendations made by local 

government and the public” (PL-105-263). This legislation provided the mechanism for 

significant changes to take place in the Las Vegas area of the Mojave Desert relative to human 

occupation in the Mojave Desert wherein over 58,600 hectares (145,000 acres) of Federal land 

are identified for disposal and urban development. 

A series of other related public laws have connections to the Southern Nevada Public 

Lands Management Act and facilitate the transfer or disposal of public lands. These laws include 

the Lincoln County Conservation, Recreation, and Development Act of 2004 (PL-108-424); the 

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Lincoln County Land Act of 2000 (PL-106-298); the Clark County Conservation of Public Land 

and Natural Resource Act of 2002 (PL-107-282); the Fiscal Year 2004 Appropriations Act 

amending the Southern Nevada Public Lands Management Act (PL -105-263); the Lake Tahoe 

Restoration Act; the Mesquite Lands Act of 1986 (PL-99-548) and 1988 and PL-104-208 (1996 

amendment to the Mesquite Lands Act of 1988); the Ivanpah Valley Airport Public Lands 

Transfer Act of 2000; and the Federal Land Transaction Facilitation Act of 2000. 

E. Other Natural or Manmade Factors Affecting its Continued Existence 

1. Climate Change 

Climate change and drought were not regarded as threats to the desert tortoise in the 1994 

Recovery Plan. Since that time it has become apparent that the combined effects of global 

climate change (i.e., increased ambient temperatures and altered precipitation patterns) and 

drought may become significant factors in the long-term persistence of the species. The Earth’s 

climate has warmed by nearly 1.5 degrees Fahrenheit over the past 100 years (Walther et al. 

2002), and anthropogenic emissions of greenhouse gases play a major role in this process 

(Weltzin et al. 2003). While this warming is not uniform with regard to time and space, the rate 

of warming during the last 30 years has generally been greater than at any other time during the 

last 1,000 years (Walther et al. 2002). In many regions there is an asymmetry in warming, as 

well as precipitation, which is likely to contribute to variation in ecological dynamics across 

ecosystems. There is now sufficient evidence that recent climatic changes have affected a broad 

range of organisms with diverse geographical distributions (Walther et al. 2002). Interactions 

between altered precipitation patterns and other aspects of global change are likely to affect 

natural and managed terrestrial ecosystems. For example, climate models predict that Joshua 

trees would likely no longer be able to persist within Joshua Tree National Park through the 21st 

century (Cole et al. 2005). While little is known regarding direct effects of climate change on the 

desert tortoise and its habitat, predictions can be made about how global and regional 

precipitation regimes may be altered and the consequences of these changes (Weltzin et al. 2003; 

Seager et al. 2007). 

The Intergovernmental Panel on Climate Change has suggested that increasingly reliable 

climate change projections are now available as the result of improved modeling capabilities and 

advanced understanding of climate systems (Christensen et al. 2007). The Intergovernmental 

Panel on Climate Change’s 2007 report discussed the results of 21 Atmosphere-Ocean General 

Circulation Models that were run to predict regional changes in temperature and precipitation in 

2080 to 2099 compared to conditions that occurred between 1980 and 1999. Generally, 

predictions for the geographic range of the desert tortoise’s listed population suggest more 

frequent and/or prolonged droughts. For example, annual mean temperature is likely to increase 

by 3.5 to 4.0 degrees Celsius (6.3 to 7.2 degrees Fahrenheit), with the greatest increases 

occurring in summer (June-July-August mean up to 5 degrees Celsius [9 degrees Fahrenheit] 

increase) (Christensen et al. 2007). In summer, the highest temperatures will likely increase even 

more than the average temperatures. Precipitation will likely decrease by 5 to 15 percent 

annually in the region with winter precipitation decreasing in the range of 5 to 20 percent. More 

than half of the models predict that changes in summer precipitation may be more moderate 

(decrease by as much as 10 percent) with the possibility for a 5 percent increase (Christensen et 

132
al. 2007). This prediction for more drying in winter than in summer differs from predictions for 

much of the United States. Because germination of the tortoise’s food plants is highly dependent 

on cool season rains, the forage base could be reduced due to increasing temperatures and 

decreasing precipitation in winter. Drought is a normal phenomenon in the Mojave Desert 

(Peterson 1994a; Hereford et al. 2006). Extended periods of drought, however, have the potential 

to affect desert tortoises and their habitats through physiological effects to individuals (i.e., 

stress) and limited forage availability. 

Experiments in Nevada at the Free-Air Carbon Dioxide (CO2) Enrichment Facility to 

predict the possible complex ecological and biogeochemical changes in semidesert ecosystems 

caused by increasing atmospheric CO2 have been ongoing since 1997 (Hamerlynck et al. 2000; 

Smith et al. 2000; Huxman and Smith 2001). Because deserts are both water- and nutrientlimited systems and many native desert plants are slow-growing, it is still too early to say with 

any confidence how even the most intensively studied desert shrub communities of the 

southwestern United States will respond to rising CO2 (Lioubimtseva and Adams 2004). 

However, results from the Free-Air CO2 Enrichment Facility site demonstrate that the non-native 

grass Bromus tectorum responds to increases in CO2 (a component required for photosynthesis) 

with far greater productivity than that of native plants during wet years (Smith et al. 2000). 

However, the overall response of non-native grasses to increased CO2 is uncertain, given 

expected reductions in precipitation. As discussed in sections A(4)(b) and A(5), Increasing Fuel 

Load and Fire, colonization by non-native annual grasses is known to increase the frequency and 

intensity of fires, both of which have dramatic negative effects on desert water cycles and 

wildlife habitat (Hamerlynck et al. 2000). 

Climatic regimes are believed to influence the distribution of plants and animals through 

species-specific physiological thresholds of temperature and precipitation tolerance. Warming 

temperatures and altered precipitation patterns may result in distributions shifting northward 

and/or to higher elevations, depending on resource availability (Walther et al. 2002). We may 

expect this response in the desert tortoise to reduce the viability of lands currently identified as 

“refuges” or critical habitat for the species. Seager et al. (2007) ran a series of climate models 

and simulations on the precipitation history and future of the southwestern United States and 

parts of northern Mexico that consistently showed a severe drying trend in this region throughout 

the 21st century, especially in areas where evapotranspiration exceeds precipitation (such as most 

desert regions). 

Some evidence suggests, however, that desert tortoises may be capable of adapting to 

changes in the environment through modification of their behavior, periods of activity, and diet 

(Morafka and Berry 2002). The desert tortoise evolved millions of years before the formation of 

the North American deserts, and the species experienced both more mesic and more xeric 

conditions within the last several thousand year (Morafka and Berry 2002). Perhaps as the 

habitats they occupied changed and became more arid, the tortoise was able to adapt and succeed 

in desert climes and exploit a broad ecological range. The probability that the desert tortoise will 

be able to survive ongoing changes in vegetation and food sources or temperature and 

precipitation patterns remains to be seen, especially in light of continued anthropogenic 

alterations of the environment (Morafka and Berry 2002). Models demonstrate large shifts in 

plant distributions that over a long period of time may allow opportunities for migration and 

adaptation. Under the current scenario, however, where change may occur within a few decades, 

133
it cannot be predicted whether or not plants and animals would be able to readily migrate into 

new habitats (Thompson et al. 2003). 

Direct climatic effects on growth and development, spatial distribution, and species 

interactions are apparent in amphibians and reptiles, which, in common with other ectotherms, 

are heavily influenced by environmental conditions. Both seasonal temperature and humidity 

affect their reproductive physiology and population dynamics (Walther et al. 2002). In addition, 

desert tortoises have temperature-dependent sex determination (i.e., the sex of the hatchlings is 

determined by the temperatures in the nest), with 1:1 sex ratios produced at approximately 32.5o 

C, all males produced at 30.5o C and below, and all females produced at 32.5o C and above 

(Rostal et al. 2002). Although there has been some speculation that global temperature increases 

may skew sex ratios or eliminate male offspring altogether for some turtles (Janzen 1994), there 

is also evidence that temperature-dependent sex determination systems may be able to evolve 

through maternal nesting behavior if gradual changes in climate result in skewed sex ratios 

(Janzen and Morjan 2002). Sex ratios of reptiles may be robust to moderate temperature 

increases as long eggs experience daily fluctuating temperatures (Booth 2006). The 

heterogeneous environment in which tortoises nest does provide opportunities among diverse 

potential nest sites with exposure to a variety of temperature regimes. The survival of reptile 

species with temperature-dependent sex determination through cycles of warming and cooling 

over the last 100,000 years suggests that changes in climate were such that species were capable 

of shifting the time of nesting, choice of nest sites, the range occupied, or even temperature at 

which the sexes were produced (Booth 2006). Rapid changes in climate may challenge the 

ability of the desert tortoise to make such shifts. While it remains unclear as to how global and 

regional changes in climate may affect the desert tortoise, continued research and monitoring 

relative to behavioral and life history traits of the species under climate change will inform 

conservation and management decisions regarding recovery of the species in the Mojave Desert. 

(a) Drought. Data do exist on some of the effects of drought on the desert tortoise. 

Drought is a normal phenomenon in the Mojave Desert; desert tortoises have been inhabitants of 

this region for over 10,000 years and have adapted to variable conditions (Nagy and Medica 

1986; Peterson 1994a,b; 1996a; Henen 1997; Hereford et al. 2006). As noted above, extended 

periods of drought may affect desert tortoises through physiological effects to individuals (i.e., 

stress) and limited forage availability. For example, unlike some other desert vertebrates, 

tortoises acquire much of their water and maintain overall positive energy balance by drinking 

free water (Peterson 1996a; Wilson et al. 2001). 

The effect of drought on demographic parameters of tortoise populations (i.e., birth, 

death, recruitment, and growth rates) is not well understood (Avery et al. 2002; Boarman 2002). 

However, studies have attributed many adverse effects to periods of drought, including 

dehydration, malnutrition, and starvation; reduced reproductive output of females; altered 

behavior such as failure to seek shelter, reduced movement, and surface activity (O’Connor et al. 

1994; Homer et al. 1996; Duda et al. 1999; Berry et al. 2002b); and increased susceptibility to 

predation and disease (Peterson 1994a,b). 

Since 1975, a tortoise population on the Beaver Dam Slope in Arizona and Utah 

experienced high mortality, where malnutrition caused by reduced nutrient availability was 

134
considered responsible for osteoporosis and subsequent mortality (Jacobson 1994). Increased 

mortality in the Ivanpah Valley in 1981 and 1982 was attributed to drought conditions (Turner et 

al. 1984), and abnormally high levels of mortality were recorded in the east and west Mojave 

Desert during a three-year drought period (1988 through 1990). Deaths in the Ivanpah Valley 

study site were attributed to drought-induced starvation and dehydration (Turner et al. 1984). 

Research conducted in the early 1980s indicated a strong correlation between clutch 

frequency (the number of clutches produced by a female in one reproductive season) and 

biomass of annual plants used by tortoises for food (Turner et al. 1986, 1987). Studies conducted 

at five sites (Joshua Tree National Park, Mojave National Preserve, Palm Springs, Piute Valley, 

and St. George) supported the results in Turner et al. (1984, 1986, 1987). Studies indicated that 

in high-rainfall years with corresponding abundant food plant availability, more females 

reproduced and reproducing females laid more clutches per reproductive season, compared with 

low-rainfall years (Lovich et al. 1999). Clutch size (number of eggs per clutch) was relatively 

constant regardless of conditions; however, Avery et al. (2002) noted that females at higher 

elevations with greater annual rainfall had a larger mean clutch size. 

Recent studies also indicate that even a relatively short-term drought combined with little 

or no biomass of annual plants can cause a severe reduction in adult tortoise survival. A study of 

adult tortoise survival rates at two sites in the eastern Mojave desert (near or adjacent to PiuteEldorado critical habitat unit) attributed die-offs in 1996 to a period of drought that began in the 

summer of 1995, coupled with failure of annual vegetation production in 1996 (Longshore et al. 

2003). During three years of no or minimal biomass production of annual plants (1996, 1997, 

and 1999), the survival of adult tortoises decreased. In 1996, 30 percent (15 individuals) of radiomonitored adults died following a drought that began in the summer of 1995. Although the 

researchers obtained no physiological evidence, they believed these deaths likely resulted from 

dehydration, as there was no substantial evidence of other mortality mechanisms, such as disease 

or predation (Longshore et al. 2003). 

2. Garbage, Trash, and Balloons 

Turtles and tortoises are known to eat non-food objects, such as rocks, balloons, plastic, and 

other garbage. Such objects can become lodged in the gastrointestinal tract or entangle heads and 

legs, causing injury or death (Burge 1989; USFWS 1994). Unauthorized deposition of refuse is 

prevalent near towns, cities, and settlements in remote areas as well as at the urban-desert interface. 

However, based on current available data, garbage and litter do not appear to be a widespread or 

major threat to tortoise populations, except through the attraction of ravens and other predators. 

This indirect effect of predator subsidy may contribute to a more important problem, as 

discussed in section C(3), Predation (Boarman 2002). 

3. Noise and Vibration 

The 1994 Recovery Plan cited noise and vibration as having potentially significant effects 

on desert tortoise’s behavior, communication, and hearing apparatus (USFWS 1994). Very 

limited additional data have been obtained specific to this potential. Studies on the effects of 

flight noise from jet aircraft and sonic booms on hearing, behavior, heart rate, and oxygen 

135
 

consumption of desert tortoises concluded that hearing loss and physiological changes are not 

likely to be dangerous during occasional short-term exposures; however, those results cannot be 

extrapolated to chronic exposures over a tortoise’s lifetime. The authors advise that their results 

are “best viewed as a first-order effort to determine the effects of subsonic and supersonic 

aircraft noise on a desert reptile.” They recommend that changes in tortoise activity with 

repeated exposure to aircraft noise should be investigated under natural conditions, including 

during food and water deprivation, torpor, or exposure to dangers such as rivals and predators 

(Bowles et al. 1999). 

4. Non-motorized Recreation and Miscellaneous Human Activities 

Non-motorized recreation includes activities such as camping, hunting, target practice, 

rock collecting, hiking, horseback riding, biking, and sight-seeing. While there are no data 

correlating these activities with impacts to the desert tortoise, it may be surmised based on 

information on visitor-use days that these activities bring with them many of threats associated 

with increased human presence, such as loss of habitat from development of recreational 

facilities; handling and disturbance of tortoises; increased collection, road kill, and vandalism of 

tortoises; and increased raven populations (USFWS 1994; Boarman 2002). Off-trail use can 

degrade habitat by damaging vegetation and soil crusts (Belnap 1996) and by compacting soils. 

Very few studies have been conducted to document the effects of non-motorized 

activities to desert tortoises. One study measured the effect of surface disturbance from foot, 

bike, and vehicle tracks on the nitrogenase activity in cyanobacterial-lichen soil crusts, a 

dominant source of nitrogen for cold-desert ecosystems (Belnap 1996). Results showed that the 

levels of nitrogenase activity were reduced by 30 to 100 percent, depending on the degree of soil 

disruption and the microbiotic composition of the soils (Belnap 1996). This study demonstrated 

that anthropogenic surface disturbances may have serious implications for the nitrogen budgets 

of cold-desert ecosystems, which may be confounded by increased levels of atmospheric 

pollution and nitrogen deposition associated with increased human populations (see Brooks 

2003). However, soil crusts retain greater water content than bare soils, and non-native plants 

colonize and out-compete native species on disturbed soils (DeFalco et al. 2001). 

5. Unauthorized Propagation of Pet Tortoises 

Unauthorized breeding of pet tortoises can lead to pressures on wild tortoise populations, 

as well as management agencies. Wolff and Seal (1993) noted that the implications of infectious 

disease spread by the release of captive-bred animals and relocation of wild animals are a major 

concern in conservation biology. Captive releases have the potential to introduce disease into 

wild populations of desert tortoises and may also result in genetic contamination (i.e., 

inappropriate mixing to tortoises from different parts of the range and with different genetic 

backgrounds). Because of population declines in the Desert Tortoise Natural Area in the 1980s, 

hundreds of animals showing clinical signs of upper respiratory tract disease were removed and 

evaluated (Jacobson et al. 1995). Tomlinson and Hardenbrook (1993) reported that the highest 

prevalence of clinical signs of upper respiratory tract disease was observed in tortoises removed 

from areas where previous releases of captive animals had occurred. 

136
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APPENDIX B 

UNDERSTANDING DISEASE IN DESERT TORTOISE POPULATIONS: A BRIEF 

SUMMARY OF KNOWLEDGE AND RECOMMENDATIONS PERTINENT TO 

CONSERVATION 

by 

The Desert Tortoise Science Advisory Committee 

(Peter Hudson, Kristin Berry, C. Richard Tracy, Earl McCoy, Katherine Ralls, Michael Reed, 

and Robert Steidl) 

Taking into account recent research presented to the committee by 

Kenneth Hunter and Mary Brown 

A White Paper Presented to the U.S. Fish and Wildlife Service 

September 2007 

A. INTRODUCTION 

The objective of this document is to identify what is understood about the dynamics of 

infectious diseases in desert tortoises and to propose recovery recommendations and research 

activities that would be of direct assistance to the recovery of the desert tortoise. 

To date the available evidence indicates that Upper Respiratory Tract Disease (URTD), 

as caused by the etiological agents Mycoplasma agassizii and M. testudineum, is probably the 

most important infectious disease for desert tortoises in terms of the impact it has on the size of 

desert tortoise populations. Less is known about other diseases that have been identified in the 

desert tortoise (e.g., herpesvirus, cutaneous dyskeratosis), and we hope that continued study of 

Mycoplasma will help to form a model that will facilitate investigations of other diseases. We are 

aware that Mycoplasma spp. in other hosts are associated with a range of secondary respiratory 

tract infections and may also influence the susceptibility of the host to parasitic agents that infect 

other parts of the body. Indeed, there remains the possibility that other virulent infections may 

cause population declines, but at this point in time the putative cause of URTD is a consequence 

of infection with Mycoplasma. 

Mycoplasma are bacteria in the Class Mollicutes, which characteristically have no cell 

wall, have small genomes, and require cholesterol to grow in culture. We do not know if 

Mycoplasma grows more rapidly in stressed hosts because they have more cholesterol or because 

the host is immuno-suppressed as a consequence of hormonal changes. Several species of 

Mycoplasma are pathogenic in humans, including M. pneumoniae, an important cause of the 

respiratory disorder pneumonia, but spillover from one host species to another is unlikely 

because Mycoplasma species are usually highly host-specific. In desert tortoises there are two 

species, the better known M. agassizii and the more recently identified M. testudineum; we use 

the term Mycoplasma to refer to both of these infections unless otherwise stated, but clearly we 

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need to know more about the virulence, transmissibility, and interaction between the two species 

before we can provide separate recommendations for each pathogen. 

B. A SUMMARY OF IMPORTANT OBSERVATIONS ON MYCOPLASMA 

The following summary is based on experimental and observational studies of both the 

desert tortoise and the gopher tortoise. 

1. Mycoplasma agassizii is the putative cause of URTD in desert and gopher tortoises. 

Koch’s Postulates have been satisfied for this pathogen and for M. testudineum. 

2. Mycoplasma appears to be highly virulent in some populations; at times the infection 

appears acute, although at other times the infections are chronic or may even appear 

quiescent. We know there are multiple strains of Mycoplasma and suspect several 

circulate within some populations. Variation in virulence and expression of toxin genes 

may account for some of the variation in observed die-offs between populations. 

Theoretically, there is a possibility that increased virulence could be selected for amongst 

tortoises kept in captivity as a consequence of social structure, good condition, and high 

density, and these more virulent strains could then be introduced into the wild; however, 

clear evidence in support of this hypothesis is lacking. 

3. There is circumstantial evidence to suppose that environmentally induced trauma, 

particularly drought, inadequate nutrition, and toxicants will lead to reduced resistance to 

disease, increased bacteremia (live bacteria in the blood stream), increased transmission 

of disease, presence of visible acute disease symptoms, high tortoise mortality, and 

population declines. We suspect from the information we have seen that these 

environmentally induced effects are more important to the manifestation of acute disease 

outbreaks than variation in virulence between strains, but further research is needed to 

test between these hypotheses. Indeed, the two hypotheses are not mutually exclusive, 

and both may be acting at different times. 

4. An enzyme-linked immunosorbent assay (ELISA) has been used to detect the presence of 

antibodies to Mycoplasma. Recently, the ELISA has been refined by conversion to the 

titer system with a sensitivity of 98.5% and a specificity of 99.9%. A proportion of 

seropositive tortoises do exhibit moderate to severe clinical signs of disease, and these are 

usually culture positive. 

5. Our epizootiological understanding of the dynamics of infection is derived from ELISA 

tests, which simply tell us if an individual has been exposed and thus considered 

seropositive. The ELISA does not tell us if an individual is indeed infected, could be 

infectious, or may have been infected and has cleared the infection. Indeed, the evidence 

is that the development of acquired immunity does not clear the infection but keeps the 

infection level in check. 

6. Seropositive tortoises have not been recorded from all populations, but the definition of 

seropositive and sample size (hence power) varies greatly between studies, making 

comparisons difficult. More insight on the timing and dynamics of this infection could be 

obtained if studies recorded seropositivity in relation to an age estimate. There is 

evidence that some populations in remote areas appear uninfected, although showing 

disease-free status requires large sample sizes and careful tests. In general, some 

populations appear to have an endemic and often chronic infection whereby we see 

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relatively constant levels of seropositivity in the range of 20-25%. Other populations 

exhibit an increasing proportion of seropositive individuals, and these often exhibit acute 

infections with severe signs of disease and mortality with high level of seropositivity in 

the range of 50-75% for a relatively short period. 

7. There is interesting evidence that desert tortoises, previously unexposed to infection, 

carry natural antibodies against Mycoplasma. This finding, if confirmed, could be of 

immense importance in understanding the dynamics and causes of acute infection and 

may indeed help with managing the disease in natural populations. 

C. THE PUTATIVE EXPLANATION OF THE DYNAMICS OF MYCOPLASMA 

INFECTIONS IN DESERT TORTOISE POPULATIONS 

1. First working hypothesis: Die-offs of tortoises associated with mycoplasmosis are 

initiated by environmental stressors including drought, reduced nutrition, and toxicants 

that cause chronic physiological stress in an individual and thereby increase susceptibility 

and transmission, so generating an epidemic outbreak of acute disease. Note that many of 

these stressors are caused by anthropogenic activities that have reduced the plane of 

nutrition or reduced availability of water, and these stressors may well have a negative 

impact on population change in the absence of mycoplasmosis. By definition, any 

mycoplasmosis-induced die-offs can only occur when the pathogen is present in the 

population, and introduction of the pathogen or a new strain could also lead to an 

epidemic in susceptibles. 

Predictions from this hypothesis include: 

a. Outbreaks do not occur in unstressed populations. 

b. Stressed tortoises are more susceptible to infection, and chronically infected 

individuals are more likely to be infectious. 

c. Die-offs will be less extreme when Mycoplasma is absent. 

Specific research questions arising from this hypothesis include: 

a. Are population declines through environmental stress less severe when 

Mycoplasma is absent? 

b. Do tortoises exposed to simulated drought conditions become more susceptible to 

infection and increase bacteria shedding? 

c. Do tortoises on a low plane of nutrition have increases in susceptibility and 

infectiousness? 

2. A second hypothesis, which is not mutually exclusive to the first, is that there are 

multiple strains of Mycoplasma, and these vary in virulence and transmissibility such that 

when introduced into a naïve tortoise populations cause significant die-offs. 

Predictions from this hypothesis include: 

a. Die-offs are associated with novel strains of Mycoplasma and not previously 

circulating strains. 

b. Outbreaks occur more often in populations subject to tortoise introductions. 

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c. Outbreaks can occur during periods when the population is not subject to 

environmental stress. 

Specific research questions arising from this hypothesis: 

a. Does exposure to an avirulent strain provide protection against more virulent 

strains? 

b. Are virulent strains more common in captive-held than wild tortoises? 

D. SOME TORTOISE MANAGEMENT ACTIVITIES THAT INFLUENCE DISEASE 

SPREAD 

1. The release of infected tortoises either from captivity or the translocation of tortoises 

from one site to another can introduce Mycoplasma or new strains that may invade naïve 

populations and cause a significant die-off. 

2. The removal of recovered individuals from a population can increase contact rate 

between infected and susceptible hosts so initiating an epidemic. In this respect, we have 

concerns that the Desert Tortoise Conservation Center in Clark County (NV) euthanizes 

all seropositive individuals that have been collected from the wild or submitted as 

captives. 

3. Improvement of habitat, such as the control of invasive plants and the reduction in 

environmental stressors, will reduce the impact of disease-induced die-offs. 

E. RECOMMENDATIONS FOR THE CONTROL OF MYCOPLASMA DISEASE AND 

TO AID RECOVERY OF THE DESERT TORTOISE 

Recommendations relating to translocation: 

1. Do not translocate animals during or after a period of drought or severe environmental 

stress. Translocation should consider both the state of the habitat the tortoises were taken 

from and the state of the habitat the tortoises are introduced into. For example, 

exceptional plant productivity may immediately follow a drought year and may provide 

suitable translocation conditions, although the same conditions following a catastrophic 

fire may only provide non-native forage species which would not be suitable for 

translocation. This recommendation will reduce the chances of inadvertently initiating an 

epidemic when animals may be transmitting or are highly susceptible to infection. 

2. Undertake a full health evaluation (details in Appendix B-1) of all tortoises prior to 

translocation. This should include two ELISA tests for Mycoplasma, undertaken at 6­

week intervals. Animals should be tested for important secondary infections. This will 

become important when a suitable test for herpesvirus becomes available. The use of 2 

ELISAs reduces the likelihood of false results. A full health evaluation will help to ensure 

translocated animals are healthy and supported by additional screening for pathogens. 

3. Seronegative (and culture-negative) animals with no other outward signs of compromised 

health can either be relocated or allocated to research or breeding programs as 

appropriate. 

4. Further tests should be undertaken on all seropositive individuals. This is subject to 

protocols with Western Blots being developed by Dr. Ken Hunter, University of Nevada156
Reno, which could help distinguish between individuals that are ELISA-positive and 

infected from individuals that are ELISA-positive and uninfected. Particular care needs to 

be taken when the prevalence is low since we cannot rule out the possibility that 

individuals who exhibit a weak immune response, and thus appear ELISA-negative, are 

indeed highly susceptible individuals which may well die or act as important transmitters 

to novel infections and, as such, should not be translocated. Uninfected ELISA-positive 

animals can be used in research, breeding, and even release programs. Infected ELISApositive animals can be used in breeding and research programs, but cannot be released to 

supplement wild populations. Under the advice of a veterinarian, some individuals with 

an acute infection should be euthanized, but detailed post-mortem information on the 

histopathology of disease should also be obtained. This recommendation helps to prevent 

the selective euthanasia of animals with high levels of immunity that may well be the most 

resistant individuals in the wild and ensures that maximum information on the disease is 

obtained from every individual sacrificed. 

5. Existing protocols for handling tortoises need to be revised to incorporate new and better 

methods to reduce stress and hence susceptibility to infection. For example, protocols 

need to incorporate methods to reduce voiding of bladders. At the same time, protocols 

need to evaluate the research and management activities that could potentially increase 

the likelihood of exposure. This could include reducing the contact rates of individuals 

after handling. 

6. The research program noted in these recommendations should include: 

a. A study on the sub-lethal effects of infection on fecundity and survival of 

tortoises (ELISA –ve, +ve infected, +ve uninfected). This will help to identify 

suitable females for breeding programs and provide data on the impact of 

infection on long-term abundance. This research will help identify which 

individuals should be included in the breeding program. 

b. Seasonal monitoring of shedding rate of bacteria in infected individuals to 

identify which time of year, age, and sex cohort is responsible for transmission. 

This research will help us identify which cohorts may be infectious and indicate 

possible intervention strategies in wild populations that could be instigated to 

stop temporal and spatial spread of disease and indeed novel Mycoplasma 

strains. 

Recommendations relating to head-starting: 

We define head-starting as the rearing of uninfected juveniles in captivity before their 

release into a population of similar genetic structure for the express purposes of increasing the 

size of that breeding population and/or improving its age structure. 

1. All captive-bred offspring must be kept separated from infected tortoises by impermeable 

barriers and care taken to ensure these individuals are not exposed. This is to prevent 

infection of young tortoises before release. 

2. There is a high priority for breeding individuals from small, rapidly declining and 

genetically distinct populations. While not all fecund and infected tortoises may enter the 

breeding program, this will ensure the genetic variation of wild populations is 

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maintained that may prove important in the development of resistance against diverse 

Mycoplasma strains. 

3. Animals without a known origin should not be used in a breeding program, but could be 

used in research programs. This will prevent mixing of genotypes and the release of 

genetically susceptible individuals into areas which do not match local Mycoplasma 

strains. 

Recommendations relating to desert tortoise holding facilities: 

We suggest implementation of these recommendations at existing facilities (e.g., Desert 

Tortoise Conservation Center (DTCC) in Las Vegas, Nevada, and facilities in Washington 

County, Utah), as well as consideration when planning future facilities. 

1. Euthanizing seropositive individuals should stop immediately, unless the animals exhibit 

acute disease symptoms and are suffering and euthanasia is recommended by a veterinary 

surgeon. This recommendation will prevent the removal of potentially highly resistant 

individuals from wild populations, improve the head-starting/breeding program, and 

provide individuals for research into the disease. We seek to maximize the information 

obtained from euthanized tortoises and to obtain insight into the biology of this disease. 

2. All animals handled at facilities require a health evaluation using full diagnostic tests as 

outlined in Appendix B-1. Seropositive individuals deemed suitable for a breeding 

program will provide a substantial increase in the number available for head-starting. 

Moreover, this approach will help protect the genetic variation observed in wild tortoise 

populations. 

3. Establish a scientific oversight board to oversee and develop plans for holding facilities, 

research priorities, and protocols. The board would provide recommendations to facility 

managers each season regarding the disposition of tortoises in holding. Our 

recommendations are broad, and a more focused research protocol which takes account 

of the logistic difficulties is required. 

4. Include the ability to hold both seropositive and seronegative tortoises at facilities as 

needed for key research into disease. The ability to undertake key research at holding 

facilities will facilitate progress in understanding disease. 

5. The increased demands on feeding and caring for tortoises will require an increase in 

resources allocated to the facilities. Increased veterinary and professional care and new 

pens and research facilities will also be necessary. We seek further input from others with 

knowledge to help develop what is needed. 

6. The DTCC, in particular, has great potential to function as a center for scientific research, 

training, and education. In support of these functions, facility upgrades will be required. 

We suggest garnering range-wide support for upgrades to this facility, as benefits to 

desert tortoises could be far reaching. 

Recommendations for managing natural populations: 

1. Strategies for managing natural animal populations depend on the disease status of the 

population, deemed broadly as a) uninfected, b) recently infected with infection spread, 

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or c) infection status endemic. An endemic population is defined here as one where the 

proportion that is seropositive is above zero and remains stable over time. 

2. Release of tortoises in general: Do not release infected individuals into the wild. 

Improved educational strategies and assistance are needed, so the general public is aware 

that pet/captive tortoises should not be released. Assistance could include the use of a 

phone hotline, the free collection of pet tortoises no longer wanted, the discouragement of 

breeding tortoises in captivity by private citizens, and the discouragement of keeping 

desert tortoises as pets. Consideration should also be given to increased fines for release 

of captive animals. This recommendation is aimed specifically at preventing the 

inadvertent or deliberate release of potentially infectious or highly susceptible 

individuals into a vulnerable population. 

3. All tortoises that can be identified in the wild as released individuals without a health 

check should be removed from the wild and enter a breeding, adoption, or research 

program unless they meet the criteria of not infected and genetically acceptable for that 

population. These tortoises can be identified by characteristic marks of captivity, such as 

the presence of a hole in the carapace, nail polish, or other distinguishing features. This 

recommendation aims to remove infectious or highly susceptible individuals from the 

wild that may help fuel an epidemic outbreak. 

4. We recommend no action be taken to remove infectious or seropositive individuals from 

natural populations, particularly where the data indicate the disease status of that 

population is endemic. This recommendation seeks to prevent the removal of naturally 

resistant individuals or individuals that have acquired resistance of infection from wild 

populations. Resistant individuals within a population can help slow down or even 

prevent disease spread. 

5. In populations known to be uninfected, where statistical power indicates this is <2 

percent, individual tortoises exhibiting clinical signs of acute infection can be removed 

for further testing, but should be returned to the point of capture if found to be uninfected 

by diagnostic tests. Uninfected populations that have recently become infected should be 

carefully monitored with the removal of all individuals exhibiting acute infections. We 

define acute infections here as those exhibiting a nasal or ocular discharge at an 

inappropriate time of year. This recommendation seeks to prevent an epidemic that could 

cause significant mortality of highly susceptible tortoises. 

Priority research recommendations focused at reducing disease-induced die-offs: 

Initially, it may be pertinent to recommend the implementation of terminal studies. Such 

studies will provide much needed data on the effects of disease that will be important to consider 

when proposing further research. 

1. Specific research questions arising from the working hypothesis described above (i.e., 

mycoplasmosis-induced die-offs are initiated by environmental stressors) include: 

a. Are population declines through environmental stress less severe when 

Mycoplasma is absent? 

b. Do tortoises exposed to simulated drought conditions become more susceptible to 

infection and more infectious? 

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c. Do diets high in alien plants increase susceptibility and infectiousness, or do 

tortoises feeding on diets high in native plants (e.g., with high levels of protein or 

potassium excretion potential) have lower susceptibility and infectiousness? 

2. Identify the virulent and less virulent strains circulating in wild and captive populations 

and monitor temporal and spatial change in prevalence in relation to host genetic status 

and environmental stressors. Identification of genes expressing toxin production and the 

circumstances when these genes are expressed could be a fruitful area of research. 

Studies examining the level of cross immunity between strains and variation in resistance 

in relation to the plane of nutrition and availability of water would be of great assistance. 

This research aims to examine the presence and variation in Mycoplasma strains with 

the aim of containing virulent strains. 

3. Identify which individuals are shedding, how they shed, when they shed and, for how 

long they shed infectious Mycoplasma particles. Identify whether individuals removed 

from drought-stressed or severely deteriorated habitats continue to shed Mycoplasma and 

for how long. This research will identify in more detail seasonal forces of infection, the 

period of infectiousness, and how it varies under different circumstances. 

4. Undertake trials to find if it is possible to cure individuals of Mycoplasma infections, 

even if only feasible in captive individuals. Preliminary veterinary trials with mixed 

antibiotics and anti-inflammatory steroids have met with some success and could be 

extended. 

5. Examine the behavior of infectious tortoises in comparison to uninfected tortoises in the 

wild. Obtain estimates of contact rate according to sex, age, and season. This research 

will help us understand the most critical epidemiological parameters associated with 

transmission and, with other data, allow us to produce a predictive model of outbreak. 

6. Examine the implications of releasing sick tortoises into uninfected populations. Such 

studies should occur within enclosures at captive holding facilities. 

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Appendix B-1. Health protocol for Desert Tortoises following Berry and Christopher 

(2001) 

The standard protocol evaluates clinical signs of disease and trauma and should also 

include ELISA and polymerase chain reaction tests and cultures for Mycoplasma agassizii and 

M. testudineum. 

During the health evaluation, the tortoise is evaluated for posture and behavior, whether 

appropriate for the situation or typical of poor health, as well as general appearance of the head, 

limbs, and shell (e.g., signs of muscle wasting, dehydration, low weight). The chin glands, eyes, 

nares, and beak are examined for characteristic clinical signs of health, including drainage, 

edema, presence of mucus (dried or wet), discoloration, and crusts. The mouth should be opened 

and examined for lesions or plaques. 

For most characteristics a standard veterinary ranking system should be used: none, mild, 

moderate, and severe. The shell, limbs, and head are rated for clinical signs of cutaneous 

dyskeratosis, necrosis, and trauma. For these variables, distribution, severity, and chronicity are 

important factors and are each rated separately. 

This protocol has proved useful for research of health and disease. It can also be of use in 

evaluating both wild and captive tortoises for determining disposition for research, translocation, 

adoption, and necropsy programs. For example, captive tortoises or those in ex-urban settings 

exhibit higher rates of trauma and thus may not be suitable for immediate translocation or 

adoption, even if otherwise healthy. Captive and ex-urban tortoises also are more likely to be 

sero- and culture positive for one or more species of Mycoplasma. Tortoises with moderate to 

severe shell disease may be especially suitable for research and nutritional programs. 

161
162
163
164
165
166
167
168
Appendix B-2. Other Diseases of Potential Importance to Desert Tortoise Populations 

Prepared by K.H. Berry for the Science Advisory Committee (September 2007) 

Shell diseases, herpes viruses, and other infectious agents pose potentially significant 

threats to desert tortoise populations. Here, we provide a summary of what is known on shell 

disease and herpes virus infections. 

Shell Disease 

1. Shell diseases have been recorded in tortoise populations in the eastern Mojave and 

Colorado deserts of California, but less in the western Mojave Desert (Jacobson et al. 

1994, Christopher et al. 2003). 

2. The disease has been recorded in all sizes and ages of desert tortoises, but is more 

common and severe in adults (Jacobson et al. 1994, Homer et al. 1998). 

3. The most commonly described shell disease in desert tortoises is cutaneous dyskeratosis 

(Jacobson et al. 1994, Homer et al. 1998), but shell necrosis has also been reported 

(Homer et al. 1998). 

4. The cause(s) of shell disease have not been determined, and no causative infectious agent 

has yet been identified (Jacobson et al. 1994, Homer et al. 1998). 

5. Prevalence level varies greatly; in the Mojave Desert prevalences vary from 6 percent to 

79 percent. 

6. There is some evidence that individuals with a positive nasal cultures for Mycoplasma 

agassizii are more likely to have severe shell disease, although whether this was cause or 

effect is not known. 

7. Shell disease may have been a factor in population declines at some long-term study 

sites, and greater disease levels have been shown to covary with military maneuver areas 

and elevated arsenic levels in soils (Chaffee and Berry 2006). 

8. The flaking and loss of scute laminae and thinning of bone observed in tortoises with 

cutaneous dyskeratosis may render the tortoise more vulnerable to other diseases such as 

fungal infections and multicentric visceral inflammation. 

Herpesvirus 

1. Herpesvirus infections have been reported in captive desert tortoises and have been 

associated with illness and mortality (Johnson et al. 2006). Herpes infections have also 

been recorded in other species of tortoises. 

2. An ELISA test (THV-1) was developed and validated for a herpesvirus for the European 

tortoise (Origgi et al. 2001). This ELISA test has not been validated for Gopherus 

agassizii or other species of Gopherus. However, tests of captive desert tortoises living in 

the Mojave Desert indicated that 27 percent were seropositive for the herpes ELISA and 

demonstrated previous exposure to a herpesvirus (Johnson et al. 2006). 

169
References: Appendix B 

Baseman, J.B., and J.G. Tully. 1997. Mycoplasmas: sophisticated, reemerging, and hardened 

their notoriety. Emerging Infectious Diseases 3:21-32. 

Berry, K.H. 2000. Preliminary Report on the Spring Survey of Desert Tortoises at the Goffs 

Permanent Study Plot and Special Project on Effects of Roads. U. S. Geological Survey, 

Western Ecological Research Center, Riverside, CA 

Berry, K.H. 2004. Protocol- May 2004. Salvaging injured, recently dead, ill, and dying wild, 

free-roaming desert tortoises (Gopherus agassizii). Prepared for Federal Fish and 

Wildlife Permit TE006556-12. 

Berry, K.H. 2006. The Health Status of Resident Desert Tortoises (Gopherus agassizii) in the 

Fort Irwin Translocation Area, San Bernardino County, California. Progress Report for 

2005. U.S. Geological Survey, Moreno Valley, CA. Report to the U.S. Army, NTC Ft. 

Irwin. 

Berry, K.H., and A. Demmon. 2005. Clinic and field training for desert tortoise health 

assessments at the Marine Corps Air Ground Combat Center, Twentynine Palms, 

California. May 22-28, 2004. Final Report for the Marine Air Ground Task Force 

Training Command at Twentynine Palms, CA. U.S. Geological Survey, Moreno Valley, 

CA. 

Berry, K.H., and M.M. Christopher. 2001. Guidelines for the field evaluation of desert tortoise 

health and disease. Journal of Wildlife Diseases 34:427-450. 

Berry, K.H., and R. Jones. 2004. Highlights from the November 2002 Workshop on Desert 

Tortoise Health and Disease. Report from the U.S. Geological Survey and California 

Department of Fish and Game on the Workshop held at Soda Springs, California, 14-17 

November 2002. 

Berry, K.H., B.L. Homer, W. Alley, M. Chaffee, and G. Haxel. 2001. Health and elevated 

mortality rates in desert tortoise populations: the role of arsenic and other potential 

toxicants. Abstract, Arsenic Group Meeting, Denver Federal Center, Denver, CO. Feb. 

21-22, 2001. 

Berry, K.H., E.K. Spangenberg, B.L. Homer, and E.R. Jacobson. 2002. Deaths of desert tortoises 

following periods of drought and research manipulation. Chelonian Conservation and 

Biology 4:436-448. 

Berry, K.H., L.D. Wendland, A. Demmon, and M.B. Brown. 2005. A comparison of lymph and 

plasma sample results form ELISA tests for Mycoplasma agassizii in desert tortoises. 

Presentation and abstract from the Desert Tortoise Council Symposium, Tucson, AZ. 

February 2005. 

170
Brown, D.R., B.C. Crenshaw, G.S. McLaughlin, I.M. Schumacher, C.E. McKenna, P.A. Klein, 

E.R. Jacobson, and M.B. Brown. 1995. Taxonomic analysis of the tortoise mycoplasmas 

Mycoplasma agassizii and Mycoplasma testudinis by 16S rRNA gene sequence 

comparison. International Journal of Systematic Bacteriology 45:348-350. 

Brown, D.R., J.L. Merritt, E.R. Jacobson, P.A. Klein, J.G. Tully, and M.B. Brown. 2004. 

Mycoplasma testudineum sp. nov., from a desert tortoise (Gopherus agassizii) with upper 

respiratory tract disease. International Journal of Systematic and Evolutionary 

Microbiology. 45:1527-1529. 

Brown, D.R., I.M. Schumacher, G.S. McLaughlin, L.D. Wendland, M.B. Brown, P.A. Klein, and 

E.R. Jacobson. 2002. Application of diagnostic tests for mycoplasmal infections of desert 

and gopher tortoises, with management recommendations. Chelonian Conservation and 

Biology 4:497-507. 

Brown, M.B., D.R. Brown, P.A. Klein, G.S. McLaughlin, I.M. Schumacher, E.R. Jacobson, H.P. 

Adams, and J.G. Tully. 2001. Mycoplasma agassizii sp. nov., isolated from the upper 

respiratory tract of the desert tortoise Gopherus agassizii) and the gopher tortoise 

(Gopherus polyphemus). International Journal of Systematic and Evolutionary 

Microbiology 51:413-418. 

Brown, M.B., K.H. Berry, I.M. Schumacher, K.A. Nagy, M.M. Christopher, and P.A. Klein. 

1999. Seroepidemiology of upper respiratory tract disease in the desert tortoise in the 

western Mojave Desert of California. Journal of Wildlife Diseases 35:716-727. 

Brown, M.B., K.H. Berry, C. Melendez Torres, M.A. Hasskamp, L. Wendland, F.R. Mendez de 

la Cruz, and M.F. Villa Andrade. 2006. Health status of wild and captive desert tortoises 

from the Hermosillo and Alamos areas of Mexico. Abstract from the Desert Tortoise 

Council Symposium, Tucson, AZ. February 2006. 

Brown, M.B., G.S. McLaughlin, P.A. Klein, B.C. Crenshaw, I.M. Schumacher, D.R. Brown, and 

E.R. Jacobson. 1999. Upper respiratory tract disease in the gopher tortoise is caused by 

Mycoplasma agassizii. Journal of Clinical Microbiology 37:2262-2269. 

Brown, M.B., I.M. Schumacher, P.A. Klein, K. Harris, T. Correll, and E.R. Jacobson. 1994. 

Mycoplasma agassizii causes upper respiratory tract disease in the desert tortoise. 

Infection and Immunity 62:4580-4586. 

Chaffee, M.A., and K.H. Berry. 2006. Abundance and distribution of selected elements in soils, 

stream sediments, and selected forage plants from desert tortoise habitats in the Mojave 

and Colorado deserts, USA. Journal of Arid Environments 67 Supplement:35-87. 

Christopher, M.M., K.H. Berry, I.R. Wallis, K.A. Nagy, B.T. Henen, and C.C. Peterson. 1999. 

Reference intervals and physiologic alterations in hematologic and biochemical values of 

free-ranging desert tortoises in the Mojave Desert. Journal of Wildlife Diseases 35:212­

238. 

171
Christopher, M.M., K.H. Berry, B.T. Henen, and K.A. Nagy. 2003. Clinical disease and 

laboratory abnormalities in free-ranging desert tortoises in California (1990-1995). 

Journal of Wildlife Diseases 39:35-56. 

Domico, L. 2001. Purification of desert tortoise (Gopherus agassizii) metallothionein, a potential 

biomarker of heavy metal exposure. M.S. Thesis. University of Florida, College of 

Veterinary Medicine. 

Gottdenker, N.L., and E.R. Jacobson. 1995. Effect of venipuncture sites on hematologic and 

clinical biochemical values in desert tortoises (Gopherus agassizii). American Journal of 

Veterinary Research 56:19-21. 

Henen, B.T., C.C. Peterson, I.R. Wallis, K.H. Berry, and K.A. Nagy. 1998. Effects of climatic 

variation on field metabolism and water relations of desert tortoises. Oecologia 117:365­

373. 

Hernandez-Divers, S.M., S.J. Hernandez-Divers, and J. Wyneken. 2002. Angiographic, anatomic 

and clinical technique descriptions of a subcarapacial venipuncture site for chelonians. 

Journal of Herpetological Medicine and Surgery 12:32-37. 

Hill, A.C. 1985. Mycoplasma testudinis, a new species isolated from a tortoise. International 

Journal of Systematic Bacteriology 35:489-492. 

Homer, B.L., K.H. Berry, M.B. Brown, and E.R. Jacobson. 1998. Pathology of spontaneously 

occurring diseases in free-ranging California desert tortoises (Gopherus agassizii). 

Journal of Wildlife Diseases 34:508-523. 

Homer, B.L., C. Li, K.H. Berry, N.D. Denslow, E.R. Jacobson, R.H. Sawyer, and J.E. Williams. 

2001. Soluble scute proteins of healthy and ill desert tortoises (Gopherus agassizii). 

American Journal of Veterinary Research 62:104-110. 

Hunter, K.W., S.A. duPre, F.C. Sandmeier, and C.R. Tracy. 2007. Natural IgM antibodies to 

Mycoplasma agassizii in the desert tortoise (Gopherus agassizii). Report to the Desert 

Tortoise Scientific Advisory Committee, June 11-12, 2007. 

Jacobson, E.R., and K.H. Berry. 2004. Necropsies of six desert tortoises (Gopherus agassizii) 

from California. University of Florida, Gainesville, and U.S. Geological Survey, Moreno 

Valley, CA. 

Jacobson, E.R., M.B. Brown, I.M. Schumacher, B.R. Collins, R.K. Harris, and P.A. Klein. 1995. 

Mycoplasmosis and the desert tortoise (Gopherus agassizii) in Las Vegas Valley, 

Nevada. Chelonian Conservation and Biology 1:279-284. 

Jacobson, E.R., J.M. Gaskin, M.B. Brown, R.K. Harris, C.H. Gardiner, J.L. LaPointe, H.P. 

Adams, and C. Reggiardo. 1991. Chronic upper respiratory tract disease of free-ranging 

desert tortoises (Xerobates agassizii). Journal of Wildlife Diseases 27:296-316. 

172
Johnson, A.J., D.J. Morafka, and E.R. Jacobson. 2006. Seroprevalence of Mycoplasma agassizii 

and tortoise herpesvirus in captive desert tortoises (Gopherus agassizii) from the Greater 

Barstow Area, Mojave Desert, California. Journal of Arid Environments 67 

Supplement:192-201. 

Johnson, A.J., A.P. Pessier, J.F.X. Wellehan, R. Brown, and E.R. Jacobson. 2005. Identification 

of a novel herpesvirus form a California desert tortoise (Gopherus agassizii). Veterinary 

Microbiology 111:107-116. 

Lederle, P.E., K.R. Rautenstrauch, D.L. Rakestraw, K.K. Zander, and J.L. Boone. 1997. Upper 

respiratory tract disease and mycoplasmosis in desert tortoises from Nevada. Journal of 

Wildlife Diseases 33:759-765. 

Marschang, R.E., C.B. Gleiser, T. Papp, A.J.P. Pfitzner, R. Böhm, and B.N. Roth. 2006. 

Comparison of 11 herpesvirus isolates form tortoises using partial sequences form three 

conserved genes. Veterinary Microbiology 117:258-266. 

McLaughlin, G.S. 1997. Upper respiratory tract disease in gopher tortoises, Gopherus 

polyphemus: pathology, immune responses, transmission, and implications for 

conservation and management. Ph.D. Dissertation, University of Florida. 

Muro, J., A. Ramis, J. Pastor, R. Velarde, J. Tarres, and S. Lavin. 1998. Chronic rhinitis 

associated with herpesviral infection in captive spur-thighed tortoises from Spain. Journal 

of Wildlife Diseases 34: 487-495. 

Oli, M.K., M. Venkataraman, P.A. Klein, L.D. Wendland, and M.B. Brown. 2006. Population 

dynamics of infectious diseases: a discrete time model. Ecological Modeling 198:183­

194. 

Origgi, F.C. 2001. Development of serological and molecular diagnostic tests for herpesvirus 

exposure detection in tortoises. Ph.D. Dissertation, University of Florida. 

Origgi, F., A. Johnson, and E.R. Jacobson. 2003. Validation of the ELISA test for herpesvirus 

exposure detection in desert tortoises: options and limitations. Abstract from the Desert 

Tortoise Council Symposium, Las Vegas, NV. February 2003. 

Origgi, F.C. P.A. Klein, K. Mathes, S. Blahak, R.E. Marschang, S.J. Tucker, and E.R. Jacobson. 

2001. Enzyme-linked immunosorbent assay for detecting herpesvirus exposure in 

Mediterranean Tortoises (Spur-Thighed Tortoise [Testudo graeca] and Hermann’s 

Tortoise [Testudo hermanni]). Journal of Clinical Microbiology 39:3156-3163. 

Origgi, F.C., P.A. Klein, S.J. Tucker, and E.R. Jacobson. 2003. Application of 

immunoperoxidase-based techniques to detect herpesvirus infection in tortoises. Journal 

of Veterinary Diagnostic Investigation 15:133-140. 

Origgi, F.C., C.H. Romero, D.C. Bloom, P.A. Klein, J.M. Gaskin, S.J. Tucker, and E.R. 

Jacobson. 2004. Experimental transmission of a herpesvirus in Greek tortoises (Testudo 

graeca). Veterinary Pathology 41:50-61. 

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Pettan-Brewer, K.C.B., M.L. Drew, E. Ramsay, F.C. Mohr, and L.J. Lowenstine. 1996. 

Herpesvirus particles associated with oral and respiratory lesions in a California desert 

tortoise (Gopherus agassizii). Journal of Wildlife Diseases 32:521-526. 

Schumacher, I.M., M.B. Brown, E.R. Jacobson, B.R. Collins, and P.A. Klein. 1993. Detection of 

antibodies to a pathogenic mycoplasma in desert tortoises (Gopherus agassizii) with 

upper respiratory tract disease. Journal of Clinical Microbiology 31:1454-1460. 

Schumacher, I.M., D.B. Hardenbrook, M.B. Brown, E.R. Jacobson, and P.A. Klein. 1997. 

Relationship between clinical signs of upper respiratory tract disease and antibodies to 

Mycoplasma agassizii in desert tortoises from Nevada. Journal of Wildlife Diseases 

33:261-266. 

Schumacher, I.M., D.C. Rostal, R. Yates, D.R. Brown, E.R. Jacobson, and P.A. Klein. 1999. 

Transfer and persistence of maternal antibodies against Mycoplasma agassizii in desert 

tortoise (Gopherus agassizii) hatchlings. American Journal of Veterinary Research 

60:826-831. 

Seltzer, M.D., and K.H. Berry. 2005. Laser ablation ICP-MS profiling and semi-quantitative 

determination of trace element concentrations in desert tortoise shells: documenting the 

uptake of elemental toxicants. Science and the Total Environment 339:253-265. 

Snipes, K.P., R.W. Kasten, J.M. Calagoan, and J.T. Boothby. 1995. Molecular characterization 

of Pasteurella testudinis isolated from desert tortoises (Gopherus agassizii) with and 

without upper respiratory tract disease. Journal of Wildlife Diseases 31:22-29. 

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Brown. 2007. An improved ELISA for Mycoplasma agassizii exposure: a valuable tool in 

the management of environmentally sensitive tortoise populations. Clinical and Vaccine 

Immunology 14:1190-1195. 

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diseases in wildlife. Rev. Sci. Tech. Off. Int. Epiz. 21:139-157. 

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APPENDIX C 

DRAFT DECISION SUPPORT SYSTEM FOR DESERT TORTOISE RECOVERY: A 

TOOL FOR EVALUATING RECOVERY ACTION EFFECTIVENESS 

August 29, 2007 

A. INTRODUCTION 

1. Purpose of this Appendix 

This appendix describes the processing steps, data inputs, and outputs of a prototype 

decision support system developed for the Fish and Wildlife Service’s Desert Tortoise Recovery 

Office (DTRO) to aid in the revision and implementation of the recovery plan for the desert 

tortoise. The decision support system is the product of a larger process to consult land managers 

with jurisdiction over desert tortoise habitat through a series of recovery planning workshops. 

These workshops were conducted during March-May 2007 at which managers provided 

information on geographic distribution of threats, management actions, and other information 

described below. 

The DTRO decision support system identifies and prioritizes recovery actions that are 

most likely to ameliorate threats to tortoise populations at any geographic extent within the 

tortoise’s range. To do this, the decision support system relies primarily on GIS data of the 

spatial extent of threats (i.e., where threats occur geographically). These data were compiled 

partly through existing (published) sources and partly through manager consultation. The 

decision support system also makes use of managers’ understanding of recovery action-threat 

relationships (i.e., what are the most appropriate actions given a set of threats faced by the 

species?) and the relationship between threats and tortoise mortality (some threats are more 

deadly than others). Future versions of the decision support system may permit managers to 

conduct gap analysis on their current/planned recovery actions (i.e., compare ideal to current or 

planned management actions to identify gaps in management prescriptions for a given area) or to 

evaluate actions in terms of their near- vs. long-term contribution to recovery. The decision 

support system may also be used to develop prioritizations that account for economic, political, 

and operational constraints that managers face when implementing recovery. 

2. Background on Decision Support Systems 

Decision making as an area of study originates in organization science (Simon 1960). 

Decision support systems are computer technologies used to support complex decision-making 

in organizations (Keen and Morton 1978). These technologies involve an interactive system 

which uses decision rules, models, databases, and formal representations of the decision 

maker(s)’ requests to indicate specific actions to solve problems. It thus assists complex decision 

processes and increases their efficiency (Ekbia 2004). 

Initially, decision support systems were used mostly by small groups of experts. 

However, this led to mistrust by other stakeholders because they had not been involved in the 

process. Inevitably, decision-making was inhibited by the perceived ‘black-box’ nature of the 

process (Feick and Hall 2004; Ekbia and Reynolds 2006). Decision support systems must be able 

175
to take on a plethora of viewpoints from stakeholders with differing objectives, resources, and 

knowledge. Decision support systems have therefore evolved from a ‘closed’ expert-oriented to 

an ‘open’ user-oriented technology. This trend has stimulated movement towards using 

technology to increase the democratization and transparency of the decision-making process via 

public participation (Ekbia and Reynolds 2006; Malczewski 2006). 

The development of decision support systems provides a vehicle for adaptive 

management through the process of developing the initial prototype, consulting it regularly, 

evaluating its performance, and updating it on a regular basis (Starfield and Bleloch 1991). Use 

of decision support systems allows different types and levels of information to be pooled, 

compared, weighed, and interpreted. Furthermore, arguments and discussion about the 

information are typically more focused in a logical, goal-oriented fashion. Also, developing and 

applying a decision support system makes it apparent where information is missing and where 

there is a need for research or monitoring programs. Irrespective of the benefits of using decision 

support systems, the process of building a decision support system is always stimulating and 

effective in better understanding the basis and limitations of existing information and its 

applicability for management decisions (Starfield and Bleloch 1991). 

B. DECISION SUPPORT SYSTEM ROAD MAP 

The remainder of this appendix describes the processing steps, data inputs, and outputs of 

the decision support system for desert tortoise recovery management. The following flow chart 

diagram (Figure C-1) illustrates the overall modeling process. It can be used as a “road map” to 

the text description that follows. While the diagram may seem complex, each component 

essentially represents a separate model, with its own scientific or management utility. Each 

model is leveraged on the previous to produce the overall assessment of risk to desert tortoise 

populations and management priorities to mitigate that risk. It is important to note that this is a 

provisional system, and most of the incorporated models are based on preliminary subjective 

analysis and expert opinion. However, each model is transparent and can be evaluated and 

revised independently of the others as new information or better models become available. In 

addition, sensitivity analyses still need to be conducted to determine the relative importance of 

different assumptions (e.g., relative impacts of threats to tortoise demography or relative 

effectiveness of recovery actions on abating threats) and to identify priorities for model 

improvement. In fact, one value of this prototype system is that the relative importance of the 

various components can be evaluated in light of the big picture (Nicholson et al. 2002). The 

prototype is presented here precisely because there is no better alternative available (Starfield 

1997). The steps and component models can be summarized as follows: 

• Spatial Threats Model: integrate threats data and associate with degrees of threat 

• Tortoise mortality models 

o Threat-Mortality Interaction Model: estimate the contribution of each threat to 

mortality mechanisms 

o Relative Mortality Model: estimate the contribution of each mortality mechanism to 

overall mortality 

o Demographic Impact Model: estimate contributions of each threat to overall 

demographic impact (e.g., mortality) 

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• Models of the risk to tortoise populations on the ground 

o Single Risk/Threat Model: combine degrees of threat with demographic impact 

(‘deadliness;’ its contribution to mortality) to estimate severity of each threat to the 

population 

o Pre-action Aggregate Risk Model: estimate the aggregate measure of the risk posed to 

the population by all threats 

• Recovery action models 

o Recovery Action Effectiveness Model: estimate the effectiveness of recovery actions 

in mitigating threats 

o Recovery Action Risk Reduction Model: combine the estimated risk to populations 

with recovery action effectiveness to estimate the reduction in risk 

o Post-action Aggregate Risk Model: estimate the aggregate measure of the risk posed 

to the population by all threats after management actions are applied 

• Spatial Summary/Prioritization: prioritize recovery actions by their estimated effectiveness 

in risk reduction 

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178 

Figure C-1. Flowchart illustrating the decision support system for desert tortoise recovery. The numbers in the boxes refer 

the text. 
1. INTEGRATE THREATS DATA AND ASSOCIATE WITH DEGREES OF THREAT 

Spatial Threats 

Model 

(1) 

The Spatial Threats Model involves two steps. The first step adds a ‘degree 

of threat’ rating to each geographic threat data layer (computerized data associating threats with 

specific geographic locations). This rating is derived from a threats-mapping exercise, during 

which land managers were asked to answer a series of questions about threats with which they 

were familiar (Table C-1). The second step integrates GIS threat layers from multiple sources 

into a single layer representing each threat. Sources of threat data included previously published 

datasets and maps that managers created during the threats-mapping exercise. Appendix C-1 

contains a list of data sources included in the model. 

Table C-1. Questions and possible responses on the threats questionnaire completed by managers 

during recovery planning workshops. 

Threat 

Characteristic Question Possible Responses 

Intensity How would you describe the overall 

intensity of the threat at this location? 

Low, Medium, High, Unknown 

Trend In general, how has the threat at this 

location changed over time? 

Increasing, Decreasing, Stable, 

Unknown 

Frequency In general, how frequently does this 

threat occur at this location? 

Rarely (almost never occurs) 

Occasionally (occurs from to time) 

Often (occurs frequently) 

Constantly (always present) 

Unknown 

The decision support system combines the threats information contributed by the 

managers with data collected from published sources. Where the published data sources lacked 

information about degree of threat, a default, intermediate rating was assigned to these data 

layers. Figure C-2 illustrates how degree of threat was assigned to geographic features. The final 

step in assigning degree of threat was to normalize (i.e., standardize) output values to a 

percentage scale (0-1). Outputs for subsequent steps in the model were also summarized in this 

manner. This technique allows for the comparison of threat severity both before and after an 

action is taken. 

179
 

Degree of threat rating in 

this polygon derived from 

manager responses to 

questionnaire. 

An intermediate rating was 

applied where no 

information was available 

Figure C-2. Method for assigning degree of threat to threat polygons. 

2. ESTIMATE CONTRIBUTION OF EACH THREAT 

TO OVERALL DEMOGRAPHIC IMPACT Multiply, 

Sum 

Demographic 

Impact Model 

(2.3) 

Estimating the ultimate relative impact of the 

various threats to tortoise populations involves rating 

the ‘deadliness’ of each threat with regard to tortoise 

demography. This is accomplished by combining 

two submodels: 1) the Threat-Mortality Interaction 

Model, which estimates the contribution of each threat to specific mortality mechanisms (relative 

to population-level effects; for example, a threat responsible for the mortality of 100 adult 

tortoises has greater demographic impact than another threat responsible for the mortality of 100 

hatchlings because few of these hatchlings would naturally contribute to the adult population), 

and 2) the Relative Mortality Model, which estimates the contribution of each mortality 

mechanism to overall tortoise mortality. 

Threat - Mortality 

Interaction Model 

(2.1) 

Relative Mortality 

Model 

(2.2) 

2.1 Estimate the contribution of each threat to mortality mechanisms 

The Threat-Mortality Interaction Model uses a threat interaction survey developed by the 

Science Advisory Committee and DTRO. This survey is intended to assist in analyzing how, and 

the extent to which, various potential threats interact with each other and how they contribute to 

tortoise mortality. Survey responses relate to range-wide (or recovery unit-wide) threat 

conditions and are not specific to more localized areas. Data from 35 respondents from the 

tortoise science and management community were available at the time of decision support 

system development. In the survey, respondents were asked to rate the effect of individual threats 

on individual mortality mechanisms (Figure C-3). 

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Figure C-3. The threats interaction survey asked respondents to rate the influence of threats on mortality 

mechanisms on a scale of 1 (low) – 4 (high). These ratings were used to derive a rating for each threat’s 

contribution to all mortality mechanisms. 

Following is a list of the mortality mechanisms respondents considered in the survey. 

This list includes factors most directly responsible for tortoise mortality and population declines 

(as opposed to indirect factors that contribute to one or more of these mortality mechanisms). 

Catastrophic, permanent habitat loss Drowning 

Burial Falling 

Inadvertent crushing/trampling Predation - ravens 

Burning Predation - free-roaming dogs 

Dehydration Predation - other 

Nutritional compromise (starvation) Collection 

Disease Vandalism (shooting, mutilation, crushing) 

Using the survey responses, the decision support system team calculated an average 

contribution of each threat to all mortality mechanisms. When determining a threat’s 

contribution to a mortality mechanism, both direct and indirect threat contributions were 

considered, as illustrated in Figure C-4. Appendix C-2 further illustrates how direct and indirect 

threat contributions to mortality are estimated. 

Figure C-4. Illustration of how direct and indirect threats contribute to mortality mechanisms from the 

perspective of the threat, Invasive Plants. 

181
 

2.2 Estimate the contribution of mortality mechanisms to overall mortality 

In the Relative Mortality Model, each mortality mechanism was assigned a weight that 

described its significance relative to its demographic impact. To illustrate this point, if in a given 

year 25 percent of a population of tortoises died, what were the direct causes of death, and how 

do these causes compare with one another in terms of total numbers? To generate this weight, 

DTRO staff independently rated each mortality mechanism in a pair-wise fashion. This yielded a 

relative weight for each mortality mechanism. Appendix C-3(a) includes the complete list of 

pair-wise ratings. 

Pair-wise comparisons were completed for each mortality mechanism combination. 

These pair-wise ratings were analyzed using an Analytical Hierarchy Process (Saaty 1992), 

which resulted in an overall set of relative weights for each mortality mechanism (Appendix C3[b]). Note that these same weights could be developed with a larger group of scientists or 

managers or replaced with quantitative data from future research to provide more reliable results. 

2.3 Calculate the contribution of each threat to overall mortality 

This step produces the Demographic Impact Model by combining the results from the 

previous steps to derive an overall weighted score for each threat. That score describes the 

contribution of a single threat to overall tortoise mortality. Table C-2 illustrates how each factor 

was combined. Appendix C-4 includes a complete table of these results. 

Table C-2. Illustration of how overall threat contribution to mortality is calculated. 

Percent 

Contribution Mortality Contribution of 

Single to Mortality Mechanism MM to overall Overall Contribution of 

Threat Mechanism (MM) Mortality Threat to Mortality 

Invasive 20.61% Burning 9% 20.61% x 9% = 1.86% Plants 

Invasive Nutritional 16.93% 4% 16.93% x 4%= 0.68% Plants Compromise 

Invasive 1.72% Disease 7% 1.72% x 7% = 0.02% Plants 

Total Estimated Contribution of Invasive Plants to Desert Tortoise Mortality 2.56% 

3. MODEL RISK TO POPULATIONS 

3.1 Combine Degree of Threat with Mortality 

Factor to Estimate Threat Severity 

This step creates the Single Risk/Threat 

Model by combining the measures of degree of 

threat described in Section 2 with the threat 

contribution to mortality in Section 3. This step 

yields a severity rating for each threat to desert 

tortoise populations within a geographic area of 

Spatial Threats 

Model 

(1) 

Demographic 

Impact Model 

(2.3) 

Multiply 

Single Risk/Threat 

Models 

(3.1) 

182
interest (e.g., recovery unit). The rating represents both degree of threat 

(intensity and frequency) and the mortality risk associated with that threat, as 

calculated in the previous step. 

3.2 Estimate Aggregate Threat Severity Sum 

Single Risk/Threat 

Models 

(3.1) 

This step provides a synopsis of threats across the tortoises’ range. It is a 

GIS processing step that involves summing each threat layer using the severity 

ratings developed in the previous step (3.1). The output is an aggregate rating of 

threat (risk) posed to the desert tortoise, reported at the spatial unit of 1 square 

kilometer across the tortoises’ range (Figure C-5). 

Pre-action 

Aggregate Risk 

Model 

(3.2) 

Figure C-5. Aggregated severity of threats across the range of the Mojave population of the desert tortoise 

estimated from the prototype decision support system. Warmer colors indicate greater severity of threats 

to the tortoise. Note that this representation is preliminary and is based on incomplete data and 

provisional underlying models. 

183
 

4. ESTIMATE EFFECTS OF RECOVERY ACTIONS 

4.1 Effectiveness of Action on Threat 

Recovery Action 

Effectiveness 

Model 

(4.1) 

The Recovery Action Effectiveness Model is a table that relates recovery actions to the 

threats they address. It was developed with manager input during the recovery planning 

workshops. During each workshop, managers were asked to rate the relationship between 

recovery actions and threats on a scale of high, medium, and low, where high meant that the 

action was well suited to addressing a particular threat. A fourth option, “not applicable,” 

indicated no relationship between an action and a threat. Responses from each manager on each 

threat-action combination were converted to a numeric range and averaged to derive an overall 

rating for each action on each threat. Figure C-6 illustrates the results of that exercise, and a 

complete table of these ratings is included in Appendix C-5. 

RECOVERY AIR CAPTIVE DESIGNATED 

ACTIONS/THREATS AGRICULTURE POLLUTION RELEASES COLLECTION OHV AREAS DISEASE 

Close Roads 1 3 1.5 1 

Connect Functional Habitat 1 

Control Ravens 

Designate Roads 1 3 1.5 1 

Environmental Education 3 1 2.67 2.25 2.5 1.5 

Fence Roads 1 3 1 

Figure C-6. Land managers rated the strength of relationships between recovery actions and threats in 

terms of effectiveness using a HIGH (3) to LOW (1) scale. These ratings were used to calculate the 

relative expected effect of an action on a threat in the decision support system. 

4.2 Threat Severity (Risk) Reduction as a 

Result of an Action 

Recovery Action 

Effectiveness 

Model 

(4.1) 

The Recovery Action Risk Reduction 

Model combines the threat severity (risk) before 

an action is implemented with a factor 

representing the effectiveness of that action on a 

given threat. The result of this calculation yields 

an estimated reduction of a threat as a result of an action. When the estimated reduction of each 

threat present in an area is summed, the result is a total estimated reduction caused by single 

action on all threats in that area. This calculation is performed for each potential action. Figure 

C-7 illustrates this calculation, and Appendix C-6 includes a table showing total threat (risk) 

reduction for each recovery unit. 

Recovery Action 

Risk Reduction 

Model 

(4.2) 

Multiply, 

Sum 

Single Risk/Threat 

Models 

(3.1) 

184
Figure C-7. Illustrative example of how the reduction in risk as a result of an action is calculated. 

Effectiveness of action is expressed as a percentage. 

4.3 Estimate Aggregate Measure of the Risk Posed to the 

Population by All Threats After Recovery Actions are 

Implemented 

This step provides a synoptic view of remaining threat 

risk across the tortoises’ range after individual recovery actions 

are implemented. It is a GIS processing step that involves 

subtracting the estimated reduction of a threat as a result of an 

action (4.2) from the aggregate risk model produced in 3.2. The 

output is a visual representation of the aggregate rating of threat 

(risk) posed to desert tortoise reported at the spatial unit of 1 square kilometer across the 

tortoises’ range (Figure C-8). 

4.4 Implementation Effort (Optional) 

This component of the model may be used for ‘if-then’ scenarios where land managers 

want to envision the amount of threat reduction they might expect to see when an action is 

implemented only partially. For example, a land manager may use this feature to see how much 

he/she can reduce the threat of invasive species by removing 50 percent of invasive plants from 

an area rather than 100 percent of them. This type of calculation can be associated with 

implementation cost (i.e., how much will a $15,000 investment in weed control reduce the threat 

of invasive species in a given area?) and other management-related factors. Since the primary 

goal of the decision support system is to recommend comprehensive actions for the recovery 

plan, this feature has not yet been implemented in the current model. By default, the model 

assumes that each action is implemented to its fullest possible extent. 

Pre-action 

Aggregate Risk 

Model 

(3.2) 

Minus 

Post-action 

Aggregate Risk 

Model 

(for each action) 

(4.3) 

Recovery Action 

Risk Reduction 

Model 

(4.2) 

185
Figure C-8. Expected risk reduction as a result of the hypothetical action of closing roads across the range 

of the desert tortoise. The map on the left represents the aggregate threat severity (risk) from Figure C-5, 

and the map on the right represents post-action threat severity (risk) as a result of the hypothetical action 

of closing all roads. Warmer colors indicate greater severity of threats to the tortoise. Note that this 

representation is hypothetical, preliminary, and is based on incomplete data and provisional underlying 

models. 

5. PRIORITIZE RECOVERY ACTIONS 

When the estimated risk reduction is calculated for all 

possible actions within a given area, these can then be prioritized 

according to total risk reduction, as illustrated in Table C-3. Complete recovery action rankings 

for each recovery unit are provided in Appendix C-7. 

Spatial Summary/ 

Prioritization 

Recovery Action 

(5) 

Risk Reduction 

Model 

(4.2) 

Table C-3. Highest and lowest ranked recovery actions by risk reduction in 

the Upper Virgin River Recovery Unit. 

ACTION 

UPPER VIRGIN 

RIVER RANK 

Law Enforcement 

Fence Roads 

Environmental Education 

: 

Manage Burros/Horses 

Install Railroad Barriers 

Remove Toxicants / Unexploded Ordnance 

5.51 

4.75 

4.58 

: 

0.01 

0.00 

0.00 

1 

2 

3 

: 

16 

17 

18 

6. POTENTIAL ALTERNATIVE APPLICATIONS OF THE DECISION SUPPORT SYSTEM 

There are several alternative uses of the decision support system that may be worthwhile 

at an operational level by land managers. Following is a partial description. 

186 
 

6.1 Conduct GAP Analysis of Existing Management Actions 

The decision support system can be used to compare the effects of a variety of 

management actions on threats in any geographic unit. Specifically, the prioritized list and maps 

of recovery actions produced by the decision support system can be compared to existing 

management actions to identify gaps in management prescriptions for a given area. 

6.2 Comparing Actions with Near- And Long-Term Implications for Recovery 

In its current state, the decision support system prioritizes actions that would lead to 

decreases in tortoise mortality (population effects). In some cases, however, it may be 

advantageous to prioritize actions based on effect on habitat, since habitat response is generally 

considered to be observable in shorter time periods than tortoise population effects. In effect, this 

type of assessment would guide managers toward actions for which the effects can be observed 

earlier in the recovery process. 

With some basic modifications, the decision support system could be used to prioritize 

actions based on their potential effectiveness at protecting or restoring tortoise habitat. This 

would be done by selecting only actions that directly impact habitat to be run in the model. These 

results may be compared to the mortality based assessment to identify how well actions rate 

according to both habitat and population effects (Figure C-9). 

Figure C-9. Illustration of how recovery actions (RAs) can be assessed in terms of mortality risk 

reduction (RAMRAT) and benefit to tortoise habitat (RAMHAT). Delta RAMRAT means ‘change in 

RAMRAT,’ and Delta RAMHAT means ‘change in RAMHAT.’ 

187
6.3 Land Manager Prioritization Model 

The outputs of this model can be incorporated into a land manager decision support 

system to help them develop their own prioritizations. This would incorporate management 

constraints (e.g., budget, available personnel, degree of controversy) into the overall recovery 

action recommendations. Including implementation effort, which would affect the recommended 

actions, land managers could input their own actions, rate their effectiveness, weight their own 

mortality mechanisms and threat contributions, and run the model to get customized outputs of 

risk reduction. 

Literature Cited 

Ekbia, H.R. 2004. Rethinking decision support systems: lessons learned from ecosystem 

management. Whitepaper. The Redlands Institute, University of Redlands, Redlands, 

California. 

Ekbia, H., and Reynolds, K. 2006. Decision support for sustainable forestry: enhancing the basic 

rational model. Pages 497-514 in A. Thompson and K.M. Reynolds (eds.), Forestry 

management: the past and the future. Springer Verlag. 

Feick, R., and B. Hall. 2004. A method for examining the spatial dimension of multi-criteria 

weight sensitivity. International Journal of Geographic Information Science 18:815-840. 

Keen, P.G.W., and M.S.S. Morton. 1978. Decision support systems: an organizational 

perspective. Addison-Wesley, Reading, Massachusetts. 

Malczewski J. 2006. GIS-based multicriteria decision analysis: a survey of the literature. 

International Journal of Geographical Information Science 20:249-268. 

Nicolson, C.R., A.M. Starfield, G.P. Kofinas, and J.A. Kruse. 2002. Ten heuristics for 

interdisciplinary modeling projects. Ecosystems 5:376-384. 

Saaty, T.L. 1992. Multi-criteria decision making - the analytic hierarchy process. RWS 

Publications, Pittsburgh, Pennsylvania. 

Simon, H.A. 1960. The new science of management decision (vol. 3). Harper, New York. 

Starfield, A.M. 1997. A pragmatic approach to modeling for wildlife management. Journal of 

Wildlife Management 61:261-270. 

Starfield, A.M., and A.L. Bleloch. 1991. Building models for conservation and wildlife 

management. Interaction Book Company, Edina, Minnesota. 

188
Appendices 

C-1. Threat Layers Used in the DTRO Decision Support System 

C-2. Threat-Mortality Interaction Model 

C-3. Relative Mortality Model 

C-4. Demographic Impact Model 

C-5. Recovery Action Effectiveness Model 

C-6. Post-action Risk Reduction Model 

C-7. Prioritized Recovery Actions by Recovery Unit 

189
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix C-1. Threat Layers Used in the DTRO Decision Support System 

This table lists the threat data sources used in the prototype decision support system. N/A 

indicates data not available, but the threat is listed as a placeholder. Dates were not available for 

some datasets. Incorporation of additional, new, or revised data will improve the decision 

support system model output. 

Threat Type Dataset Title Dataset Source Date 

Agriculture 

Land Use and Land Cover for the 

Southwest US, Agriculture USGS 1990 

Air Pollution DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Captive Releases Captive Release Zone Redlands Institute, Univ. Redlands 2007 

Collection DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Disease N/A 

Energy/Mineral 

Development MAS/MILS mineral location USGS 1998 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Locatable Minerals, AZ Strip, AZ BLM, Arizona Strip District Office 

Mineral Materials, AZ Strip, AZ BLM, Arizona Strip District Office 

Fluid Mineral Leasing (Oil and Gas), 

AZ Strip, AZ BLM, Arizona Strip District Office 

Nevada Mining Lease Potential BLM, Nevada State Office 

Nevada Mining Material Sites BLM, Nevada State Office 

NDOT Material Right-of-Way BLM, Nevada State Office 

Nevada Oil and Gas Lease, Ely Field 

Office BLM, Nevada State Office 

Nevada Oil and Gas Lease, Las Vegas 

Field Office BLM, Nevada State Office 

Fire Recovery Units Fire Risk Area Redlands Institute, Univ. Redlands 2007 

Free-Roaming 

Dogs Feral Dog Zone Redlands Institute, Univ. Redlands 2007 

DMG Free-roaming Dog Occurrences Desert Managers Group 

Grazing CA Grazing Allotments BLM 2007 

NV Grazing Allotments BLM, Nevada State Office 2005 

AZ Livestock Grazing Allotments BLM, Arizona Strip District Office 2007 

CA Herd Management Area BLM, Sacramento, CA 1999 

NV Herd Areas BLM, Nevada State Office 

AZ BLM wild horse and burro herd 

areas Arizona BLM Field Offices 2000 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Invasive Plants Weed Sentry 2004 infestation, Brassica Clark Co., NV 2004 

Weed Sentry 2005 infestation, Brassica Clark Co., NV 2005 

Brassica tournefortii locations, Lake 

Mead NRA NPS, Lake Mead NRA 2006 

Prob. Finding Brassica, 2005 LSD 

Survey Jill Heaton, UNR 2005 

Prob. Finding Brome, 2005 LSD Survey Jill Heaton, UNR 2005 

Prob. Finding Schismus, 2005 LSD 

Survey Jill Heaton, UNR 2005 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

190 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Military 

Operations SW US Military Bases 

US Army Corps of Engineers, 

Engineer Research & Development 

Center 2005 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Non-Motorized 

Recreation Mohave Non-Motorized Recreation Redlands Institute, Univ. Redlands 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Other Predators CA, AZ, NV, UT Other Predators Redlands Institute, Univ. Redlands 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Off-Road 

Vehicles DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Paved Roads Arizona Strip Transportation BLM, Arizona Strip District Office 2007 

Roads - Mojave Desert Mojave Desert Ecosystem Project 1998 

Railroads Railroads of the Southwest US USGS 1998 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Ravens Raven Nest Field Survey, 1990-97 Bill Boarman 1997 

Raven Nest Field Survey, 2004 Redlands Institute, Univ. Redlands 2004 

Raven Nest Field Survey, 2005 Redlands Institute, Univ. Redlands 2005 

NV Raven Locations Nevada Department of Wildlife 2003 

Clark Co. Raven Locations USDA-ADC 2005 

Clark Co. Raven Survey Clark County 

Estimated Number of Ravens, 2005 

LDS Survey Jill Heaton, UNR 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Supplemental 

Water Sources Water Development Sites, Guzzlers Nevada Department of Wildlife 2005 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Toxicant US Toxic Release Inventory EPA 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Unpaved Roads Arizona Strip Transportation BLM, Arizona Strip District Office 2007 

Roads - Mojave Desert Mojave Desert Ecosystem Project 1998 

BLM Routes BLM 2001 

Urbanization U.S. Census Urbanized Areas 

Department of Commerce, Census 

Bureau, Geography Division 2004 

20 Year Urban Growth, 2020 California Resources Agency 2000 

50 Year Urban Growth, 2050 California Resources Agency 2000 

Mojave Urban Growth 2020 Desert Research Institute 2000 

Clark Co. BLM Disposal Lands – Rural 

Comprehensive Planning, Clark Co., 

NV 2007 

Clark Co. BLM Disposal Lands 

Comprehensive Planning, Clark Co., 

NV 2004 

Nevada Disposal Lands BLM 2005 

Urban Land cover Areas in Clark 

County, NV 2001 Clark Co., NV 2001 

Urban Land cover Areas in Clark 

County, NV 2006 Clark Co., NV 2006 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Utility Corridors Southern California Utility Lines 

Environmental Systems Research 

Institute (ESRI) 1993 

SW Electrical - detailed lines US Department of Energy 

SW Electrical - main lines US Department of Energy 

US Natural Gas lines US Department of Energy 

191 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

US Natural Gas lines PennWell MAPSearch 

Energy Corridor - centerline US Department of Energy 

Energy Corridor - 1500ft buffer US Department of Energy 

Nevada Gas Lines BLM, Nevada State Office 

Nevada Power Lines BLM, Nevada State Office 

Nevada Utility Corridors BLM, Nevada State Office 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

Vandalism Redlands Institute, Univ. Redlands 2007 

Waste Disposal 

Landfills in the West Mojave Planning 

Area Redlands Institute, Univ. Redlands 2003 

AZ Landfills, Mohave Co., AZ 

Mohave County Public Works, 

Engineering Division 2005 

DMG Dump Database Desert Managers Group 

California Solid Waste Information 

System, 2007 

California Integrated Waste 

Management Board 2007 

Probability of Finding Trash, 2005 LDS 

Survey Jill Heaton, UNR 2005 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

DTRO Workshop User Input Data Redlands Institute, Univ. Redlands 2007 

192 
 

Appendix C-2. Threat-Mortality Interaction Model 

This model starts with the estimates from 35 respondents on the strength of linkage 

(“effect level”) between different land uses/threats/activities to other threats and mortality 

mechanisms on a scale of 0 (no link) to 4 (Very High link). The respondents represented a wide 

variety of habitat units and expertise. Their responses were averaged over all estimates provided 

for a particular linkage – so sometimes the average was over 30 estimated values, sometimes 

only two. 

From the threats interaction survey, we estimate for each threat: 

• The direct contributions (red in Figure C2-A below) to Mortality Mechanisms 

• The indirect contributions (blue in Figure C2-A below) to other threats 

Figure C2-A: Direct and indirect contributions of the threat Invasive Species to mortality. 

Indirect threats are threats that contribute to another direct threat. To get the contribution 

of that indirect link to the actual mortality mechanism, we multiply the percentage contribution 

of the indirect link by the contribution of the direct threat link to the Mortality Mechanism. For 

example, in Figure C2-A, the contribution of the indirect link of Invasive Plants to Decrease 

Native Plants on the mortality mechanism Nutritional Compromise is 13 percent x 13.84 percent 

= 1.8 percent. We repeat that calculation for all links, direct and indirect, and sum the resulting 

contributions, and we have an estimate for the overall contribution of each single threat to that 

mortality mechanism (Figure C2-B). 

193
 

Figure C2-B. Direct and indirect contributions of the threat Invasive Species to mortality. 

In Tabular form, the total contribution (direct and indirect) of the threat Invasive Plants to 

the mortality mechanism Nutritional Compromise, is calculated as follows: 

Start threat Intermediate threat Mortality Mechanism Overall Link Contribution 

Invasive 

Plants None - direct Nutritional Compromise 14.02% 

Invasive 

Plants Decrease Native Plants Nutritional Compromise 13% x 13.84% = 1.80% 

Invasive 

Plants 

Habitat Fragmentation/ 

Degradation Nutritional Compromise 9% x 12.39% = 1.11% 

Total (direct + indirect) Contribution of Invasive Plants to Nutritional Compromise 16.93% 

194
 

 

 

 

APPENDIX C-3. RELATIVE MORTALITY MODEL 

Table C3-A. Pairwise comparison of mortality mechanisms on a scale of 1 (low) to 9 (high). For 

example, habitat loss is estimated to contribute to desert tortoise mortality by a factor of 9 times that of 

drowning. 

habitat loss 8 : 1 burial burial 1 : 9 crushing 

6 : 1 crushing 1 : 6 burning 

6 : 1 burning 1 : 4 dehydration 

8 : 1 dehydration 1 : 3 starvation 

9 : 1 starvation 1 : 5 disease 

5 : 1 disease 1 : 1 drowning 

9 : 1 drowning 1 : 1 falling 

9 : 1 falling 1 : 2 predation - ravens 

8 : 1 predation - ravens 1 : 2 predation - dogs 

9 : 1 predation - dogs 1 : 3 predation - other 

8 : 1 predation - other 1 : 1 removals 

9 : 1 removals 2 : 1 shooting/vandalism 

9 : 1 shooting/vandalism 

crushing 4 : 1 burning burning 1 : 1 dehydration 

4 : 1 dehydration 2 : 1 starvation 

6 : 1 starvation 1 : 1 disease 

2 : 1 disease 6 : 1 drowning 

9 : 1 drowning 6 : 1 falling 

8 : 1 falling 5 : 1 predation - ravens 

6 : 1 predation - ravens 3 : 1 predation - dogs 

3 : 1 predation - dogs 3 : 1 predation - other 

7 : 1 predation - other 4 : 1 removals 

7 : 1 removals 6 : 1 shooting/vandalism 

8 : 1 shooting/vandalism 

dehydration 2 : 1 starvation starvation 1 : 2 disease 

2 : 1 disease 4 : 1 drowning 

5 : 1 drowning 2 : 1 falling 

5 : 1 falling 2 : 1 predation - ravens 

4 : 1 predation - ravens 2 : 1 predation - dogs 

3 : 1 predation - dogs 1 : 4 predation - other 

1 : 3 predation - other 2 : 1 removals 

3 : 1 removals 2 : 1 shooting/vandalism 

5 : 1 shooting/vandalism 

disease 6 : 1 drowning drowning 1 : 1 falling 

5 : 1 falling 1 : 4 predation - ravens 

2 : 1 predation - ravens 1 : 3 predation - dogs 

2 : 1 predation - dogs 1 : 4 predation - other 

1 : 2 predation - other 1 : 2 removals 

3 : 1 removals 1 : 1 shooting/vandalism 

5 : 1 shooting/vandalism 

195
 

 

 

Table C3-A. Continued. 

falling 1 : 3 predation - ravens predation - ravens 2 : 1 predation - dogs 

1 : 2 predation - dogs 1 : 2 predation - other 

1 : 5 predation - other 2 : 1 removals 

1 : 1 removals 2 : 1 shooting/vandalism 

1 : 1 shooting/vandalism 

predation - dogs 1 : 4 predation - other predation - other 6 : 1 removals 

1 : 1 removals 1 : 1 shooting/vandalism 

1 : 1 shooting/vandalism

removals 6 : 1 shooting/vandalism

Table C3-B. Estimated relative contribution of each mortality 

mechanism to overall mortality, calculated from Table C3-A using 

the principal eigenvalue method from the Analytic Hierarchy 

Process (Saaty 1992). 

Mortality Mechanism Percent Contribution 

Catastrophic Permanent Habitat Loss 32 % 

Inadvertent crushing/trampling 17 % 

Burning 9 % 

Predation - Other 8 % 

Dehydration 7 % 

Disease 7 % 

Nutritional Compromise 4 % 

Collection 4 % 

Predation - Ravens 3 % 

Predation - free-roaming dogs 3 % 

Vandalism 2 % 

Burial 2 % 

Falling 2 % 

Drowning 1 % 

196
 

Appendix C-4. Demographic Impact Model 

This model estimates the contribution of each single threat to overall desert tortoise 

mortality by multiplying 

the total contributions (direct and indirect) of each threat to individual mortality mechanisms 

from C-2, 

BY 

the relative contribution of each mortality mechanism to overall desert tortoise mortality (Table 

C3-B). 

We calculate this product for each mortality mechanism to which the threat contributes (directly 

and/or indirectly) and sum over them to get the overall contribution of that single threat to desert 

tortoise mortality. In the following Table we do that for the sample threat, Invasive Plants: 

Mortality 

Single threat Mechanism Overall Contribution to Mortality 

Invasive Plants Burning 9% x 20.61% = 1.86% 

Invasive Plants Nutritional 

Compromise 4% x 16.93% = 0.68% 

Invasive Plants Disease 7% x 19.06% X 9% = 0.02% 

Total Estimated Contribution of Invasive Plants to Desert Tortoise Mortality 2.56% 

Table C4-A lists the estimated Contributions to Overall Mortality for each threat/action 

that was included in the threats interaction survey. The numbers in Table C4-A are fed directly 

into the GIS system to calculate threat severity maps. 

197
Table C4-A. Contribution of threats to overall DT mortality. Note 

that this table is based on incomplete data and provisional 

underlying models. 

Contribution to 

Threat Overall Mortality 

Urbanization 14.1 % 

Paved Roads 14.1 % 

Construction Activities 12.3 % 

Energy/Mineral Development 8.0 % 

Unpaved Roads 7.0 % 

Recreation 7.0 % 

Off-Road Vehicles 6.6 % 

Transportation Networks 6.0 % 

Drought 5.9 % 

Military Operations 5.3 % 

Physical Structures 5.3 % 

Agriculture 4.7 % 

Other 4.2 % 

Supplemental Food Sources 4.0 % 

Supplemental Water Sources 4.0 % 

Utility Corridors/Networks 3.6 % 

Fire 2.9 % 

Invasive Plants 2.6 % 

Non-Motorized Recreation 2.3 % 

Grazing 2.2 % 

Major Waste Disposal (Landfills, etc.) 2.2 % 

Disease 2.2 % 

Habitat Fragmentation/Degradation 1.7 % 

Release Of Captives 1.4 % 

Railroads 1.4 % 

Nutritional Compromise 1.4 % 

Chemical Contaminants 1.1 % 

Ranching 1.1 % 

Research 0.9 % 

Decrease Native Plants 0.9 % 

Land Exchanges/Transfers 0.6 % 

Surface Dust 0.5 % 

Air Pollution 0.5 % 

Garbage/Trash 0.5 % 

Mine Shafts/Pits 0.0 % 

198
Appendix C-5. Recovery Action Effectiveness Model 

This model estimates the effectiveness on a scale of 1 (low) to 3 (high) of individual recovery actions in m

threats to desert tortoise populations. The scores are averaged from manager rankings provided at recovery plann

199 

RECOVERY ACTIONS/THREATS 

AGRICULTURE 

AIR POLLUTION

CAPTIVE RELEASES 

COLLECTION

DESIGNATED OHV 

AREAS 

DISEASE 

DROUGHT

DROWNING

ENERGY/MINERAL

DEVELOPMENT (Incl.

mine shafts/pits) 

FIRE

FREE-ROAMING

Close Roads 1 3 1.5 1 2.5 

Connect Functional Habitat 1 1 2 

Control Ravens Designate Roads 1 3 1.5 

1 

2.5 

Environmental Education 3 1 2.67 2.25 2.5 1.5 1 1.67 2.75 2.7Fence Roads 

1 

3 

1 

1 

Install Aqueduct Barrier 3 Install Railroad Barriers Install Urban/Other Barriers 3 1 1 3 Law Enforcement 1 1 3 3 3 2.67 1 1 1 2 2.3Manage Burros/Horses Manage Grazing 1 Manage Landfills 3 Remove Toxicants/Unexploded Ordnance Restore Habitat 3 3 2 2 2 2.33 Restrict Competitive/Organized Events 2

 1

 1 2 

Secure Habitat 2 2 2 2 Sign/Fence Boundaries 

3 

2 

1 

1 2 2 

Withdraw Mining 2 3 
 

200 

RECOVERY ACTIONS/THREATS NON-MOTORIZED

RECREATION

OTHER PREDATORS

(non-raven/dogs)

PAVED ROADS 

RAILROADS

RAVENS

SUPPLEMENTAL

WATER SOURCES 

TOXICANTS UNAUTHORIZED

OFF-ROAD VEHICLES US

E

UNPAVED ROADS 

URBANIZATION 

UTLITY CORRIDORS 

Close Roads 1.5 3 2 2 3 3 

Connect Functional Habitat 1 2 

Control Ravens 3 Designate Roads 1.5 3 2 

2 

3 3 

Environmental Education 2 3 2 2.5 3 2.5 3 Fence Roads 2 3 Install Aqueduct Barrier Install Railroad Barriers 3 Install Urban/Other Barriers 3 3 3 Law Enforcement 2 1 1 1 1.5 1 2 1 Manage Burros/Horses Manage Grazing Manage Landfills 3 3 3 Remove Toxicants/Unexploded Ordnance 3 Restore Habitat 3 1 3 3 3 Restrict Competitive/Organized Events 2 3 2 2 Secure Habitat 2 3 2 2.33 Sign/Fence Boundaries 3 1 3 Withdraw Mining 3 2 
20

1

Appendix C-6. Post-action Risk Reduction Model 

This model estimates the relative reduction in overall risk to desert tortoise populations within each recov

individual recovery actions. Values represent relative risk reduction calculations between recovery actions within (values are not comparable between recovery units). Recovery actions sorted in decreasing relative importance fo

are provided in Appendix C-7. 

Upper 

Virgin Northeastern Eastern Co

Action River Mojave Mojave DClose Roads 2.96 24.20 5.21 

Connect Functional Habitat 0.50 7.40 0.95 

Control Ravens 0.01 1.98 0.03 

Designate Roads 2.96 24.20 5.21 

Environmental Education 4.49 20.82 7.02 

Fence Roads 4.71 5.84 2.34 

Install Railroad Barriers 0.00 0.20 0.06 

Install Urban/Other Barriers 4.54 21.73 0.83 

Law Enforcement 5.48 16.95 4.18 

Manage Burros/Horses 0.01 0.63 0.13 

Manage Grazing 0.05 2.34 0.35 

Manage Landfills 0.18 7.11 0.62 

Remove Toxicants/Unexploded Ordnance 0.00 1.50 1.19 

Restore Habitat 1.25 18.71 5.44 

Restrict Competitive/Organized Events 1.91 10.11 2.56 

Secure Habitat 2.91 15.77 2.29 

Sign/Fence Boundaries 3.25 12.85 2.23 Withdraw Mining 0.20 4.02 1.98 
20

2

Upper Virgin River Law Enforcement Fence Roads Install Urban/Other Barriers Environmental Education Sign/Fence Boundaries Close Roads Designate Roads Secure Habitat Restrict Competitive/Organized Events Restore Habitat Connect Functional Habitat Withdraw Mining Manage Landfill Manage Grazing Control Ravens Install Railroad Barriers Remove Toxicants/Ordnance Manage Burros/HManage Burros/Horses Install Railroad Barriers 

Control Ravens Withdraw Mining Restrict Competitive/Organized Events 

Manage Grazing Connect Functional Habitat Secure Habitat 

Manage Landfill Restore Habitat Close Roads 

Remove Toxicants/Ordnance Designate Roads 

Install Urban/Other Barriers 

Sign/Fence Boundaries Fence Roads 

Environmental ELaw Enforcemen

Appendix C-7. Prioritized Recovery Actions by Recovery Unit 

The sections below sort the Post-action Risk Reduction Model (Appendix C-6) into prioritized lists of rec

each recovery unit. The pie charts illustrate the relative reduction in overall risk to desert tortoise populations witunit for each recovery action. 
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3

Northeastern Mojave Close Roads Designate Roads Install Urban/Other Barriers Environmental Education Restore Habitat Law Enforcement Secure Habitat Sign/Fence Boundaries Restrict Competitive/Organized Events Connect Functional Habitat Manage Landfill Fence Roads Withdraw Mining Manage Grazing Control Ravens Remove Toxicants/Ordnance Manage Burros/Horses Install Railroad Barriers 

Install Railroad Barriers Control Ravens Withdraw Mining Restrict Competitive/Organized Events Designate Roads 

Remove Toxicants/Ordnance Manage Grazing Connect Functional Habitat Secure Habitat Sign/Fence Boundaries 

Manage Burros/HManage Landfill Restore Habitat Close Roads Environmental E

Install Urban/Other Barriers Fence Roads Law Enforcemen
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Eastern Mojave Environmental Education Restore Habitat Close Roads Designate Roads Law Enforcement Restrict Competitive/Organized Events Fence Roads Secure Habitat Sign/Fence Boundaries Withdraw Mining Remove Toxicants/Ordnance Connect Functional Habitat Install Urban/Other Barriers Manage Landfill Manage Grazing Manage Burros/Horses Install Railroad Barriers 

Environmental Education Designate Roads Fence Roads Withdraw Mining 

Restore Habitat Law Enforcement Secure Habitat Remove Toxicants/Ordnance 

Close Roads Restrict CompSign/Fence BConnect Func

Control Ravens Install Urban/Other Barriers Manage Landfill Manage Graz

Manage Burros/Horses Install Railroad Barriers Control Rave
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5

Colorado Desert Environmental Education Restore Habitat Close Roads Designate Roads Law Enforcement Secure Habitat Restrict Competitive/Organized Events Withdraw Mining Sign/Fence Boundaries Install Urban/Other Barriers Fence Roads Connect Functional Habitat Manage Grazing Manage Landfill Remove Toxicants/Ordnance Manage Burros/Horses Control Ravens Install Railroad Barriers 

Environmental Education Restore Habitat Close Roads Designate Roads Law Enforcement Secure Habitat Restrict Competitive/Organized Events Withdraw Mining Sign/Fence BounInstall Urban/Other Barriers Fence Roads Connect FunctioManage Grazing Manage Landfill Remove ToxicanManage Burros/Horses Control Ravens Install Railroad B
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Western Mojave Environmental Education Close Roads Designate Roads Restore Habitat Law Enforcement Secure Habitat Fence Roads Withdraw Mining Restrict Competitive/Organized Events Sign/Fence Boundaries Install Urban/Other Barriers Connect Functional Habitat Remove Toxicants/Ordnance Manage Grazing Manage Landfill Control Ravens Manage Burros/Horses 

Environmental Education Restore Habitat Fence Roads Sign/Fence Boundaries 

Close Roads Law Enforcement Withdraw Mining Install Urban/Other Barriers 

Designate RoadSecure Habitat Restrict CompetConnect Functio

Install Railroad Barriers Remove Toxicants/Ordnance Manage Grazing Manage Landfill 

Control Ravens Manage Burros/Horses Install Railroad B
APPENDIX D 

RECOMMENDED SPECIFICATIONS FOR DESERT TORTOISE EXCLUSION 

FENCING (SEPTEMBER 2005) 

These specifications were developed to standardize fence materials and construction 

procedures to confine tortoises or exclude them from harmful situations, primarily roads and 

highways. Prior to commencing any field work, all field workers should comply with all 

stipulations and measures developed by the jurisdictional land manager and the U.S. Fish and 

Wildlife Service for conducting such activities in desert tortoise habitat, which will include, at a 

minimum, completing a desert tortoise education program. 

Fence Construction 

Materials 

Fences should be constructed with durable materials (i.e., 16 gauge or heavier) suitable to 

resist desert environments, alkaline and acidic soils, wind, and erosion. Fence material should 

consist of 1-inch horizontal by 2-inch vertical, galvanized welded wire, 36 inches in width. Other 

materials include: Hog rings, steel T-posts, and smooth or barbed livestock wire. Hog rings 

should be used to attach the fence material to existing strand fence. Steel T-posts (5 to 6-foot) are 

used for new fence construction. If fence is constructed within the range of bighorn sheep, 6-foot 

T-posts should be used (see New Fence Construction below). Standard smooth livestock wire 

fencing should be used for new fence construction, on which tortoise-proof fencing would be 

attached. 

Retrofitting Existing Livestock Fence 

Option 1 (see drawing). Fence material should be buried a minimum of 12 inches below 

the ground surface, leaving 22-24 inches above ground. A trench should be dug or a cut made 

with a blade on heavy equipment to allow 12 inches of fence to be buried below the natural level 

of the ground. The top end of the tortoise fence should be secured to the livestock wire with hog 

rings at 12 to 18-inch intervals. Distances between T-posts should not exceed 10 feet, unless the 

tortoise fence is being attached to an existing right-of-way fence that has larger interspaces 

between posts. The fence must be perpendicular to the ground surface, or slightly angled away 

from the road, towards the side encountered by tortoises. After the fence has been installed and 

secured to the top wire and T-posts, excavated soil will be replaced and compacted to minimize 

soil erosion. 

Option 2 (see drawing). In situations where burying the fence is not practical because of 

rocky or undigable substrate, the fence material should be bent at a 90Ε angle to produce a lower 

section approximately 14 inches wide which will be placed parallel to, and in direct contact with, 

the ground surface; the remaining 22-inch wide upper section should be placed vertically against 

the existing fence, perpendicular to the ground and attached to the existing fence with hog rings 

at 12 to18-inch intervals. The lower section in contact with the ground should be placed within 

the enclosure in the direction of potential tortoise encounters and level with the ground surface. 

Soil and cobble (approximately 2 to 4 inches in diameter; can use larger rocks where soil is 

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shallow) should be placed on top of the lower section of fence material on the ground covering it 

with up to 4 inches of material, leaving a minimum of 18 inches of open space between the 

cobble surface and the top of the tortoise-proof fence. Care should be taken to ensure that the 

fence material parallel to the ground surface is adequately covered and is flush with the ground 

surface. 

New Fence Construction 

Options 1 or 2 should be followed except in areas that require special construction and 

engineering such as wash-out sections (see below). T-posts should be driven approximately 24 

inches below the ground surface spaced approximately 10 feet apart. Livestock wire should be 

stretched between the T-posts, 18 to 24 inches above the ground to match the top edge of the 

fence material; desert tortoise-proof fencing should be attached to this wire with hog rings placed 

at 12 to 18-inch intervals. Smooth (barb-less) livestock wire should be used except where 

grazing occurs. 

If fence is constructed within the range of bighorn sheep, two smooth-strand wires are 

required at the top of the T-post, approximately 4 inches apart, to make the wire(s) more visible 

to sheep. A 20 to 24-inch gap must exist between the top of the fence material and the lowest 

smooth-strand wire at the top of the T-post. The lower of the top two smooth-strand wires must 

be at least 43 inches above the ground surface. 

(72-inch T-posts: 24 inches below ground + 18 inches of tortoise fence above ground + 

20 to 24-inch gap to lower top wire + 4 inches to upper top wire = 66 to 70 inches). 

Inspection of Desert Tortoise Barriers 

The risk level for a desert tortoise encountering a breach in the fence is greatest in the 

spring and fall, particularly around the time of precipitation including the period during which 

precipitation occurs and at least several days afterward. All desert tortoise fences and cattle 

guards should be inspected on a regular basis sufficient to maintain an effective barrier to 

tortoise movement. Inspections should be documented in writing and include any observations of 

entrapped animals; repairs needed including bent T-posts, leaning or non-perpendicular fencing, 

cuts, breaks, and gaps; cattle guards without escape paths for tortoises or needed maintenance; 

tortoises and tortoise burrows including carcasses; and recommendations for supplies and 

equipment needed to complete repairs and maintenance. 

All fence and cattle guard inventories should be inspected at least twice per year. 

However, during the first 2 to 3 years all inspections will be conducted quarterly at a minimum, 

to identify and document breaches, and problem areas such as wash-outs, vandalism, and cattle 

guards that fill-in with soil or gravel. GPS coordinates and mileages from existing highway 

markers should be recorded in order to pinpoint problem locations and build a database of 

problem locations that may require more frequent checking. Following 2 to 3 years of initial 

inspection, subsequent inspections should focus on known problem areas which will be inspected 

more frequently than twice per year. In addition to semi-annual inspections, problem areas prone 

to wash-outs should be inspected following precipitation that produces potentially fence208
 

damaging water flow. A database of problem areas will be established whereby checking fences 

in such areas can be done efficiently. 

Repair and Maintenance of Desert Tortoise Barriers 

Repairs of fence wash-outs: (1) realign the fence out of the wash if possible to avoid the 

problem area, or (2) re-construct tortoise-proof fencing using techniques that will ensure that an 

effective desert tortoise barrier is established that will not require frequent repairs and 

maintenance. 

Gaps and breaks will require either: (a) repairs to the existing fence in place, with similar 

diameter and composition of original material, (b) replacement of the damaged section to the 

nearest T-post, with new fence material that original fence standards, (c) burying fence, and/or 

(d) restoring zero ground clearance by filling in gaps or holes under the fence and replacing 

cobble over fence constructed under Option 2. Tortoise-proof fencing should be constructed and 

maintained at cattle guards to ensure that a desert tortoise barrier exists at all times. 

All fence damage should be repaired in a timely manner to ensure that tortoises do not 

travel through damaged sections. Similarly, cattle guards will be cleaned out of deposited 

material underneath them in a timely manner. In addition to periodic inspections, debris that 

accumulates along the fence should be removed. All cattle guards that serve as tortoise barriers 

should be installed and maintained to ensure that any tortoise that falls underneath has a path of 

escape without crossing the intended barrier. 

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U.S. Department of the Interior 

U.S. Fish & Wildlife Service 

Region 8, California and Nevada 

Ecological Services 

2800 Cottage Way, W-2606 

Sacramento, California 95825 

http://www.fws.gov 

May 2008