i

DISCLAIMER

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

recover and/or protect listed species. We, the U.S. Fish and Wildlife Service, 

publish recovery plans, sometimes preparing them with the assistance of recovery 

teams, contractors, State agencies, and others. Recovery teams serve as 

independent advisors to the U.S. Fish and Wildlife Service. Objectives of the 

recovery plan will be attained and 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 or the official 

positions or approval of any individuals or agencies involved in the recovery plan 

formulation other than our own. They represent our official position only after 

they have been signed by the Director, Regional Director, or Operations Manager 

as approved. Approved recovery plans are subject to modification as dictated by 

new findings, changes in species status, and the completion of recovery actions. 

Literature Citation Should Read As Follows: 

U.S. Fish and Wildlife Service. 2007. Recovery Plan for the Sierra Nevada 

Bighorn Sheep. Sacramento, California. xiv + 199 pages. 

An electronic version of this recovery plan also will be made available at 

http://www.fws.gov/cno/es/recoveryplans.html and 

http://endangered.fws.gov/recovery/index.html#plans.
ii

ACKNOWLEDGEMENTS 

This recovery plan was prepared by the Sierra Nevada Bighorn Sheep Recovery 

Team, with important contributions from Mr. Carl Benz, Dr. Vern Bleich, Dr. 

Walter Boyce, Ms. Paula Brown, Ms. Diana Craig, Dr. Ben Gonzales, Dr. David 

Graber, Mr. Troy Kelly, Dr. Howard Quigley, Dr. Peter Stine, Mr. Steve Torres, 

Dr. Tom Stephenson, Dr. Nancy East, Mr. Brian Croft, and Dr. John D. 

Wehausen. The recovery team benefited greatly from numerous discussions with 

Dr. Holly Ernest, Mr. Mike Lawrence, Ms. Kathy Noland, Mr. Christopher 

Papouchis, Ms. Wendy Philpot, Ms. Lynn Sadler, Mr. Steve Thompson, Mr. John 

Walter, Mr. Harold Werner, Dr. David S. Zezulak, Ms. Genny Wilson, Ms. Amy 

Baumer, Mr. Joe Echenique, and Ms. Marianne Lienassar. 
iii

SIERRA NEVADA BIGHORN SHEEP RECOVERY TEAM 

Stakeholder Team Members 

Brian Adkins, Bishop Paiute Tribe, Bishop, California 

Amy Baumer, Inyo National Forest, Bishop, California 

Katie Bellomo, People for Mono Basin Preservation, Lee Vining, California 

Bob Bissel, Society for the Conservation of Bighorn Sheep 

Paula Brown, Sierra Nevada Bighorn Sheep Foundation, Bishop, California 

Deirdre E. Flynn, California Wool Growers Association, Sacramento, California 

Joe Echenique, Echenique Livestock Company, Bakersfield, California 

Lesa Eldman, California Wool Growers Association 

Fred Fulstone, F.I.M. Livestock 

Gary Guenther, Wilderness Watch, Mammoth Lakes, California 

Debbie House, Los Angeles Department of Water and Power, Bishop, Califonria 

Mickey Jarvis, California Cattleman’s Association, Bishop, California 

Ron Keil, Inyo National Forest, U.S. forest Service, Bishop, California 

Brenda Lacey, California Woolgrowers Association, Bishop, California 

Mike Lawrence, Bridgeport Ranger District, U.S. Forest Service, Bridgeport, 

California 

Ray Lee, Foundation for North American Wild Sheep, Cody, Wyoming 

Craig London, Rock Creek Pack Station, Bishop, California 

Dan Lyster, Mono County Government, Mono County, California 

Owen Malloy, The Sierra Club – Range of Light Chapter, Mammoth Lakes, 

California 

Sally Miller, The Wilderness Society, Lee Vining, California 

George Millovich, Inyo-Mono Agricultural Commission 

Paul McFarland, Friends of the Inyo, Lee Vining, California 

Steve Nelson, Bureau of Land Management, Bishop, California 

Kathy Noland, Inyo National Forest, U.S. Forest Service, Bishop, California 

Chris Papouchis, Mountain Lion Foundation, Sacramento, California 

Cheryl Probert, Humboldt-Toiyabe National Forest 

Toni Richards, Bishop Paiute Tribe, Bishop, California 

Terri Russi, Bureau of Land Management, Bishop, California 

Lynn Sadler, Mountain Lion Foundation, Sacramento, California 

Steve Thompson, Yosemite National Park, National Park Service, California 

Brian Tillemans, Los Angeles Department of Water and Power, Bishop, 

California 

Todd Vogel, Sierra Mountaineering Center, Bishop, California 

John Walter, The Sierra Club – Range of Light Chapter, Mammoth Lakes, 

California 

Harold Werner, Sequoia-Kings Canyon National Parks, National Park Service, 

California 
iv

Science Team 

Mr. Carl Benz, U.S. Fish and Wildlife Service, Ventura, California 

Dr. Vern Bleich, California Department of Fish and Game, Bishop, California 

Dr. Walter Boyce, University of California, Davis, California 

Ms. Diane Craig, U.S. Forest Service, Pacific Southwest Region, Vallejo, 

California 

Dr. Nancy East, University of California, Davis, California 

Dr. David Graber, National Park Service, California 

Dr. Howard Quigley, Hornocker Wildlife Institute, Bozeman, Montana 

Dr. Peter Stine, Sierra Nevada Research Center, Sacramento, California 

Mr. Steve Torres, California Department of Fish and Game, Sacramento, 

California 

Dr. John D. Wehausen, University of California, White Mountain Research 

Station, Bishop, California 
v

EXECUTIVE SUMMARY 

Current Species Status: Sierra Nevada bighorn sheep (Ovis canadensis sierrae 

= O. c. californiana at the time of listing) were listed as an endangered species on 

January 3, 2000, following emergency listing on April 20, 1999. In 1995 the 

Sierra Nevada bighorn sheep hit a population low of about 100 individuals, 

distributed across 5 separate areas of the southern and central Sierra Nevada, 

before increasing to about 125 in 1999. Since 1999, conditions have been 

particularly favorable for population growth. Based on the most current 

information, the total population has grown to 325-350 individuals. 

Habitat Requirements and Limiting Factors: Sierra Nevada bighorn sheep use 

habitats ranging from the highest elevations along the crest of the Sierra Nevada 

(4,000+ meters [13,120+ feet]) to winter ranges at the eastern base of the range as 

low as 1,450 meters (4,760 feet). These habitats range from alpine to Great Basin 

sagebrush scrub. Primary elements of preferred habitats are visual openness and 

close proximity to steep rocky terrain used to escape from predators. Forage 

resources vary greatly across habitats used by Sierra Nevada bighorn sheep, and 

plant species eaten vary accordingly. Of particular importance to population 

parameters is the nutrient content of forage. Nutrient quality of diets varies 

greatly with season and elevation and is limited primarily by effects of 

temperature and soil moisture on plant growth and population density. Because 

of the relationship between elevation and temperature, low-elevation winter 

ranges provide an important source of high quality forage early in the growing 

season. 

Factors limiting Sierra Nevada bighorn sheep recovery include disease, predation, 

low population numbers and limited distribution, availability of open habitat, and 

potential further loss of genetic diversity due to small population sizes and 

inadequate migration between them. Since the vast majority of Sierra Nevada 

bighorn sheep habitat is publicly-owned land, loss of habitat has not been a 

limiting factor. However, management of bighorn sheep habitat (e.g., fire 

suppression) can result in habitat alterations and loss of key dispersal corridors 

connecting herds, which could be limiting factors. 

Recovery Objective: The recovery objective is to attain population sizes and 

geographic distribution of bighorn sheep in the Sierra Nevada that assure longterm viability of the overall population and thereby allow its delisting as an 

endangered species. 

Recovery Priority: The Sierra Nevada bighorn sheep has a recovery priority 

number of 3. Recovery priorities for listed species range from 1 to 18, with 1 

being the highest priority. The priority system uses the criteria of: (1) degree of 
vi

threat, (2) recovery potential, and (3) taxonomy (level of genetic distinctiveness). 

A fourth factor, conflict, is a supplementary element characterizing whether or not 

recovery actions are likely to be in conflict with construction or other 

development projects. A priority of 3 has been assigned to the Sierra Nevada 

bighorn sheep for the following reasons: (1) there is a high degree of threat 

because the population is small in size and its distribution is fragmented; (2) there 

is a high recovery potential; and (3) the listed entity, as described, is a distinct 

population (which receives the same rating level as a subspecies). 

Downlisting Criteria: Potential bighorn sheep habitat in the Sierra Nevada was 

divided into 16 herd units (Figure 1), and those herd units were grouped into four 

recovery units on the basis of natural breaks in habitat distribution. Of these 16 

herd units, 12 were identified as essential to recovery of the species because of 

habitat characteristics that make them the most likely areas where recovery will 

occur (Figure 4). Two criteria must be met for downlisting. 

Downlisting Criterion A1: A minimum of 50 yearling and adult females exist in 

the Kern Recovery Unit (Great Western Divide), 155 in the Southern Recovery 

Unit (Olancha Peak to Coyote Ridge), 50 in the Central Recovery Unit (Mount 

Tom to Laurel Mountain), and 50 in the Northern Recovery Unit (Mount Gibbs 

and Mount Warren), for a minimum total of 305 females. The number of females 

is the limiting factor in reproductive output because one male can produce 

offspring with several females. Consequently, we have not set a delisting 

criterion that considers the male population size within recovery units. However, 

Delisting Criterion B2 does address males in terms of their occupation of some 

herd units prior to delisting. 

Downlisting Criterion A2: The measures to prevent contact between domestic 

sheep/goats and bighorn sheep have been implemented and are successful. 

Delisting Criteria: Three delisting criteria were developed based on biological 

parameters, distribution of the herd units, and research on threats to the 

population. All three must be met for delisting. 

Delisting Criterion B1: The minimum number of females required for 

downlisting per recovery unit (Table 5) has been maintained as an average for one 

bighorn sheep generation (7 years) with no intervention (ie. population 

management, buffering populations through translocations, captive breeding, 

etc.). Herd status for delisting must entail at least three censuses, one at the 

beginning of the period (qualifying for downlisting), one at the end of the period, 

and one intermediate count for each herd unit. Maintaining this number of 

females over a generation should be sufficient to indicate that predation is 

managed and that the number of individuals within the population is large enough 
vii

to promote regular use of winter range. Sierra Nevada bighorn sheep need herd 

sizes to reach a certain threshold before they will utilize areas that predators may 

inhabit. This herd size provides for better herd vigilance against predation. 

Delisting Criterion B2: Bighorn sheep of both sexes are distributed such that at 

least two herd units are occupied in the Kern Recovery Unit, six in the Southern 

Recovery Unit, two in the Central Recovery Unit, and two in the Northern 

Recovery Unit, for a total of 12 herd units. Currently, seven of those herd units 

are occupied. Based on current information these herd units are most likely to 

include those essential herd units identified in Figure 4 and Table 4. 

Delisting Criterion B3: A population viability analysis projects that all recovery 

units are viable. Recovery tasks related to monitoring and research have been 

accomplished, allowing the severity of secondary threats (including recreational 

disturbance, competition, loss of genetic diversity, and habitat changes due to 

altered fire regimes) to be adequately assessed. These threats have either been 

ameliorated or have been determined not to pose a significant risk to the 

population. 

Delisting Criterion B4: Regulatory mechanisms and land management 

commitments have been established that provide for long-term protection of 

Sierra Nevada bighorn sheep and both their summer and winter habitat. 

Protection considered long-term can be provided through appropriate institutional 

practices and cooperative agreements between agencies, landowners, and 

conservation organizations. 

Actions Needed: 

The following actions are needed immediately: 

1. Protect existing herds through: 

a. maximization of population growth; 

b. predator management 

2. Augmenting small herds through translocations; larger numbers of 

individuals are more likely to make adequate use of winter range essential 

for achieving positive population growth because they are able to be more 

vigilant to the presence of potential predators. 

3. Preventing contact between Sierra Nevada bighorn sheep and domestic 

sheep or goats. 
viii

Future actions include: 

1. Reintroduce bighorn sheep to vacant herd units that are essential to 

recovery (Figure 4 and Table 4). 

2. Monitor genetic variation of all herd units; take action to maintain variation 

if necessary 

This recovery plan calls for development of a captive breeding contingency plan 

and separate implementation plans for: (1) bighorn sheep monitoring; (2) bighorn 

sheep translocation; (3) predator management; (4) genetic management; and (5) 

management of a disease outbreak. 

Recovery Costs: Cost estimates of all recovery (Part II) tasks except task 1.1 are 

made in the Implementation Schedule (p. 69), totaling $21,730,000 over 20 years. 

Additional costs to identify and acquire important habitat not in public ownership 

(Task 1.1) will be determined as parcels are identified and acquired. 

Date of Recovery: With optimal population growth rates, recovery criteria might 

be met to allow downlisting within 10 years (2017) and delisting within another 

10 years (2027). Under less than optimal scenarios, including unexpected 

catastrophes, one or more additional decades might be needed. 
ix

TABLE OF CONTENTS 

I. INTRODUCTION ........................................................................................................ 1 

A. BRIEF OVERVIEW............................................................................................... 1 

1. Listing of Bighorn Sheep in the Sierra Nevada ................................................ 1 

2. Origin, Morphology, and Taxonomy................................................................ 1 

B. ECOLOGY.............................................................................................................. 2 

1. Habitat............................................................................................................... 2 

2. Food Habits and Nutrition ................................................................................ 3 

3. Behavior............................................................................................................ 4 

4. Metapopulation structure .................................................................................. 6 

a. Inbreeding and Small Populations .............................................................. 6 

b. The Balance between Extinction and Colonization.................................... 7 

5. Population Dynamics........................................................................................ 7 

a. Reproduction............................................................................................... 7 

b. Mortality Factors......................................................................................... 8 

c. Population Regulation............................................................................... 10 

6. Interspecific Competition and Human Disturbance........................................ 11 

C. ABUNDANCE AND DISTRIBUTION ............................................................... 12 

1. Historical Distribution, Abundance, and Trends ............................................ 12

2. Recent Distribution, Abundance, and Trends..................................................15 

D. REASONS FOR LISTING................................................................................... 21 

1. The Present or Threatened Destruction, Modification, or Curtailment of its 

Habitat or Range ............................................................................................. 21 

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

Purposes .......................................................................................................... 21 

3. Disease or Predation ....................................................................................... 21 

4. The Inadequacy of Existing Regulatory Mechanisms .................................... 22 

5. Other Natural or Manmade Factors Affecting its Continued Existence......... 23 

E. Past and Current Management and Conservation Activities ................................ 24
x

1. Federal Agencies............................................................................................. 24 

a. U.S. Department of the Interior - Fish and Wildlife Service.................... 24 

b. U.S. Department of the Interior - National Park Service.......................... 26 

c. U.S. Department of Agriculture - Forest Service ..................................... 28 

2. State Agencies................................................................................................. 30 

II. RECOVERY............................................................................................................... 33 

A. Conservation Principles Used in Developing This Recovery Plan....................... 33

1. Population Dynamics...................................................................................... 33 

2. Genetic Considerations ................................................................................... 34 

3. Ecosystem Integrity ........................................................................................ 36 

B. Objectives ............................................................................................................. 37

1. Conservation Challenge and Goals................................................................. 37 

2. Recovery Criteria............................................................................................ 37 

a. Downlisting Criteria.................................................................................. 38 

b. Delisting Criteria....................................................................................... 44 

c. Recovery Units.......................................................................................... 45 

C. Recovery Strategy................................................................................................. 47

D. Narrative Outline of Recovery Actions ................................................................ 48

E. Recommended Strategy for Preventing Contact Between Domestic Sheep or 

Goats and Sierra Nevada Bighorn Sheep............................................................. .61

1. Background..................................................................................................... 61 

2. Strategy ........................................................................................................... 63 

3. Recommendations ...........................................................................................64 

III. IMPLEMENTATION SCHEDULE.......................................................................... 73 

IV. LITERATURE CITED.............................................................................................. 81

V. APPENDICES ............................................................................................................ 97

Appendix A Pack Llamas as Potential Sources of Diseases for Sierra Nevada 

Bighorn Sheep..................................................................................... 99 

Appendix B Sierra Nevada Bighorn Sheep and Domestic Livestock: Preliminary 

Risk Assessment of Disease Transmission in the Eastern Sierra ..... 105 
xi

Appendix C Translocation Considerations for Sierra Nevada Bighorn Sheep ..... 123

Appendix D Considerations for Developing a Monitoring Plan for Bighorn Sheep 

in the Sierra Nevada.......................................................................... 137 

Appendix E Considerations for a Predator Management Plan.............................. 153 

Appendix F Public Information and Outreach Plan.............................................. 157 

Appendix G Summary of Threats and Recommended Recovery Actions ............ 165 

Appendix H Genetic Management of Sierra Nevada Bighorn Sheep ................... 167 

Appendix I Captive Breeding Contingency Plan, Executive Summary .............. 183 

Appendix J Comments Received on the Draft Plan............................................. 187 

 
xii

TABLES 

Table 1 Causes of known bighorn sheep mortalities in the Sierra Nevada by 

population, 1975-2000 .....................................................................................10 

Table 2 Probable locations of historic bighorn sheep herds in the Sierra Nevada........14 

Table 3 Minimum numbers of Sierra Nevada bighorn sheep existing at the time of 

emergency endangered listing in spring 1999 .................................................20 

Table 4 Recovery units and herd units (essential and non-essential) used as the 

 basis of recovery goals.....................................................................................41 

Table 5 Minimum numbers of females and occupied herd units required for 

downlisting and delisting of Sierra Nevada bighorn sheep, by recover 

 units..................................................................................................................47 

Table 6 U.S. Forest Service and Bureau of Land Management sheep grazing 

allotments within 23 kilometers (14 miles) of Sierra Nevada bighorn sheep 

herd units..........................................................................................................62 

Table C-1 Potential sites for bighorn sheep wintering groups in the central and southern 

Sierra Nevada grouped by Recovery Unit .....................................................127 

Table H-1 Bottleneck test results based on variable microsatellite loci .........................180 

Table H-2 Expected heterozygosity ................................................................................181 

Table H-3 Modeled effects of moving sheep from the Wheeler Ridge herd to the Mount 

Langley herd ..................................................................................................181

FIGURES 

Figure 1 Essential and non-essential herd units within the four recovery units.............13 

Figure 2 Minimum summer population sizes for bighorn sheep in the Sierra Nevada, 

1977-2004. (A) Yearling and adult females. (B) All bighorn sheep ..............16 

Figure 3 Mountain lion depredation permits issued in Inyo and Mono Counties, 1972-

2004, and bighorn sheep winter range census results for the Mount Baxter 

essential herd unit ............................................................................................17 
xiii

Figure 4 Essential herd units within the four recovery units..........................................40 

Figure B-1 Sierra Nevada bighorn sheep ram movements in the Northern Recovery 

 Unit determined by radio telemetry as of 7 June 2006 ..................................116 

Figure B-2 Sierra Nevada bighorn sheep ram S20 locations and movements in the 

 Northern Recovery Unit determined by radio telemetry as of 

 7 June 2006 ....................................................................................................117 

Figure B-3 Sierra Nevada bighorn sheep ram movements in the Central Recovery 

 Unit determined by radio telemetry as of 7 June 2006 ..................................118 

Figure B-4 Sierra Nevada bighorn sheep ram movement between the Northern and 

 Central Recovery Units determined by radio telemetry as of 

 7 June 2006 ...................................................................................................119 

Figure B-5 Domestic sheep grazing allotments and their proximity to Sierra Nevada 

 bighorn sheep locations as of 7 June 2006.....................................................120 

Figure B-6 Domestic sheep grazing allotments and their proximity to Sierra Nevada 

 bighorn sheep locations in the Northern Recovery Unit as of 

 7 June 2006 ....................................................................................................121 
xiv
1

I. INTRODUCTION 

A. BRIEF OVERVIEW 

1. LISTING OF BIGHORN SHEEP IN THE SIERRA NEVADA 

In 1878, State legislation provided temporary protection from hunting for all 

bighorn sheep (Ovis canadensis) in California. In 1883, that protection became 

permanent, a status that remains for bighorn sheep in the Sierra Nevada (Wehausen et al.

1987). In 1972, the California subspecies (O. c. californiana), as defined by Cowan 

(1940) and including surviving native herds in the Sierra Nevada, was listed as rare under 

the 1970 California Endangered Species Act (California Department of Fish and Game 

1974); that category was changed to threatened in 1984. In 1999, the California Fish and 

Game Commission upgraded the status of the Sierra Nevada bighorn sheep to 

endangered. On April 20, 1999, we (the U.S. Fish and Wildlife Service) granted 

emergency endangered status to bighorn sheep inhabiting the central and southern Sierra 

Nevada of California as a distinct population segment (DPS) and, simultaneously, 

published a proposed rule to list the species as endangered (U.S. Fish and Wildlife 

Service 1999a, 1999b). The final rule granting endangered status to that population 

segment was published on January 3, 2000 (U.S. Fish and Wildlife Service 2000). 

2. ORIGIN, MORPHOLOGY, AND TAXONOMY 

Wild sheep crossed the Bering land bridge from Siberia during the Pleistocene 

and subsequently spread through western North America as far south as Baja California 

and northern mainland Mexico (Cowan 1940). Divergence from their closest Asian 

relative (Siberian snow sheep; Ovis nivicola) occurred about 600,000 years ago (Ramey 

1993). In North America, wild sheep have diverged into two extant species – thinhorn 

sheep (Ovis dalli), which occupy Alaska and northwestern Canada, and bighorn sheep 

(Ovis canadensis), which range from southern Canada to Mexico. The seven subspecies 

of bighorn sheep proposed by Cowan (1940) have come under recent taxonomic scrutiny. 

New genetic (Ramey 1993, 1995; Boyce et al. 1997, Gutierrez-Espeleta et al. 1998) and 

morphological data (Wehausen and Ramey 1993, 2000), in addition to the reanalysis of 

Cowan’s original data (Ramey 1993), do not support Cowan’s original subspecies 

distinctions. 

Lack of support for the traditional taxonomy includes the classification of bighorn 

sheep from the Sierra Nevada. Based on only four immature specimens collected in the 

Sierra Nevada, Grinnell (1912) designated Sierra Nevada bighorn sheep a distinct 

subspecies (Ovis cervina sierrae). Cowan (1940) failed to find support for Grinnell's 

Sierra Nevada subspecies. He included sheep from the Sierra Nevada instead under the 

California bighorn (O. canadensis californiana) subspecies, the distribution of which 

extended north to British Columbia between the Cascade and Rocky Mountains and 
2

extended south to the southern Sierra Nevada. Cowan (1940) considered bighorn sheep 

immediately east of the southern Sierra Nevada to belong to a different subspecies (O. c. 

nelsoni); he noted, however, that he could not statistically distinguish bighorn sheep in 

the Sierra Nevada from those to the east or to the north and suggested that they 

represented intergrades (Wehausen 1991a). Nevertheless, they were classified as 

California bighorn sheep for over half a century (Shackleton 1985) and have received 

State rare, threatened and, eventually, endangered status under the California Endangered 

Species Act as this taxon since 1972. 

In contrast to Cowan=s (1940) classification, recent genetic research based on 

analysis of the mitochondrial DNA control region has found bighorn sheep from the 

Sierra Nevada are allied more with those occupying the adjacent desert region than with 

populations to the north (Ramey 1993, 1995). However, Sierra Nevada bighorn sheep 

were found to be the only distinctive group in the desert region, which extends east to 

Utah and New Mexico and south to northern Mexico (Ramey 1993, 1995). Sequence 

data for a 515 base pair section of the mtDNA control region revealed a unique haplotype 

(sets of closely linked alleles, or genes, inherited as units) in all bighorn sheep in the 

Sierra Nevada (Wehausen, unpubl. data). Additionally, the sequence of the Sierra 

Nevada haplotype is as different from the many haplotypes of desert bighorn sheep as are 

those of Rocky Mountain bighorn. In that unique Sierra Nevada clade are also three 

related haplotypes found mixed with desert bighorn haplotypes in populations to the 

immediate east of the southern Sierra Nevada (Wehausen, unpubl. data). Recent 

morphometric analyses of skull shape (Wehausen and Ramey 2000) corroborate genetic 

results; bighorn sheep from the Sierra Nevada are distinguishable from those immediately 

to the east and north. On the basis of concurrence between genetic and morphometric 

data, Wehausen and Ramey (2000) reassigned populations of California bighorn outside 

of the Sierra Nevada to other subspecies, leaving bighorn sheep in the Sierra Nevada as 

their own subspecies. By the rules of zoological nomenclature, they again assume 

Grinnell=s (1912) subspecies name sierrae (Wehausen et al. 2005). With that 

nomenclature change, the California bighorn subspecies was terminated. Concurrent 

with the proposed designation of critical habitat for Sierra Nevada bighorn, on July 25, 

2007, the U.S. Fish and Wildlife Service formally proposed a taxonomic revision to 

amend the final listing rule from DPS to subspecies, Ovis canadensis sierrae. 

B. ECOLOGY 

1. HABITAT 

Survival of bighorn sheep in their habitat requires two characteristics. The first is 

agility on precipitous rocky slopes, which is their primary means of evading predators. 

The second is keen eyesight, which is their primary means of detecting predators. Short 

legs and a stocky build allow agility on rocks but preclude the fleetness, in less rocky 

terrain, that is necessary to outrun coursing predators that will pursue their prey at full 
3

speed rather than employ ambush tactics. Consequently, bighorn sheep select open 

habitats that allow detection of predators at sufficient distances to allow adequate leadtime to reach the safety of precipitous terrain. Optimal bighorn sheep habitat is visually 

open and contains steep, generally rocky, slopes. Sierra Nevada bighorn sheep avoid 

forests and thick brush, but will use open woodland habitats on rocky slopes. Fire can 

play an important role in creating or improving bighorn sheep habitat in some ecosystems 

by increasing the visibility of predators. Large expanses lacking precipitous escape 

terrain, such as the Owens Valley, can be substantial barriers to movement. Even within 

mountain ranges like the Sierra Nevada, bighorn sheep habitat is patchy and the 

population structure is naturally fragmented (Bleich et al. 1990a). 

Bighorn sheep in the Sierra Nevada utilize a wide range of elevations, from alpine 

peaks in excess of 4,000 meters (13,120 feet) to the base of the eastern escarpment as low 

as 1,450 meters (4,760 feet) (Wehausen 1980). Within this elevational range there is a 

wide variety of vegetation communities, including (from lowest to highest): (1) Great 

Basin sagebrush-bitterbrush-bunchgrass scrub; (2) pinyon-juniper woodland and 

mountain mahogany scrub; (3) mid-elevation and subalpine forests, woodlands, and 

meadows; and (4) alpine meadows and other alpine habitats varying from cliffs to 

plateaus. Because of the overall aridity of this region, meadow habitats are patchy in 

distribution and occur only where the water table is high due to factors like snow 

accumulation. The Great Basin scrub and alpine communities offer the most desirable 

habitats for bighorn sheep in terms of visual openness. However, because of the aridity 

of the eastern slope of the Sierra Nevada, many of the mid-elevation vegetation 

communities have some locations near precipitous rocks with sufficiently sparse plant 

cover to allow use by bighorn sheep (Wehausen 1980). Because of their extreme visual 

openness and steep rocky nature, alpine environments in the Sierra Nevada provide large 

expanses of habitat broken only by canyons containing forests and willow stands, which 

bighorn sheep may avoid. In contrast, low elevation winter habitat has been limited to 

small areas where topographic and visual features are suitable (Riegelhuth 1965; 

McCullough and Schneegas 1966; Wehausen 1979, 1980). High elevation habitat in the 

Sierra Nevada has been noted for its aridity relative to other alpine habitats because 

precipitation is scant and unpredictable during the summer season when temperatures 

permit plant growth (Major and Bamberg 1967). As a result, the vegetation depends 

substantially on snowmelt for moisture. Snow and resulting soil moisture show great 

spatial variation (Major 1977). Vegetation patterns vary concomitantly with moisture, 

ranging from meadow patches to areas almost devoid of plants (Major and Taylor 1977). 

2. FOOD HABITS AND NUTRITION 

Bighorn sheep are ungulates (hooved, typically herbivorous, quadraped mammal) 

that possess a large rumen and reticulum (compartments of the stomach of a mammal that 

chews the cud) relative to body weight (Krausman et al. 1993), which permits flexibility 

in plants consumed and, notably, allows the digestion of graminoids (grasses, sedges, and 
4

rushes) in all phenological stages (Hanley 1982). This flexibility in food consumption, in 

turn, allows flexibility in feeding habitats utilized. Wehausen (1980) and Moore (1991) 

provided detailed information on the species composition of diets of bighorn sheep on 

different seasonal ranges in the Sierra Nevada. Those authors found great variation in 

diets, from those dominated by graminoids to diets dominated by non-graminoid species. 

Wehausen (1980) provided nutritional data on plant species in different phenological 

stages and noted that bighorn sheep altered their diets based on what provided the best 

nutrition at the time. Wehausen (1980, 1992a), Wehausen and Hansen (1988), and 

Moore (1991) provided curves of fecal crude protein, which indexes digestibility of the 

forage consumed and, thus, general diet quality (Wehausen 1995). Analyses of fecal 

nitrogen patterns over 14 years for one wintering area indicated that timing of the first 

soaking winter storm (2.5 centimeters or about an inch of precipitation) that initiated 

plant growth most affected winter-spring diet quality for bighorn sheep utilizing low 

elevation winter ranges. Earlier initiation of plant growth resulted in improved diet 

quality later in the growing season. In addition, warmer winter temperatures aided plant 

growth and thereby improved diet quality (Wehausen 1992a). The amount of snowfall 

from the previous winter appeared to positively influence diet quality on summer ranges, 

presumably through the influence of summer snow pack on soil moisture for alpine plants 

(Wehausen 1980); overall, summer diet quality was higher following a winter with heavy 

snowfall. 

Phosphorus may be somewhat lacking in the diets of bighorn sheep in the Sierra 

Nevada. Klickoff (1965) found alpine soils in the region of Yosemite National Park 

consistently deficient in this mineral, which may reflect leaching of soils by snowmelt 

(Major and Bamberg 1967). Wehausen (1983a) found notably lower levels of 

phosphorus relative to crude protein (a covariate correcting for phenological stage) for 

alpine graminoids in the central and southern Sierra Nevada when compared to the 

nearby White Mountains. Wehausen (1980) found bighorn sheep in the Sierra Nevada 

consistently selected alpine plants of higher phosphorus content, sometimes at the cost of 

higher protein levels. It is not known if lower phosphorus levels in the Sierra Nevada 

have population-level effects on bighorn sheep there. 

3. BEHAVIOR 

Bighorn sheep exhibit a variety of behavioral adaptations to avoid predation. One 

such adaptation is group living (Hamilton 1971, Alexander 1974); groups provide more 

eyes and ears, allowing members to spend less time surveying for predators and more 

time feeding. Studies of this phenomenon have shown that increased in-group size up to 

six (or more) bighorn sheep confers an advantage in the proportion of time allocated to 

feeding (Berger 1978, Risenhoover and Bailey 1985). The selfish herd concept of 

Hamilton (1971) suggests that yet greater group sizes may confer further behavioral 

comfort. Such comfort may be an important factor enabling bighorn sheep to utilize 
5

habitats with greater risks of predation, notably low elevation winter ranges in the Sierra 

Nevada. 

 

Bighorn sheep are primarily diurnal (active during the daylight hours) (Krausman 

et al. 1985). Coupled with their strong reliance on keen eyesight to detect predators, 

diurnal behavior minimizes predation risks. Nights generally are spent on rocky slopes, 

but bighorn sheep may venture a short distance away from rocky escape terrain to feed 

during daylight. How far they venture from safer habitat varies and is apparently 

influenced by visual openness (both habitat and weather influences), wind, gender, 

season (e.g., whether vulnerable young are present), and abundance of predators. 

Bighorn sheep commonly exhibit seasonal changes in habitat use that reflect 

various resource needs. Surface water, although important in many desert ranges, is 

rarely utilized by bighorn sheep in the Sierra Nevada. Instead, bighorn sheep in the 

Sierra Nevada obtain needed moisture from forage or occasional consumption of snow. 

Because of relationships between elevation and temperature (Major 1977) and the 

influences of those variables on plant growth (Wehausen 1980), altitudinal migration in 

high mountain ranges like the Sierra Nevada allows bighorn sheep to maximize nutrient 

intake (Hebert 1973, Wehausen and Hansen 1988, Wehausen 1996). In past years, 

bighorn sheep in the Sierra Nevada used low elevation ranges extensively in winter and 

early spring, alpine ranges in summer and fall, and some intermediate ranges during 

transition periods (Wehausen 1980). These seasonal migration patterns changed during 

the second half of the 1980s, when Sierra Nevada bighorn sheep stopped using the lowelevation winter range (Wehausen 1996) (see also section I.C.2 for additional discussion). 

Male and female bighorn sheep commonly live in separate groups during much of 

the year, and often occupy different habitats (Geist and Petocz 1977, Wehausen 1980, 

Bleich et al. 1997). In the Sierra Nevada, both sexes may share common winter ranges, 

but they show progressive segregation from winter to spring (Wehausen 1980). During 

summer, the two sexes utilize different habitats, with females restricted largely to alpine 

environments along the crest and males often at somewhat lower elevations in subalpine 

habitats west of the crest (Wehausen 1980). Males again join females during the 

breeding season in late fall. 

Bighorn sheep have developed conservative philopatric behaviors (reluctance to 

disperse from their home range) that make them slow to colonize unoccupied habitat 

(Geist 1967, 1971). These behaviors are likely an adaptation to the naturally fragmented 

habitats that bighorn sheep commonly occupy. 
6

4. METAPOPULATION STRUCTURE 

a. Inbreeding and Small Populations 

The naturally fragmented distribution of bighorn sheep has led to the application 

of a broad landscape approach to their population ecology. This approach groups 

geographically distinct herds into metapopulations, which are networks of interacting 

herds (Schwartz et al. 1986, Bleich et al. 1990a, 1996, Torres et al. 1996). Thus, this 

approach considers long-term viability not of individual herds, per se, but rather of entire 

metapopulations; consequently, both genetic and demographic factors are considered. 

Increasing coefficients of inbreeding (mating among relatives) and genetic drift (random 

changes in gene frequencies) accompany decreasing population sizes and, over time, can 

lead to decreasing levels of heterozygosity (a measure of genetic diversity) that may have 

negative demographic effects through inbreeding depression (reduction in fitness due to 

mating among relatives) (Soulé 1980) and loss of adaptability. At some level, inbreeding 

and associated low genetic variation are likely to be a conservation problem for bighorn 

sheep, but that level is not known and will be influenced by their general history of 

inbreeding and other factors that challenge them. It has been suggested that lamb 

survival and horn growth in bighorn sheep are influenced by inbreeding (Sausman 1982, 

Stewart and Butts 1982, Fitzsimmons et al. 1995). Moreover, there is growing evidence 

that disease resistance is related to levels of heterozygosity (Carrington et al. 1999, 

Coltman et al. 1999). 

A small amount of genetic exchange among herds via movements by males can 

counteract inbreeding and associated increases in homozygosity (having two identical 

forms of a gene) that might otherwise develop within small, isolated populations 

(Schwartz et al. 1986). Males have a much greater tendency than females to explore new 

ranges, which they may do in search of other females with which to breed (Bleich et al. 

1996). If geographic distances between groups of females within metapopulations are 

not great, gene migration via males occurs readily (Epps et al. 2005). In the absence of 

such a metapopulation structure, populations will be isolated and may benefit from 

genetic enrichment via induced migration by individuals translocated between herds 

(Epps et al. 2006). 

Substructuring also can occur within what are often designated as single herds of 

bighorn sheep (Geist 1971, Holl and Bleich 1983, Festa-Bianchet 1986, Wehausen 

1992a, Jaeger 1994, Andrew et al. 1997, Rubin et al. 1998). Such substructuring is 

defined by separate home range patterns. Although more evident in females, it can occur 

in both sexes. Because separate female groups often reflect matrilines (maternal lines) 

(Festa-Bianchet 1986), differences in (maternally inherited) mitochondrial DNA profiles 

between them may be detectable (Bleich et al. 1996, Boyce et al. 1999). Population 

substructuring has been recognized in Sierra Nevada bighorn sheep (Wehausen 1979) and 

was incorporated in a previous conservation plan for these bighorn sheep (Sierra Nevada 
7

Bighorn Interagency Advisory Group 1984). Bleich et al. (1996) suggested that separate 

female groups are the fundamental building blocks of bighorn sheep metapopulations. 

b. The Balance between Extinction and Colonization 

The other important long-term process in metapopulation dynamics is the balance 

between rates of natural extinction and colonization among constituent populations. 

Colonization rates must exceed extinction rates for a metapopulation to persist (Hanski 

1991). This balance has not occurred for Sierra Nevada bighorn sheep since about 1850 

due to the high rate of local extinctions, resulting in an increasingly fragmented 

distribution. In addition to fragmentation resulting from past extinctions, the 

reintroduction program during 1979-88 (Bleich et al. 1996) and the more recent collapse 

of all herds together resulted in small, isolated groups of bighorn sheep. These small 

groups showed a greater propensity to winter at high elevations, resulting in greater 

vulnerability to extirpation due to small population size and difficulty surviving severe 

winter climates. 

5. POPULATION DYNAMICS 

Populations change in size over time through gains and losses of individuals from 

reproduction, immigration, mortality, and emigration. Immigration and emigration are 

sufficiently infrequent events in bighorn sheep (Geist 1971) that they can be largely 

ignored. Thus, this section addresses reproduction, mortality, and population regulation 

through density-dependent feedback loops. Generally, variation in recruitment (surviving 

young), rather than adult survivorship (survival), drives the dynamics of wild ungulate 

populations (Gaillard et al. 1998, 2000). However, bighorn sheep can incur all-age dieoffs from occasional disease epizootics (epidemic disease in animals) or other events that 

radically affect population dynamics due to significant effects on adult survivorship. 

Changes in adult survivorship have notably greater effects on population dynamics than 

variation in recruitment (Gaillard et al 2000). 

a. Reproduction 

Bighorn sheep generally give birth to single young, but there is a low incidence of 

twins (Buechner 1960). Bighorn sheep occupying many desert mountain ranges have 

protracted lambing seasons covering many months, while those living under colder 

winter temperature regimes give birth during short periods in late spring and early 

summer (Thompson and Turner 1982, Bunnell 1982, Rubin et al. 2000, Wehausen 2005). 

Bighorn sheep in the Sierra Nevada fit this latter pattern (Wehausen 1980). The birthing 

season there can begin as early as the second half of April, and end as late as early July 

(Wehausen 1991a), with most births occurring in May and June (Wehausen 1996). 

Occasional later-born lambs have been seen. Timing of births correlates with the 

nutritional regime of females; later birthing appears to be a consequence of lower annual 
8

nutrient intake (Wehausen 1996). The gestation period for bighorn sheep is 

approximately 174 days (Shackleton et al. 1984, Hass 1995). The breeding (rutting) 

season in the Sierra Nevada, therefore, occurs during late fall and early winter (mostly 

November and December), when bighorn sheep are usually still at high elevations. 

Nutrient intake can also influence birth rates (Wehausen 1984), including the 

frequency with which adult females produce young and the age at which young females 

first bear offspring. Two years of age is the youngest that females in the Sierra Nevada 

are known to give birth, and age at first lambing may be as high as 4 years under poor 

nutritional circumstances, as has been recorded for Dall’s sheep (Ovis dalli; Bunnell and 

Olson 1981). Measuring the actual proportion of females producing young is difficult 

because of possible unrecorded losses soon after birth. The upper range of summer ratios 

of lambs to females recorded shortly after the birthing season in the Sierra Nevada has 

been 75-83:100 (Wehausen 1980, Chow 1991), while the lowest reported value was 

30:100 (Wehausen 1980). 

Survivorship of lambs to yearling age also can vary with environmental and 

nutritional factors. For the Mount Baxter and Sawmill Canyon herds in the Sierra 

Nevada during 1965-79, 73 percent of the variation in winter lamb:female ratios was 

explained by variation in precipitation 8 to 12 months prior to conception (Wehausen 

1980). That model suggested that variation in the production of young, rather than 

offspring survival, was the primary variable affecting winter recruitment ratios during 

that period. However, with decreasing use of winter ranges during the 1980s, lamb 

survival declined considerably in that population (Wehausen 1996). Thus, lamb survival 

may be sensitive to habitat use patterns and associated environmental factors. 

b. Mortality Factors 

1. Diseases and Parasitism 

Numerous diseases of bighorn sheep have been documented (Bunch et al. 1999), 

of which pneumonia and psoroptic scabies have had the greatest population-level effects. 

Bighorn sheep show a high susceptibility to pneumonia, usually caused by bacteria of the 

genus Pasteurella (some species now called Mannheimia; Post 1971). Pneumonia caused 

by Pasteurella alone, or in combination with other pathogens, is the most significant 

disease threat for bighorn sheep (Bunch et al. 1999). Lungworms of the genus 

Protostrongylus can be important contributors to pneumonia and mortality in bighorn 

sheep in the Rocky Mountains (Forrester 1971, Woodard et al. 1974), and methods have 

been developed to control these nematode parasites in some wild populations (Schmidt et 

al. 1979). Bighorn sheep in the Sierra Nevada carry Protostrongylus lungworms, but 

parasite loads have been too low to be considered a management concern (Wehausen 

1979, 1980). 
9

Many early die-offs of bighorn sheep, including some in the Sierra Nevada, were 

attributed to scabies thought to have been contracted from domestic sheep (Jones 1950, 

Buechner 1960). Over the past 20 years, this disease has been a significant mortality 

factor among bighorn sheep in the San Andres Mountains of New Mexico (Lange et al. 

1980, Hoban 1990, Rominger and Weisenberger 2000). Scabies also has been found 

recently in bighorn sheep in California, east of the Sierra Nevada (Clark et al. 1988). 

However, in a large sampling of bighorn sheep in the Sierra Nevada during 1979-88, no 

clinical evidence of scabies was noted. Similarly, serum samples from those sheep 

showed no evidence of exposure to Psoroptes (Mazet et al. 1992). 

Other infectious diseases may be of concern for bighorn sheep in selected 

instances. Bluetongue virus was responsible for die-offs of bighorn sheep in the Lava 

Beds enclosure in California (Blaisdell 1975) and at the Red Rock facility in New 

Mexico (Singer et al. 1998). For the Red Rock facility, a comparative study of 

bluetongue exposure in adjacent cattle indicated that those bovids likely were not the 

source of infection (Singer et al. 1998). Similarly, Singer et al. (1997) found that neither 

deer nor cattle caused the Lava Beds die-off. Bluetongue is known to be present east of 

the southern Sierra Nevada in the Owens Valley, but the midges that transmit it do not 

occur at the elevations occupied by bighorn sheep during the summer when transmission 

would typically occur. 

The importance of these diseases and their role in the listing and management of 

Sierra Nevada bighorn sheep is discussed further in section I.D.3 and appendix B. 

2. Predation and Other Mortality Factors 

Bighorn sheep die from a variety of causes other than disease, including predation 

and accidents. Of particular interest relative to the conservation of endangered 

populations are factors that remove animals at younger ages when considerable 

reproductive potential remains. 

Various predators kill wild sheep in North America, including wolves, mountain 

lions, coyotes, bears, bobcats, wolverines, and eagles (Kelly 1980, Berger 1991, Nichols 

and Bunnell 1999, Bleich 1999). Wolves are not known to have occurred in the central 

and southern Sierra Nevada in the original range of bighorn sheep (Young and Goldman 

1944). In the Sierra Nevada, mountain lions have been the primary predator of bighorn 

sheep, accounting for 96 percent of losses attributed to predation (Table 1). Of 147 

bighorn sheep deaths recorded in the Sierra Nevada from 1975 to 2000, a minimum of 

54.5 percent could be attributed to predation; the actual percentage could be considerably 
10

Table 1. Causes of known bighorn sheep mortalities in the Sierra Nevada by population, 

1975-2000. Sources include Andaloro and Ramey (1981), Chow et al. (1993), Wehausen 

(1996) and many unpublished records. Data include radio collared individuals and remains 

of uncollared individuals encountered during field surveys. Baxter includes the Mount 

Baxter and Sawmill Canyon herd units, and Mono Basin includes the Mount Warren and 

Mount Gibbs herd units. 

Predation 

Herd 

Lion Coyote Bobcat 

Avalanche/ 

Accidents 

Post 

Release 

Exposure

Highway 

Collision 

Not 

Known 

Langley 7 4 

Williamson 5 2 

Baxter 50 1 27 

Wheeler 3 15 2 

Mono Basin 12 2 1 3 5 1 7 

Totals 77 2 1 19 5 1 42 

Percent 52.4 1.4 0.7 12.9 3.4 0.7 28.6 

higher due to numerous mortalities for which no definitive cause could be assigned 

(Table 1). 

During the 1990s, bighorn sheep in the Sierra Nevada incurred major winter 

losses while remaining at high elevations during the winter, a change in habitat selection 

that Wehausen (1996) suggested was a response to increased mountain lion predation on 

winter ranges. Those losses were a key factor that put these sheep in danger of 

extinction. The development of winter range avoidance and the demographic 

consequences of that behavioral change are discussed in detail in I.C.2. 

c. Population Regulation 

No population increases indefinitely. Various factors can limit population 

growth, depending on the species and its ecological niche. Large herbivores frequently 

exhibit S-shaped population growth curves, in which the rate of increase declines with 

increasing population size (Caughley and Sinclair 1994). This occurs primarily because 

of declining reproductive success associated with increasing population density 

(McCullough 1979). 

Recent strong population increases for bighorn sheep herds in the Sierra Nevada, 

beginning in the late 1990s, have provided opportunities to investigate such density-
11

dependent relationships. We have consistently high quality demographic data for the 

Wheeler Ridge and Mount Langley herd units, and both have exhibited strong densitydependent relationships for ratios of lambs to adult females. The most graphic of these 

occurred for the Mount Langley herd, where a 3-fold increase from 11 to 33 females over 

6 years produced a nearly linear decline in summer ratios of lambs to adult female from 

1.00 to 0.41 for a period in which the population carrying capacity may have been limited 

by minimal use of low elevation winter ranges (Wehausen and Stephenson 2005b). 

The Wheeler Ridge herd exhibited similar strong declines in winter lamb:adult 

female ratios with increasing population sizes. However, that herd had similar 

relationships for the period prior to low elevation winter range use and after those winter 

ranges were re-occupied. Additionally, following re-colonization of that winter range, 

the winter ratio of lambs to adult females more than doubled, from 0.42 to 0.89, then 

showed the second episode of decline with further population increases (Wehausen and 

Stephenson 2004). These findings indicate that population density in conjunction with 

forage utilization may tightly regulate bighorn sheep herds in the Sierra Nevada. It 

appears that density-dependent effects precipitate expansion of habitat use to fully utilize 

the large nutrient base of low elevation winter ranges. This has been observed at Wheeler 

Ridge and Mount Langley, both of which exhibited greatly expanded use of low elevation 

winter ranges after lamb:adult female ratios dropped to about 0.40, and both have seen a 

major increase in that ratio beginning a year after expanded winter range use began. 

These findings have important implications for recovery goals. First, they 

underline the importance of utilization of low elevation winter ranges to achieve adequate 

population sizes. Second, even with the use of such winter ranges, the observed densitydependent recruitment relationships and population trajectories indicate that population 

carrying capacities will be limited in most herds. For instance, under current habitat use 

patterns, it appears that the Wheeler Ridge herd is limited in size by its summer range and 

may not support more than 50 females. These findings are used in section II.B.2 to 

develop attainable recovery goals. 

6. INTERSPECIFIC COMPETITION AND HUMAN DISTURBANCE 

Interspecific competition occurs when a resource shared by two species is in short 

supply for at least one of those species (Krebs 1972). For bighorn sheep exhibiting 

altitudinal migration, questions of competition commonly have focused on winter ranges, 

where grazing animals are more concentrated and forage is more limited (Stelfox 1976). 

Both native deer (Odocoileus hemionus) and introduced tule elk (Cervus canadensis 

nannodes) have overlapped winter ranges used by bighorn sheep in the Sierra Nevada 

(Riegelhuth 1965). However, quantitative studies of utilization of key forage species on 

the Mount Williamson and Mount Baxter winter ranges did not suggest any competition 

(Wehausen 1979, 1980). Wehausen (1992b) attributed limitations on nutrient intake by 

bighorn sheep on these ranges to nutritive quality rather than quantity of forage. 
12

Leopold (1933) considered bighorn sheep to be a wilderness species because they 

fail to thrive in contact with urban development. Human disturbance has been suggested 

to be detrimental to bighorn sheep in a variety of situations (Graham 1980, MacArthur et 

al. 1982, Etchberger et al. 1989, Papouchis et al. 2001). Similarly, Dunaway (1971) 

postulated that disturbance of bighorn sheep in the Sierra Nevada by humans was a factor 

limiting populations. Results of subsequent research did not support that hypothesis 

(Wehausen et al. 1977, Hicks and Elder 1979, Wehausen 1980). Bighorn sheep have 

habituated to human activity in many places in the Rocky Mountains, and occasionally in 

desert habitats. Any conclusions about the effects of human disturbance, however, must 

be limited to the situations studied. Thus, the question should be revisited as situations 

change in a direction that suggests disturbance could be detrimental, such as increased 

presence of humans in bighorn sheep habitat. 

C. ABUNDANCE AND DISTRIBUTION 

1. HISTORICAL DISTRIBUTION, ABUNDANCE, AND TRENDS 

Bighorn sheep herds were once scattered along and east of the alpine crest of the 

Sierra Nevada from the Sonora Pass area south to Olancha Peak (Figure 1). They also 

occurred in similar habitat west of the Kern River as far south as Maggie Mountain, with 

concentrated use in the regions of Mineral King, Big Arroyo, and Red Spur (Jones 1950). 

Additional evidence suggested that herds utilized nonalpine habitat farther south near 

Walker Pass (Jones 1949, Garlinger 1987, Wehausen et al. 1987). Whether those 

southernmost herds were taxonomically the same as those that occurred farther north in 

the Sierra Nevada is unknown. 

The total population of bighorn sheep in the Sierra Nevada prior to settlement is 

unknown, but it probably exceeded 1,000 individuals. In some cases, early records 

provide clear evidence of the occurrence of populations now extirpated. However, the 

overall historical record is incomplete and may lack records of some herds that might 

have disappeared early in recorded history. Wehausen (1988) postulated some additional 

areas that might have supported populations of bighorn sheep, but records for these areas 

are lacking. 

Population losses for bighorn sheep apparently began shortly after the 

immigration of Europeans to the Sierra Nevada in the mid-1800s, and those losses 

continued through most of the twentieth century (Wehausen et al. 1987). Of 16 areas in 

the Sierra Nevada that likely had separate bighorn sheep herds (excluding the 

southernmost non-alpine region), only nine are known to have persisted to the beginning 
13

Figure 1 - Essential and non-essential herd units within the four recovery units (indicated 

by colors). Recovery units are likely to support bighorn sheep, based on analysis of 

historic distribution and current habitat characteristics. A subset of these herd units is 

essential to recovery of the Sierra Nevada bighorn sheep (see section II.B.2 and Figure 

4). 
14

of the twentieth century (Table 2). By 1948, the number of areas thought to support 

bighorn sheep had dropped to five (Jones 1950). Jones (1950) documented bighorn sheep 

in three areas and postulated their existence in two other regions based on sign and 

reported observations; he also produced an estimate of 390 bighorn in those five herds. 

By the 1970s, sheep remained in only two of those areas, but the one known as the Mount 

Baxter herd was found later to represent two demographically distinct, contiguous herds 

(Mount Baxter and Sawmill Canyon in Table 2; Wehausen 1979, 1980). 

Table 2. Probable locations of historic bighorn sheep herds in the Sierra Nevada, based on 

historic records and habitat characteristics. 

Region/Population 

Last Records of 

Viable Native 

Herds 

Sources for Sightings, 

Skulls, or other Data 

KERN RIVER 1800s Jones 1950 

Mineral King 

Big Arroyo, Kaweah Peaks 1800s Jones 1950 

SOUTHERN 

Olancha Peak 1920s Jones 1949 

Mount Langley 1960s Wehausen 1979 

Mount Williamson Extant Wehausen 1980, 1999 

Mount Baxter Extant Wehausen 1980, 1999 

Sawmill Canyon Extant Wehausen 1980, 1999 

Taboose Creek, Birch Mountain 1920s Ober 1914, Jones 1949 

CENTRAL 

Mount Tom to Mount Emerson 1920s Ober 1914, 1931; Wolfe 1979 

Pine Creek to Rock Creek 1920s Jones 1949 

McGee Creek to Convict Creek 1940s Jones 1949 

NORTHERN 

Mount Ritter to Dana Plateau 1870s Muir 1894, Jones 1949 

Mount Warren, Tioga Crest skulls only Bailey 1932, Jones 1949 

Mount Conness 

Shepherds Crest skulls only Jones 1949 

Matterhorn Peak area skulls only Jones 1949 

Sonora Pass 1878 Grinnell and Storer 1924 

Specific causes of most population losses in the Sierra Nevada are unknown. 

Market hunting for mining towns may have played a role in some areas. A die-off in the 

1870s west of the Kern River was attributed to scabies (Jones 1950), presumably 

contracted from domestic sheep. Die-offs from pneumonia contracted from domestic 
15

sheep may have been the most important cause of losses, but have not been documented. 

Beginning in the 1860s, and extending into the twentieth century, large numbers of 

domestic sheep were grazed seasonally in the Sierra Nevada (Austin 1906, Vankat 1970). 

2. RECENT DISTRIBUTION, ABUNDANCE, AND TRENDS 

Bighorn sheep persisted in only two areas in the Sierra Nevada by the 1970s, 

constituting three herds (Wehausen 1979, 1980). Intensive field studies from 1975 to 

1979 provided the first accurate census data for those herds. The contiguous Mount 

Baxter and Sawmill Canyon herds together contained at least 220 sheep in 1978 

(Wehausen 1980), with 150 in the Mount Baxter herd and 70 in the Sawmill Canyon 

herd. Detailed annual monitoring of the Mount Baxter and Sawmill Canyon herds 

through 1986 repeatedly verified similar large numbers (Wehausen 1987, Figure 2). In 

contrast, the Mount Williamson herd contained only 30 sheep in 1978. The Mount 

Williamson herd was found to be static at 30 individuals during winter censuses in 1983 

and 1985 (Wehausen 1983b; Figure 2). 

Because of large size and productivity, the Mount Baxter and Sawmill Canyon 

herds were used as sources of reintroduction stock beginning in 1979, with subsequent 

removals in 1980, 1982, 1986, 1987, and 1988, totaling 103 individuals. Those sheep 

were used to reestablish populations at Wheeler Ridge (1979, 1980, 1982, 1986), Mount 

Langley (1980, 1982, 1987), Lee Vining Canyon (1986, 1988), and the south Warner 

Mountains in northeastern California (1980; Bleich et al. 1990b). The Warner Mountains 

population died out in 1988, following contact with domestic sheep (Weaver and Clark 

1988), but the other three persist (Figures 1, 2). 

The Wheeler Ridge and Mount Langley herds began increasing soon after they 

were reintroduced. In contrast, the Lee Vining Canyon population declined initially due 

to post-release mortality from particularly inclement weather, followed by reductions due 

to mountain lion predation while on winter-spring range in Lee Vining Canyon (Chow 

1991). Following supplementation in 1988 and removal of one mountain lion from Lee 

Vining Canyon in each of three consecutive winters (Bleich et al. 1990b), this population 

increased rapidly (Chow 1991; Figure 2). 
16

Figure 2. Minimum summer population sizes of Sierra Nevada bighorn sheep, 1977-

2004. (A) Yearling and adult females. (B) All bighorn sheep. (From Andaloro and 

Ramey 1981; Chow 1991; Moore and Chow 1990; Ramey and Brown 1986; Wehausen 

1980, 1983b, 1987, 1999, 2001, 2002; Wehausen and Stephenson 2004, 2005b). Mono 

Basin (Lee Vining Canyon, Lundy Canyon, Mt. Warren, and Mt. Gibbs) includes the Mt. 

Warren and Mt. Gibbs essential herd units (see Figures 1 and 4). Where data on males 

were incomplete, the typical ratio of 7 adult males per 10 adult females was used to 

project total population size. 

1975 1980 1985 1990 1995 2000 2005

0

5 0

100

150

EWES

To tal

B a x te r, S a w m ill

 & B u b b s

W illia m s o n

W h e e le r

L a n g le y M o n o B a s in

A

1975 1980 1985 1990 1995 2000 2005

0

100

200

300

400

SHEEP

To tal

B a x te r, S a w m ill, &

 B u b b s

W illia m s o n

L a n g le y M o n o B a s in

W h e e le r

B
17

Figure 3. Mountain lion depredation permits issued in Inyo and Mono Counties, 1972-

2004, and bighorn sheep winter range census results for the Mount Baxter essential herd 

unit (Wehausen 1996, 1999, 2001; Wehausen and Stephenson 2004, 2005). 

Beginning in the 1970s, mountain lions apparently became an increasing source 

of mortality for Sierra Nevada bighorn sheep populations. Wehausen (1996) reported 

evidence of rapid increases in mountain lion activity and kills on the winter ranges of the 

Mount Baxter and Sawmill Canyon herds between 1976 and 1988, with documented kills 

totaling 49 bighorn sheep. More detailed analysis of those kills by the years in which 

they occurred shows two distinct periods of steeply increasing numbers of kills (1974-82 

and 1983-88) punctuated by a large decline in kills in 1983 following the removal of one 

lion in 1982. Mountain lion depredation problems involving livestock and pets along the 

eastern Sierra Nevada in Inyo and Mono Counties also increased notably during the 

1980s, especially in the middle of that decade (Figure 3). 

Bighorn sheep herds in the Sierra Nevada ceased regular use of low elevation 

winter ranges during the 1980s. The timing of those changes in winter habitat use varied 

by herd from 1983 for the Sawmill Canyon herd to 1986 for the Mount Williamson herd 

and 1987 for the Mount Baxter herd (Figure 3). Similar changes in winter range use were 

observed for reintroduced herds. Wehausen (1996) considered three possible 

explanations for this behavioral change and concluded that widespread increases in 

mountain lion predation of bighorn sheep on winter ranges was the only one that 

plausibly explained this widespread phenomenon that was not synchronous, yet occurred 

over relatively few years. 

However, other influences may have affected the habitat preference of bighorn 

sheep during this period. Extremely high densities of mule deer were present at the same 

time, with a subsequent population crash exacerbated by long-term drought (Kucera 

1970 1975 1980 1985 1990 1995 2000 2005

0

2 0

4 0

6 0

8 0

100

120

140

160

0

5

1 0

1 5

2 0

YEAR

SHEEP

PERMITS

sheep

perm its
18

1988). In addition to the risk of predation, changes in forage availability and quality due 

to a variety of factors may have influenced habitat selection. Nevertheless, the failure of 

bighorn sheep to move to lower elevations during the year likely resulted in direct and 

indirect impacts to the population (Wehausen 1996). 

Population Declines 

Regardless of the cause, Sierra Nevada bighorn sheep that remained at high 

elevations during the winter were exposed to extreme cold, deep snow and avalanches in 

heavy winters. Remaining at high elevation during winter also resulted in notably lower 

nutrient intake (Wehausen 1996). For the Mount Baxter and Sawmill Canyon herds, the 

consequences were manifested in later lambing and poor lamb survival, which led to 

recruitment well below that needed to balance adult mortality. This diminished 

recruitment resulted in a population decline (Wehausen 1996) that reached a low in the 

reproductive base of about 17 females by 1995 (Wehausen and Chang 1995), or about 15 

percent of peak numbers. Summer field surveys in the Mount Williamson herd range 

beginning in 1996 coupled with fecal DNA analyses suggested that this population might 

have reached a reproductive base low of about five females in 1995. 

Reintroduced herds also remained at high elevations during the winter and 

suffered similar impacts. Significant losses to one such herd occurred because of the 

severe winter of 1995. Winter losses in the Wheeler Ridge herd that year included 12 

sheep that died in a single snow avalanche, with only 18 known to have survived that 

winter. Earlier surveys of that herd (Ramey and Brown 1986, Wehausen 1991b) 

indicated that it might not have reached 40 individuals between the time of its 

reintroduction in 1979 and 1995. The population trajectory for that herd lacked an initial 

exponential phase (Figure 2), which probably reflected low carrying capacity due to 

minimal use of low elevation winter range relative to the number of sheep translocated. 

The population in Lee Vining Canyon suffered excessive losses from particularly 

inclement weather immediately after sheep were translocated in 1986, followed by lion 

predation that threatened to extirpate this fledgling herd. Following supplementation 

with eight females and three males in 1988 and the removal of three mountain lions 

during 1988 to 1990, this herd exhibited strong recovery (Chow 1991; Figure 2), and had 

grown to at least 77 and possibly 86 individuals by 1993 (Chang 1993). A less-thancomplete count the following summer yielded a minimum of 43 for that area, and a 

potential maximum of only 69 (Jensen 1994). Beginning in the mid 1990s, a decline in 

the use of the Lee Vining Canyon winter range became apparent. During the winter and 

spring of 1995, few bighorn sheep used low-elevation winter range and many sheep 

disappeared. Repeated thorough counts of this herd the following summer consistently 

produced only 29 bighorn sheep (Wehausen and Chang 1995), representing a loss of at 

least 50 individuals. Additional winter declines occurred in 1998 and 1999 (Wehausen 

and Chang 1998, Wehausen 1999). Further mountain lion predation was documented in 
19

the spring of 1998 in Lee Vining Canyon, and no females have been found on that winter 

range since then. In the summer of 1998, the reproductive bases for the Mount Warren 

and Mount Gibbs essential herd units were only seven and two females, respectively. 

The former declined to three a year later; however, genotype matches from recent fecal 

DNA analyses indicate that at least one of the females missing in 1999 had apparently 

moved to Lundy Canyon. Only 22 adult bighorn sheep are known to have existed in the 

two essential herd units in the Mono Basin at the time of emergency listing in 1999 

(Table 3). 

The Mount Langley herd also appears to have suffered a major reduction in the 

winter of 1995 due to heavy snowfall. Repeated census efforts beginning in the summer 

of 1996 accounted for only 6 females and 11 males that survived that winter (Wehausen 

1999), in contrast to 42 bighorn sheep counted there in the summer of 1990 (Moore and 

Chow 1990). 

After increasing from 250 in 1978 to almost 300 in 1985 during the initial phase 

of the reintroduction program, the total number of bighorn sheep in the Sierra Nevada 

declined about 60% to just over 100 in 1995, with a reproductive base of about 50 

females (Wehausen and Stephenson 2005).. The winter of 1995 was particularly 

difficult, with sheep attempting to live at high elevations, and apparently played a major 

role in that decline (Wehausen and Chang 1995, 1997). 

Population Recovery 

Bighorn sheep numbers have increased dramatically in the Sierra Nevada since 

the low in 1995. The first 4 years had somewhat slow and inconsistent overall increases 

due to further losses in the Mono Basin and delayed recovery in some other herds (Figure 

2). At the time of emergency endangered listing in spring 1999, a minimum of 117 sheep 

could be definitely accounted for throughout the Sierra Nevada; but additional data 

suggested that the actual total was probably somewhat higher (Wehausen 1999). 

Subsequent data increased that minimum to 122 sheep (Table 3). 
20

Table 3. Minimum numbers of Sierra Nevada bighorn sheep existing at the time of 

emergency endangered listing in spring 1999, based on counts in 1998 (Wehausen 1999) and 

subsequent years (Wehausen 2001) and known mortalities. Baxter includes the Mount 

Baxter and Sawmill Canyon essential herd units, and Mono Basin includes the Mount 

Warren and Mount Gibbs essential herd units. 

BIGHORN SHEEP IN 1999 

Population Ewes Rams Lambs Total 

Langley 10 7 1 18 

Williamson 6 1 3 10 

Baxter 13 9 3 25 

Wheeler 18 16 10 44 

Mono Basin 8 14 3 25 

TOTALS 55 47 20 122 

Data on mountain lions indicate that their population along the eastern Sierra 

Nevada declined markedly in the 1990s, especially toward the end of that decade, and hit 

a low in 1999 (Figure 3). Following the emergency endangered listing of Sierra Nevada 

bighorn sheep, a program of focused control of mountain lions was initiated. In 2000, 

that program began placing telemetry collars on mountain lions near bighorn sheep 

ranges and closely monitoring them in an effort to be as selective as possible in the 

removal of mountain lions for the benefit of bighorn sheep. On average, one mountain 

lion per year has been removed to protect bighorn sheep under that program. 

The overall population of bighorn sheep in the Sierra Nevada showed dramatic 

annual increases after 1999 (Figure 2). Six years after emergency listing, the minimum 

number of yearling and adult females that could be accounted for had increased by 265 

percent from 55 to at least 146 B an annual compounded increase rate of 17.7 percent 

(Wehausen and Stephenson 2005a). The minimum number of lambs that could be 

accounted for in 2004 was 66. With the addition of adult males, the total population in 

2004 can be projected at 325 to 350 (Figure 2). While evidence of density-dependent 

population regulation has emerged for two herds (see I.B.5; Wehausen and Stephenson 

2004, 2005b), one of those (Mount Langley) has only recently begun to use low elevation 

winter ranges again. The Mount Baxter herd also is in the process of expanding use of 

low elevation winter ranges. Those habitat expansions are expected to increase carrying 

capacities for both herds and can be expected to result in a further increase in overall 

numbers. These recent winter range utilizations are in addition to extensive use of winter 

range in the Wheeler Ridge herd unit. 
21

D. REASONS FOR LISTING 

The following discussion is organized according to the listing criteria under 

section 4(a)(1) of the Endangered Species Act. 

1. THE PRESENT OR THREATENED DESTRUCTION, MODIFICATION, OR 

CURTAILMENT OF ITS HABITAT OR RANGE 

Almost all of the historical and currently occupied habitat of bighorn sheep in the 

Sierra Nevada is in public ownership and administered by the U.S. Forest Service, 

National Park Service, or Bureau of Land Management. While there are some small 

parcels that are owned by the Los Angeles Department of Water and Power or are 

patented mining claims, they amount to a very small fraction of the habitat. Thus, habitat 

throughout the historic range of Sierra Nevada bighorn sheep remains essentially intact; it 

is neither fragmented nor degraded. Consequently, habitat loss was not a reason for 

listing. 

2. OVERUTILIZATION FOR COMMERCIAL, RECREATIONAL, SCIENTIFIC, OR 

EDUCATIONAL PURPOSES 

While unregulated hunting may have played a role in early population declines 

(Wehausen 1988), there is no evidence that commercial, recreational, scientific, or 

educational activities currently are significant threats. Poaching of Sierra Nevada 

bighorn sheep has not been documented in recent decades. 

3. DISEASE OR PREDATION 

Disease 

The potential for the transfer of virulent disease organisms from domestic sheep 

to bighorn sheep in the Sierra Nevada was a key factor in listing the Sierra Nevada 

bighorn sheep. As discussed earlier, pneumonia, caused by Pasteurella alone, or in 

combination with other pathogens, is the most significant disease threat for bighorn sheep 

(Bunch et al. 1999). Sheep in general are susceptible to pneumonia and bighorn sheep 

appear particularly susceptible. Although die-offs of bighorn sheep due to disease have 

occurred that are unrelated to domestic sheep (Miller et al. 1991), the history of bighorn 

sheep in the United States provides numerous examples of major die-offs following 

contact with domestic sheep (Goodson 1982, Foreyt and Jessup 1982, Singer et al. 2001, 

Coggins 2002), and pneumonia epizootics can extirpate entire populations (Martin et al. 

1996). 

 

Transmission of pathogens from domestic sheep bands to populations of bighorn 

sheep under range conditions is extremely difficult to document conclusively because 
22

researchers cannot collect pre- and post- epizootic samples from the domestic and wild 

sheep that are involved. This would require researchers to predict when and where an 

epizootic was going to occur. Because of these difficulties, there is no conclusive 

evidence that directly documents the transmission of pneumonia-causing pathogens from 

domestic sheep to bighorn sheep under free-ranging conditions. However, numerous 

independent trials in captive bighorn sheep have resulted in mortality of bighorn sheep 

due to respiratory disease following contact with domestic sheep (Onderka and Wishart 

1988; Foreyt 1989, 1990, 1994; Callan et al. 1991). In addition, inoculations of bighorn 

sheep with Pasteurella from the respiratory tract of healthy domestic sheep (Onderka et 

al. 1988, Foreyt et al. 1994, Foreyt and Silflow 1996) has resulted in respiratory disease 

and death of the bighorn sheep, but not of domestic sheep treated identically. Given the 

evidence from these captivity and inoculation studies in combination with the field 

observations of pneumonia related die-offs, mentioned previously, disease contracted 

from domestic sheep is considered a potentially significant source of mortality that 

requires management. 

Diseases transferred through contact with domestic sheep are suspected to have 

played a major role in the disappearance of certain bighorn sheep herds in the Sierra 

Nevada beginning around 1870 (Wehausen 1985). Currently, domestic sheep grazing on 

both private and federal land occurs adjacent to Sierra Nevada bighorn sheep 

subpopulations. The potential for contact between the species occurs when stray 

domestic sheep enter bighorn sheep habitat, or when bighorn sheep encounter domestic 

sheep herds. 

See Appendix B for a more detailed discussion of disease and the risk of 

transmission between domestic sheep and Sierra Nevada bighorn sheep. 

Predation 

Mountain lion predation of bighorn sheep on winter ranges has accounted for the 

majority of documented mortalities since the late 1970s. This predation increased from 

the 1970s to the 1980s and is postulated as the cause of a coincident and marked decrease 

in winter range use by bighorn sheep in the Sierra Nevada (Wehausen 1996). Subsequent 

population declines have been attributed to this change in winter habitat selection. 

During 1982 and 1988 to 1990, four mountain lions that preyed on bighorn sheep in two 

winter ranges were removed to help protect those sheep herds (Stephenson pres. comm. 

2007). 

4. THE INADEQUACY OF EXISTING REGULATORY MECHANISMS 

In 1883, an earlier moratorium on the take of bighorn sheep in California was 

extended indefinitely (Wehausen et al. 1987), and bighorn sheep in the Sierra Nevada 

remain a fully protected species. In 1972, California listed the California bighorn sheep 
23

as “rare.” The designation was changed to “threatened” in 1984 to standardize the 

terminology of the amended California Endangered Species Act (Sierra Nevada Bighorn 

Sheep Interagency Advisory Group 1997), and the California Fish and Game 

Commission upgraded the species' status to “endangered” in 1999. 

In 1971, Inyo National Forest established sanctuaries totaling about 16,500 

hectares (41,000 acres) for the Mount Baxter and Mount Williamson herds of Sierra 

Nevada bighorn sheep and called them the California Bighorn Sheep Zoological Areas 

(Wehausen 1979; Inyo National Forest 1988). Those sanctuaries were designated to 

regulate human use in some areas (Hicks and Elder 1979), and reduce domestic 

sheep/wild sheep interaction by constructing a fence below the winter range of the Mount 

Baxter herd along the U.S. Forest Service and Bureau of Land Management boundary 

(Wehausen 1979). Adjacent summer range on National Park Service land also was 

designated to reduce human disturbance (Wehausen 1979), and those restrictions 

continue. 

Numerous efforts for the conservation of bighorn sheep in the Sierra Nevada have 

taken place in recent decades including but not limited to: (1) intensive field studies; (2) 

reestablishment of three additional populations in historical habitat; (3) creation, in 1981, 

of the Sierra Nevada Bighorn Sheep Interagency Advisory Group, including 

representatives from Federal, State, and local resource management agencies, which has 

produced the Sierra Nevada Bighorn Sheep Recovery and Conservation Plan (1984) and 

a Conservation Strategy for Sierra Nevada Bighorn Sheep (1997); and (4) removal of 

four mountain lions that were taking Sierra Nevada bighorn sheep, which played a 

significant role in efforts to reestablish the Mount Warren herd (Chow 1991). 

Despite these efforts, the bighorn sheep population declined significantly in the 15 

years prior to listing (Figure 2). Regulatory mechanisms to address the threats 

contributing to the listing of the Sierra Nevada bighorn sheep were inadequate. First, 

although efforts had been underway for many years, the U.S. Forest Service was unable 

to eliminate, or even reduce, the threat of contact between domestic sheep and Sierra 

Nevada bighorn sheep by eliminating or modifying grazing allotments. Second, because 

of the passage of Proposition 117 in 1990 by the California Legislature, the California 

Department of Fish and Game lost the authority to remove mountain lions to protect the 

Sierra Nevada bighorn sheep. However, between the Federal emergency and final 

listings, the California State Legislature enacted AB 560, which amended Proposition 

117 and allowed the California Department of Fish and Game to remove mountain lions 

that are a threat to bighorn sheep in California. 

5. OTHER NATURAL OR MANMADE FACTORS AFFECTING ITS CONTINUED 

EXISTENCE 

At the time of its listing, the Sierra Nevada bighorn sheep population was very 
24

small, with only about 125 adults among five geographic areas (Wehausen 2001), and 

little probability of interchange among those areas. Additionally, multiple independent 

groups of females, defined by distinct home range patterns, were known in some of those 

areas and resulted in yet smaller population units (Wehausen and Chang 1997, Wehausen 

2001). Evidence has suggested that many of these contained five or fewer females in 

recent years (Wehausen 2001). Thus, small population effects alone made these bighorn 

sheep vulnerable to extinction. These effects might be random naturally occurring 

population fluctuations (see section II.A.1), loss of genetic variation (see section II.A.2), 

or both. 

E. PAST AND CURRENT MANAGEMENT AND CONSERVATION 

ACTIVITIES 

1. FEDERAL AGENCIES 

 

a. U.S. Department of the Interior - Fish and Wildlife Service 

 

The Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531 et seq.), 

requires that the Secretary of Interior identify wildlife and plant species that are 

endangered or threatened, based on the best available scientific and commercial 

information. As part of the program to accomplish this purpose, we maintain a list of 

species regarded as candidates for listing. We maintain this list for a variety of reasons 

including: to provide advance knowledge of potential listings that could affect decisions 

of environmental planners and developers; to solicit input from interested parties to 

identify those candidate species that may not require protection under the Act or 

additional species that may require the Act’s protections; and to solicit information 

needed to prioritize the order in which species will be proposed for listing. 

On September 18, 1985, we published a Notice of Review in which we designated 

the Sierra Nevada bighorn sheep as a Category 2 candidate and solicited status 

information (U.S. Fish and Wildlife Service 1985). Category 2 candidate species 

included species for which we had information indicating that proposing to list as 

endangered or threatened was possibly appropriate, but for which sufficient data on 

biological vulnerability and threats were not currently available to support a proposed 

rule. Category 1 candidates were those species for which we had sufficient information 

on file to support issuance of proposed listing rules. In our January 6, 1989 and 

November 21, 1991 Notices of Review (U.S. Fish and Wildlife Service 1989, 1991), we 

retained the Sierra Nevada bighorn sheep in Category 2. Beginning with the February 28, 

1996, Notice of Review (U.S. Fish and Wildlife Service 1996), we discontinued the 

designation of multiple categories of candidates, and now consider only species that meet 

the definition of former Category 1 as candidates for listing. At that point, the Sierra 

Nevada bighorn sheep was not identified as a candidate. 
25

Nevertheless, we remained in contact with the California Department of Fish and 

Game and participated in the Sierra Nevada Bighorn Sheep Interagency Advisory Group 

regarding the status of the species. In 1998, as new information became available 

regarding the continual decline in the Sierra Nevada bighorn sheep population, we 

initiated a status review. On April 20, 1999, we published an emergency rule to list the 

Sierra Nevada distinct population segment (DPS) of California bighorn sheep as 

endangered (U.S. Fish and Wildlife Service 1999a), as well as a proposed rule (U.S. Fish 

and Wildlife Service 1999b) to list the species as endangered. The emergency rule 

provided Federal protection pursuant to the Act for a period of 240 days. After a 

thorough review of all comments received on the proposed rule, we published a final rule 

listing the Sierra Nevada bighorn sheep DPS as endangered in accordance with section 4 

of the Act on January 3, 2000 (U.S. Fish and Wildlife Service 2000). 

Section 4 further directs us to develop and implement recovery plans for listed 

species; this recovery plan was developed according to that direction and following our 

“Policy and Guidelines for Planning and Coordinating Recovery of Endangered and 

Threatened Species” (U.S. Fish and Wildlife Service 1990). Once a species has 

recovered and is removed from the list, we must, in cooperation with the State 

government, “effectively monitor for not less than 5 years” the species’ status, and we 

must be prepared to restore the species to the list if necessary. Section 5 of the Act 

authorizes the Department of the Interior to acquire habitat essential to preserving listed 

species, and section 6 directs us to cooperate with the States to maintain adequate 

programs for their conservation. Through section 7 of the Act, Federal agencies are 

required to use their authorities to carry out programs for the conservation of listed 

species and to consult with us when a Federal action may have an effect on listed species. 

Section 9 of the Act provides for protection of listed species, and section 10 permits 

exceptions to the protections granted under section 9. The exceptions are permitted in the 

form of scientific, recovery, and incidental take permits, and other circumstances as 

detailed in section 10. 

During the period of Federal protection provided by the emergency rule, we 

worked with the Inyo National Forest and the California Department of Fish and Game 

regarding measures to protect the bighorn sheep. We assumed the lead agency role in the 

development of a Final Environmental Assessment for Predator Damage Management to 

Protect the Federally Endangered Sierra Nevada Bighorn Sheep (U.S. Department of 

Agriculture Wildlife Services 1999). This document was prepared by the U.S. 

Department of Agriculture, Wildlife Services, and identified the cooperating agencies: 

the California Department of Fish and Game, U.S. Forest Service, and National Park 

Service. This environmental assessment was for the proposed program to protect the 

bighorn sheep from predation on and around its current range. 

In response to the threat of disease transfer from domestic sheep to Sierra Nevada 

bighorn sheep and to facilitate a consistent and comprehensive approach to consulting on 
26

the taking of Sierra Nevada bighorn sheep under the Act, we organized an interagency 

team of biologists and rangeland management specialists from the Bureau of Land 

Management, California Department of Fish and Game, U.S. Forest Service, and Los 

Angeles Department of Water and Power to develop a grazing strategy for domestic 

sheep for the Owens Valley. This strategy (U.S. Fish and Wildlife Service 2001) was 

based on analyses of the risk of disease transmission between domestic sheep and 

bighorn sheep for each of the allotments/leases within the Owens Valley on the Inyo 

National Forest (seven allotments and one trail), Humboldt-Toiyabe National Forest (one 

allotment), Bureau of Land Management (one allotment and one trail), and Los Angeles 

Department of Water and Power (three leases). Based on this strategy, domestic 

livestock grazing within the Owens Valley has been modified by the Bureau of Land 

Management, U.S. Forest Service, and Los Angeles Department of Water and Power, 

including a July 2000 Environmental Assessment and Decision Notice that closed two 

grazing allotments on the Inyo National Forest. 

Pursuant to section 7 of the Endangered Species Act, we have been in formal and 

informal consultation with the Inyo National Forest, Humboldt-Toiyabe National Forest, 

and the Bureau of Land Management on their grazing operations. All agencies are 

working cooperatively to identify high-risk areas and address unacceptable risks, so that 

domestic sheep grazing does not threaten the existence of the bighorn sheep. 

b. U.S. Department of the Interior - National Park Service 

Historical Management 

A significant portion of the historic summer range of the Mount Baxter herd 

occurred, and to some extent still does occur in Kings Canyon National Park (Wehausen 

1980). Since reestablishment in 1980 (Bleich et al. 1990b), the Mount Langley herd has 

utilized a limited part of the Sequoia National Park during the summer (Moore and Chow 

1990). Males of the reestablished Lee Vining herd have occasionally visited Yosemite 

National Park, and it is surmised that should the herd recover fully, parts of the crest in 

the national park will be included in summer range. Lastly, to replace the herd(s) that 

once occupied the Great Western Divide (Wehausen 1979), an eventual reintroduction is 

planned to occur entirely inside Sequoia National Park. Similarly, the bighorn sheep 

currently occupying the Bubbs Creek herd unit live year round in Kings Canyon National 

Park. 

During the early 1960s, biologists from Sequoia and Kings Canyon National 

Parks conducted surveys along the crest, trying to locate remaining bands of bighorn 

sheep (Riegelhuth 1965). The National Park Service was a substantial sponsor of the 

definitive research conducted by Dr. John Wehausen from 1976 through 1979 (Wehausen 

1980). 
27

Following the lead of the U.S. Forest Service, Sequoia and Kings Canyon 

National Parks in the early 1970s closed “the female/lamb range of the Sierra Nevada 

bighorn sheep . . . to all pack animals and to off-trail travel by humans [in the national 

park].” This closure was later codified in the Superintendent’s Compendium. The 

associated map identified an area representing the known range of females and lambs 

within King Canyon National Park. Because off-trail travel by pack stock is impractical 

along the crest of the Sierra Nevada and the occasional use by mountaineers and climbers 

does not pose a significant threat to bighorn sheep, and because the areas used by bighorn 

sheep will be in a state of flux for the indefinite future, the permanent closure was 

terminated in 2001. 

Representatives of the National Park Service have participated in the Sierra 

Nevada Bighorn Sheep Interagency Advisory Group since its inception in 1981. In 

addition to the Recovery and Conservation Plan authored by that group (Sierra Nevada 

Bighorn Sheep Interagency Advisory Group 1984), Sequoia and Kings Canyon National 

Parks produced a “Bighorn Sheep Management Plan” for those parks (National Park 

Service 1986) that outlined steps to recover populations, such as the Great Western 

Divide herd, that historically used the national parks. 

In 1985, the Yosemite Association solicited funds from the Goldman Fund and 

the Sacramento Safari Club that were paid to the Lee Vining Canyon grazing allotment 

holder in exchange for vacating the allotment, which was then later terminated by the 

U.S. Forest Service. Subsequently, the National Park Service conducted follow-up 

monitoring and research after bighorn sheep were translocated there in 1986 (Chow 1991, 

Moore 1991). 

During the late 1980s, the National Park Service sponsored and conducted aerial 

and ground surveys to establish the availability of winter and summer habitat in the Great 

Western Divide and Kern River as a necessary precursor to eventual translocations there. 

Current Management on National Park Service Lands 

 

National Park Service biologists from Sequoia, Kings Canyon, and Yosemite 

National Parks participated in preparation of this recovery plan and will participate in its 

implementation, particularly by sponsoring the use of National Park lands by existing 

herds of Sierra Nevada bighorn sheep and the reestablishment of Sierra Nevada bighorn 

sheep in the Great Western Divide area of Sequoia National Park. 
28

c. U.S. Department of Agriculture - Forest Service 

Historical Management 

Much of the historic habitat of the Sierra Nevada bighorn sheep occurs on 

National Forest System lands within the Pacific Southwest Region (Inyo, Sequoia, Sierra, 

and Stanislaus National Forests) and the Intermountain Region (Humboldt-Toiyabe 

National Forest). The current populations primarily occupy the Inyo and HumboldtToiyabe National Forests, but some use also occurs in the Sequoia/Kings Canyon 

National Park, Yosemite National Park, and the Sierra National Forests. 

The U.S. Forest Service is authorized by Acts of Congress and by regulations 

issued by the Secretary of Agriculture to administer, manage, and protect National Forest 

System lands for multiple uses, including the provisions of habitat for fish, wildlife, and 

plants. Typically, the U.S. Forest Service is responsible for managing habitats (e.g., 

food, water, and cover) on National Forest System lands and coordinating with the 

appropriate State agency regarding management of the animal populations. 36 CFR 

219.19 directs the U.S. Forest Service to manage fish and wildlife habitat to maintain 

viable populations of existing native and desired nonnative vertebrate species. One way 

this mandate is met is through the Forest Service Sensitive Species Program, under which 

each Region establishes a list of sensitive plant and animal species that are given special 

consideration under the multiple use mandate. The objectives of the program are to 

ensure the continued existence of viable, well-distributed populations and to prevent a 

trend toward listing under the Endangered Species Act of 1973. Each National Forest is 

required to develop a Land and Resource Management Plan, which sets the framework 

for multiple use management of the Forest and incorporates management strategies to 

maintain viable populations within the Forest and to promote recovery of federally listed 

species. In addition, the U.S. Forest Service, like other Federal agencies, has 

responsibilities under the Federal Endangered Species Act (section 7a). Accordingly, the 

U.S. Forest Service coordinates and consults with us on activities it conducts, funds, or 

authorizes that may affect federally listed endangered, threatened, or proposed species 

and designated or proposed critical habitat. 

In 1940, concern about bighorn sheep in the Sierra Nevada (Dixon 1936) 

prompted the National Park Service and Sierra Club to jointly propose the creation of a 

sanctuary on Inyo National Forest land for the Mount Baxter population (Colby 1940a, 

1940b; Blake 1940). The U.S. Forest Service and California Department of Fish and 

Game rejected this proposal because insufficient information existed to justify the need, 

as well as because of concern that the publicity of such a sanctuary might exacerbate 

poaching, rather than having the opposite effect (Blake 1941). 
29

The U.S. Forest Service became active in the management of Sierra Nevada 

bighorn sheep in 1971, when the Inyo National Forest created two Bighorn Sheep 

Zoological Areas (Mount Baxter and Mount Williamson Units) for the two surviving 

native herds (Dunaway 1971). These areas, totaling 1,823 hectares (4,505 acres) outside 

designated wilderness areas, were created to give top priority to the requirements of the 

bighorn sheep through protection and maintenance of their habitat and through the 

regulation of human use in certain sections of the bighorn range to minimize human 

disturbance. Similar restrictions were applied to adjacent habitat of these herds under 

National Park Service management (Wehausen 1985). The U.S. Forest Service has been 

a member of the Sierra Nevada Bighorn Sheep Interagency Advisory Group since its 

inception in 1981, and assisted in the funding and development by that group of a 

Recovery and Conservation Plan in 1984 and the Conservation Strategy in 1997. 

California bighorn sheep were classified as a Regional Forester’s Sensitive Species in 

California in 1982. In 1985, the Inyo National Forest facilitated, in cooperation with the 

California Department of Fish and Game and other members of the Interagency Advisory 

Group, the reintroduction of bighorn sheep to the Lee Vining Canyon area. On 

November 25, 1998, due to the rapid decline of Sierra Nevada bighorn sheep, the Pacific 

Southwest Region Regional Forester issued a letter directing the Forest Supervisors of the 

National Forests within the historic range of the Sierra Nevada bighorn sheep to take 

specific actions to provide habitat and other assistance contributing to the viability of the 

Sierra Nevada bighorn sheep. Various management actions were initiated by this letter; 

these included providing funding to U.S. Department of Agriculture Wildlife Services to 

monitor mountain lion activity within occupied bighorn sheep habitat, working with 

permittees to modify grazing management to reduce the risk of disease transmission, 

initiating informal consultation with the Fish and Wildlife Service, and using prescribed 

fire to improve winter range. 

Current Management on National Forest System Lands 

Since the emergency listing of the Sierra Nevada bighorn sheep on April 20, 

1999, the U.S. Forest Service has been consulting with the Fish and Wildlife Service on 

various Federal actions allowed under their Forest Land and Resource Management Plan 

with the potential to affect Sierra Nevada bighorn sheep or their habitat. These actions 

include term grazing permits for domestic sheep allotments adjacent to occupied bighorn 

sheep habitat, recreational use of occupied bighorn sheep habitat, helicopter use within 

and adjacent to bighorn habitat, prescribed fire, normal fire suppression activities, and 

special use permits for outfitter guides and packers. In May 2000, a temporary 

Emergency Forest Order was issued, which prohibited dogs and domestic goats from 

entering key Sierra Nevada bighorn sheep habitat areas on the Inyo National Forest. The 

final version of this Forest Order is currently being prepared. 

The Inyo National Forest continues to use prescribed fire within bighorn sheep 

winter range in an attempt to open up habitats, decrease cover for mountain lions, and 
30

potentially allow bighorn sheep increased access to areas with highly nutritional food 

sources. 

2. STATE AGENCIES 

The first management action for Sierra Nevada bighorn sheep was full protection 

from hunting. Decimation of native sheep occurred quickly following the influx of gold 

miners in the mid-1800s, and declines of native game led the State Legislature to enact 

legal protections beginning in the 1870s. For wild sheep, legal protection first occurred 

in 1876, when a law of 1872 that provided seasonal protection for elk, deer, and 

pronghorn was amended to include all bighorn sheep. Two years later this law was 

further amended to establish a 4-year moratorium on the taking of any pronghorn, elk, 

mountain sheep, or female deer; in 1883, the moratorium was extended indefinitely for 

bighorn sheep (Wehausen et al. 1987). Sierra Nevada bighorn sheep remain fully 

protected by the State of California. 

In 1972, the California subspecies, as defined by Cowan (1940) and including 

surviving native populations in the Sierra Nevada, was listed as rare under the 1970 

California Endangered Species Act (California Department of Fish and Game 1974). 

This category was changed to threatened in 1984. Through the listing process, the Fish 

and Game Commission recommended development and implementation of a recovery 

plan, including field research and reintroductions. Intensive field study began in 1975, 

and the results of those investigations led to a series of translocations beginning in 1979. 

A conservation and recovery plan was completed in 1984 (Sierra Bighorn Interagency 

Advisory Group 1984). The goals of that plan were: (1) to create two additional 

populations numbering at least 100 bighorn sheep that could serve as translocation stock 

in the event of catastrophic decline of the Mount Baxter herd, and (2) to reestablish 

bighorn sheep populations throughout historic ranges in the Sierra Nevada where it was 

biologically and politically feasible. To date, no reintroduced population has met the first 

goal, while unforeseen ecosystem level changes have resulted in a major reduction of the 

Mount Baxter population. 

It is the responsibility of the California Department of Fish and Game (Fish and 

Game Code Section 1802) to conserve, protect, and manage fish, wildlife, native plants, 

and habitat necessary for biologically sustainable populations of those species. It also is 

the policy of the State to conserve, protect, restore, and enhance endangered or threatened 

species and their habitats. The role of the California Department of Fish and Game, as 

trustee for fish and wildlife resources, includes working with other State, Federal, and 

private entities to further conservation and recovery of threatened and endangered species 

on their lands. Conservation goals for bighorn sheep (California Department of Fish and 

Game 1983) are to: 

1. Maintain, improve, and expand bighorn sheep habitat where possible or feasible. 
31

2. Reestablish bighorn sheep populations on historic ranges where feasible. 

3. Increase bighorn sheep populations so that all races become numerous enough to no 

longer require classification as rare or fully protected. 

4. Provide for aesthetic, educational, and recreational uses of bighorn sheep. 

The California Department of Fish and Game supports the concept of regional 

management for the long-term viability of bighorn sheep populations. In support of this 

strategy, the California Department of Fish and Game’s Bighorn Sheep Conservation 

Program maintains an inventory of the distribution of bighorn sheep in California. The 

populations of bighorn sheep in California are grouped into metapopulations, or 'systems' 

of populations, that best represent logical regions to manage for the long-term viability of 

the species. This regional approach recognizes the importance of inter-mountain areas 

that allow movement and exchange of individuals between populations, the 

recolonization of vacant habitats, and the need for interagency coordination of land 

management. The concept of regional populations considers not only vegetative and 

geographic boundaries, but also man-made barriers that define distributions and which 

have resulted in the fragmentation of habitat. Given the need to understand the status and 

dynamics of regional populations of bighorn sheep, this type of inventory should provide 

an index for documenting regional population changes over time and a basis for 

evaluating the success or failure of management actions at a meaningful level. 

Although a metapopulation approach is an important biological principle for 

understanding the long-term survival of bighorn sheep populations, it is equally important 

as a management concept that establishes a priority for regional coordination for bighorn 

sheep population and habitat management. For example, data regarding extinction and 

recolonization are limited, and we therefore have an incomplete biological justification 

for considering some regions as true metapopulations. Nevertheless, given the need for 

regional management of bighorn sheep populations, the California Department of Fish 

and Game has defined the metapopulations based on the best information available for 

the regions, and utilizes this regional strategy for the management of bighorn sheep 

throughout the State. 

In 1997, a conservation strategy was produced for bighorn sheep in the Sierra 

Nevada that reflected the significant changes in the status of those animals (Sierra 

Nevada Bighorn Sheep Interagency Advisory Group 1997). Unfortunately, funding 

constraints encountered by the California Department of Fish and Game limited the 

recovery efforts identified in this conservation strategy. We and the Fish and Game 

Commission took emergency action in 1999 to list the Sierra Nevada bighorn sheep as 

endangered under the State and Federal Endangered Species Acts. This action was in 

response to a significant decline in the population size, from approximately 310 in 1985 
32

to an estimated 125 adults in 1999. With the small population of Sierra Nevada bighorn 

sheep in decline, the threat of this unique population becoming extinct was great. 

Due to the high level of public attention and concern, the California Department 

of Fish and Game was provided funding (in 1999) through the legislature to implement a 

population recovery program for bighorn sheep in the Sierra Nevada. This funding will 

support the start of a long-term comprehensive population recovery program, and the 

recovery potential for Sierra Nevada bighorn sheep populations is high if conservation 

actions are taken immediately. Elements of the recovery program include monitoring the 

population, intensively reducing mortality, reestablishing additional populations in 

historic range, and preparing for and potentially implementing captive breeding efforts to 

increase population size and maintain genetic diversity. 
33

II. RECOVERY 

A. CONSERVATION PRINCIPLES USED IN DEVELOPING THIS RECOVERY 

PLAN 

The following sections apply general conservation principles in the context of our 

current knowledge regarding Sierra Nevada bighorn sheep and outline the relationship of 

these principles to the recovery criteria for this species. Conservation theory recognizes 

that population dynamics and genetic issues need to be addressed in species conservation. 

Although threats to population persistence are of more immediate importance to Sierra 

Nevada bighorn sheep, potential loss of genetic variation also has implications for the 

long-term conservation of this taxon (Lande 1988). Fundamentally, the recovery strategy 

revolves around three main conservation issues: population dynamics, genetic variation, 

and ecosystem integrity. 

1. POPULATION DYNAMICS 

Demographic processes are especially important considerations in the 

conservation of small populations (Gilpin and Soulé 1986). Variation in birth, death, 

immigration, and emigration rates, as well as the age and sex structure of populations, 

can cause fluctuations in population size that make small populations especially 

vulnerable to extinction. Lande (1988) noted that a shortcoming of some past recovery 

plans was an inadequate emphasis on the implications of such population parameters for 

recovery and cautioned that, for many wild populations, risks concerning population 

parameters are of more immediate importance than genetic concerns. 

Spatial distribution of animals across the landscape is an important consideration. 

Sierra Nevada bighorn sheep, like other forms of bighorn sheep and many other taxa, are 

distributed as a collection of subpopulations, each occupying a patch of suitable habitat 

within a matrix of otherwise less suitable or unsuitable habitat. The complex topography 

and the vegetation structure of the southern and central Sierra landscape, coupled with the 

intrinsic biology and behavior of these bighorn sheep, has resulted in a naturally 

fragmented distribution of animals, a metapopulation (Bleich et al. 1990a). This 

metapopulation is composed of multiple subpopulations that interact intermittently to 

varying degrees, depending on site-specific geography, movement characteristics of 

males (occasional) and females (rare), and chance. 

Metapopulation structure has profound implications for the conservation of Sierra 

Nevada bighorn sheep. Conservation objectives for this taxon must simultaneously 

address all levels of population organization to achieve recovery goals. Recovery units, 

herd units, and separate female groups within herd units are all relevant to overall 

recovery of Sierra Nevada bighorn sheep. For further detail on the definitions of these 

terms, refer to the discussion of recovery objectives (section II.C.2). 
34

Metapopulations typically are assumed to exist in a state of balance between 

population extinction and colonization (Hanski and Gilpin 1991). However, bighorn 

sheep are relatively slow colonizers (Geist 1967, 1971, Bleich et al. 1996) and, therefore, 

metapopulation extinction-colonization processes must be considered over appropriate 

periods. Although bighorn sheep typically have a naturally fragmented distribution 

(Bleich et al. 1990a), any external factor that further fragments existing populations poses 

a heightened threat to persistence (Schwartz et al. 1986, Bleich et al. 1996). Hanski and 

Gilpin (1991) cautioned that species subject to accelerated habitat and/or population 

fragmentation must be managed carefully, as they may not necessarily be able to function 

as a metapopulation in equilibrium. This situation may be exacerbated in the Sierra 

Nevada because the metapopulation is largely linear in geographic distribution, resulting 

in fewer populations that could serve as sources of colonists. 

There is little threat to Sierra Nevada bighorn sheep due to habitat loss. Virtually 

all land that provides habitat for the Sierra Nevada bighorn sheep is managed by the 

Federal government and is likely to remain in a wild condition for the indefinite future. 

However, population fragmentation due to decreased habitat quality resulting from an 

altered fire regime, random natural fluctuations in population parameters or deleterious 

effects of disease or predation could affect overall metapopulation dynamics. 

Population processes are of primary concern in the recovery of Sierra Nevada 

bighorn sheep due to their small numbers (an estimated 325 to 350 individuals in 2004). 

Furthermore, Sierra Nevada bighorn sheep occur as discrete female groups with 

significance to the distributional structure of the population (Wehausen 1979). Because 

these female groups are independent segments of populations, they are the fundamental 

demographic units and should be treated as the basic conservation units (Soulé 1987). 

In the southern Sierra Nevada, most herds of bighorn sheep were reduced to such 

low levels at the time of listing that random natural variation in population and 

environmental factors posed serious immediate threats. For example, some female 

groups consisted of only five females at the time of listing. Therefore, recovery efforts 

for Sierra Nevada bighorn sheep have focused on actions that increase sizes of individual 

female groups (decreasing adult mortality rates, increasing recruitment, and augmentation 

through translocations) and increasing overall distribution through reintroductions to 

historic ranges. 

2. GENETIC CONSIDERATIONS 

The Sierra Nevada bighorn sheep was recently recognized as a unique subspecies 

(see I.A.2.). As such, this taxon appears to have distinctive genetic characteristics that 

may include adaptations to conditions in the Sierra Nevada. One of the fundamental 
35

objectives of this recovery program is the conservation of the unique gene pool embodied 

in the remaining animals of this metapopulation. 

Maintaining genetic variation is an important conservation goal because loss of 

genetic variability can result in inbreeding depression (a loss of fitness) and the inability 

of populations to respond to long-term environmental changes (Gilpin and Soulé 1986, 

Ralls et al. 1988, Lande 1988, Meffe and Carroll 1994, Fitzsimmons et al. 1995). Rate of 

evolutionary change in a population is proportional to the amount of genetic variation 

available (Fisher 1958), and loss of genetic diversity reduces future evolutionary options 

(Meffe 1999). By reducing the fitness of individuals, loss of genetic variation also can 

reduce the growth rates and resilience of populations (Lacy 1997). 

Loss of genetic variation is a special concern among small populations because 

heterozygosity is lost more quickly in small populations than in large ones (Meffe and 

Carroll 1994). In the past, occasional long-range movements north or south along the 

Sierra Nevada, especially by males, likely helped to maintain gene flow, but it is unclear 

to what extent such movements now occur. The current, fragmented distribution of 

populations of these animals likely reduces connectivity among groups. In small herds of 

bighorn sheep, random natural variability in population parameters can be an overriding 

determinant of population survival and is mitigated by immigration of both sexes. If 

small herds become isolated and stay small, they potentially face an increased loss of 

genetic variability, in addition to the risks to persistence associated with stochastic 

demographic events (e.g., several consecutive years of low reproduction and/or high 

mortality within a small herd). Even if gene flow is maintained among female groups 

throughout the Sierra Nevada, the overall small population size (approximately 325-350 

individuals in 2004) is of concern. Thus, an important goal of this recovery plan is to 

increase the abundance of Sierra Nevada bighorn sheep to the level that the habitat can 

sustain, combined with further examination and consideration of existing and future 

genetic variation in this metapopulation. 

Although genetic variation among bighorn sheep herds in the Sierra Nevada is not 

known to confer adaptive advantage in local environments, genetic theory holds that 

existing genetic variation should be maintained "in as near a natural geographic 

distribution as possible, so that evolutionary and ecological processes may be allowed to 

continue" (Meffe and Carroll 1994). Adaptation to future changes in the environment, 

such as may occur through global climate change, may depend on maintenance of genetic 

diversity within this taxon. 

 

Because the most immediate problem facing bighorn sheep in the Sierra Nevada 

concerns depleted population sizes, the potential implications of loss of genetic 

heterozygosity implied by genetic theory should not override management objectives to 

maintain and expand the number and size of herds throughout much of the Sierra Nevada 

bighorn sheep’s historic range. Nonetheless, as more is learned about the actual genetic 
36

diversity in the remaining individuals, it may be necessary to incorporate genetic 

management, such as moving males between some populations. 

3. ECOSYSTEM INTEGRITY 

Loss of habitat is recognized as the primary cause of species endangerment and 

the leading threat to global biodiversity (Groombridge 1992, Noss and Murphy 1995). It 

is also considered the most significant threat to the viability of many bighorn sheep 

populations (Bleich et al. 1996). However, habitat loss is not considered a proximate 

threat to the conservation of the Sierra Nevada bighorn sheep. Virtually all habitat used 

by this taxon is managed by the Federal government. 

A stable and functional ecosystem is of paramount concern. For Sierra Nevada 

bighorn sheep, a primary emphasis is continued access to suitable habitat. Habitat 

conditions within the range of Sierra Nevada bighorn sheep generally are not subject to 

obvious human-induced changes. What is primarily at stake for these animals is 

continuing, safe access to preferred habitats, notably winter ranges. Recent declines in 

population sizes have been linked to the decreased use of key resources on winter ranges. 

A basic premise of the recovery strategy, therefore, is to reduce factors that inhibit the 

ability of Sierra Nevada bighorn sheep to utilize all components of their habitat. 

However, such actions need to take place in the context of all ecosystem components; 

potential effects of actions to enhance bighorn sheep herds on other components of the 

ecosystem must be considered. 

Maintaining ecosystem integrity for the Sierra Nevada bighorn sheep should 

revolve around providing suitable habitat conditions and safe access to those habitats. 

Safe access implies that exposure to exotic diseases and unsustainable levels of predation 

are prevented. Exposure to diseases carried by domestic sheep or goats that may be lethal 

to bighorn sheep is a significant threat that could have catastrophic effects on recovery 

efforts for this taxon. All habitats, both summer and winter, should be managed to 

prevent contact between bighorn sheep and domestic sheep or goats. Similarly, predation 

should be managed within herds that are still at low levels. Bighorn sheep in the Sierra 

Nevada appear to be especially vulnerable to predation when herds are low in number, 

and that small group size may preclude the use of important foraging areas. As long as 

the populations of this taxon remain below viable levels, special predator management 

actions are warranted to ensure adequate use of important foraging habitat. However, it 

is also important to recognize that top predators play a crucial and irreplaceable role in 

maintaining the integrity of a variety of ecosystems (Terborgh et al. 1999), including, 

potentially, the ecosystem inhabited by Sierra Nevada bighorn sheep. 

Habitat factors, such as visual openness, that may have been influenced by past 

management practices, also must be addressed. Because recovery is contingent on full 

use of the nutritional resources available to these bighorn sheep, the vegetative structure 
37

of some winter ranges needs to be considered with respect to the recovery strategy. Fire 

suppression of lands within some winter ranges has been a common management practice 

over the last century. The implications of fire suppression for vegetation succession and 

the loss of visual openness in some winter range habitat are not fully understood. Thus, 

consideration should be given to how the habitat changes induced by fire suppression 

might affect use of some winter ranges by bighorn sheep. 

B. OBJECTIVES 

1. CONSERVATION CHALLENGE AND GOALS 

“Given its small population size and recent population declines [Sierra Nevada 

bighorn sheep] are currently more deserving of conservation attention than any other 

group of bighorn sheep. Sierra Nevada bighorn sheep are currently one of the rarest 

mammalian taxa in North America” (Wehausen and Ramey 2000). 

The challenge and objective of this plan is (1) to define a desired future size and 

distribution of the overall bighorn sheep population in the Sierra Nevada, at which point 

continued protection under the Federal and California Endangered Species Acts is no 

longer needed and, (2) to outline steps necessary to reach that condition. From a species 

perspective, the conservation challenges of these bighorn sheep concern long-term 

viability of the overall population and preservation of this unique gene pool. From an 

ecosystem standpoint, the challenge involves finding the long-term population viability 

of bighorn sheep relative to other elements of the ecosystems involved, as well as 

returning this large native herbivore to most of those regions of the Sierra Nevada from 

which it has been extirpated. Thus, the conservation goal of this recovery plan is to 

restore Sierra Nevada bighorn sheep in a geographic distribution throughout most of their 

native range with genetic representation that assures their long-term viability as a unique 

life form. The ultimate goals of this recovery plan are to: 1) recover the Sierra Nevada 

bighorn sheep to a self-sustaining population size and geographic distribution that buffers 

them against extinction; 2) maintain long-term viability through establishment of 

programs and mechanisms that ensures the protection of these populations from outside 

threats following a potential delisting. 

2. RECOVERY CRITERIA 

A species is considered to be endangered when it is in danger of extinction 

throughout all or a significant portion of its range, likely to become extinct in the near 

future, and it is considered to be threatened when it is likely to become an endangered 

species within the foreseeable future throughout all or a significant portion of its range. 

Downlisting criteria identify the conditions at which the status of the species has 

improved to the point that it is no longer endangered, and may be proposed to be 
38

reclassified as threatened. Delisting criteria represent the minimum conditions necessary 

to propose removing the taxon from the endangered species list. 

a. Downlisting Criteria 

This plan concerns the bighorn sheep in the southern and central Sierra Nevada, 

from near Olancha Peak and the Great Western Divide north to Twin Lakes, near 

Bridgeport, California. In this region 16 herd units have been identified (Table 4, Figure 

1). These areas are known from sightings or skulls to have been occupied historically. 

We based herd units in the Draft Recovery Plan for the Sierra Nevada Bighorn Sheep 

(U.S. Fish and Wildlife Service 2003) on topography, terrain features, and habitat 

openness. The resulting lines were largely the result of expert opinion, which identified 

the herd unit boundaries based on these features and knowledge about bighorn sheep 

movement and habitat utilization patterns in the Sierra Nevada. 

In 2004-2005, the California Department of Fish and Game developed a model 

that looked at variables of habitat selection that included slope, elevation, aspect, 

hillshade, distance to escape terrain, vegetation, and terrain ruggedness relative to known 

sheep locations during the winter and summer. The model identified the relative 

probability, from 0 to 100 percent, that bighorn sheep were likely to select a given area 

within the Sierra Nevada based on that area’s habitat characteristics. These probabilities 

were identified for both summer and winter seasons. All areas with probabilities greater 

than 90 percent were identified as either winter or summer range for the Sierra Nevada 

bighorn sheep (i.e. if the winter range probability value was greater than 90 percent for a 

given area, that area was identified as winter range; if the summer range probability value 

for a given area was greater than 90 percent, that area was considered to be summer 

range). 

The predicted areas of summer and winter range largely conformed with the herd 

units identified in the 2003 draft recovery plan, but some modifications to the herd unit 

boundaries were made based on the model results. The Twin Lakes (non-essential) and 

Mount Langley (essential) herd units were increased in size, the Bubbs Creek (nonessential) herd unit was added, and the Sawmill Canyon (essential) herd unit was slightly 

modified. In addition, the Mount Warren and Lundy Canyon Herd Units were combined, 

and the Wheeler Ridge and Mount Tom Herd Units were combined. 

Some areas that the model predicted as summer or winter range were not included 

in the new herd unit boundaries because they were not located in areas that would 

facilitate movement between them and other areas of predicted summer or winter range. 

Conversely, some areas within the herd units that the model did not identify as summer or 

winter range were still included because they provide the required connectivity between 

summer and winter range to facilitate migration. 
39

Eight of the herd units currently support bighorn sheep. Herds to be reestablished in the remaining units are expected to support geographically distinct groups 

of females. It is possible, however, that some may support more than a single group of 

females exhibiting distinct home range patterns. Of the 16 herd units, 12 herd units have 

been identified as essential because they are most likely to support recovery of the 

species (Figure 4, Table 4). 

We have determined that Twin Lakes, Green Creek, Bubbs Creek, and Coyote 

Ridge Herd Units are not essential for the conservation of the Sierra Nevada bighorn 

sheep. These herd units are considered not essential because we believe that the 12 

essential units will provide the necessary habitat and area to insure the viability and longterm survival of the Sierra Nevada bighorn sheep at the local and DPS population levels. 

These are the herd units where recovery actions will be focused in order to 

achieve the recovery criteria below. 
40

Figure 4 - Essential herd units within the four recovery units. These are locations 

essential to the recovery of the bighorn sheep. 
41

Table 4. Recovery units and herd units (essential and non-essential) used as the basis of 

recovery goals (see Figure 1). Asterisks identify herd units that must be occupied for 

delisting (i.e., are essential). 

Recovery Units and Herd Units Minimum Elevation (ft)

Kern Recovery Unit

1. Laurel Creek* 6800

2. Big Arroyo* 6900 

Southern Recovery Unit

3. Olancha Peak* 4800 

4. Mount Langley* 4800 

5. Mount Williamson* 6200 

6. Bubbs Creek 6800 

7. Mount Baxter* 4900 

8. Sawmill Canyon* 4800 

9. Taboose Creek* 6800 

10. Coyote Ridge 5600 

Central Recovery Unit

11. Wheeler Ridge* 5600 

12. Convict Creek* 7900 

Northern Recovery Unit

13. Mount Gibbs* 7600 

14. Mount Warren* 7600 

15. Green Creek 9000 

16. Twin Lakes 7200 

Three natural breaks in the distribution of the 16 herd units separate them into 

four distinct regions. Those four larger regions are termed recovery units, and are treated 

as the basic units for recovery of this taxon. Within recovery units, males are expected to 

move between herd units. However, movement between recovery units is likely to occur 

less frequently. Movements by males are likely to be the primary source of natural gene 

flow. 

The rate at which females in the Sierra Nevada colonize vacant habitat is 

unknown. Dispersal between adjacent herd units within recovery units should occur with 

considerably higher probability than across the gaps that define recovery units, and thus 

has implications for the natural recolonization of herd units that become extirpated. 

However, inter-herd movements also can spread diseases (Dobson and May 1986, Bleich 

et al. 1990a, 1996). Consequently, unoccupied areas between some recovery units may 

be considered zones of isolation that could limit the spread of epizootics throughout the 

range of Sierra Nevada bighorn sheep. 
42

Downlisting Criterion A1: Downlisting will require a minimum total of 305 

females at least 1 year of age. At least 50 of those females must be in the Kern Recovery 

Unit, 155 females in the Southern Recovery Unit, 50 females in the Central Recovery 

Unit, and 50 females in the Northern Recovery Unit (Table 5). The number of females is 

the limiting factor in reproductive output because one male can produce offspring with 

several females. Consequently, we have not set a delisting criterion that considers the 

male population size within recovery units. However, Delisting Criterion B2 does 

address males in terms of their occupation of some herd units prior to delisting. 

Justification: The relative number of requisite females for each of the four 

recovery units is based on differences in habitat quantity and quality among the herd 

units. Analyses of recent population growth curves for the Mount Langley and Wheeler 

Ridge herds have shown density-dependent patterns of lamb recruitment that allowed 

quantitative estimates of carrying capacities. Population carrying capacities also could be 

estimated for two other herds in the late 1970s when population growth rates indicated 

that they were at or close to carrying capacity. Habitat differences between those four 

populations and other herd units were used to estimate unknown carrying capacities. 

Habitat characteristics that were considered included the amount and minimum elevations 

(Table 4) of winter ranges and relative amount of high elevation habitat where it was 

likely to be limiting. Resulting carrying capacities varied from 15 to 80 females. Those 

carrying capacities were summed for each recovery unit for the essential herd units 

(Table 4), and that sum was halved to arrive at the minimum number of females needed 

by actual count for downlisting and delisting. That total was then adjusted to average at 

least 25 females per herd unit. The 50 percent criterion was based on recognition of the 

following: 

(1) There is a need for these goals to be realistic and attainable. The data used as the 

basis of downlisting will be minimum counts that likely will be less than actual 

sizes for many herds. There is evidence that minimum counts for some Sierra 

Nevada herds have recently accounted for essentially every female. However, as 

herds increase in size, it is anticipated that it will become more difficult to make 

such complete counts. This may be particularly difficult for some herds that will 

be reintroduced to more remote areas in the Sierra Nevada where the intensive, 

repeated ground efforts needed for complete counts will not be possible. The 

greater number of herds that will need to be monitored also may decrease the 

efficiency of counts of individual herds through dilution of effort. Relative to 

recovery goals, use of data from minimum counts as the basis of recovery goals 

provides an important buffer in the form of uncounted sheep. 

(2) Carrying capacities used were estimates that involve error. While the magnitude 

of that error is not known, it is very unlikely to approach 50% of the estimated 

carrying capacity. An alternative approach in which a minimum average of 25 

females per herd unit identified for recovery is applied to all recovery units 
43

produces essentially the same downlisting numbers listed in Table 5. The 

dynamics of populations may not be synchronous; thus, all herds might not be at 

or near carrying capacity at the same time. Dropping downlisting requirements 

well below estimated carrying capacities provided for that possibility. 

(3) Growth of the last herd to be reintroduced to the Kern Recovery Unit can be 

expected to limit attainment of overall downlisting criteria, at which time many 

other herds probably will have approached carrying capacity. Consequently, 

when minimum goals are actually reached, total numbers can be expected to 

exceed those goals by a considerable margin. If carrying capacities estimated for 

these recovery goals are not significant overestimates, the actual total number of 

females may approach or exceed 500 when downlisting criteria are attained, 

which could put the total population over 1000. Prior to reaching those goals, 

there also will have been a substantial period of overall population growth, which 

will provide an additional metric of demographic health. 

Downlisting can occur upon reaching these reproductive base thresholds, which 

will minimize extinction risk through: (1) considerable geographic distribution; (2) 

sufficient numbers to provide multiple sources of sheep for translocation to help any 

faltering herds and/or to establish sheep in unoccupied areas identified as necessary for 

recovery; and, (3) minimal loss of genetic variation through drift. The recovery plan’s 

science team has determined that occupation of all four geographic conservation areas 

(Recovery Units) is necessary to: (1) develop sufficient numbers of sheep; (2) have sheep 

in enough isolated areas to make it highly unlikely that all would go extinct 

simultaneously from a stochastic event; (3) minimize the loss of genetic diversity; and (4) 

to protect against ecological changes brought on by climate change. Because of the 

possibility of natural, independent dynamics among the different herds, minimum sizes 

were set for each of the recovery units, but not for any individual herd units. However, 

based on current information recovery is most likely to occur in the essential herd units 

depicted in Table 4 and Figure 4. 

Downlisting Criterion A2: The measures to prevent contact between domestic 

sheep/goats and bighorn sheep have been implemented and are successful. 

Justification: Any contact between domestic sheep or goats and bighorn sheep 

could lead to the loss of entire herds of bighorn sheep in the Sierra Nevada. Hence, 

potential for contact between bighorn sheep and domestic sheep or goats must be 

eliminated to avoid the possibility of a catastrophic epizootic. Bighorn sheep and 

domestic sheep or goats can come into direct contact through the movements of either 

species. As recovery proceeds, and the numbers and geographic distribution of bighorn 

sheep increase, the potential for contact also will increase. 
44

b. Delisting Criteria 

Delisting Criterion B1: The number of female bighorn sheep required for 

downlisting by recovery unit (Table 5) will be maintained as an average for at least seven 

years (one generation) without intervention (i.e. population management, buffering 

populations through translocations, captive breeding, etc.). Herd status for delisting must 

entail at least three censuses, one at the beginning of the period (qualifying for 

downlisting), one at the end of the period, and one intermediate count for each herd unit. 

Delisting Criterion B2: Bighorn sheep of both sexes will be present in a 

minimum of 12 specifically identified herd units distributed as two in the Kern Recovery 

Unit, six in the Southern Recovery Unit, two in the Central Recovery Unit, and two in the 

Northern Recovery Unit (Table 4 and Figure 4). 

Justification: The target number of occupied herd units for delisting (Table 5) 

was based on realistic expectations. There is uncertainty about whether it will be 

possible to establish herds of bighorn in three of the herd units (Coyote Ridge, Green 

Creek, and Twin Lakes; Figure 1, Table 4) because of habitat limitations; thus, those 

three were not included in the delisting criteria. Additionally, the Bubbs Creek herd unit 

is not required to be occupied in the delisting criteria. Bighorn sheep discovered there in 

2001 were likely a recent colonization. That herd unit is west of the crest of the Sierra 

Nevada where snowfall is much greater than the east side of the range. Because there are 

no historical records of bighorn sheep in the Bubbs Creek region, there is uncertainty as 

to the long-term viability of this herd unit. Consequently, it is not required to contain 

bighorn sheep for delisting. 

These criteria result in a total requirement of 12 occupied essential herd units 

(Figure 4) and 305 females at least 1 year of age necessary for delisting (Table 5). With a 

natural adult sex ratio of about 70 males:100 females (Wehausen 1980), the minimum 

total population at both downlisting and delisting will be about 520 adults. Because this 

number is based on minimum requirements for each recovery unit, the total population 

will almost certainly be higher and probably will be considerably higher with young of 

the year included and larger numbers well above minima in some recovery units, as 

discussed above. The time requirement of one generation will assure the maintenance of 

these populations and distribution conditions across all recovery units while much of the 

population is replaced through mortality and recruitment. In addition, a period of 

substantial population growth will necessarily precede the initial attainment of conditions 

necessary for delisting. Thus, a period of favorable population conditions encompassing 

multiple generations will precede attainment of minimum population requirements for 

delisting. 
45

Delisting Criterion B3: A population viability analysis projects that all recovery 

units are viable. Recovery tasks related to monitoring and research have been 

accomplished, allowing the severity of secondary threats (including vegetation 

succession, recreational disturbance, and loss of genetic diversity) to be adequately 

assessed. Threats have either been ameliorated or have been determined not to pose a 

significant risk to the population. 

Justification: Before we determine that the Sierra Nevada bighorn sheep warrants 

delisting, additional information is needed regarding which threats significantly endanger 

the population. Research is needed on the threats noted above which may have potential 

for long-term adverse effects on the population. Research and monitoring tasks should 

assess which threats are significant and if necessary identify appropriate management 

actions to implement. 

Delisting Criterion B4: Regulatory mechanisms and land management 

commitments have been established that provide for long-term protection of Sierra 

Nevada bighorn sheep and both their summer and winter habitat. Protection considered 

long-term can be provided through appropriate institutional practices and cooperative 

agreements between agencies, landowners, and conservation organizations. For example, 

management plans (e.g., forest plans) for Federal lands should provide adequate 

assurances of habitat protection prior to consideration of delisting. Reasonable assurance 

must exist, on a case-by-case basis, that conditions that brought about population stability 

will be maintained. 

Justification: Delisting would no longer require protection under the Endangered 

Species Act; therefore, continued protection by other means must be assured. This 

protection should include alternative regulatory mechanisms, land management 

commitments, or conservation programs that would provide the long-term protection 

needed for continued population viability. 

c. Recovery Units 

The delisting criteria include only 12 of the 16 herd units within the four recovery 

units because of uncertainty as to whether viable bighorn sheep herds can persist in four 

of those units (numbers 6, 10, 15, and 16 in Table 4). The recovery plan’s science team 

has determined that all four recovery units and the 12 essential units (Figure 4) within 

those recovery units are necessary for the recovery of the species for multiple reasons. 

First, it may be necessary for all 12 herd units to be occupied to attain the minimum total 

population size of 305 females. 

Second, given the likelihood that the four recovery units may function as 

independent metapopulations to some extent, it is important to develop sufficient 

distribution in each to buffer them against catastrophic losses of individual herds. There 
46

is also a need to have enough recovery units as a buffer against a catastrophic loss of an 

entire recovery unit. By the nature of the distribution of habitat in the Sierra Nevada, 

only one recovery unit (Southern) has enough herd units to potentially support a large 

population of sheep. Two of the remaining three recovery units (Kern and Central) 

contain only two herd units each, while the Northern Recovery Unit has four, of which 

the two northernmost may not support many sheep and are not considered essential to 

recovery. The Southern Recovery Unit provided the translocation stock for the early 

reintroduction, and should be able to do the same in the future to restore sheep to vacant 

habitat that exists (i.e., herd units that are essential to recovery) or might become vacant 

in other recovery units. The limited number of herd units in those other recovery units 

makes them less reliable as potential sources of translocation stock, should a catastrophe 

occur in the Southern Recovery Unit, requiring sources of stock from other recovery units 

for restoration. The uncertainties about the overall population sizes that those smaller 

recovery units may support is an important reason why all four recovery units are needed 

to assure the future of these sheep. 

Third, it is also important to have as many bighorn sheep in each recovery unit to 

minimize the loss of genetic diversity through genetic drift. Similarly, there is a need to 

maximize geographic continuity in the distribution of herds in order to facilitate genetic 

interchange among herd units within recovery units, as well as some interchange among 

recovery units. Stemming further loss of genetic diversity in Sierra Nevada bighorn 

sheep may prove to be the greatest challenge for their recovery (Appendix H). 

Fourth, it is important to provide recovery units and essential herd units that 

protect sheep and their habitat across a range of latitudes. Gradual climate changes are 

likely to induce ecological changes in southern recovery units and essential herd units 

over time. These changes would likely preclude the recovery of populations in these 

areas. Consequently, bighorn sheep populations in more northerly latitudes can buffer 

the rangewide population against the loss of populations in essential herd units that are 

further to the south. 
47

Table 5. Minimum number of females and occupied herd units (see Table 4) required for 

downlisting and delisting of Sierra Nevada Bighorn Sheep by recovery units. As of 

2005, at least 146 additional females were needed for downlisting, and 4 herd units 

needed for delisting were vacant. 

Herd Units Occupied Females at least 1 year of age 

Recovery 

Unit Current Potential 

Delisting/ 

Downlisting

Additional 

Needed 

Delisting/ 

Downlisting 

Minimum 

2005 

Minimum

2004 

Minimum

Kern 0 2 2 2 50 0 0 

Southern 5 8 6 1 155 102 92 

Central 1 2 2 1 50 45 40 

Northern 2 4 2 0 50 12 16 

Total 8 16 12 4 305 159 148 

C. RECOVERY STRATEGY 

Because bighorn sheep are naturally slow to disperse and colonize new habitat, 

recovery of Sierra Nevada bighorn sheep within a reasonable period will ultimately 

depend on translocations of bighorn sheep into unoccupied herd units that are needed for 

recovery, or to aid in the recovery of occupied herd units. A translocation program will 

require one or more sources of Sierra Nevada bighorn sheep with known bacterial and 

viral histories. Identifying and developing those sources from the current limited herds is 

one of the greatest challenges to recovering this subspecies. The rate of recovery will, in 

part, be tied to the number of herds capable of producing bighorn sheep for translocation. 

The protection and enhancement of existing herds to maximize population growth is the 

first step. The major threats to existing herds have been decreased survivorship and 

reproductive success associated with remaining at high elevations throughout the year, 

and potential outbreaks of disease contracted from domestic sheep or goats. Therefore, 

predator management (to reduce direct mortality and encourage use of low-elevation 

wintering ranges) and changes in domestic sheep grazing practices (to prevent contact) 

are key aspects of the recovery strategy. This strategy will necessarily be supplemented 

by habitat management (to promote open habitat where predators are readily visible) and 

perhaps establishment of a captive breeding facility. Genetic considerations are also 

critical because the small size and isolation of existing populations threatens to reduce the 

variability of this unique gene pool. Because maintaining a viable metapopulation will 

require a broad, minimally fragmented spatial distribution of subpopulations over the 

landscape, recovery criteria have been defined based on population sizes and occupied 

herd units within specified recovery units (section II.B.2). 
48

Monitoring and research are necessary to provide the basis for adaptive 

management and, as such, are essential components of this recovery plan. Recovery 

actions for the bighorn sheep will depend on regularly updated information on population 

parameters and habitat use patterns for each herd. Similarly, a detailed assessment of the 

genetic population structure of each herd is necessary as the basis for genetic 

management. Monitoring of mountain lions near bighorn sheep winter ranges will 

greatly enhance efforts to protect herds. Finally, outreach to enlist public support for 

recovery efforts will be important to the success of this plan. 

D. NARRATIVE OUTLINE OF RECOVERY ACTIONS 

1 Protect bighorn sheep habitat. 

1.1 Identify and acquire important habitat not in public ownership from 

willing landowners. While the vast majority of historic bighorn sheep 

range in the Sierra Nevada is in public ownership, a small number of inholdings exist. A list of all private land holdings that might affect bighorn 

sheep should be developed and prioritized relative to importance to 

bighorn sheep. Key parcels should be acquired or protected under 

conservation easements. See Task 2.3.1 and Section E (below) for more 

detail on implementation of this recovery action. 

1.2 Maintain and/or enhance integrity of bighorn sheep habitat. Habitat 

integrity could be compromised by fire suppression that affects vegetation 

succession (see Task 2.2.3), or a variety of human uses (see Task 2.4). 

Human activities resulting in blockage or alteration of movement corridors 

(e.g., San Joaquin Ridge) would have ramifications for gene flow between 

or among populations (Bleich et al. 1990a, 1996). Further, the potential 

for natural recolonization of vacant habitats would be severely reduced. 

Although these issues are considered with respect to bighorn sheep 

behavior and population parameters, they also are important relative to 

structural attributes of the habitat. All proposed Federal actions in the 

vicinity of bighorn sheep habitat should be analyzed relative to influences 

on that habitat and, ultimately for negative impacts to the viability of 

bighorn sheep. 

2 Increase population growth by enhancing survivorship and reproductive 

output of bighorn sheep. Recovery of these bighorn sheep requires an overall 

population increase. Enhancing survivorship and reproduction wherever possible 

will speed recovery. To the extent that these parameters are enhanced through 

increased nutrient intake by more extensive use of habitat, the carrying capacity 

of herd units also will be increased.
49

2.1 Prepare and implement a management plan to temporarily protect 

Sierra Nevada bighorn sheep herds from predation losses, where 

needed, until viable herd sizes are reached. The management plan must 

address the immediate needs for selective predator management while 

allowing for a long-range approach that restores and maintains the health 

of the larger predator-prey system. Known predation losses have been 

primarily attributed to mountain lions (Table 1). Thus, efforts to prevent 

further losses should focus on this predator, but not ignore other potential 

predators. 

Individual mountain lions can vary in behavior, including whether they 

prey on bighorn sheep and whether immigrating lions become potential 

threats for each herd when resident lions are removed. Therefore, this 

management plan should attempt to set up criteria to remove only lions 

that are a threat. Radio-collaring and careful monitoring of mountain lions 

near bighorn sheep winter ranges will help with selective removal (see 

Task 5.2 and Appendix E). Additionally, the need to protect bighorn 

sheep should be carefully balanced with concerns for the viability of the 

mountain lion population. Potential effects of mountain lions on winter 

habitat selection by bighorn sheep should be included in this predator 

management plan; this aspect is addressed below in Task 2.2. 

Predator management should be viewed as a temporary measure. It should 

be terminated when herd units reach a reproductive base of 25 females, 

with the possible exception of herd units serving as sources of 

translocation stock. It should be reinstated if a herd unit subsequently 

declines below 20 females and predators are preventing recovery of that 

herd unit. Biologists familiar with bighorn sheep have independently 

arrived at a threshold of 25 females as the minimum number for herd 

viability (Sierra Nevada Bighorn Sheep Interagency Advisory Group 

1997, Fisher et al. 1999, U.S. Fish and Wildlife Service 2000). 

2.2 Increase use of low elevation winter ranges. Increased use of low 

elevation winter ranges will increase nutrient intake and thereby enhance 

reproductive output and success. Increased low elevation winter range use 

will also decrease mortality associated with the use of high elevations 

during severe winters. 

2.2.1 Reduce influences of predation on winter habitat selection by 

Sierra Nevada bighorn sheep. Adult survivorship and 

recruitment can be negatively affected when bighorn sheep avoid 

low elevation winter ranges. Winter habitat selection may 

influence population dynamics more than direct losses from 
50

predation. Reducing influences of predators on winter habitat 

selection may, therefore, be important. Until some herds build 

sufficient numbers, it could be necessary to remove mountain lions 

from key winter range areas or condition mountain lions to avoid 

those areas (see Task 6.5). If aversive conditioning is successful, 

the maintenance of home ranges by conditioned resident lions may 

discourage immigration of unconditioned lions and thereby reduce 

the number of lions that need to be removed. 

2.2.2 Supplement small female groups where appropriate to attain 

threshold herd sizes that will encourage behavioral attributes 

favorable to winter range use. Because bighorn sheep find 

security in groups, habitat selection during winter may be affected 

by the number of bighorn sheep available to form groups. Adding 

healthy females to small female groups in herd units that are 

needed for recovery (identified with asterisks in Table 4) may 

produce significant increases in uses of winter ranges and, thereby, 

increase adult survivorship as well as recruitment rates. Further, 

behavior of bighorn sheep previously translocated in the Sierra 

Nevada indicates that females translocated from populations that 

use low elevations will initially attempt to do the same on new 

ranges. The ability to augment small herds is currently limited by 

the lack of sources of bighorn sheep that can be moved. The 

development of sources of bighorn sheep to move is fundamental 

to achieving this task and is addressed in task 3.2. 

2.2.3 Enhance bighorn sheep winter range habitat to increase 

visibility where appropriate. Favorable attributes of bighorn 

sheep habitat are steepness, rockiness, and visual openness. 

Although steepness and rockiness cannot be changed, openness 

can be modified via management of vegetation. In the past, fires 

may have burned in bighorn sheep habitat much more frequently 

than has occurred over the past century. Early ground and aerial 

photos indicate that habitats in the eastern Sierra Nevada had little 

vegetation tall enough to obstruct vision of bighorn sheep, and 

pinyon pine woodlands largely have developed since 1860 (Miller 

and Tausch 2001). In opening up habitats, fire can decrease the 

effectiveness of mountain lions as ambush predators and, perhaps, 

allow bighorn sheep greater access to low elevation winter ranges 

that provide nutritious forage. Policies to let fires burn in bighorn 

sheep habitat, coupled with prescribed fire or other methods of 

habitat manipulation, should be used to enhance winter ranges 

where visibility for bighorn sheep needs to be increased. Such 
51

habitat enhancements will likely produce greater connectivity 

among herd units and promote greater gene flow needed to 

conserve genetic diversity (see Appendix H). 

2.3 Minimize probability of bighorn sheep contracting diseases causing 

mortality and morbidity. Introduced diseases have probably been the 

primary cause of extirpation of bighorn sheep herds in North America. 

They represent one of the greatest threats. 

2.3.1 Prevent contact between bighorn sheep and domestic sheep or 

goats. Prevention of contact between domestic sheep or goats and 

bighorn sheep will require coordination and cooperation between 

grazing permittees, land management agencies, and regulatory 

agencies. We recognize the need to provide specific guidance to 

land managers regarding allotments and grazing practices that are 

likely to result in contact between domestic sheep or goats and 

bighorn sheep. A risk assessment is currently being developed to 

be used as a tool for analyzing grazing practices on certain 

allotments. Land management agencies should utilize this risk 

assessment and coordinate with other agencies to implement 

measures that will prevent contact between domestic sheep and 

bighorn sheep. These measures may include seasonal grazing 

restrictions, implementation of specific herding practices (penning, 

trailing restrictions, etc.), or removal of bighorn sheep from certain 

high-risk areas, but may require the ultimate closure of some 

allotments that cannot be grazed in a manner that prevents contact. 

Based on current data on bighorn sheep movements, we are 

recommending the closure of some high-risk allotments and 

seasonal restrictions on other allotments in the interim (See Section 

E below). In addition, we recognize the need to address the 

potential for contact between domestic sheep or goats and bighorn 

sheep on private lands, so we are recommending a strategy of 

landowner education, conservation easements, and land acquisition 

(See Section E below). In addition, we are recommending a 

strategy for incorporation of the risk assessment for analysis of 

future disease transmission risk on other allotments that may 

become higher risk as bighorn sheep expand their current 

distribution (See Section E below). 

2.3.2 Develop an action plan in the event that a pneumonia outbreak 

occurs. History is replete with examples of decimation and 

extirpation of bighorn sheep herds from pneumonia epizootics. 
52

Quick and decisive actions may save part of a herd, or other nearby 

herds, in such an event. The development of an action plan prior 

to such an occurrence may be critically important to taking timely 

actions. This plan should include actions needed if a bighorn 

sheep is found in contact with domestic sheep or goats. 

2.4 Manage human use locally where it is found to cause bighorn sheep to 

avoid important habitat and thereby compromises survivorship or 

reproductive success. This action will take place only if research (see 

Task 6.4) results in a recommendation to limit human use in some areas; at 

present there appear to be few locations where recreational disturbance has 

the potential to significantly affect bighorn sheep. Focused research on 

effects of human activities on bighorn sheep will determine whether any 

limitations on human use are required. If it is concluded that limitations 

will be beneficial, appropriate actions should be taken to limit human use 

that is found to be detrimental. Disturbance by humans (or possibly by 

off-trail domestic dogs) will be significant to bighorn sheep if nutrient 

intake of a herd is compromised by avoiding key foraging areas because of 

human activity. Both quality and quantity of forage vary greatly across 

the landscape, and bighorn sheep visit key locations where more nutritious 

forage is available. If bighorn sheep are regularly displaced from such 

areas and cannot procure equivalent nutrient intake at an alternative site, 

population parameters of the herd will be negatively affected. If they 

frequently flee encounters with humans, there may also be an unnecessary 

waste of energy that can have population-level effects. 

3 Increase the number of herds, and thereby the number of bighorn sheep. It 

will be necessary to increase the geographic distribution and overall numbers of 

bighorn sheep in the Sierra Nevada to attain criteria necessary for downlisting and 

delisting. 

3.1 Develop and implement a strategy for translocations. Because of the 

slow rates of natural colonization by bighorn sheep, recovery can be 

accelerated by translocations to originate herds in unoccupied herd units 

that are needed for recovery and to augment currently occupied herd units 

that are needed for recovery. Because there are domestic sheep grazing 

allotments in close proximity to the unoccupied Green Creek and Twin 

Lakes Herd Units and because these areas are not needed for recovery, 

these herd units should not be considered for translocations. It will be 

important to utilize the limited number of Sierra Nevada bighorn sheep 

available for translocations in a way that maximizes recovery of Sierra 

Nevada bighorn sheep in the shortest period. A strategy is needed that 

clearly identifies issues, options, and tradeoffs, and analyzes different herd 
53

units as potential recipients of translocated bighorn sheep (See Appendix 

C). This strategy should seek to avoid translocations that could result in 

introduction of disease-causing pathogens into a herd that is not adapted to 

them. Extensive records of disease and pathogen sampling histories need 

to be kept for translocation stock herds and for existing herds that may 

receive translocated bighorns to reduce the likelihood of introducing 

pathogens that the recipient herd is not adapted to. 

3.2 Develop sources of translocation stock. Availability of bighorn sheep to 

be translocated has been, and continues to be, the primary factor limiting 

recovery of bighorn sheep in the Sierra Nevada. Only one source of stock 

was available for previous restoration efforts (see section I.C.2). The 

vulnerability of that situation led to the proposal to develop additional 

such sources as the primary goal of an earlier conservation plan for these 

bighorn sheep (Sierra Nevada Bighorn Interagency Advisory Group 

1984). Additional sources of translocation stock will continue to be a 

fundamental need. 

3.2.1 Manage wild herds as sources of stock. Developing sources of 

translocation stock will depend on sufficient recovery of at least 

one existing herd to the point where bighorn sheep can be removed 

for translocation. All or most of the first available translocation 

stock should be used to develop one or more additional sources of 

such stock. However, a small fraction may be used for increasing 

the size of populations that will not be translocation stock, or to 

increase the number of herd units that are occupied. This strategy 

will increase the rate of recovery of these bighorn sheep. 

3.2.2 Develop criteria for and, if appropriate, implement a captive 

breeding program. In addition to wild populations as a source of 

translocation stock, a captive breeding facility might be necessary 

in the future. Such a facility may produce bighorn sheep more 

rapidly, but it also could pose risks. Aspects of captive breeding as 

a potential program have been investigated and a detailed captive 

breeding contingency plan was developed, which can be found at: 

http://www.vgl.ucdavis.edu/wildlife/sheep_plan.html (see 

Appendix I for executive summary). 

4 Implement a genetic management plan to maintain genetic diversity of Sierra 

Nevada bighorn sheep. The plan must use data on genetic variation gathered 

in Task 6.1. Restoration of bighorn sheep to unoccupied herd units that are 

needed for recovery in the Sierra Nevada will be accomplished largely through 

translocations. However, translocations alone may not maximize conservation of 
54

the genetic variation that currently exists. There is a need to consider long-term 

genetic management in conjunction with the translocation strategy to best 

conserve genetic variation throughout the range of these bighorn sheep. Task 6.1 

has been completed and the genetic management plan can be found in Appendix 

H. 

5 Monitor status and trends of bighorn sheep herds, their habitat, and threats 

to them. Recovery of bighorn sheep in the Sierra Nevada will require an adaptive 

approach, one in which decisions made will depend on current information about 

key resources. Consequently, monitoring of those resources is a fundamental 

component of this recovery plan. 

5.1 Develop and implement a monitoring plan for population abundance 

and distribution of bighorn sheep herds in the Sierra Nevada. 

Management actions will be dependent on the best possible data on the 

population status of each herd. Downlisting and delisting criteria also are 

dependent on that information and were developed in part with the 

recognition that minimum counts will be the most conservative data to use 

as the basis of management decisions. Appendix D considers further 

details of this monitoring, and provides recommendations that will form 

the basis for development of detailed monitoring strategies. 

Recent population dynamics of Sierra Nevada bighorn sheep indicate that 

recovery to adequate population levels will occur only with increased use 

of winter ranges. Trends in the use of winter ranges need to be monitored 

in conjunction with population monitoring to project future population 

trends. They will also allow efforts to focus on herds that are reluctant to 

use winter ranges. 

5.2 Monitor key predators in the vicinity of winter ranges. Efforts toward 

the recovery of Sierra Nevada bighorn sheep necessarily take place in a 

larger ecosystem context. Because management of predators, especially 

mountain lions, is a component of this recovery plan, careful monitoring 

of these predators near bighorn sheep populations is important. Such 

monitoring will provide data on how individual mountain lions, and 

mountain lions in general, use habitat in the vicinity of each population of 

bighorn sheep, and will allow an assessment of which mountain lions pose 

the greatest threats to bighorn sheep, and when those threats are greatest 

(see Appendix E). 

5.3 Monitor vegetation structure and composition changes likely to affect 

bighorn sheep population parameters. In the absence of regular fires, 

vegetation succession can slowly decrease openness in bighorn sheep 
55

habitat. Vegetation structure and its concomitant effects on visibility 

should be monitored on a long-term basis. 

5.4 Monitor exposure to disease organisms of concern. When bighorn 

sheep in the Sierra Nevada are captured for management operations, 

appropriate sampling and testing of those animals for disease pathogens 

should take place to develop a continuing database that will potentially 

detect changes over time. A large database already exists from captures 

beginning in 1979. This database will continually be updated and will be 

used when making decisions regarding translocations from source stock 

herds to recipient herds. 

6 Initiate or continue needed research. An adaptive approach to management 

will require development or continuation of existing research. 

6.1 Investigate genetic population structure of existing herds. The 

conservation of the gene pool of bighorn sheep in the Sierra Nevada will 

depend on a detailed understanding of the distribution of genetic variation 

and the dynamics within that genetic population structure. There is need 

to develop a genetic database and to use it as the foundation for a genetic 

management plan (see Task 4). Specific data needs: (1) current amount 

of genetic variation compared with other metapopulations of bighorn 

sheep; (2) distribution of genetic variation among the different herds; and 

(3) population genetic changes in each herd to determine if future erosion 

of genetic diversity is likely to be a problem. These studies are possible 

with modern laboratory techniques by using a variety of sources of DNA. 

6.2 As adequate input data become available, develop a population 

viability analysis (PVA) for the Sierra Nevada bighorn sheep 

metapopulation. We attempted to define recovery goals and criteria that 

were attainable and realistic based on our current knowledge about the 

population ecology of these sheep. PVA sometimes can identify a key 

variable that is particularly influential to long-term population viability. 

However, as a modeling procedure, PVA results can be greatly influenced 

by values used for input parameters. Because some uncertainty will 

surround most such values, it will be particularly important to use 

sensitivity analyses to investigate the influences of input values on 

conclusions. 

6.3 Further investigate habitat use patterns of bighorn sheep herds. A 

large database of sightings of bighorn sheep in the Sierra Nevada has been 

accumulated by researchers over the past 25 years (Figure 1). Population 

substructuring of female groups also has been identified and postulated 
56

based on marked bighorn sheep. However, because of sampling 

limitations, these data do not provide details of habitat use throughout the 

year or the degree of separation of female groups. Global positioning 

system collars may provide an efficient method of developing detailed, 

accurate information on the seasonal distribution and habitat selection 

patterns of these bighorn sheep. 

 

6.4 Investigate and analyze human use patterns relative to habitat use 

patterns of bighorn sheep. Earlier investigations of hypotheses 

concerning human disturbance (Dunaway 1971) dismissed it as not 

important for the Mount Baxter herd, but possibly a factor for the Mount 

Williamson herd (Wehausen et al. 1977, Hicks and Elder 1979, Wehausen 

1980). Bighorn sheep have been reintroduced to three additional areas 

since the earlier studies, but these new herds have not been investigated to 

determine the possible impacts of human disturbance. There is a need to 

investigate patterns of use by humans and domestic dogs including 

intensity, trends, and types of use in and near existing bighorn sheep 

habitat to identify areas of possible conflict. If areas of concern are 

identified, intensive studies to investigate whether human disturbance may 

be displacing bighorn sheep from favorable habitat can be initiated. 

Potential reintroduction sites also should be investigated to identify areas 

of possible conflict. 

6.5 Investigate the potential for altering habitat use patterns of mountain 

lions on bighorn sheep winter ranges by aversive conditioning. 

Altering the behavior or distribution of mountain lions through aversive 

conditioning may provide an alternative to temporary management 

involving removal of mountain lions that may kill bighorn sheep. If 

effective, this approach may allow the recovery of bighorn sheep with less 

intervention. Aversive conditioning of mountain lions is an untested 

concept, and it can be investigated in situations that minimize risks to 

bighorn sheep. 

6.6 Investigate future introduction sites relative to predator, domestic 

sheep or goats, and other potential conflicts. Like the genetic 

management plan, this investigation should be coordinated with the 

translocation strategy. One product of a translocation strategy will be the 

identification of priority for future reintroduction sites that is based on 

habitat characteristics and spatial relationship to existing herds. Once this 

priority is established, sites of top priority should be investigated for 

potential conflict with predators, domestic sheep, domestic goats, or other 

concerns. 
57

6.7 Investigate and, if appropriate, develop a plan for decreasing the 

mortality of bighorn sheep remaining at high elevations in extreme 

winters. The bighorn sheep on Mount Warren have experienced major 

population declines during recent severe winters while attempting to live 

at high elevations year around. While an emphasis of this plan is to 

attempt to develop more low elevation winter range use, it also is 

important to maintain numbers of bighorn sheep until such changes in 

habitat use patterns take place. Supplemental feeding of bighorn sheep at 

high elevations during severe winters could be crucial to their survival. 

This subject should be explored in detail and an action plan developed as 

appropriate. 

6.8 Attempt to develop long-term data to elucidate predator-prey 

dynamics of this ecosystem as they affect bighorn sheep. During the 

1980s, bighorn sheep in the Sierra Nevada began to avoid low elevation 

winter ranges, a pattern of behavior that has, in turn, led to major declines 

in the population. This dynamic appears to reflect predator-prey processes 

that are not fully understood but that clearly can affect the bighorn sheep 

population. A better understanding of the larger predator-prey system is 

needed and will require long-term information. Some of the components 

of this system (bighorn sheep, mountain lions, and possibly other 

predators) will be tracked as part of the monitoring for this recovery effort. 

Mule deer, the primary prey of mountain lions, are a key component of 

this ecosystem. Monitoring the dynamics of the mule deer population is 

basic to developing an understanding of this predator-prey system. Other 

potentially important components that are not currently monitored should 

be identified and efforts made to add them to the monitoring scheme to 

understand the dynamics of this system. 

6. 9 Investigate likely effects of climate change on bighorn sheep habitat. 

Climate change models predict changes in temperature and precipitation in 

the range of Sierra Nevada bighorn sheep (e.g. Knowles and Cayan 2004, 

Lenihan and Drapek 2006, Diaz and Eischeid 2007). In particular, these 

include milder winters, less precipitation falling as snow over a shorter 

winter period, and possibly increased total annual precipitation. These 

changes could potentially cause earlier seasonal drying of high-elevation 

meadows, conifer trees invading higher elevations, and changes in 

summer- and winter-range quality and accessibility in the Sierra Nevada. 

Additional factors may include the interaction of invasive alien plant 

species with climate change and increased atmospheric nitrogen 

fertilization from air pollution. These effects would alter the distribution 

of high-quality bighorn summer and winter habitats, which would 

influence recovery. 
58

7 Engage in public outreach and sharing of information. The overriding 

purpose of the Sierra Nevada bighorn sheep public information and outreach 

effort is to foster understanding, respect, and concern for this species, and 

understanding of and support for conservation measures and recovery actions. A 

number of recovery actions outlined in this recovery plan will directly affect 

public use in the eastern Sierra Nevada and, conversely, human activities may 

affect recovery actions. It is therefore imperative that strong public information 

and awareness programs be implemented. Agencies working on recovery of this 

species should work with the public to ensure that they are informed about 

potential human actions that may affect bighorn sheep. The agencies should also 

seek to understand the publics land use needs, so that workable solutions to 

bighorn and human land use conflicts are developed. Conservation efforts are 

more likely to succeed if efforts are understood and supported by the populace. 

Enlisting public support for recovery efforts will require an information and 

outreach program on the ecology of Sierra Nevada bighorn sheep, the threats this 

species is currently facing, and how recovery actions will reduce those threats. 

Special efforts should be made to target and collaborate with private landowners 

near occupied herd units on the issue of disease transmission between domestic 

sheep or goats and bighorn sheep on their lands. This is of key importance in 

implementing our recommended strategy to prevent contact between domestic 

sheep or goats and bighorn sheep (see Section E below). Appendix F contains a 

detailed plan for developing an effective outreach and information program.

Public information and outreach on Sierra Nevada bighorn sheep has been 

occurring and is ongoing. The Sierra Nevada Bighorn Sheep Interagency 

Advisory Group, the Sierra Nevada Bighorn Sheep Foundation, the Inyo National 

Forest, and the Interagency Domestic Sheep Grazing Strategy Working Group 

have conducted media interviews and hosted public meetings focused on Sierra 

Nevada bighorn sheep ecology, management, and threats. However, additional 

efforts are possible and desirable. In addition, there should be a higher degree of 

coordination among individual programs and other recovery activities. Increased 

coordination would not only allow each program to present the most accurate and 

updated information, but it would also let the general public see that the recovery 

of Sierra Nevada bighorn sheep is a collaborative effort supported by multiple 

agencies, organizations, and individuals. Specific recovery actions to accomplish 

the identified goals are as follows: 

7.1 Conduct a survey of public uses of Sierra Nevada bighorn sheep 

habitat and public attitudes regarding Sierra Nevada bighorn sheep. 

Results of the survey will be used to (1) prioritize the public information 

and outreach action items, (2) determine the best methods to accomplish 

the action items with the highest likelihood of meeting the recovery plan 
59

goals, and (3) establish a baseline from which the success of the action 

items in meeting the recovery plan goals can be measured by comparing to 

a resurvey 1 year after implementation. 

7.2 Develop and distribute information related to recovery efforts. The 

results of the public survey (Task 7.1) should be used to determine the 

specific topical information and most effective method(s) of disseminating 

this information to target audiences. This information should be available 

from the key agencies involved in this recovery effort. A general brochure 

or information sheet should be developed that contains a brief overview of 

the status of Sierra Nevada bighorn sheep, as well as specific suggestions 

on what people can do to help the species. In addition, information on a 

variety of topics germane to the recovery of Sierra Nevada bighorn sheep 

should be summarized and made available to the public in booklet form. 

During implementation of recovery efforts, the public should be fully 

informed as early as possible regarding actions required or restricted while 

in Sierra Nevada bighorn sheep habitat. Further, the finalized recovery 

plan, along with a cover letter, should be widely distributed to affected and 

interested people, including hikers and other recreationists, ranchers, 

ranchette owners with domestic sheep or goats, commercial packers, 

environmental groups, mountain lion and bighorn sheep advocacy groups, 

and affected local, State, and Federal agencies. Moreover, the recovery 

plan should reach people who would not typically be exposed to 

traditional programs (i.e., individuals who might not frequent visitor’s 

centers or who do not have school-aged children). Special efforts should 

be made to target and inform private landowners near occupied herd units. 

7.3 Continue, update, and coordinate existing informational and outreach 

programs and develop further programs as needed. The results of the 

public survey (Task 7.1) should be used to develop the most effective 

informational and outreach programs. However, there is an immediate 

need to update existing programs to provide an accurate view of our 

current knowledge regarding Sierra Nevada bighorn sheep. Information 

should strive to highlight not only how the activities of each individual 

agency or organization contribute to the recovery of Sierra Nevada 

bighorn sheep, but also how these activities complement those of other 

agencies or organizations. Existing bighorn sheep educational materials 

should be reviewed and modified to be applicable to Sierra Nevada 

bighorn sheep. 
60

8 Establish an implementation advisory team for coordination and 

communication. Numerous Federal, State, and private agencies share 

responsibility for bighorn sheep in the Sierra Nevada along with stakeholders. 

Efforts to recover these bighorn sheep will require considerable coordination and 

communication among these different entities. This coordination will be greatly 

enhanced through the formation of an advisory team that meets at least twice 

annually. This team should include agency representatives, appropriate 

specialists, and key stakeholders. 
61

E. RECOMMENDED STRATEGY FOR PREVENTING CONTACT BETWEEN 

DOMESTIC SHEEP OR GOATS AND SIERRA NEVADA BIGHORN SHEEP 

1. Background 

As discussed previously and in Appendix B, preventing contact between domestic 

sheep or goats, hereafter jointly referred to as "domestic sheep", and Sierra Nevada 

bighorn sheep is critical to recovery of this species. Given evidence described in this 

plan from captive studies, inoculation studies, and field observations of pneumonia 

related die-offs, disease contracted from domestic sheep is a potentially significant source 

of mortality that requires management. In November of 2006, a panel of 11 veterinarians 

from the Idaho Department of Fish and Game, Washington State University, University 

of Washington, Ministry of the Environment (British Columbia, Canada), California 

Department of Fish and Game (CDFG), the U.S. Geological Survey, Colorado Division 

of Wildlife, Nevada Department of Agriculture, and the University of Idaho’s Caine 

Veterinary Teaching and Research Center met to review the issue of contact between 

domestic sheep and bighorn sheep for the Payette National Forest’s Risk Analysis of 

Disease Transmission Between Domestic Sheep and Bighorn Sheep (Payette National 

Forest 2006). They concluded that contact between domestic sheep and bighorn sheep 

increases the risk of subsequent bighorn sheep mortality and reduced recruitment due 

primarily to respiratory disease, but they also acknowledged that the complete range of 

causal mechanisms that lead to die-offs in bighorn sheep herds is not fully understood. 

Given the conclusion that contact between bighorns and domestic sheep increases the 

likelihood of bighorn mortality, they recommended that management actions should seek 

to prevent contact between domestic sheep and bighorn sheep (Payette Science Panel 

2006). Because of the potential for contact between domestic sheep and Sierra Nevada 

bighorn sheep and the adverse effects that such contact could have on persistence of this 

endangered species, we have developed a recommended strategy for preventing contact. 

Singer et al. (2001) identified a buffer of 23 kilometers (14 miles) as a general 

guideline of separation between bighorn sheep and domestic sheep when undertaking 

efforts to restore bighorn populations. While we recognize the importance of this 

distance as a general rule, we acknowledge that it is based on a broad look at many 

populations of bighorn sheep and is not specific to bighorn sheep that occur in the Sierra 

Nevada. Therefore, a closer look at disease risk for specific bighorn sheep herds in the 

Sierra Nevada may arrive at somewhat different guidelines. Consequently, we have not 

used the Singer et al. (2001) buffer distance as a means to identify high-risk allotments or 

allotments that may affect bighorn sheep, but have used it to narrow the number of 

allotments within the scope of our analysis. 

Within the historic range of the Sierra Nevada bighorn sheep there are +/- 29 

domestic sheep grazing allotments within 23 kilometers of currently occupied recovery 

plan herd units that are managed by the Humboldt-Toiyabe National Forest, Inyo 

National Forest, and the Bureau of Land Management – Bishop Field Office (BLM) 

(Table 6). In addition, there are approximately 147,000 hectares (363,237 acres) of lands 
62

Table 6: U.S. Forest Service and Bureau of Land Management Sheep Grazing Allotments 

within 23 kilometers of Sierra Nevada Bighorn Sheep Herd Units 

Agency Allotment Name Status/Current 

Management Nearest Herd Unit 

Humboldt-Toiyabe National Forest Poison Creek Active Twin Lakes 

Humboldt-Toiyabe National Forest South Swauger Active Twin Lakes 

Humboldt-Toiyabe National Forest Rickey (North) Active Twin Lakes 

Humboldt-Toiyabe National Forest Rickey (South) Active Twin Lakes 

Humboldt-Toiyabe National Forest Summers Meadow Inactive Twin Lakes 

Humboldt-Toiyabe National Forest Cameron Canyon Active Green Creek 

Humboldt-Toiyabe National Forest Tamarack Active Green Creek 

Humboldt-Toiyabe National Forest Dunderberg Active Mt. Warren 

Humboldt-Toiyabe National Forest Jordan Basin Inactive Mt. Warren 

Inyo National Forest Horse Meadow Vacant Mt. Gibbs/Mt. Warren 

Inyo National Forest Bloody Canyon Vacant Mt. Gibbs 

Inyo National Forest Algers Lake Vacant Mt. Gibbs 

Inyo National Forest June Lake - West Vacant Mt. Gibbs 

Inyo National Forest June Lake - East Active Mt. Gibbs 

Inyo National Forest Mono Mills Inactive Mt. Gibbs 

Inyo National Forest Dexter Creek Active Mt. Gibbs 

Inyo National Forest Sherwin/Deadman - West Active Mt. Gibbs/Convict Creek 

Inyo National Forest Sherwin/Deadma - East Active Mt. Gibbs/Convict Creek 

Inyo National Forest McGee Inactive Convict Creek 

Inyo National Forest Watterson Meadow Active Convict Creek 

Inyo National Forest Rock Creek - East Active Convict Creek 

Inyo National Forest Rock Creek - West Inactive Convict Creek 

Inyo National Forest Rock Creek - Hilton Unit Active Convict Creek 

Inyo National Forest Casa Diablo Active Convict Creek 

BLM - Bishop Walters Ranch Active Twin Lakes 

BLM - Bishop Travertine Hills Active Twin Lakes/Green Creek

BLM - Bishop Mount Biedeman Active Twin Lakes/Green Creek

BLM - Bishop Green Creek Active Green Creek 

BLM - Bishop Dog Creek Active Green Creek/Mt. Warren 

BLM - Bishop Little Mormon Active Green Creek/Mt. Warren 

BLM - Bishop Rancheria Gulch Active Mt. Warren 

BLM - Bishop Mono Mills Active Mt. Warren/Mt Gibbs 

BLM - Bishop Casa Diablo Active Convict Creek 

BLM - Bishop Little Round Valley Active Convict Creek 

BLM - Bishop Volcanic Tablelands Active Convict Creek/Wheeler 

Ridge 

BLM - Bishop Mormon Ranch Active Green Creek 

owned by private individuals, municipalities, and the Los Angeles Department of Water 

and Power within 23 kilometers of occupied herd units. 

For the purposes of our recommendations, we have considered Highway 395 as a 

potential management boundary (hereafter referred to as “management boundary”) as it 

relates to bighorn sheep movement. While it is possible that bighorn sheep will cross the 
63

highway, use of this management boundary is intended to assist in reducing the 

likelihood of disease transmission. Highway 395 is not an absolute barrier to bighorn 

sheep movement, and is therefore regarded only as a potential management boundary. 

Management actions to prevent bighorn sheep from occupying areas east of Highway 395 

should be implemented to increase the effectiveness of this management boundary. Use 

of the risk assessment for analyzing disease risk on grazing allotments east of Highway 

395 has been incorporated into the recommendations of Section E. 

Recently, the University of California at Davis and CDFG jointly developed a risk 

model for disease transmission between domestic sheep and Sierra Nevada bighorn sheep 

(Clifford et al. 2007). The authors used 2002 to 2006 Sierra Nevada bighorn sheep 

location data and current modeling techniques to estimate the areas that bighorn sheep are 

likely to use during the spring-summer season (March through September) and the rut 

season (October through November). These are referred to in this section as the springsummer and rut season utilization areas, respectively. For allotments west of Highway 

395, estimated utilization areas during the spring-summer season overlap with the 

Tamarack, Cameron Canyon, Dunderberg, Jordan Basin, Horse Meadow, Bloody 

Canyon, Algers Lake, Green Creek (BLM), Dog Creek (BLM), Rickey (south), 

Summer’s Meadow, and Rickey (north) allotments. In addition, Johnson et al. (2006) 

modeled bighorn sheep summer range habitat and showed areas of summer range that 

overlap or are immediately adjacent to the Tamarack, Cameron Canyon, Dunderberg, and 

Jordan Basin allotments . CDFG has also recorded bighorn sheep locations on or 

immediately adjacent to the Tamarack, Dunderderg, Cameron Canyon, Jordan Basin, 

Bloody Canyon, and Alger’s Lake allotments during the spring-summer season (Clifford 

et al. 2007). 

 

For allotments west of Highway 395, estimated utilization areas during the rut 

season overlap with the Tamarack, Cameron Canyon, Dunderberg, Jordan Basin, Horse 

Meadow, Bloody Canyon, Algers Lake, Green Creek (BLM), Dog Creek (BLM), Rickey 

(south), Summer’s Meadow, Rickey (north), Rock Creek, and Little Round Valley 

(BLM) allotments. CDFG has also recorded bighorn sheep locations on or immediately 

adjacent to the Cameron Canyon, Summer’s Meadow, Dunderberg, Jordan Basin, Bloody 

Canyon, and Rock Creek allotments during the rut season (Clifford et al. 2007). 

2. Strategy 

A team of veterinarians, wildlife biologists, range managers, and grazing 

permittees is currently developing a risk assessment that land managers can use as a tool 

to assess the potential risk that allotments pose under certain grazing practices. All 

further references to a “risk assessment” in this section refer to this pending analysis. 

The risk assessment will account for bighorn sheep management activities when 

analyzing the risk of disease transmission on certain allotments. We do not know when 

the team will complete the risk assessment, but the need for specific guidance remains. 

Consequently, we have developed an approach for management of this risk that addresses 

the following issues: 1) recommendations regarding some domestic sheep grazing 

allotments and private lands based on current knowledge of bighorn movements, range 
64

utilization, and domestic sheep grazing practices; 2) development and use of the risk 

assessment as a tool in the assessment of future contact risk on other allotments and 

private lands that are not currently close to bighorn herds and to be used in the interim 

period prior to the completion of recommendations regarding allotments in item one; and 

3) recommendations regarding restrictions on translocations of bighorn sheep in certain 

locations. The details of this strategy involve recommending permanent or seasonal 

closures of some allotments, seeking opportunities to purchase or transfer private grazing 

lands, managing translocation of bighorn sheep so that the risk of contact is minimized in 

certain areas, managing contact between bighorn sheep and domestic sheep on allotments 

that remain active, using the risk assessment to annually evaluate allotments in certain 

areas, taking advantage of opportunities to buy-out allotments or to retire them if they are 

relinquished volunarily, eliminating other non-compatible uses (e.g., goat packing) in 

areas where they put bighorn sheep and risk, and annually assessing our efforts to prevent 

contact between bighorn sheep and domestic sheep. Each of these details is discussed 

further below. 

3. Recommendations 

Based on the information provided in Section E.1 (above) we recommend the following: 

Recommendation 1 (Closures of High-Risk Allotments): We recommend that the Inyo 

and Humboldt-Toiyabe National Forests and the Bureau of Land Management – Bishop 

Field Office close domestic sheep grazing allotments that pose a high risk of disease 

transmission or consider other uses that are not potential threats to Sierra Nevada bighorn 

sheep. As of this writing, we believe the Dunderberg, Tamarack, Cameron Canyon, 

Rickey (south), Green Creek (BLM), and Dog Creek (BLM) allotments pose a relatively 

high risk to Sierra Nevada bighorn sheep, with Dunderberg representing the greatest 

current risk. Therefore, based on the best available information, such as documented 

bighorn sheep movement patterns and modeling of areas that bighorn sheep are likely to 

use, we recommend closure of these allotments to domestic sheep grazing. 

We understand allotment closures require an analysis pursuant to agency procedures and 

other applicable Federal laws, and thus some time will be required for such closures to 

proceed. We recommend the Inyo and Humboldt-Toiyabe National Forests and the 

Bureau of Land Management – Bishop Field Office initiate such analyses in 2007 (i.e., 

site specific suitability analyses) pursuant to their respective land management plans to 

consider permanent closure of these allottments to domestic sheep. The Jordan Basin, 

Summer’s Meadow, Horse Meadow, Alger’s Lake, June Lake (west), and Bloody 

Canyon allotments should remain vacant or inactive, be closed, or be converted to uses 

that are not a potential threat to Sierra Nevada bighorn sheep. 

The Service is currently participating on a subgroup of the recovery team, including 

scientists and stakeholders, in the development of a “risk assessment tool” to help land 

managers better quantify the relative risk domestic sheep pose to bighorn sheep in these 

various allotments. Unfortunately, this tool is not yet completed and is not available for 

use, but it is expected to be completed in early 2008. Once the risk assessment tool is 
65

completed, the land management agencies should incorporate its use into the analyses 

recommended above concerning allotment closures. In the event that information from 

the risk assessment or other sources indicates a high risk of contact between bighorn and 

domestic sheep on a given allotment, land management agencies should immediately 

close the allotment, on an emergency basis, while they complete their analysis. We 

recognize that the Forest Service is not currently permitting grazing on the Dunderberg 

allotment due to recent movements of bighorn sheep in that area. We recommend that 

this allotment remain in a non-permitted status until the Forest Service can complete its 

suitability analysis. 

It is possible that use of the risk assessment tool may alter our future understanding of the 

risk of contact between domestic and bighorn sheep in these allotments. If the land 

management entities, through use of the risk assessment, determine that permittees can 

graze domestic sheep on some of the allotments listed above under certain management 

prescriptions that prevent contact, they may consider allowing grazing under those 

management prescriptions. Following such a determination, the alternative of continuing 

to graze domestic sheep on applicable allotments with the implementation of those 

management prescriptions should be fully evaluated in each agency’s site-specific 

suitability analysis. 

Rationale: Of the allotments west of Highway 395, data on known bighorn sheep 

locations and predicted spring-summer and rut utilization areas indicate that bighorn 

sheep are likely to enter the Dunderberg, Tamarack, Cameron Canyon, Rickey (south), 

Green Creek (BLM), Dog Creek (BLM), Jordan Basin, Summer’s Meadow, Horse 

Meadow, Alger’s Lake, June Lake (west), and Bloody Canyon allotments at any time of 

the year, which greatly increases the risk of contact. This may preclude the ability to 

implement avoidance measures such as seasonal grazing restrictions that might be 

successful on other allotments where the risk of contact only occurs during the rut season. 

Under the 2005 and 2006 domestic sheep grazing practices and allotment arrangement, 

the probability of an outbreak in the Northern Recovery Unit that results in significant 

mortality is 40 percent over the next 50 years and 50 percent over the next 70 years. In 

addition, an outbreak that starts in this Northern Recovery Unit has about a 7 percent 

(range 4.6 to 9.1 percent) chance of spreading to the Central Recovery Unit and causing 

significant mortality (Clifford et al. 2007). These probabilities will increase as bighorn 

populations increase in these recovery units. Therefore, it is prudent to begin analysis of 

closure of these allotments. Other allotments that fall within the spring-summer 

utilization areas are east of Highway 395. Because Highway 395 is considered a 

management boundary, it is appropriate to wait for completion of the risk assessment 

before analyzing risk on these allotments. 

Recommendation 2 (Seasonal Allotment Closures): In contrast to the allotments 

identified in Recommendation 1, domestic sheep grazing on some allotments poses a risk 

of contact only during the bighorn sheep rut. We recommend that allotments in this 

category be considered for seasonal closure. In 2007, the Inyo National Forest and the 

Bureau of Land Management – Bishop Field Office should begin site specific suitability 

analyses pursuant to their respective land management plans to consider seasonal closure 
66

of the Rock Creek (west) allotment and the portion of the BLM’s Little Round Valley 

(the portion between Rock Creek and Hilton Creek) allotment that is west of Highway 

395 to domestic sheep grazing during the bighorn rut. If the appropriate land 

management entities, through use of the risk assessment, determine that permittees can 

graze any or all of these allotments during the rut under certain management prescriptions 

that prevent contact, grazing may continue during the rut season under those management 

prescriptions. Following such a determination, the alternative of continuing to graze 

domestic sheep during the bighorn rut on applicable allotments with the implementation 

of those management prescriptions should be fully evaluated in each agency’s sitespecific suitability analysis. 

Rationale: Of the allotments west of Highway 395, data on known bighorn sheep 

locations and predicted spring-summer and rut utilization areas indicate that male bighorn 

sheep are likely to enter the Rock Creek (west) and the western portion of the Little 

Round Valley (BLM) allotments during the rut season, which greatly increases the risk of 

contact if domestic sheep are utilizing these allotments. Other allotments that fall within 

the rut season utilization areas are east of Highway 395, which is a management 

boundary as it relates to bighorn sheep movement. Because Highway 395 is considered a 

management boundary, it is appropriate to wait for completion of the risk assessment 

before analyzing risk on these allotments. 

Recommendation 3 (Purchase of Lands or Conservation Easements ): The Service, 

CDFG, and land management agencies should work with land owners to secure 

permanent management restriction, conservation easements, or purchase of Los Angeles 

Department of Water and Power, County and Municipal lands, and privately owned 

parcels that are suitable for domestic sheep grazing and are overlapped by all predicted 

utilization areas modeled in Clifford et al (2007). Conservation easements should require 

the elimination of domestic sheep grazing on these parcels. The Service and CDFG 

should give priority to parcels that currently have domestic sheep grazing on them and 

are within the predicted spring-summer range utilization areas. 

Rationale: The rationale for this recommendation is the same as that provided above for 

Recommendations 1 and 2. Permanent management restrictions, land acquisitions, and 

conservation easements are a primary tool available for preventing contact between 

domestic sheep and bighorn sheep on these lands. 

Recommendation 4 (Voluntary Land Transfer or Exchange): The Service, CDFG, and 

land management agencies should work with land owners to secure voluntary land 

transfer or exchange between the appropriate land management agencies and Los 

Angeles Department of Water and Power, County and Municipal lands, and privately 

owned parcels that are suitable for domestic sheep grazing and are overlapped by the 

predicted utilization areas modeled in Clifford et al (2007). Land transfers or exchanges 

should require the elimination of domestic sheep grazing on these parcels. The Service, 

CDFG, and land management agencies should give priority to parcels that currently have 

domestic sheep grazing on them and are within the predicted spring-summer range 

utilization areas. 
67

Rationale: The rationale for this recommendation is the same as that provided above for 

Recommendations 1 and 2. Land transfer and exchanges with the appropriate land 

management agency may also be useful tools for preventing contact between domestic 

sheep and bighorn sheep on these lands. 

Recommendation 5 (Translocation of Bighorn Sheep): CDFG should not perform active 

translocation of bighorn sheep into the Green Creek or Twin Lakes Herd Units, which the 

recovery plan identifies as non-essential for recovery. Populations in the Mount Warren 

Herd Unit should be allowed to naturally expand into the Green Creek Herd Unit over 

time under careful monitoring and management (see Recommendation 6 below). CDFG, 

the Inyo National Forest, the BLM – Bishop Field Office, and grazing permitees should 

coordinate with each other and utilize the risk assessment prior to any translocations into 

the Convict Creek Herd Unit to determine if grazing on the McGee, Little Round Valley, 

or Rock Creek (Hilton Unit) allotments should be eliminated or modified in any way to 

prevent contact between domestic sheep and translocated bighorn sheep. 

Rationale: Translocations into the Green Creek and Twin Lakes Herd Units are not 

needed for recovery and would rapidly place bighorn sheep in close proximity to active 

domestic sheep grazing operations on the Poison Creek, Rickey, and South Swauger 

allotments, which would greatly increase the risk of contact between domestic sheep and 

bighorn sheep. 

Translocations are the best tool for increasing population size in the essential Convict 

Creek Herd Unit. To prevent contact, the Service, CDFG and the appropriate land 

management agencies would need to evaluate and implement appropriate grazing 

management actions and/or restrictions for domestic sheep grazing on the McGee, Little 

Round Valley, or Rock Creek (Hilton Unit) allotments prior to translocations into the 

Convict Creek Herd Unit. Removal of bighorn sheep is not considered a viable 

management alternative in this area because the Convict Creek Herd Unit is essential to 

recovery of the species. Consequently, CDFG will actively work toward establishment of 

a bighorn sheep herd in this area. 

Recommendation 6 (Management of Contact with Domestic Sheep on Active Allotments): 

CDFG, land management agencies and permittees should work cooperatively to manage 

bighorn sheep and domestic sheep in a manner that prevents contact between the bighorn 

populations and domestic sheep on the active sheep grazing allotments north of Twin 

Lakes (Poison Creek, Rickey (north), and South Swauger). 

Although no bighorn sheep occur in the Green Creek Herd Unit as of this writing, CDFG 

could choose to manage bighorn sheep in the Green Creek Unit if the bighorn sheep 

arrive in that area through natural dispersal. However, all parties should work 

cooperatively to keep bighorn sheep from areas north of the non-essential Green Creek 

Herd Unit. If bighorn sheep wander north of this unit, the agencies should work 

cooperatively using all appropriate means to discourage or remove bighorn sheep from 

these areas. If bighorn sheep naturally expand into the non-essential Green Creek Herd 
68

Unit, CDFG may need to manage this unit at a lower population level to reduce the 

likelihood of bighorns moving further north. This management approach is necessary to 

protect the bighorn sheep herds to the south in the recovery units. It will reduce the 

likelihood that bighorn will come into contact with domestic sheep in the open grazing 

allotments north of Twin Lakes, and potentially imperil bighorn to the south if they 

become diseased and return south. 

 

For these management actions to be successful, a significant portion of the Mount Warren 

Herd and the Green Creek Herd will need to be radio collared and intensively monitored 

during the domestic sheep grazing season and regularly monitored during the non-grazing 

season to assess population size and individual animal movement. The frequency of data 

collection during the monitoring effort will be dependent on limitations in technology, 

but this frequency should always remain at a level that is sufficient to achieve the goal of 

this recommendation. Domestic sheep herds will need to be monitored daily during the 

grazing season to ensure that individual sheep or groups of sheep do not wander off the 

allotment and that all domestic sheep released on the allotment can be accounted for at all 

times. Land and resource managers may be able to sustain zones of no contact between 

wild and domestic sheep through sustained, effective levels of monitoring and removal of 

Sierra Nevada bighorn sheep from areas not needed for recovery. Permittees are also 

important participants in maintaining a zone of no contact by ensuring that they strictly 

adhere to their grazing permit requirements. 

Similar management actions will need to occur to prevent contact of Sierra Nevada 

bighorn sheep and domestic sheep that are actively grazed east of Highway 395 and with 

domestic sheep that are kept as pets within the communities of the Mono and Owens 

Basins if the risk assessment determines that contact cannot be prevented through other 

management actions. The resource and land management agencies, grazing permittees, 

and the public will need to report any sightings of bighorn sheep immediately to CDFG. 

 

Rationale: Avoiding contact between domestic sheep and bighorn sheep to prevent 

disease transmission is identified as a high-priority recovery action. Efforts to remove 

bighorn sheep from areas north of the Green Creek Herd Unit would help prevent contact 

between domestic sheep and bighorn sheep while eliminating the need for closure of 

active domestic sheep grazing allotments north of the Twin Lakes area. The Green 

Creek and Twin Lakes Herd Units are not needed for recovery of the Sierra Nevada 

bighorn sheep. Preventing contact between domestic sheep and bighorn sheep will 

require that all possible measures for managing domestic sheep and wild sheep are used 

to achieve this goal. Because bighorn sheep may naturally expand into areas north of the 

Green Creek Herd Unit, bighorn sheep may need to be removed from these areas to 

prevent contact with domestic sheep on the Poison Creek, South Swauger, and Rickey 

(North Unit) allotments. Removal of bighorn sheep in these areas to prevent contact is 

considered a viable management alternative because the Green Creek and Twin Lakes 

Herd Units do not need to be occupied to achieve recovery. Consequently, the removal 

of bighorn sheep should be considered as a method to prevent contact without 

compromising the recovery of the species. 
69

Movement of bighorn sheep across Highway 395 has been documented, although to date, 

the known occurrences have been few. As Sierra Nevada bighorn sheep populations 

increase in size, the likelihood that bighorn sheep will move onto allotments east of 

Highway 395 may increase as well as the possible wanderings of bighorn sheep into a 

local ranch or community. This movement could result in contact between wild bighorn 

sheep and domestic sheep. Therefore, removal of bighorn sheep from these areas, to 

prevent contact, is considered a viable management alternative. 

It must be appreciated that managing bighorn sheep dispersal under this recommendation 

will be a challenge and will require contributions of staff and financial resources from 

stakeholders. Bighorn sheep will need to be monitored, and decisions to intervene in 

bighorn dispersal will require close coordination among State, federal, and local entities. 

It also must be appreciated that it is still possible, though unlikely, that eventually 

bighorn sheep may successfully disperse north of the Twin Lakes into domestic sheep 

allotments even with aggressive monitoring and oversight by the parties. 

Recommendation 7 (Outreach): A private landowner notification and outreach program 

should be instituted to inform landowners identified under Recommendation 6 of the 

potential consequences to bighorn sheep if domestic sheep grazing on their parcels make 

contact with bighorn sheep. 

Rationale: CDFG and the Service will not be able to acquire or place conservation 

easements on all private lands in high-risk areas in a timely manner, if at all, so notifying 

and informing landowners may minimize the likelihood of domestic sheep grazing on 

these parcels in the interim. The success of the Sierra Nevada bighorn sheep recovery 

effort depends, in part, on the partnerships formed and maintained with local landowners, 

land users, and citizens of the eastern Sierra. These partnerships are key to ensuring the 

recovery of bighorn sheep through enhanced communication regarding bighorn sheep 

recovery needs and identification and support of compatible land use practices 

 

Recommendation 8 (Annual Evaluations of Allotments Near Convict Creek Herd Unit 

and East of Highway 395): There are several allotments, that were not discussed in 

Recommendations 1 and 2, that may need to be assessed in the future due to 

translocations of bighorn sheep and/or to natural movements of bighorn sheep. These 

allotments fall into two general categories: (1) those near the Convict Creek Herd Unit 

and (2) those east of Highway 395. Following completion of the risk assessment, the 

Inyo National Forest and the BLM – Bishop Field Office should coordinate at least 

annually with the Service and CDFG to determine if recent bighorn sheep movements 

may require an evaluation using this assessment of domestic sheep grazing on the Rock 

Creek (Hilton Unit), Little Round Valley (BLM) (portion that is west of Hilton Creek), 

and McGee allotments which are near the Convict Creek Herd Unit. In addition, they 

should determine whether the risk assessment should be used to evaluate some allotments 

east of Highway 395. If any of these allotments requires re-evaluation, the land 

management entities should use the risk assessment to determine if closure or changes in 

grazing practices are necessary. 
70

Rationale: Natural movement of bighorn sheep into the Convict Creek Herd Unit and 

potential translocations into this unit will change the level of risk posed by the Rock 

Creek (Hilton Unit), Little Round Valley (BLM) (portion that is west of Hilton Creek), 

and McGee allotments. Natural growth and expansion of bighorn sheep in some portions 

of the Northern or Central Recovery Unit has the potential to increase the contact risk 

posed by some allotments east of Highway 395. Annual evaluation of bighorn sheep 

movements to determine if the risk assessment should be utilized will allow for 

adjustment and/or restrictions in grazing practices on these allotments over time so 

contact is prevented. 

Recommendation 9 (Grazing Buy-outs): The Service, CDFG, and land management 

agencies should work with non-governmental organizations to offer grazing buy-outs to 

permittees on the allotments discussed in Recommendation 8, and any other allotment of 

concern discussed in this plan. If buy-outs are successful or if the permittee voluntarily 

relinquishes his grazing permit, these allotments should be closed or consider other uses 

that are not a threat to Sierra Nevada bighorn sheep. 

Rationale: In order to prevent the need for potential emergency closure of allotments in 

the event that bighorn sheep move into the Convict Creek Herd Unit, or any other 

allotment of concern discussed in this plan, buy-outs should be pursued. This would 

eliminate the need for expensive management actions that CDFG and land management 

agencies would have to implement to prevent contact in these areas. 

Recommendation 10 (Voluntary Relinquishments): If any permittee agrees to voluntarily 

relinquish any allotment identified in this plan, the Inyo and Humboldt-Toiyabe National 

Forests and the BLM – Bishop Field Office should consider permanent closure to 

domestic sheep grazing or consider other uses that are not a threat to Sierra Nevada 

bighorn sheep. 

Rationale: In order to prevent the need for potential emergency closure of allotments in 

the event that bighorn sheep move into any of the allotments identified in this plan, 

voluntary relinquishment should be pursued. In addition, voluntary relinquishment 

would allow bighorn sheep to naturally move into an allotment without risking contact 

with domestic sheep. This would also eliminate the need for expensive management 

actions that CDFG and land management agencies would have to implement to prevent 

contact in these areas. 

Recommendation 11 (Other Non-compatible Recreation Use): The appropriate land 

management agencies should continue or make permanent those orders necessary to 

eliminate goat packing, or any other non-compatible recreation use (or any other activity 

not considered as grazing in this plan), within Sierra Nevada bighorn sheep herd units. 

Rationale: Previous forest orders have been initiated to ensure the closure of goat 

packing in Sierra Nevada bighorn sheep allotments. These orders, and others which may 

be deemed necessary upon completion of the risk assessment, should either be regularly 
71

renewed or made permanent to prevent contact between domestic goats used for 

recreation (or any other activity not considered as grazing in this plan) and bighorn sheep. 

Recommendation 12 (Annual Assessment): CDFG, the Service and federal land 

management agencies should annually assess efforts to prevent contact between Sierra 

Nevada bighorn sheep and domestic sheep. This assessment should be done at least 

annually; but may be required more frequently to enhance the effectiveness of measures 

implemented for preventing contact. The goal is to evaluate the effectiveness of these 

efforts over time and make changes, as necessary. 

Rationale: As Sierra Nevada bighorn sheep populations recover, their population will 

increase in size and their distribution within the herd units will change. Furthermore, 

resource and land management agencies will better understand the effectiveness of their 

management actions. Therefore, it is imperative that management be adaptive to new 

information as it becomes available. Changes may not need to occur annually, however, 

because of the substantial threat disease poses to recovery of the Sierra Nevada bighorn 

sheep, the effectiveness of ongoing efforts should be assessed annually. 
72
73

III. IMPLEMENTATION SCHEDULE 

The Implementation Schedule that follows outlines actions as identified in the 

Narrative Outline of Recovery Actions (section II.D) and estimates costs for the recovery 

of Sierra Nevada bighorn sheep. It is a guide for meeting the objectives discussed in Part 

II of this recovery plan. This Schedule indicates task priorities, task numbers, task 

descriptions, duration of tasks, responsible agencies, and estimated costs. The agencies 

responsible for committing funds are not necessarily the entities that will carry out the 

tasks. The agency or agencies with the lead responsibility for each task are indicated in 

the table. Initiation of these actions is subject to the availability of funds. 

The Implementation Schedule indicates speculative, future costs (preparation of 

additional plans, or research programs, etc.) as “to be determined.” Indirect costs, such 

as those incurred by: (1) agencies and groups contributing time and materials, or (2) 

public agencies performing administrative or regulatory functions are not included in cost 

totals. Costs of continuous tasks are estimated assuming a 20-year time to recovery. 

Though the Implementation Schedule does not distinguish between public and private 

costs, no identifiable or specific expenditures by the private sector are likely to be 

necessary, other than voluntary efforts contributed by nonprofit conservation 

organizations and citizen groups. Priorities (column 1 of the following table) 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. 

Priority 2 An action that must be taken to prevent a significant decline in species 

population/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. 

Abbreviations used in the Implementation Schedule: 

TBD To be determined 

cont. Continuous 

† Continued implementation of task expected to be necessary after delisting. 

‡ Task expected to be necessary until delisting of species. 

* Lead responsible agency 

Agencies and Organizations 

BLM Bureau of Land Management 

CDFG California Department of Fish and Game 

CT CalTrans 

LADWP Los Angeles Department of Water and Power 

FWS U.S. Fish and Wildlife Service 
74

FS U.S. Forest Service 

NPS National Park Service 

UC University of California, White Mountain Research Station 

USGS U.S. Geological Survey, Biological Resources Division
75

1 RECOVERY PLAN IMPLEMENTATION SCHEDULE FOR SIERRA NEVADA BIGHORN SHEEP 

Priority Estimated Cost # 

Task # 

Task Description Task 

Duration (Years) 

Responsible Agencies 

Total Estimated Cost ($1,000s) 

FY 

08 

FY 

08 

1 2.1 Prepare and implement a 

management plan to temporarily protect Sierra Nevada bighorn sheep herds from predation losses, where needed, until viable herd sizes are reached. 

cont. CDFG* 7,000 350 350 

1 2.2.1 Reduce potential predator 

influences on winter habitat selection where appropriate 

cont. CDFG* 1,000 50 50 

1 2.2.2 Supplement small female 

groups where appropriate to attain threshold herd sizes that will encourage behavioral attributes favorable to winter range use 

cont. CDFG* 300 

(estimated cost $3,000 per animal captured; number captured per year TBD) 

TBD TBD 

1 2.3.1 Prevent contact between 

bighorn sheep and domestic sheep or goats 

cont.† FS*, FWS, 

BLM*, LADWP, CDFG 

150 7.5 7.5 
76

1 3.1 Develop and implement a 

strategy for translocations 

cont. FS, NPS, 

FWS, CDFG* 

600 30 30 

1 3.2.1 Manage wild herds as 

sources of stock 

cont. CDFG* costs included 

in other tasks 

1 5.2 Monitor key predators in the 

vicinity of winter ranges 

cont.‡ CDFG* included in 

2.2.1 

2 1.2 Maintain and/or enhance 

integrity of bighorn sheep habitat 

cont.‡ NPS*, FS*, 

FWS, CDFG 

TBD TBD TBD 

2 2.2.3 Enhance bighorn sheep 

winter range habitat to increase visibility where appropriate 

cont. FS*, NPS*, 

CDFG 

600 30 30 

2 2.3.2 Develop an action plan in the 

event that a pneumonia outbreak occurs 

1 CDFG* 10 10 

2 3.2.2 Develop criteria for and, if 

appropriate, implement a captive breeding program 

cont. FS, FWS, 

CDFG* 

5,000 250 250 

2 5.1 Develop and implement a 

monitoring plan for population abundance and distribution of bighorn sheep herds in the Sierra Nevada 

cont.† CDFG*, 

UC* 

4,000 200 200 

2 5.4 Monitor exposure to disease 

organisms of concern 

cont.‡ CDFG* 75 3.75 3.75 
77

2 6.1 Investigate genetic 

population structure of existing herds 

5 CDFG, UC* 200 40 40 

2 8. Establish an implementation 

advisory team for coordination and communication 

cont.‡ CDFG*, 

FWS, FS, BLM, NPS 

20 1 1 

3 1.1 Identify and acquire 

important habitat not in public ownership from willing landowners. 

cont. FS*, FWS, 

CT, CDFG 

TBD TBD TBD 

3 2.4 Manage human use locally 

where it is found to cause bighorn sheep to avoid important habitat and, thereby, compromises survivorship or reproductive success. 

1 FS*, NPS*, 

FWS, CDFG 

5 

3 4 Implement a genetic 

management plan to maintain genetic diversity of Sierra Nevada bighorn sheep. The plan must use data on genetic variation gathered in Task 6.1. 

cont.‡ CDFG* 20 

Implementation costs included in 3.1 

 

3 5.3 Monitor vegetation structure 

and composition changes likely to affect bighorn sheep population parameters 

10 FS*, NPS*, 

CDFG 

100 10 10 
78

3 6.2 Develop a population 

viability analysis (PVA) for the Sierra Nevada Bighorn Sheep 

2 CDFG*, UC 100 

3 6.3 Further investigate habitat 

use patterns of bighorn sheep herds 

cont. CDFG* 200 10 10 

3 6.4 Investigate and analyze 

human use patterns relative to habitat use patterns of bighorn sheep 

cont. FS, NPS, 

CDFG* 

100 5 5 

3 6.5 Investigate the potential for 

altering habitat use patterns of mountain lions on bighorn sheep winter ranges by aversive conditioning 

10 CDFG* 100 10 10 

3 6.6 Investigate future 

reintroduction sites relative to potential predator and domestic sheep problems and other potential conflicts 

cont. FS, NPS, 

CDFG* 

200 10 10 

3 6.7 Investigate and, if 

appropriate, develop a plan for decreasing mortality of bighorn sheep remaining at high elevation in extreme winters 

1 FS, CDFG* 30 
79

3 6.8 Attempt to develop long term 

data that will help elucidate predator-prey dynamics of this ecosystem as they affect bighorn sheep 

cont. FS, NPS, 

UC, CDFG* 

1,550 30 80 

3 6.9 Investigate effects of climate 

change on bighorn sheep habitat 

TBD FS, NPS, 

USGS*, CDFG 

120 TBD TBD 

3 7.1 Conduct a survey of public 

uses of bighorn sheep habitat and public attitudes regarding bighorn sheep 

1 FS*, NPS*, 

FWS, CDFG 

40 40 

3 7.2 Develop and distribute 

information related to recovery efforts 

cont.‡ FS, NPS, 

FWS*, CDFG* 

110 10 10 

3 7.3 Continue, update, and 

coordinate, existing informational and outreach programs and develop further programs as needed 

cont.‡ FS, NPS, 

FWS*, CDFG* 

100 5 5 

2 Total estimated cost (over 20-year timeframe): $21,730,000 + additional costs that cannot be determined at this t
80
81

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97

V. APPENDICES 

A. Pack llamas as potential sources of diseases for Sierra Nevada bighorn sheep 

B. Sierra Nevada bighorn sheep and domestic livestock: Preliminary risk assessment 

of disease transmission in the eastern Sierra 

C. Translocation considerations for Sierra Nevada bighorn sheep 

D. Considerations for developing a monitoring plan for bighorn sheep in the Sierra 

Nevada

E. Considerations for a predator management plan 

F. Public information and outreach plan 

G. Summary of threats and recommended recovery actions 

H. Genetic management of Sierra Nevada bighorn sheep 

I. Captive Breeding Contingency Plan, Executive Summary 

J. Comments received on the draft plan 
98
99

APPENDIX A PACK LLAMAS AS POTENTIAL SOURCES OF DISEASES 

FOR SIERRA NEVADA BIGHORN SHEEP 

Abstract: The interspecies transmission of infectious pathogens is dependent on 

characteristics of the two species, the disease agents, and the environment and requires 

effective contact between the host species. The requirements for transmission of diseases 

potentially shared by pack llamas and Sierra Nevada bighorn sheep are not satisfied in the 

context of the epidemiology of known diseases of new world camelids in the United 

States, the management of pack llamas in the back country, and the ecology and natural 

history of free ranging Sierra Nevada bighorn sheep. Current scientific evidence suggests 

that llamas utilized as pack animals present minimal risk of transmission of known 

pathogens to Sierra Nevada bighorn sheep and does not support the exclusion of llamas 

from Sierra Nevada bighorn sheep habitat due to the risk of disease transmission. 

Prevention of overuse of trails by llama packers, requirement of evidence of preventive 

health programs in llama herds for issuance of trail use permits, and good sanitation and 

husbandry practices by llama packers on the trail will further reduce the already very 

small risks and further protect the endangered Sierra Nevada bighorn sheep. 

Literature Review: The transmission of infectious disease agents from one species to 

another depends on characteristics of the host species, (susceptibility and infectiousness), 

characteristics of the pathogen (infectivity, virulence and environmental stability), and 

effective contact between the host species (Thrusfield 1995). In order for a llama (Llama 

glama) to transmit a pathogenic virus, bacterium, or parasite to a bighorn sheep, the agent 

must be present in the llama in a form and quantity adequate for successful transmission, 

the disease agent must be infective enough to be passed between species either by direct 

contact or indirectly via a vector or inanimate physical vehicle, and there must be 

effective contact with the bighorn sheep adequate to allow transmission. The agent must 

be able to survive environmental conditions during the transmission and the bighorn 

sheep must in turn be susceptible to the pathogen. 

A literature review (Thedford and Johnson 1989) and a standard text (Fowler 1998) on 

the infectious diseases of new world camelids indicated that most llamas in the United 

States are healthy and most medical problems are related to management or environment. 

Many disease agents that are infectious to both new world camelids and bighorn sheep 

are rare in llamas in the United States, are more easily acquired from the environment or 

sympatric wildlife than from the llama, are not present at adequate levels in the 

environment to infect bighorn sheep, or are unlikely to survive environmental conditions 

during indirect transmission. 

 

Due to their economic value, pack llamas are generally tethered or otherwise kept close 

to their owners on the trail (Fowler 1998). In the unlikely event that a llama would 

escape into a free ranging situation, it would be unable to keep up with Sierra Nevada 

bighorn sheep in the steep, rocky terrain they frequent. In addition, Sierra Nevada 

bighorn sheep naturally keep a wide flight distance from humans, making direct physical 

contact between pack llamas and bighorn sheep highly unlikely and reducing the 

opportunity for transmission of infectious disease. Depending on the number, size, and 
100

distribution of llama pack strings, indirect transmission of disease agents from 

contaminated pastures, artificial feed, and/or standing water sources is theoretically 

possible. A few disease agents warrant individual discussion as they have demonstrated 

pathogenicity in bighorn sheep: Pasteurella hemolytic pneumonia; Mycobacterium 

paratuberculosis (Johne’s disease); Contagious ecthyma virus (CE, soremouth); and 

Psoroptes spp. (Scabies). 

Pasteurella hemolytica pneumonia 

Pasteurella pneumonia is a major cause of epizootic disease outbreaks in captive and free 

ranging bighorn sheep populations resulting in high adult mortality with poor lamb 

survivorship in subsequent years. In separate trials, Rocky Mountain bighorn sheep were 

placed in direct contact with llamas, domestic sheep, exotic mouflon sheep (Ovis 

musimon), domestic goats, mountain goats (Oreamnos americana), domestic cattle 

(Foreyt 1994), elk (Cervus elaphus), and deer (Odocoileus virginianus and Odocoileus 

hemionus hemionus) (Foreyt 1992) and domestic horses and cattle (Foreyt and Lagerquist 

1996) to determine if contact with other wild and domestic ungulate species exposed 

bighorn sheep to Pasteurella pneumonia. Except for the llamas and horses, essentially all 

the ungulates including the bighorn sheep were pharyngeal carriers of isolates of 

Pasteurella hemolytica when the experiment started. Foreyt tested 17 llamas to use as 

Pasteurella carriers in the trials but found none that were culture positive. All bighorn 

sheep exposed to the domestic sheep and the mouflon (Foreyt 1994), and one exposed to 

domestic cattle (Foreyt and Lagerquist 1996), succumbed to Pasteurella pneumonia 

while those exposed to the other ungulates including the llamas remained normal. 

Pasteurella multocida infection can cause a hemorrhagic septicemia-like disease in old 

world camels (Thedford and Johnson 1989). However, Pasteurella pneumonia in new 

world camelids has not been reported in the literature. Based on available data, there is 

no scientific evidence that contact with llamas will result in respiratory disease from 

Pasteurella spp. in bighorn sheep (Foreyt 1994). 

Mycobacterium paratuberculosis (Johne’s Disease) 

Much controversy surrounds the potential for transmission of Johne’s disease 

(Mycobacterium paratuberculosis) from llamas to free ranging bighorn sheep (Fowler 

1998). Johne’s disease is considered a disease of confinement, usually requiring intense 

sustained exposure to feces of infected, shedding animals as seen in domestic livestock 

and captive wild ungulates. Generally, adult ungulates are much less susceptible to 

infection and require greater exposure than juveniles. Mycobacterium paratuberculosis

infection has been documented in several species of free ranging ungulates in the United 

States (Chiodini and Van Kruiningen 1983, Shulaw et al. 1986, Riemann et al. 1979, 

Jessup 1981). Williams et al. (1979) reported on cases of Johne’s disease in bighorn 

sheep and in a mountain goat (Oreamnos americana) in the Mount Evans area of 

Colorado. The source and epizootiology of the disease were not clear in these cases. In a 

follow-up study, M. paratuberculosis was isolated from tissues and/or feces from nine of 

nine bighorn sheep/domestic sheep hybrids experimentally inoculated with an M. 
101

paratuberculosis isolate from the Mount Evans cases and two of three bighorn sheep 

hybrids exposed to runoff from contaminated animal pens (Williams et al. 1983). 

Johne’s disease has been documented in new world camelids in England (Fowler 1998) 

and in Australia (Ridge et al. 1995) but is rarely diagnosed in llamas in the United States, 

with only four cases documented in Colorado (2), Oklahoma (1) and Minnesota (1) 

(Fowler 1998). Casual contact with the feces from a subclinically infected pack llama 

shedding Mycobacterium paratuberculosis is considered unlikely to provide adequate 

exposure to infect a bighorn sheep. The rare occurrence of this disease in llamas in North 

America makes it highly unlikely that any exposure will occur. There is no scientific 

evidence that llamas present a risk of transmission of Johne’s disease to bighorn sheep. 

 

Contagious ecthyma virus (CE, soremouth) 

Contagious ecthyma is a cause of painful scabs and lesions on the mouths and faces of 

bighorn lambs and on the teats of bighorn females, and can result in difficulty in nursing 

and stunted growth of lambs. Clinical cases of contagious ecthyma have been diagnosed 

in bighorn sheep in Nevada, New Mexico, Colorado, Canada and California (Jessup and 

Boyce1993) and serologic evidence of exposure is not uncommon in desert bighorn (Ovis 

canadensis nelsoni) and Peninsular bighorn sheep (Ovis canadensis cremnobates) in 

California (California Department of Fish and Game, unpublished data). Clark et al. 

(1993) surveyed Sierra Nevada bighorn sheep sera retrospectively for contagious 

ecthyma exposure and found 2 of 14 (14 percent) seropositive accessions. More recent 

data from five Pine Creek animals captured in 1999 showed one of five negative and four 

of five inconclusive results on contagious ecthyma complement fixation tests (California 

Department of Fish and Game, unpublished data). 

Transmission can be direct or indirect, as contagious ecthyma virus can be transmitted by 

insect vectors and may survive for years in scabs and soil. Contagious ecthyma is seen in 

camelids in Peru, and at least one case is documented in the United States. The natural 

reservoir for contagious ecthyma infecting llamas is probably the domestic sheep (Fowler 

1998). Direct transmission of contagious ecthyma virus is highly unlikely due to lack of 

physical contact with bighorn sheep. While the contamination of pastures with 

contagious ecthyma virus is theoretically possible, the rare occurrence of contagious 

ecthyma in llamas in the United States makes it highly unlikely. Closely managed pack 

llamas, kept under good husbandry and sanitation conditions and with no evidence of 

clinical contagious ecthyma, present little or no risk to Sierra Nevada bighorn sheep. 

Psoroptes spp. (Scabies) 

Psoroptes scabies is an ectoparasitic disease that has caused declines in bighorn sheep 

populations throughout the west from the late 19th century to the present. Serologic 

evidence of exposure is not uncommon in desert bighorn sheep in California (Clark et al. 

1993), and clinical cases have been observed in several desert mountain ranges in 

California (California Department of Fish and Game, unpublished data). Of 110 Sierra 

Nevada bighorn sheep tested retrospectively, none showed evidence of previous exposure 
102

to Psoroptes spp. (Clark et al. 1993). Two llamas, a cria and his dam (offspring and 

mother), are the only documented cases of Psoroptes in new world camelids in the United 

States. Based on morphological and epidemiological studies, the authors determined that 

the potential for transmission of Psoroptes from llamas to other hosts is present (Foreyt et 

al. 1992). Considering the rarity of this disease in llamas in the U.S. and the unlikely 

nature of direct contact between llamas and Sierra Nevada bighorn sheep, the risk for 

interspecies transmission of this disease is extremely low. 

Conclusion 

Scientific evidence suggests that llamas utilized as pack animals present minimal risk of 

transmission of known pathogens to Sierra Nevada bighorn sheep. Diseases reported in 

new world camelids but not discussed here (e.g., tuberculosis, brucellosis) are rare or 

nonexistent in the United States in llamas, are environmentally related (anthrax, 

clostridial diseases), or require conditions of contact that do not exist in the context of 

Sierra Nevada bighorn sheep and llama management. Due to the endangered status of the 

Sierra Nevada bighorn sheep, land managers may desire a conservative approach to 

further reduce the already small risk of disease introduction from llamas. The following 

measures could be implemented: 

Prevent overuse by private and commercial llama packers. This measure will limit 

contamination of pastures, pens, and standing water sources. Limitations placed on 

numbers due to potential forest and trail impacts may be adequate to address disease 

considerations. 

Require evidence of adequate herd health care before issuance of permits. Evidence of 

herd examinations by a licensed veterinarian, regular diagnosis and treatment of 

gastrointestinal parasites, and exclusion of animals showing signs of infectious disease 

from the pack string can be reflected in a health certificate that is renewed on a periodic 

(annual) basis. 

These additional precautions impose little if any additional burden on either land 

managers or llama packers, and will further protect the small and endangered populations 

of Sierra Nevada bighorn sheep. 
103

Literature Cited 

Chiodini, R. J. and H. J. Van Kruiningen. 1983. Eastern white-tailed deer as a reservoir 

of ruminant paratuberculosis. Journal of the American Veterinary Medical 

Association 182(2):168-169. 

Clark, R. K., W. M. Boyce, D. A. Jessup, and L. F. Elliot. 1993. Survey of pathogen 

exposure among population clusters of bighorn sheep (Ovis canadensis) in 

California. Journal of Zoo and Wildlife Medicine 24(1):48-53. 

Foreyt, W. J., L. G. Rickard, and W. M. Boyce. 1992. Psoroptes sp. in two llamas 

(Lama glama) in Washington. Journal of Parasitology 78(1)153-155. 

Foreyt, W. J. 1992. Experimental contact association between bighorn sheep, elk and 

deer with known Pasteurella haemolytica infections. Biennial Symposium of the 

Northern Wild Sheep and Goat Council. 8:213-218. 

Foreyt, W. J. 1994. Effects of controlled contact exposure between healthy bighorn 

sheep and llamas, domestic goats, mountain goats, cattle, domestic sheep, or 

mouflon sheep. Biennial Symposium of the Northern Wild Sheep and Goat 

Council. 9:7-14. 

Foreyt, W. J., and J. E. Lagerquist. 1996 . Experimental contact of bighorn sheep (Ovis 

canadensis) with horses and cattle, and comparison of neutrophil sensitivity to 

Pasteurella haemolytica cytotoxins. Journal of Wildlife Diseases 32(4) 594-602. 

Fowler, M. E. 1998. Infectious Diseases In Medicine and Surgery of South American 

Camelids. 148-194. Iowa State University Press, Ames, IA. 

Jessup, D. A. 1981. Paratuberculosis in tule elk in California. Journal of the American 

Veterinary Medical Association 179(11):1252-1254. 

Jessup, D. A., and W. M. Boyce. 1993. Diseases of Wild Sheep. In M. E. Fowler, ed 

Zoo and Wild Animal Medicine: Current Veterinary Therapy 3. M. E. Fowler, 

Ed. pages 554-560. 

Ridge, S. E., J. T. Harkin, R. T. Badman, A. M. Mellor and J. W. A. Larsen. 1995. 

Johne’s disease in alpacas (Lama pacos) in Australia. Australian Veterinary 

Journal 72(4) 150-153. 

Riemann, H. R., M. R. Zaman, R. Ruppanner, O. Aalund, J. B. Jorgensen, H. Worsaae, 

and D. Behymer. 1979. Paratuberculosis in cattle and free-living exotic deer. 

Journal of the American Veterinary Medical Association 174:841-843. 
104

Shulaw, W. P., J. C. Gordon, S.Bech-Nielsen, C. I. Pretzman, and G. F. Hoffsis. 1986. 

Evidence of paratuberculosis in Ohio’s white-tailed deer, as determined by an 

enzyme-linked immunosorben assay. American Journal of Veterinary Research 

47(12):2538-2542. 

Thedford, T. R., and L. W. Johnson. 1989. Infectious disease of new-world camelids. In 

Veterinary Clinics of North America: Food Animal Practice. Llama Medicine. 

5(1): 145-157. 

 

Thrusfield, M. 1995. The transmission and maintenance of infection. Chapter 6 in 

Veterinary Epidemiology. Blackwell Science, Malden, MA 

Williams, E. S., T. R. Spraker and G. G. Schoonveld. 1979. Paratuberculosis (Johne’s 

Disease) in bighorn sheep and a rocky mountain goat in Colorado. Journal of 

Wildlife Diseases 15:221-227. 

Williams, E. S., S. P. Snyder, and K. L. Martin. 1983. Experimental infections of some 

North American wild ruminants and domestic sheep with Mycobacterium 

paratuberculosis: clinical and bacteriological findings. Journal of Wildlife 

Diseases 19(3):185-191. 
105

APPENDIX B SIERRA NEVADA BIGHORN SHEEP AND DOMESTIC 

LIVESTOCK: PRELIMINARY RISK ASSESSMENT OF 

DISEASE TRANSMISSION IN THE EASTERN SIERRA 

Epidemiology

 Domestic livestock grazing allotments are commonly located within or adjacent to 

bighorn sheep habitat in some areas of the eastern Sierra Nevada. In addition, feral, 

abandoned, or lost domestic cattle, goats, and sheep may become sympatric with bighorn 

sheep. The proximity of domestic livestock to bighorn sheep raises concerns for the 

transmission of diseases to bighorn sheep. 

 

Cattle 

 

The impacts of domestic cattle (Bos taurus) grazing within bighorn sheep habitat have 

not been well documented. Bighorn sheep may avoid areas where cattle are grazed and 

not return to those areas for long periods after cattle are removed (King and Workman 

1984). The potential for cross species transmission of diseases between cattle and wild 

ungulates may vary with local environmental conditions. Bovine viral diarrhea causes a 

complex of respiratory diseases, gastrointestinal diseases, and reproductive failure and 

may be transmitted between species. Hemorrhagic disease and pneumonia resulting from 

bluetongue virus (BTV) infection have been reported in bighorn sheep (Robinson et al

1967, Noon et al 2002). Because of prolonged viremia, cattle may be an important 

reservoir of BTV for Culicoides vectors (Osburn 2000) and, thus, a potential source of 

infection for other wild and domestic ungulates in areas climatically suitable for 

Culicoides. Singer et al (1997) studied cattle, bighorn sheep and mule deer (Odocoileus 

hemionus) in an area where the three species were known to utilize common areas. Only 

cattle were seropositive to BTV but deer and bighorn sheep were seropositive to Babesia 

sp. and Psoroptes mites were found only on bighorn sheep. Singer et al. (1997) 

concluded that cattle, deer, and bighorn sheep did not share similar patterns of exposure 

to the three pathogens and, thereby, proposed that cattle did not constitute a health risk 

for bighorn sheep in that area. Foreyt (1994) reported no adverse effects on healthy 

bighorn sheep in one co-pasturing study with domestic cattle. In a follow-up study, 

however, one of five bighorn sheep co-pastured with cattle developed a fatal pneumonia 

and died on day 6 post introduction (Foreyt and Lagerquist 1996). Although cattle may 

carry Pasteurella spp. that are pathogenic to bighorn sheep, those authors hypothesized 

that “the nose to nose contact required for transmission of P. haemolytica (renamed 

Mannheimia haemolytica) is less likely to occur between bighorn sheep and cattle” than 

with domestic sheep because the social interactive behavior between bighorn sheep and 

cattle is less likely to result in nose to nose contact. They recommended that further 

studies be conducted to determine the compatibility of bighorn sheep and domestic cattle. 

Based on the limited information currently available, there is insufficient evidence to 

exclude cattle grazing in or near bighorn sheep habitat based on disease considerations. 

However, if cattle grazing increases in proximity to bighorn sheep, disease considerations 

should be reconsidered. 
106

Goats 

Domestic goats (Capra hircus) are occasionally proposed for use as pack animals or for 

brush control in or near bighorn sheep habitat. Goats can be unapparent carriers of 

various pathogens. A recent outbreak of disease in bighorn sheep in Arizona provides 

strong evidence that contact with domestic goats presents a significant disease risk for 

bighorn sheep (Heffelfinger 2004). In October 2003, 4800 domestic goats were legally 

imported into Arizona from Texas to an unfenced state land grazing allotment about 5 

miles north of bighorn sheep habitat in the Silver Bell Mountains, Pima County. In early 

November, a number of stray goats were confirmed within bighorn range. Despite efforts 

to remove the goats, by December, contact between the two species had resulted in an 

outbreak of infectious keratoconjunctivitis (inflammation of the eye) resulting in 

complete blindness in 33 bighorn sheep. During capture and treatment of these bighorn, 

contagious ecthyma (CE or soremouth) was also detected in 19 animals. Of 81 bighorn 

sheep thought to inhabit the Silver Bell Mountains, there were 14 known mortalities from 

malnutrition, predation, and other factors that were exacerbated by blindness. In 

addition, there were three stillborn lambs and three lambs that died post-partum from 

infected ewes. Thirteen bighorns are known to have recovered, but five remain 

unaccounted for. Heffelfinger (2004) provided the following links that implicated 

contact with goats as the cause of the bighorn disease outbreak: 

3⁄4 Neither disease had ever been seen before in bighorn in the Silver Bell Mountains. 

3⁄4 All bighorn observed were healthy during surveys on October 8, 2003. 

3⁄4 Goats arrived in October and were confirmed to be in bighorn habitat in 

November. Blindness and CE lesions in the bighorn appeared in early December. 

3⁄4 Both diseases are common in goat operations. 

3⁄4 Cowboys reported some of the goats came off the trailer blind and later recovered. 

3⁄4 One goat collected from sheep habitat was recovering from blindness. 

3⁄4 Genetic sequences from the bacterium, (Mycoplasma conjunctivae) found in the 

eyes of the collected goat were identical to those isolated from a blind Silver Bell 

bighorn. 

Domestic Sheep 

Bighorn sheep are closely related to domestic sheep (Ovis aries) and share many diseases 

with them, including pneumonias of viral and bacterial origin, contagious ecthyma, 

psoroptic scabies, bluetongue virus infection, and others. Chronic sinusitis in bighorn 

may result from infestation by the domestic sheep nasal bot fly (Oestrus ovis) (Bunch and 

Allen 1981) but can be avoided in domestic sheep with routine use of ivermectins. This 

may be a more significant risk from poorly managed, backyard sheep operations. 

Introduction of domestic sheep grazing into the Rocky Mountains and southwestern 

states in the late 1800s and early 1900s coincided with widespread, all-age losses of 

bighorn sheep (Buechner 1960). There is substantial, albeit circumstantial, evidence 

from outbreaks in free-ranging bighorn sheep indicating that diseases introduced by 

domestic sheep likely played an important role in the reductions of bighorn sheep 
107

populations throughout their range (Goodson 1982, Martin et al 1996). Experimental 

data support this view. Numerous independent trials in which bighorn sheep that were 

well adapted to captivity and on an excellent plane of nutrition developed respiratory 

disease and died after direct contact with domestic sheep provide compelling evidence of 

the incompatibility of the two species (Onderka and Wishart 1988; Foreyt 1989, 1990, 

1994; Callan et al.1991). Inoculations of bighorn sheep with Pasteurella isolates or 

fluids from the respiratory tract of healthy domestic sheep (Onderka et al. 1988, Foreyt et 

al. 1994, Foreyt and Silflow 1996) usually have resulted in respiratory disease and death 

of the bighorn sheep, but not of domestic sheep treated identically. By eliminating many 

of the environmental stressors that complicate field outbreaks of pneumonia in bighorn 

sheep, the aforementioned experimental studies have established a direct link between 

domestic sheep contact and respiratory disease in bighorn. In these studies, the domestic 

sheep remained free of clinical symptoms of disease while bighorn sheep succumbed to 

pneumonia. Further, in numerous additional pen trials in which a variety of other wild 

and domestic ungulate species were mixed with bighorn sheep, respiratory disease did 

not occur in bighorn sheep, except for the case cited above involving cattle (Foreyt 1992, 

1994; Foreyt and Lagerquist 1996). Thus, the hypothesized stress on bighorn sheep of 

mixing of other species with them in pens does not explain the results of the pen trials 

with domestic sheep. The alternative explanation is that healthy domestic sheep 

frequently carry strains of pneumophilic bacteria that are fatal to bighorn sheep. 

 

Outbreaks of respiratory disease from Pasteurella infections also may occur in bighorn 

sheep herds without known contact with domestic livestock (Miller et al. 1991). The 

respiratory disease complex of bighorn sheep is multi-factorial, and environmental and 

anthropogenic stressors likely allow opportunistic microorganisms to become pathogenic 

in bighorn sheep herds. The lungworm, Protostrongylus stilesi, is an important cause of 

verminous pneumonia and summer lamb mortality in overcrowded bighorn herds 

(Spraker and Hibler 1982) and is specific to bighorn sheep. Heavy infestations 

predispose bighorn lambs to severe, sometimes fatal parasitic pneumonias (Hibler et al. 

1972, Hibler et al. 1974, Woodard et al. 1974) but such infestations have not been 

observed in less mesic ranges such as the Sierra Nevada (Wehausen 1980). Some 

bighorn herds are asymptomatic carriers of types of Pasteurella that are considered 

potentially pathogenic to other populations of bighorn sheep (Sandoval et al. 1987). 

Transmission of bacteria can result in acute disease, long-term carrier status, or nothing. 

A high percentage (84-100%) of bighorn sheep typically test positive for Pasteurella spp. 

when pharyngeal swabs are cultured properly and promptly (Wild and Miller 1991, 1994, 

Ward et al. 1997). 

 

Some contacts between bighorn sheep and domestic sheep may not result in transmission 

of respiratory disease to bighorn; the outcome likely depends on a variety of factors 

including the exposure history and immune status of both the bighorn sheep and the 

domestic sheep. However, current technology does not allow us to predict which 

particular contact will result in disease transmission. Further, the onset of pneumonia in 

affected bighorn sheep may be delayed by days, weeks or months following contact with 

domestic sheep, and disease in isolated herds may not be detected for months after 
108

infection. In addition, surviving bighorn, especially wandering rams, may transmit 

pathogens to adjacent populations. 

 

Currently there is no vaccine that will protect bighorn sheep against the many types of 

Pasteurella haemolytica (now Mannheimia haemolytica) or P. multocida prevalent 

during pneumonia outbreaks. In the event that an effective vaccine were to be developed, 

the logistics of effectively vaccinating a bighorn sheep population at risk would not be 

feasible, especially in the rugged Sierra Nevada. Vaccines generally protect from disease 

but not from infection. As a result, vaccinated ewes could continue to pass pathogenic 

bacteria to their lambs, possibly resulting in high juvenile mortality for 3 to 5 years 

following an outbreak. 

 

Current evidence strongly suggests that domestic sheep and bighorn sheep are 

incompatible. Policies to maintain separation between the two species have been adopted 

by wildlife departments, as well as land management agencies (Bureau of Land 

Management 1992, 1998; Schommer and Woolever 2001). When attempting to find 

management solutions to the incompatibility between domestic and bighorn sheep, 

Schommer and Woolever (2001) concluded, “the most essential step in this sheepspecific process is to reach common understanding among all involved that 

incompatibility between domestic sheep and bighorn sheep exists and mixing the two 

species will eventually result in a bighorn sheep die-off. Without this fundamental 

understanding of the problem, collaborative efforts to develop potential solutions will 

probably not occur.” 

Risk Assessment and Behavior

Domestic Goats 

 

The potential for contact between domestic goats and bighorn sheep exists in the eastern 

Sierra Nevada through the use of pack goats, as well as goats that are raised for meat. 

Pack goats are a concern because they are used to carry supplies into the backcountry, 

particularly high elevation areas in Wilderness. Current Forest Service policy prohibits 

the use of pack goats within herd unit areas occupied by Sierra Nevada bighorn sheep; 

this policy should continue. Owners of goat herds should be informed about the risks 

associated with contact with bighorn sheep and the need to keep animals confined. The 

use of weed control goats has been suggested but particularly should be avoided in the 

eastern Sierra Nevada because such goats are often of auction origin and tend to carry 

numerous diseases. Goats are not strong herd animals and the potential for animals to 

stray is great. 

Domestic Sheep 

 

Given the potential for disease transmission that may occur following contact between 

bighorn and domestic sheep, maintaining a zone of no contact between the two species is 

essential (Martin et al. 1996, Schommer and Woolever 2001, Gross et al. 2000). 

Suggested separation distances between domestic sheep and bighorn sheep ranges, but a 
109

minimum distance of 23 km has been recommended as a general rule when performing 

translocations of bighorn sheep near domestic sheep grazing allotments (Singer et al. 

2000, Singer et al. 2001). Implicit in these recommendations is the concern that the two 

species will come into contact through straying of domestic sheep or long distance 

movements by bighorn sheep. The propensity for contact is exacerbated further by the 

interest in and ability of bighorn rams to mate with domestic ewes (Young and Manville 

1960). 

Previous recommendations for conserving Sierra Nevada bighorn sheep were based on 

limited knowledge of bighorn behavior and movements (U. S. Fish and Wildlife Service 

2001). Consequently, assumptions made when assessing risk of disease transmission 

must be reevaluated. Previously, risk was assessed largely on concern about domestic 

sheep straying into bighorn habitat. That concern is real, as exhibited by at least three 

examples in this region in the last decade: 1) 23 domestic sheep wandered from the 

Bloody Canyon allotment into Dana Fork in Yosemite National Park and were discovered 

in November 1995 (U.S. Fish and Wildlife Service 2001), 2) > 27 domestic sheep 

wandered off private land and into bighorn habitat in Jeffrey Canyon in the White 

Mountains in June 2004 (T. Stephenson, California Department of Fish and Game, 

unpublished observation), and 3) on 17 November 2004, 7 domestic sheep were observed 

wandering on the north side of Conway Summit along Highway 395 after the grazing 

season (T. Taylor, California Department of Fish and Game, unpublished observation). 

In addition, husbandry and grazing practices on some allotments are inadequate to either 

prevent or respond to contact between domestic and bighorn sheep (California 

Department of Fish and Game 2005). 

Equal importance must be given to the potential for forays by bighorn sheep, particularly 

males, to result in contact with domestic sheep. The timing and extent of such forays are 

particularly relevant such as when and where they occur relative to adjacent domestic 

sheep grazing. Movements of female bighorn sheep in the Sierra Nevada are 

characterized by seasonal philopatry. Specific females use the same winter and summer 

ranges year after year. Movements of males also are characterized by a tendency to use 

the same winter and summer ranges repeatedly; however, there are frequent exceptions. 

Since 2002, six instances of adult male bighorn traveling at lower elevations in or near 

the eastern Sierra have been documented. In November 2002, a male was observed 

crossing Bridgeport Valley east to west and disappeared in Buckeye Canyon (Tim 

Taylor, California Department of Fish and Game, unpublished observation). On 30 June 

2003, a young male was observed and captured along highway 6 just north of Hamill 

Valley (T. Stephenson, California Department of Fish and Game, unpublished 

observation). On 29 November 2003, a radio-collared adult male (S21) was struck by a 

vehicle on highway 395 at the mouth of Lundy Canyon while crossing from east to west 

(T. Stephenson, California Department of Fish and Game, unpublished observation). On 

6 August 2004, a bighorn sheep was reported traveling west across highway 395 just 

north of Conway Summit (Kathy Lucich, U.S. Forest Service, personal communication). 

During November 2005, a bighorn male (estimated age - 4 years) was observed on the 

floor of the Owens Valley, east of highway 395 and adjacent to the Black Rock Hatchery 
110

(Los Angeles Department of Water and Power, personal communication). Finally, from 

November 3 to 6, 2005, a radio-collared adult male (S20) traveled north from Lundy 

Canyon, through the Cameron Canyon allotment, to the south end of Bridgeport Valley 

and then returned to Lundy Canyon. It cannot be assumed that bighorn sheep, and in 

particular males, will remain entirely at high elevation during summer, especially as the 

rut approaches. Domestic sheep graze public and private land in the eastern Sierra 

Nevada from June into November and use elevations ranging from <7,000 feet to > 

10,500 feet. 

Considerable data from telemetered bighorn in the Sierra Nevada reveal a tendency for 

some males to make long-distance movements beyond their normal home range. It is 

notable that all radio-collared bighorn rams that made extralimital movements returned to 

their core home range within 8 months of their departure; as yet, none resulted in 

permanent colonizations of new areas. The significance of their initial departure and 

movement is surpassed only by their subsequent return, which has important implications 

when evaluating the potential for widespread disease transmission. Of the 25 bighorn 

rams collared and with sufficient data as of May 2006, seven (28 percent) have made 

substantial movements beyond their core home ranges. The movements of three males 

that traveled north from the Mt. Warren area (Figures B-1 and B-2) illustrate their 

potential to act as carriers of disease if exposed. S12 and S60 were observed on the north 

end of Kavanaugh Ridge directly above Green Creek. S20 traveled north on two separate 

occasions in 2005 (Figure B-2); during July he was in the Dunderberg allotment and 

during 2-7 November 2005, he traveled through the Cameron Canyon allotment and 

beyond. Over a span of only a few days in late October and early November 2002, S10 

circumnavigated Mount Tom while making a foray southward from Wheeler Ridge 

(Figure B-3). The most extensive movements observed were by S13, who traveled >33 

air miles (53 km) south of Lee Vining Canyon to Laurel Mountain (Figure B-4). S13’s 

departure occurred during December 2002 and he returned the following August. 

Home range extent provides one measure of the extremes in distances traveled by 

bighorn and includes movements that result from migrations and forays. Sixty-one Sierra 

bighorn had data that encompassed winter and summer ranges and were used in the 

analysis. Maximum extent of female movements ranged from 7.0 to 22.6 km. In 

comparison, maximum extent of male movements varied from 11.4 to 59.4 km. Berger 

(2004) noted that migration distances of bighorn ranged between 7 and 74 km. DeCesare 

and Pletscher (2006) observed bighorn rams moving >30 km beyond their core home 

range. 

Home ranges of male and female bighorn differed in size (t = -3.05, n = 61, P = 0.005); 

male ranges were almost twice as large on average. Mean minimum convex polygon 

home range of ewes was 53.0 km2

 (SD = 24.3). Mean size of home ranges for rams was 

100.4 km2

 (SD = 75.0). 

The movements of radio-collared bighorn sheep in the Sierra Nevada, in combination 

with observations of rams crossing adjacent valleys, illustrate the possible role that 

bighorn may play in contracting and spreading disease from the numerous domestic 
111

sheep herds in the area. The potential for bighorn rams to move into and through 

domestic sheep allotments and then return to their herd of origin are reasons to be 

concerned about potential for disease transmission. Questions remain as to what 

behavioral and ecological factors may precipitate long distance movements by specific 

rams. Social status, age, nutritional status, herd size, population density, predation risk, 

and habitat availability may be factors affecting the propensity of an animal to make 

forays. 

The proximity of bighorn sheep locations and domestic sheep allotments translates to a 

non-trivial risk of contact between the two species, and the consequent potential for 

disease transmission (Figure B-5). Of the three occupied Recovery Units, only the 

Southern Recovery Unit no longer exhibits significant risk of contact (Figure B-5). In the 

Northern Recovery Unit, bighorn sheep were located immediately adjacent to active 

allotments during 2004 (Figure B-6). In the Central Recovery Unit, the Wheeler Ridge 

Herd currently supports the largest concentration of bighorn sheep within the Sierra 

Nevada and lies within 5 kilometers of domestic sheep grazing allotments (Figure B-7). 

The 10- and 20-kilometer distances used to illustrate the zones of epidemiologic risk are 

less than some recommendations in the literature for avoiding contact. Further, they are 

less than movements observed for some rams in the Sierra Nevada. Nevertheless, such 

distances reduce the likelihood of contact. Included, at least in part, within the 20-

kilometer zones of risk are 31 federal domestic sheep grazing allotments totaling over 

350,000 acres. 

The focus here has been on the negative aspects of long distance movements by bighorn 

sheep relative to domestic sheep, but these movements have essential benefits to 

populations. Considered in an ecological and evolutionary context, such movements 

have profound genetic benefits, such as reduction of the potential for inbreeding (Mills 

and Allendorf 1996), and function to maintain metapopulation structure through the 

potential for colonization to occur (Bleich et al. 1990). 

Disease threats in the eastern Sierra Nevada also are posed by the prevalence of domestic 

sheep and goats on private land; these include larger flocks on farms, as well as 

individual animals and smaller flocks in small pastures and back yards. In many cases, 

non-commercial or hobby animals may pose a greater threat because there may be less 

awareness by their owners of the risk to bighorn. Efforts to inform these owners are 

needed to reduce the risk and ensure that agencies are notified if animals are lost or if 

contact with bighorns occurs. 

For recovery of Sierra Nevada bighorn sheep to succeed, there should be no contact 

between Sierra Nevada bighorn sheep and domestic sheep. There may be various actions 

that can be taken to achieve this goal; one of those is to evaluate risk and encourage 

resource management agencies to take actions to prevent contact. 
112

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APPENDIX C TRANSLOCATION CONSIDERATIONS FOR SIERRA 

NEVADA BIGHORN SHEEP 

The future of bighorn sheep in the Sierra Nevada hinges on the use of translocations for 

reintroductions and herd augmentations, and possibly for genetic management. The 

translocation plan called for in Task 3.1 is therefore critical to the recovery effort for 

these bighorn sheep. This appendix lays out some of the elements and issues that should 

be in that plan and a discussion of both occupied and unoccupied bighorn sheep habitat in 

the southern and central Sierra Nevada. 

A. Sources of translocation stock 

In the 1970s and 1980s, only a single herd existed in the Sierra Nevada that was 

large and productive enough to be tapped for reintroduction stock. That vulnerable 

situation was a primary concern addressed in the Sierra Nevada Bighorn Sheep Recovery 

and Conservation Plan (Sierra Nevada Bighorn Sheep Interagency Advisory Group 

1984). The same vulnerable situation exists today. Solving this problem has to be one of 

the key elements of the translocation strategy. Among the options that need to be 

explored are the establishment and maintenance of one or more wild source herds and the 

conditions under which a captive herd should be developed in parallel to produce stock 

for translocation needs to be addressed as well. The advantages of captive breeding lie 

with being able to control factors affecting survivorship and reproductive output. A 

captive herd could be managed to have optimum reproduction and survivorship without 

the environmental variation that is present in wild populations, thereby maximizing 

production of bighorn sheep. 

A captive breeding contingency plan will need to be developed to facilitate decisions 

relating to the captive breeding of bighorn sheep. The final product of a captive breeding 

herd should be healthy, behaviorally normal individuals capable of surviving and 

reproducing in the wild. The concept of captive breeding in general, along with the 

history of bighorn sheep captive breeding attempts, will need to be reviewed. A 

theoretical decision tree should be constructed to help facilitate captive breeding 

decisions and identify the point at which captive breeding is considered essential to 

prevent extinction and accelerate recovery. 

Selection guidelines for a captive breeding site need to be developed, and potential sites 

should be identified and evaluated. Also, guidelines and recommendations for 

constructing and maintaining a facility for captive breeding, selection of founder breeding 

stock, husbandry, veterinary care, and a summary of diseases that may affect a captive 

herd needs to be carefully developed. Development of this information prior to an actual 

decision to enter into a captive breeding program will greatly expedite the development 

of such a facility if it is needed. 

Population models can help in evaluating how captive breeding may facilitate recovery 

goals. The integrity of these models will depend on the input of demographic data on 

age- and cause-specific mortality, reproductive success, and census numbers. Such 
124

models also can help assess the effects that the bighorn sheep removal and augmentation 

associated with captive breeding could have on extinction probabilities in populations. 

These initial models may help guide decision-making and the construction of future 

models. 

B. Management of wild herds for translocation stock 

Issues that should be addressed in a translocation plan are: (1) how such herds are to be 

managed differently from other herds; (2) what demographic criteria will be used to 

determine when and how many bighorn sheep will be removed from a herd; (3) what 

tradeoffs and benefits are associated with waiting until a herd has grown larger before 

removing bighorn sheep for translocation; and (4) what potential behavioral implications 

for the source herd may be associated with frequent captures, and how these may relate to 

logistical difficulties of capturing bighorn sheep. 

C. Translocation strategy 

The optimal use of bighorn sheep available to translocate is a complex question. While a 

short-term plan can be developed based on current population information, it is important 

to recognize that it will need to change as the status of herds change, recovery goals are 

met, and new information on habitat is developed. Ideally, the plan will incorporate 

needed flexibility. The alternative will be to revise the plan as needed. Below are some 

of the key issues to be addressed in the plan. 

1. Prioritization of locations to receive available stock

Should available stock be used only for augmentations to assure recovery to all existing 

herds before unoccupied ranges are considered? 

Should the first bighorn sheep available for translocation be used only to create at least 

one more source of translocation stock, or should a mixed strategy be considered? 

Should the goal of the translocation strategy be to minimize the time to downlisting? 

Does such an optimization have any associated risks? In developing a long-term strategy, 

it will be important to estimate the minimum number of bighorn sheep that will need to 

be moved for reintroductions to meet recovery goals. 

How does the proximity of domestic sheep grazing allotments and the grazing practices 

implemented on those allotments affect prioritization of translocation sites? 

Translocation group size

Minimum numbers that will be moved for augmentations versus reintroductions need to 

be established. Moving smaller numbers will risk fewer bighorn sheep and may be 

desirable for some reintroductions, with the idea that the initial group can be augmented 

later. Because herd augmentations can generally be accomplished with far fewer 
125

individuals than reintroductions, it may be difficult to justify engaging in reintroductions 

until existing herds have reached sizes that afford some comfort in terms of viability. 

It has been recommended that reintroduced herds of bighorn sheep be created with at 

least 20 individuals (Wilson and Douglas 1982), and this approach has been the common 

practice, including past reintroductions in the Sierra Nevada. Establishing sufficient 

genetic variation in isolated herds has been one reason for this approach. In contrast, a 

new group of females established within a metapopulation where males will find them 

might be created with a small number of females and perhaps one male to assure 

breeding until other males discover them. This practice will better mimic natural 

colonization in bighorn sheep, where new female groups sometimes arise from a single 

dispersing female (Bleich et al. 1996). Males explore nearby habitat considerably more 

than females and in general find suitable habitat patches before females. 

There are other considerations regarding numbers of females to translocate. Regardless 

of how much research may be allocated to choosing release sites, uncertainties will 

always remain. Therefore, it will be important to proceed with an experimental approach 

to translocations so that different scenarios can be evaluated to optimize future efforts. 

Even for a reintroduction, an initial translocation of a relatively small number of 

individuals will allow an assessment of site suitability. An augmentation can follow if 

deemed appropriate to boost numbers and assure sufficient genetic diversity, but the 

failure of a reintroduction of many bighorn sheep due to unforeseen circumstances will 

be an irretrievable loss of a rare resource. Also considered should be the advantages that 

bighorn sheep obtain from group living, including better predator detection and feeding 

efficiency. Group sizes of five to six are common, and feeding efficiency shows little 

gain beyond that size (Berger 1978, Risenhoover and Bailey 1985). Thus, releases in 

new areas should attempt to provide a group of at least five bighorn sheep if possible. 

3. Timing of translocations

The intent of most or all translocations will be the establishment or augmentation of herds 

using low elevation winter ranges. Since the peak in such use of this habitat historically 

has been in late winter and early spring, this period (especially March) would be the ideal 

time to translocate bighorn sheep to these sites. There are several reasons for this 

assessment. First, these bighorn sheep have a natural tendency to descend to such sites at 

that time of year. Second, forage quality will be high during this period, which may help 

hold translocated bighorn sheep near the release site. Third, for augmentations, there are 

likely to be herds present on these winter ranges that translocated animals can join, which 

should also serve to help hold translocated bighorn sheep near the release site. Finally, 

bighorn sheep can be caught most readily at this time of year. The translocation strategy 

should consider whether there is any other time of year at which translocations might be 

successfully done. 
126

4. Potential areas to receive bighorn sheep

Below is a discussion of locations that might support herds of bighorn sheep. It combines 

habitat attributes with historical data. These locations are grouped by recovery units and 

by herd units within recovery units. The following attributes were considered in 

developing a list of potential areas that might support female groups (Table C-1): (1) 

known past use by bighorn sheep; (2) extent of high elevation snow-free winter habitat; 

(3) availability of lower elevation south or east-facing habitat and its lowest elevation and 

quality in terms of visual openness; and (4) availability of high elevation summer habitat. 

Winter habitat is the most limited habitat available in general and was the primary focus. 

Recent herd histories have indicated that some use of low elevations in late winter and 

spring is essential for herds to maintain viable sizes. Table C-1 lists minimum elevations 

for each area. Lower elevations are correlated with warmer temperatures, earlier 

initiation of forage growth, and potentially higher overall nutrient intake by bighorn 

sheep. Wehausen (1980) found that each 17.8-meter (58.4-foot) increase in elevation 

equated to a 1-day delay in initiation of forage growth and associated increases in diet 

quality. This relationship translates to a 17-day delay per 1,000 feet, or 28 days per 500 

meters. The large size attained by the Mount Baxter herd prior to changes in winter 

habitat use apparently resulted from high nutrient intake obtained on its low elevation 

winter range; this herd declined to about 15 percent of its former size while avoiding low 

elevation winter range habitat (Wehausen 1999). While lower minimum elevations allow 

greater nutrient intake by bighorn sheep herds using them, it is not known what the upper 

limit of this minimum elevation is relative to supporting a viable herd. 

Northern Recovery Unit

Bighorn sheep were recorded historically as far north as the Sonora Pass region (Grinnell 

and Storer 1924). Some patches blown free of snow exist near and east of Sonora Pass. 

However, these patches included little rocky escape terrain and were not considered 

suitable for reintroduction. It is not yet evident what sort of habitat use patterns the 

native bighorn sheep in this area might have had, but viable habitat may have included 

the Walker River Gorge and even the Sweetwater Mountains. 

Nine areas were considered to have potential habitat for bighorn sheep in this recovery 

unit (Table C-1). Three of these currently are inhabited by both sexes, and three more 

receive at least occasional use by males. Two areas are not suitable for translocations due 

to the proximity of active domestic sheep grazing operations (Green Creek and Twin 

Lakes). These areas are not included as potential areas for translocation. 

Mount Warren Herd Unit: The Mount Warren area north of Lee Vining Canyon has a 

good combination of high elevation and low elevation winter habitat and supported a 

large concentration of bighorn sheep prior to 1995. Tioga Crest is included in the herd 

unit because of close connectivity. However, since 1995 data have suggested that a 

separate female group occupies Tioga Crest. 
127

Table C-1. Potential sites for bighorn sheep wintering groups in the central and southern Sierra Nevada gUnit. 

Location Current Bighorn Sheep Use Minimum Winter Habitat Elevation (m) W

Northern Recovery Unit Twin Lakes (Victoria Peak) No 2,200 open Green Creek (Crater Crest) No 2,750 open Dunderberg Peak No 3,050 open Lundy Canyon Males 2,450 mixLee Vining Canyon (Mount Warren) Yes 2,300 mix127 Tioga Crest Yes 2,900 open Bloody Canyon (Mount Gibbs) Yes 2,775 open Parker Canyon (Mount Lewis) Males 2,700 open Alger Creek (Mount Wood) Males 2,300 open Central Recovery Unit Convict Creek (Laurel Mountain) Isolated male use 2,400 open McGee Creek (McGee Mountain) No 2,450 open Nevahbe Ridge No 2,600 open Wheeler Ridge Yes 1,700 open Mount Tom Males 1,950 open 
128

Southern Recovery Unit 

Shannon Canyon (Coyote Ridge) No 1,700 open Birch Mountain/Kid Mountain No 2,800 open Taboose Creek No 1,950 open Goodale Creek No 2,100 open Sawmill Canyon Yes 1,500 open Thibaut Canyon-Sand Mountain Yes 1,525 open Onion Valley (Kearsarge Peak) Yes 2,300 opeBubbs Creek Yes 2,075 mixShepherd Creek-Pinyon Creek Yes 2,075 mixGeorge Creek - N. Bairs Creek No 1,900 mix128 Lone Pine Creek-Hogback Creek No 2,075 mixCarroll Creek -Tuttle Creek Yes 1,750 mixCottonwood Creek - Slide Canyon Males 1,450 open Falls Creek - Ash Creek No 1,450 open Kern Recovery Unit Big Arroyo No 2,100 mixRattlesnake Creek No 2,075 mixLaurel Creek No 2,075 mix
129

Immediately to the north, Lundy Canyon has good low elevation south-facing winter 

range that rivals Lee Vining Canyon in its lowest elevation (Table C-1). In contrast, 

Lundy Canyon has very little high elevation winter habitat. Farther north, much of 

Dunderberg Peak is substantially blown free of snow in winter, but it does not connect to 

low elevation winter range. It is, however, connected to the Lundy Canyon range in 

summer. 

Mount Gibbs Herd Unit: South of Lee Vining Canyon, the region from Mount Wood 

to Mount Dana has high potential for expansion of bighorn sheep range in this recovery 

unit. There is considerable high elevation habitat blown free in winter, which connects 

well to south-facing slopes that drop to lower elevations. Males are already known to 

move between Mount Warren and this area. With the recruitment of a yearling female in 

the Mount Gibbs herd in 1997, its known reproductive base increased to two females. 

Beginning in 1999, a third female has been documented in this group (Wehausen 2000). 

It is possible that, left alone, this little group will grow and eventually expand south to 

Mount Wood. This process could be greatly accelerated by translocating some females 

into this area. It is noteworthy that just west of Parker Peak lies Koip Peak, which means 

bighorn sheep in the Paiute language. 

While many details on seasonal habitat use are lacking, the current herd in the region 

apparently uses only Mount Gibbs and part of Mount Dana during summer. Mount 

Lewis has habitat that appears to receive use only by males currently. The south-facing 

side of this mountain is steep and holds little snow in winter. It may be capable of 

supporting a small group of females. The Mount Wood area appears to be the best 

habitat in this unit. The slopes above Silver Lake provide low elevation east-facing 

winter range down to 2,316 meters (7,600 feet) that probably once received use by 

bighorn sheep, perhaps including birthing in spring in some years. 

Central Recovery Unit

Wheeler Ridge Herd Unit: The Central Recovery Unit currently has one herd on 

Wheeler Ridge, which had grown to about 70 individuals in 2000. In the winter of 1998, 

there was a reported sighting of three females above Wells Meadow, the first known use 

of this low elevation winter range in many years. In subsequent years, this excellent 

winter range showed a steep increase in use by that herd in late winter. The herd is 

increasing very rapidly and is the one prospect for a source of translocation stock in the 

near future. 

Immediately south of Wheeler Ridge is Mount Tom, which had a native herd of bighorn 

sheep that persisted into the 1930s. Ober (in litt. 1911) said of them: "on Mount Tom, 

twenty miles west of the city of Bishop, there ranges in winter and summer a beautiful 

herd numbering forty head; they course from Mount Tom on over the summit to the west 

and around the head waters of Pine Creek". Three years later Ober also noted that this 

herd numbered "about forty or fifty head; they follow the snow line in winter, and, as a 

matter of fact come very close to the little farming community of Round Valley (Ober 
130

1914).” Males from Wheeler Ridge have been known to visit Mount Tom occasionally 

since they were reintroduced in 1979, and Mount Tom is the likely first site for range 

expansion in this region via translocation. Mount Tom offers multiple habitat options. 

Low elevation winter-spring habitat extends down to 1,950 meters (6,400 feet) in 

Elderberry Canyon. High elevation winter habitat is extensive on the west side of the 

north ridge of Mount Tom, and there are even some narrow ridges that can be blown free 

of snow on the south side of the mountain. Further, the summit plateau between Basin 

Mountain and Mount Humphreys remains snow free in winter and is accessible to 

bighorn sheep traversing ridgelines from Mount Tom via Four Gables and along the crest. 

Early sighting records indicate that the bighorn sheep that inhabited this area used the 

crest in summer at least as far as Mount Emerson, and males certainly ranged farther. 

Reestablishment of this herd might go a long ways toward increasing total numbers of 

bighorn sheep in this recovery unit and thereby enhancing its viability. 

Convict Creek Herd Unit: Farther north are three areas that were probably all used 

historically by bighorn sheep to some degree: Nevahbe Ridge, McGee Mountain, and 

Convict Creek. A native herd inhabited the Convict Creek area into the 1950s (Jones 

1950). Traditional south-facing winter-spring habitat that melts off quickly after winter 

storms occurs above Convict Lake down to 2,407 meters (7,900 feet). That area is 

connected to extensive high elevation wind swept patches on Laurel and Bloody 

Mountains. Of these three northern sites, Convict Creek is the most favorable due to this 

combination. McGee Mountain has excellent south-facing winter habitat down to about 

2,438 meters (8,000 feet) that is equivalent to the slope above Convict Lake, but has only 

a small amount of high elevation winter habitat. Nevahbe Ridge has more windblown 

habitat than McGee Mountain, but the low elevation habitat is east facing and occurs 

down to only 2,590 meters (8,500 feet); thus it is much more delayed in snowmelt. 

In 1989, 11 males from Wheeler Ridge were photographed by a hiker near Rosy Finch 

and Laurel Lakes, which is a considerable distance northwest from Wheeler Ridge and 

indicative of the potential for gene exchange with the northern portion of this recovery 

unit if it can be established via translocation. There was probably also once some gene 

exchange between this recovery unit and the Northern Recovery Unit via San Joaquin 

Ridge. In 2002-2003 a radio-collared male from the Mt. Gibbs herd unit temporarily 

moved south from the Mt. Warren herd unit to Laurel Mountain in the Convict Creek 

herd unit before returning (Figure B-4), as discussed above in Appendix B. As of 2006, 

the Convict Creek herd unit is unoccupied by bighorn sheep. 

Numerous sightings of bighorn sheep on San Joaquin Ridge were recorded between 1954 

and 1957 including a male killed by a deer hunter. Connectivity across this region is less 

likely in the future because of human developments. 

There are currently U.S. Forest Service domestic sheep grazing allotments in close 

proximity to the Convict Creek area. Prior to translocations into these areas, these 

allotments should be analyzed to determine if measures need to be instituted to prevent 

contact between domestic sheep and bighorn sheep (see Section II.E above). 
131

Southern Recovery Unit

As many as 13 or more distinct female groups may have once occupied the area from 

Olancha Canyon to Coyote Flat. Of those areas listed on Table C-1, five currently 

contain female groups and another four are known to have been visited by males. These 

areas are discussed below as six general herds. 

Coyote Ridge Herd Unit: East above the south fork of Bishop Creek there are multiple 

high elevation patches of habitat on Coyote Ridge and the Inconsolable Range that 

remain snow-free in winter. There is a paucity of historical evidence that bighorn sheep 

occupied this area, but this lack of evidence could reflect an incomplete record. Bighorn 

sheep using this area might have used low elevation habitat along Bishop Creek and/or 

crossed over Coyote Flat to excellent south and east-facing winter range as low as 1,706 

meters (5,600 feet) in the Shannon Canyon area. Bishop Creek is currently treated as a 

break between the Central and Southern Recovery Units because of uncertainty about 

former use of the region of Coyote Ridge and the Big Pine Creek drainage. A Coyote 

Ridge herd would serve substantially as a link between these two recovery units. It is 

likely that historically there was gene flow through the bighorn sheep herds along the 

entire east side of the Sierra Nevada. It is noteworthy that a number of recent reported 

sightings on Coyote Ridge, the Inconsolable Range, and the west side of the Palisades 

region suggest the possibility of a small number of bighorn sheep currently occupying 

this area. 

Taboose Creek Herd Unit: Jones (1950) listed a Birch Mountain herd just south of Big 

Pine that he estimated at 15 bighorn sheep. His evidence for these bighorn sheep was 

tracks of six animals. Clyde (in litt. 1971) noted that he had never seen bighorn sheep 

sign on Birch Mountain in numerous ascents but had once seen deer (does and fawns) 

well above timberline on its slopes. Nevertheless, Ober (1914) mentioned bighorn sheep 

living from Birch Creek to Big Pine Creek, and Clyde (in litt. 1971) noted evidence on a 

variety of occasions of bighorn sheep in the upper Big Pine Creek drainage. Whether 

females were present is unknown. There are some significant areas of high windblown 

habitat on Birch and Kid Mountains that might have supported bighorn sheep. However, 

available low elevation south or east-facing habitat to complement these sites is limited to 

relatively high elevations unless the animals moved farther south to Red Mountain and 

Taboose Creeks. Alternatively, they might have dropped as low as 2,194 meters (7,200 

feet) on the northeast side of Kid Mountain. 

The Inyo National Forest Fish and Game Reports in 1921 and 1923 listed a GoodaleBirch Mountain herd; the 1921 report described it as "A considerable number ranging 

from Goodale Mountain to Birch Mountain, and wintering along the foothills in the Black 

Rock region during heavy snow.” Ober (in litt. 1911) noted, "In the winter season they 

range low on Taboose Creek and along the snow line to Goodale and Red Mountain.” 

Coincident with increasing mountain lion predation on bighorn sheep in the early 1980s, 

bighorn sheep were found wintering in Goodale Creek, where they had not been recorded 

for decades. As numbers of bighorn sheep wintering in Sawmill Canyon declined, the 

number wintering in Goodale Creek increased to a peak of 25 in 1981 and 24 in 1982, but 
132

then declined steadily. It is possible that members of the Sawmill Canyon herd were 

attempting to find a new safer area to winter. Lion predation on these bighorn sheep was 

also recorded at Goodale Creek in this period, which may have accounted for the decline 

in use there also. No use of this winter range has been known for some years. This area 

offers some patches of high elevation winter habitat, and excellent south-facing low 

elevation habitat, especially in Taboose Creek, where it occurs as low as 1,950 meters 

(6,400 feet). 

Mount Baxter and Sawmill Canyon Herd Units: What was once referred to as the 

Mount Baxter herd is now known to be multiple herds. The northernmost is the Sawmill 

Canyon herd, which ranges as far north as Mount Pinchot. South of Sawmill Canyon is 

the Mount Baxter herd proper. South of Oak Creek there appears to be a third 

independent female group that developed after abandonment of winter range use in the 

late 1980s. Its range extends south to Kearsarge Peak and Mount Gould. The herd that 

utilized the ridges and drainages of Mount Baxter in the 1970s and 1980s was large and 

productive, and it provided most of the reintroduction stock used in the Sierra Nevada. 

Bighorn sheep removed from the Sawmill Canyon herd made up the remainder. Of 

existing herds currently in the Sierra Nevada, the Mount Baxter herd has the highest 

prospect for becoming a second wild source of translocation stock in addition to the 

Wheeler Ridge herd, due to its history. Augmentation of this herd with members of the 

Wheeler Ridge herd could accelerate that prospect. 

Bubbs Creek Herd Unit: There is no historical evidence of bighorn sheep inhabiting 

Bubbs Creek, but a small herd was documented there in 2002 following a report from a 

climbing guide. Habitat in lower Bubbs Creek is a steep south-facing canyon wall about 

6 kilometers in length that terminates at the junction with the Kings River. Sheep habitat 

drops as low as 2075 meters in elevation near the Kings River and consists of steep slabs 

with considerable tall shrubby vegetation where soil permits. There are also numerous 

spring areas that support stringer meadows, as well as open talus slopes along the base of 

the slabs. Bighorn sheep appear to occupy the lower canyon year round, but also visit 

alpine habitat around Mount Gardiner in summer. Habitat in upper elevations of lower 

Bubbs Creek is limited by forest and shrub habitat on slopes that mostly lack adequate 

escape terrain for bighorn. Consequently, suitable habitat consists of a narrow 

elevational band of only about 350 meters. 

Mount Williamson Herd Unit: Females from the Mount Williamson herd ranged from 

Georges Creek to Shepherd Creek prior to its recent decline (Wehausen 1980) associated 

with avoidance of winter ranges. Of the four canyons previously used as winter range, 

only Shepherd Creek is currently used. Males were previously known to use the Symmes 

Creek and Pinyon Creek drainages in addition during summer, as well as areas west of 

the crest. Clyde (in litt. 1971) recorded considerable use farther south on Mount Russell, 

where he once encountered four males. This greater range of use may have reflected a 

much larger herd at that time, which Jones (1950) estimated subjectively at 125. Recent 

surveys of the herd have suggested that its range is currently farther north than it was up 

to 1985 when all winter range areas were used (Wehausen 2000). Any attempts to 

expand its current range through augmentation should attempt to reestablish South Bairs 
133

Creek as a winter range. Females established there will likely use Georges Creek as well. 

A small amount of historic evidence suggests that females may have once used Symmes 

and Pinyon Creeks to the north, where only males could be found in the 1970s 

(Wehausen 1979). 

Mount Langley Herd Unit: Prior to its recent decline, females from the Mount Langley 

herd used the area from Carroll Creek to Lone Pine Peak. It is not clear whether Tuttle 

Creek currently receives other than occasional use by females. South of Carroll Creek 

are Slide Canyon, which contains the road to Horseshoe Meadows, and then Cottonwood 

Creek, the top of which is also traversed by that road. Both of these canyons offer 

excellent low elevation open winter range, with Cottonwood Canyon notably more 

extensive. These winter ranges are better than those currently used from Carroll Creek to 

Diaz Creek, but would require greater distance traveled to connect them to alpine ranges. 

From Slide Canyon and the top of Cottonwood Canyon, it would be natural for bighorn 

sheep to cross a short stretch of open south-facing forest via Wonoga Peak to reach the 

large open plateau country currently used by this herd. It is hard to imagine that 

Cottonwood Canyon did not once support a large bighorn sheep herd. Males have begun 

using Cottonwood Canyon. The carrying capacity of this herd could probably increase 

dramatically if a female group used Cottonwood Canyon every winter. An alternative 

home range pattern for bighorn sheep using Cottonwood Creek would be a summer range 

to the south immediately east of the Kern Plateau at top elevations of only about 3,048 

meters (10,000 feet). While this habitat would not provide the vast open expanses of 

higher alpine habitats in the Mount Langley area, it would be nutritionally quite suitable 

and likely to support a large bighorn sheep herd. 

Olancha Peak Herd Unit: South of Cottonwood Creek, from north to south, are Ash, 

Braley, Cartago, Olancha, and Falls Creeks, all of which are potential bighorn sheep 

habitat. The southern three of these creeks are more favorable because they readily 

connect to Olancha Peak, which reaches 3,695 meters (12,123 feet) and provides some 

alpine summer habitat (the southernmost alpine habitat in the Sierra Nevada). Olancha 

Canyon is the most direct connection to this alpine habitat. The Olancha Peak herd 

would be the most southern herd in this recovery unit. Winter range would be traditional 

low elevation south-facing slopes, of which there is an abundance of excellent habitat 

reaching low elevations that will ensure high winter and spring diet qualities. Jones 

(1950) considered this region part of his Mount Langley herd, presumably because of 

reported sightings in that region at that time. 

Kern River Recovery Unit

There is good historical evidence of bighorn sheep on the Great Western Divide. They 

occurred in the Mineral King and Kaweah Peaks area, with notable concentrations on 

Red Spur and in Big Arroyo (Jones 1950). A die-off was reported in the Kaweah Peaks 

in the 1870s that was attributed to scabies (Jones 1950). 

Big Arroyo and Laurel Creek Herd Units: Bighorn sheep would have moved readily 

along the east-facing cliff areas of the Kern River Canyon in winter, but Big Arroyo, 
134

Rattlesnake Creek, and Laurel Creek would have been particularly attractive due to 

south-facing exposures on which snow melts faster and forage grows earlier. These sites 

are probably the best ones for reintroductions. Since there are no high elevation windswept areas west of the Kern River, the issues in comparing these three winter range sites 

are: (1) elevation; (2) visual openness; (3) amount of south-facing range; and (4) access 

to alpine ranges. Minimum elevations differ little among the sites (Table C-1). Big 

Arroyo may have the largest amount of low open habitat, but there appears to be ample 

habitat at each site, and all three are substantially open with some scattered trees. The 

Chagoopa Plateau largely blocks access to alpine habitat from Big Arroyo, but bighorn 

sheep can be expected to find access to the Kaweah Peaks at the upper end of the 

drainage. Alternatively, Red Spur can be immediately accessed from the Kern River 

canyon. In contrast, Rattlesnake and Laurel Creeks provide immediate access to summer 

ranges. One alternative would be to release bighorn sheep along the Kern River near Red 

Spur and let them ultimately find Big Arroyo as a preferred winter range. Laurel Creek 

has the potential advantage of having no trails and, thus, probably the least human use. 
135

Literature Cited 

Berger, J. 1978. Group size, foraging, and antipredator ploys: an analysis of bighorn 

sheep decisions. Behavioral Ecology and Sociobiology 4:91-99. 

Bleich, V. C., J. D. Wehausen, R. R. Ramey II, and J. L. Rechel. 1996. Metapopulation 

theory and mountain sheep: implications for conservation. Pages 353-373 in D. 

R. McCullough, ed. Metapopulations and wildlife conservation. Island Press, 

Covelo, CA. 

Grinnell, J., and T. I.. Storer. 1924. Animal life in the Yosemite. University of 

California Press, Berkeley, CA. 752pp. 

Jones, F. L. 1950. A survey of the Sierra Nevada Bighorn. Sierra Club Bulletin 

35(6):29-76. 

Ober, E. H. 1914. Fish and game conditions in the "land of little rain". Biennial Report 

of the State of California Fish and Game Commission 23:123-126. 

Risenhoover, K. L., and J. A. Bailey. 1985. Foraging ecology of mountain sheep: 

implications for habitat management. Journal of Wildlife Management 49:797-

804. 

Sierra Nevada Bighorn Interagency Advisory Group. 1984. Sierra Nevada bighorn 

sheep recovery and conservation plan. Inyo National Forest, Bishop, CA. 17 pp. 

Wehausen, J. D. 1979. Sierra Nevada bighorn sheep: an analysis of management 

alternatives. Admin. Report. Inyo National Forest and Sequoia, Kings Canyon, 

and Yosemite National Parks. 

Wehausen, J. D. 1980. Sierra Nevada bighorn sheep: history and population ecology. 

Ph.D. thesis, Univ. of Michigan, Ann Arbor, MI. 

Wehausen, J. D. 1999. Sierra Nevada Bighorn Sheep: 1999 population status. 

Unpublished report, University of California, Mountain Research Station, Bishop, 

CA. 

Wehausen, J. D. 2000. Sierra Nevada Bighorn Sheep: 2000 population survey results, a 

report to the California Department of Fish and Game. Unpublished report, 

University of California, White Mountain Research Station, Bishop, CA. 

Wilson, L. O., and C. L. Douglas. 1982. Revised guidelines for capturing and reestablishing desert bighorns. Transactions of the Desert Bighorn Council 26:1-7. 
136

In Litt. References 

Clyde, N. 1971. The bighorn in the Southern Sierra. Mostly half a century of casual 

recollections. Letter to game warden Vernon Burandt. March 23, 1971. 

Ober, E. H. 1911. Letter to the California Fish and Game Commission. November 20, 

1911. 
137

APPENDIX D CONSIDERATIONS FOR DEVELOPING A MONITORING 

PLAN FOR BIGHORN SHEEP IN THE SIERRA NEVADA 

The recovery plan for Sierra Nevada bighorn sheep calls for an adaptive management 

approach where timely decisions are made based on data collected on key resources. The 

bighorn sheep population is the most fundamental of those resources, and section II.D.5.1 

calls for development of a plan to monitor the basic status of that resource. Specifically, 

it calls for the monitoring of distribution and abundance, and the use of low elevation 

winter ranges. The recovery plan recognizes that winter ranges are an important source 

of nutrients and thereby significantly affect carrying capacities of herds. Those carrying 

capacities figure importantly in recovery criteria, which are formulated in the currency of 

minimum herd sizes; thus, monitoring herd sizes is essential relative to those criteria. 

Good information on herd sizes is also critical for management actions needed to reach 

recovery criteria. Range expansion into unoccupied habitat will occur primarily through 

translocations. The use of herds as translocation stock will require detailed monitoring of 

their sizes and trends. The elucidation of density-dependent patterns of population 

growth may allow the determination of the approximate population density where 

maximum sustained yield occurs. This would potentially allow optimization of 

harvesting strategies for translocation stock. At the other end of the spectrum, 

monitoring will allow the identification of populations that are failing to attain adequate 

sizes. Those populations, in turn, can be targeted for research needed to better 

understand limiting factors and to develop appropriate management actions. 

The Recovery Plan distinguishes research from monitoring. The latter concerns variables 

that undergo temporal changes that are population parameters or may have large effects 

on sheep population parameters that might be mitigated through management actions. In 

addition to the bighorn sheep population, the resources identified in the Recovery Plan 

for monitoring are: 1) key predators, notably mountain lions; 2) disease exposure; and 3) 

vegetation structure. Of those entities, only the bighorn sheep population was singled out 

to have a monitoring plan. While this appendix discusses subjects appropriate to that 

plan, it might be appropriate to expand the scope of that plan to include the other 

resources listed for monitoring, and additional ones that might be identified as potentially 

important, e.g., genetic monitoring (see Appendix H), or detailed climatic data. This 

discussion touches on some other topics for which data can be collected in conjunction 

with basic monitoring efforts. 

History of Efforts to Monitoring Bighorn Sheep Herds 

Monitoring the sizes of bighorn sheep herds in the Sierra Nevada always has posed a 

challenge because of the difficulty of accessing most of the habitat these sheep inhabit, 

coupled with high elevations occupied much of the year. Prior to the late 1970s, most 

information consisted of subjective population estimates that used unclear methods to 

derive estimates from very limited data (Wehausen 1980). 
138

A different approach to population monitoring began in 1976 in an attempt to develop 

more reliable information. That approach relied on understanding the behavior of 

different herds and attempting to make direct counts when the sheep were most 

concentrated in regions that are most accessible, either low-elevation winter ranges or 

along the crest in summer. This approach provided minimum counts that accounted for a 

high proportion of the sheep present. Initially, direct counts were made for the native 

herds when sheep were most concentrated on low-elevation winter ranges, usually in 

February and March. When possible, multiple such counts were made each year when 

sheep numbers on winter ranges appeared highest, and the highest number counted for 

each sex/age class was used for the minimum population size (Wehausen 1980, 1981, 

1982, 1983, 1987, 1996). 

No independent estimate of actual population size was used to evaluate the completeness 

of those counts. Instead, they were compared across time within and between years for 

consistency in the context of dynamics expected based on recruitment rates. In years of 

more complete counts, it was possible to correct previous counts for uncounted sheep 

(reconstructed populations). For instance, if two more 3-year old males were seen one 

year than 2-year old males the previous, those two could be added to the count from the 

previous year; and that reconstructed number of 2-year old males similarly could be 

compared with the number of yearling males counted the previous year. 

Wehausen (1987) evaluated numerous years of winter counts for the Mount Baxter, 

Sawmill Canyon, and Mount Williamson herd units prior to winter range abandonment. 

He found counts were generally more complete in winters of particularly heavy snowfall 

(1978, 1983, and 1986) and only in such winters was it conceivable that essentially every 

sheep may have been accounted for in the Mount Baxter and Sawmill Canyon herds. 

Wehausen (1987) treated those three years as complete counts to develop an algebraic 

model that predicted population changes of the Mount Baxter herd unit based on lamb 

recruitment rates. Predictions from that model were used to evaluate the completeness of 

minimum counts in years of less snowfall. The results indicated that minimum counts 

varied from a low of about 70% of the population in drier years to >90% in heavier 

winters. A recent application of mark-resight estimation to evaluate a winter minimum 

count for the Wheeler Ridge herd unit supported the concept that good winter counts may 

account for every sheep in the population, and that counts in other years still account for 

a very high proportion of the sheep (Wehausen and Stephenson 2004). 

After sheep herds in the Sierra Nevada began avoiding winter ranges in the mid 1980s 

(Wehausen 1996), data on population size became considerably more difficult to obtain 

and required efforts at high elevations during summer, where sheep are typically more 

dispersed. Nevertheless, predictable patterns of habitat use in summer also can be used to 

develop good counts with sufficient persistence in some situations. For the Mount 

Langley, Mount Warren, and Mount Gibbs herd units, summer counts always have 

produced the best data (Brown and Ramey 1987, Moore and Chow 1990, Hammett and 

Thompson 1992, Jensen 1994, Chang 1993). For most herds, attempts to develop regular 

data on population size were resumed in 1995 due to (1) concern about widespread herd 
139

declines, and (2) better counting opportunities provided by small herd sizes (Wehausen 

and Chang 1995, 1997, 1998; Wehausen 1999). 

During the low ebb in herd sizes in the Sierra Nevada during 1995-99, summer counts in 

some herds were supplemented with interpretation of sign left by sheep where this 

suggested that some sheep had not been counted. This provided an assessment of 

possible additional sheep present (Wehausen 1999). That was possible only because of 

small herd sizes, and relied on information such as sizes of lamb fecal pellets to indicate 

that the sign probably represented additional sheep. Genotyping of sheep from fecal 

samples was then added as a less subjective data source to help assess population sizes 

and trends in some herds (Wehausen 2001, 2002). 

Monitoring of all herds has depended on knowing seasonal habitat use patterns and 

attempting to interact spatially and temporally with those patterns in a way that 

maximizes the probability of finding the most females and associated sheep. Persistence 

and some luck have often been critically important to success. Habitat use patterns in the 

Sierra Nevada have shown notable changes over the past 30 years. It will be necessary 

for monitoring efforts to recognize this potential and respond to such changes. A fixed 

monitoring protocol has the potential to produce data that may be misinterpreted as 

population dynamics when they instead reflect changing sheep behavior. The decline in 

winter range use in the second half of the 1980s is a prime example. 

Past Population Monitoring Approaches

Mount Baxter and Sawmill Canyon Herds, 1976-1990 

During the 15 years beginning in 1976, these two herds were counted when they were 

most concentrated on winter ranges, mostly in February and March. Counts were done 

usually over three consecutive days. Once it was recognized that the Sawmill Canyon 

herd was demographically a separate herd, one or more days occasionally intervened 

between the counts of these two herds, e.g., if weather disrupted counts. 

Initially, the Sawmill Canyon herd was counted from two strategic positions on rocks 

high on the south side of Sawmill Creek. This was supplemented with counts made from 

the north road that leads to the canyon mouth to account for sheep on the rocks at the 

mouth of the canyon and the north-facing habitat not visible from survey points south of 

the creek. The two survey points south of the creek were chosen because most of the 

south-facing winter range was clearly visible. 

This census approach had a shortcoming in that the western-most part of the Sawmill 

Canyon winter range, where the first Jeffrey pines begin, was not sufficiently visible. 

Consequently, a second approach was developed that involved walking through the 

winter range in a pattern that maximized the likelihood of seeing all sheep there. This 

approach also began with glassing (remote observation using binoculars and spotting 

scopes) the north side of the ridge from the north road leading to the canyon mouth. It 

then involved climbing through the front rocks and traversing the south-facing winter 
140

range about mid elevation to the most western sandy slope where the Jeffrey pines begin. 

From there, further elevation was gained so that return was via the ridge top. This 

method had the advantage that sheep at the westernmost area of the winter range were 

readily found while the descent of the ridge top increased the likelihood of finding sheep 

to the north, and allowed rechecking of the sheep that had been seen in the canyon. The 

success of this census approach was illustrated well in 1982. During that winter, multiple 

counts of Sawmill Canyon showed a decline in the number of lambs from 13 to 10, while 

numbers of females and yearlings remained unchanged. All three missing lambs 

eventually were found as lion kills. 

Two days were allocated to counting the Mount Baxter herd – one for Sand Mountain 

and one for Sand Canyon to Thibaut Canyon. Sand Canyon is the short drainage midway 

between Sawmill Canyon and Black Canyon. Sand Mountain is the area between Sand 

Canyon and Sawmill Creek. Counts of Sand Mountain began with a search from below 

with binoculars and a spotting scope in an attempt to find most of the sheep groups prior 

to hiking. Hiking routes were then chosen relative to the locations of those groups. 

Those routes began either at the base of Sand Canyon or at the mouth of Sawmill Canyon 

and generally consisted of a loop that allowed all potential habitat to be surveyed, 

including upper Sand Canyon. 

Efforts to count sheep south of Sand Canyon always began by counting and classifying 

sheep in the region between Sand Canyon and Black Canyon (“Black Canyon front 

range”). Once that was completed, sheep were counted further south. That involved 

climbing to Big Ram Mine to survey the south- and north-facing rocks in Black Canyon 

and walking over to Thibaut Canyon. An area of important sheep use was the rocky 

drainage north of Thibaut Canyon (“Thibaut Gulch”). During that time, most sheep 

entered the winter range from Thibaut Canyon and worked their way north to Sand 

Mountain. It was possible to track the progress of sheep groups day by day. Many sheep 

also used that same route to leave the winter range. Thus, Thibaut Gulch was an 

important stopover location for sheep moving to or from the lower winter range 

Critically important to counts of the Mount Baxter herd was not double-counting sheep 

near the boundary between the two census polygons. This was accomplished by keeping 

careful track of sheep groups on either side of Sand Canyon during both days involved, 

particularly late the first day and early the second day. If sheep crossed that boundary 

between the two days, it was highly likely that this would be detected using the size and 

composition of the group(s) in question to identify them. 

These census methods ceased after 1990 because so few sheep continued to use those low 

elevation winter ranges. Instead, areas that sheep continued to use were checked less 

often in winter and spring during times most likely to produce sheep, notably following 

major winter storms. 
141

Mount Williamson Herd 1976-1986 

Counts of the Mount Williamson herd were made on escarpment base winter ranges 

between 1976 and 1985. Strong avoidance of those winter ranges developed after 1985, 

with only a few sheep seen in 1986 and none since then. Compared with the Mount 

Baxter and Sawmill Canyon herds, the Mount Williamson herd has only a few small 

patches of suitable escarpment base wintering habitat. What limits this habitat is poor 

visibility, primarily due to pinyon pine woodland. 

Three escarpment base patches were found to receive most use by the Mount Williamson 

herd during 1976-86: the rocky ridge and connected small point of rock between South 

Bairs Creek and Georges Creek, the south-facing slope at the mouth of South Bairs 

Creek, and the south-facing rocks near the mouth of North Bairs Creek. The best counts 

occurred following major snowstorms. Snow conditions when those good counts took 

place commonly precluded driving across Foothill Road. The Georges Creek road was 

driven as far as snow allowed and the sites preferred by sheep were visited on skis. 

However, in years of continued heavy snows, sheep remained low for numerous weeks, 

well after Foothill Road became passable. 

Of the three sites, the one between South Bairs Creek and Georges Creek was most 

preferred, followed by South Bairs Creek, and North Bairs Creek. By tracking sheep in 

snow and following groups over time, it appeared that sheep frequently descended to 

winter ranges at the north end of Mount Williamson and then worked their way south to 

the more preferred wintering sites. A lion-killed 3-year old female was once found at the 

mouth of Shepherd Creek, suggesting that they sometimes began that far north. Sheep 

also occasionally made forays to the mouth of Georges Creek from the preferred site a 

short distance to the north. Thus, while there were preferred sites, the entire escarpment 

base from Georges Creek to Shepherd Creek apparently was used as a travel corridor at 

times. 

Future Population Monitoring

Problem Analysis 

A clear definition of populations is requisite to the development of meaningful population 

statistics. Bighorn sheep populations can be substructured into separate home range 

patterns that constitute separate subpopulations. Understanding that structure is 

important to how demographic data are obtained and interpreted. An adequate 

understanding of spatial patterns of habitat use by sheep is thus an important aspect of 

future monitoring. It is particularly important for certain herd units that appear to have 

substructuring that is not fully understood. 

One important use of population monitoring data concerns when and how populations 

will be used as translocation stock to meet restoration objectives. Fundamental to the 

question of population management for translocation stock is the nature of densitydependent relationships involving demographic processes, including reproduction and 
142

recruitment. Such relationships will best be elucidated where measurements of the 

number of female sheep and sheep of young age classes are made with the least error. 

The development of such data needs to be a fundamental goal of the monitoring program 

for Sierra Nevada bighorn sheep. 

Minimum counts have served well in the past as a basis for management decisions, 

because those counts appear to have accounted for a high proportion of the herds in 

question, especially in some years, and those key years have served as baselines to 

interpret counts from intervening years. There is a need to develop periodic independent 

estimates of female numbers as an added evaluation of the completeness of minimum 

counts. Although minimum counts form a conservative basis for measuring progress 

toward recovery, as populations grow those minimum counts may represent a decreasing 

proportion of the total number, possibly increasing the value of point estimates with 

confidence intervals. In addition to determining population sizes, the distribution of 

bighorn must be quantified; in part, this may be accomplished by implementing 

additional systematic surveys to more comprehensively identify distribution. Such 

methods might include ground-based surveys or aerial telemetry, as well as the use of 

collars employing Geographic Positioning System (GPS) technology. 

The finite populations correction factor is a statistical procedure that collapses the 

variance around sample means as the sample approaches the population total (Steel and 

Torrie 1960). The reason for this correction factor is simple -- little variance is possible 

when samples are that complete, with the extreme being no variance when the total 

population is sampled. The same concept holds for minimum and reconstructed counts of 

bighorn sheep that approach or reach the population total. Such samples will have high 

resolution in tracking population dynamics relative to estimators that may incur relatively 

wide confidence intervals. Bayesian statistical procedures are potentially more efficient 

than alternative independent estimators because they use prior information (Gill 2002). 

There is a need to explore the possible development of a Bayesian statistical approach for 

survey data. 

Future monitoring of bighorn sheep population parameters in the Sierra Nevada should 

utilize as many tools as possible to develop the best possible data. Below is a discussion 

of some methods that may be useful as supplementation to past procedures to better meet 

the goals of the recovery plan. 

Helicopter Counts 

Because of the remoteness and ruggedness of much of habitat, there are limitations on 

methods that can be employed. For instance, some previous attempts to use a helicopter 

at high elevations in the Sierra Nevada have found no sheep or only a small proportion of 

those known to exist. Because of the atmospheric conditions at high elevations and 

related high speeds and elevations AGL that helicopters must fly for safety under 

conditions existing at high altitudes, it may be difficult to obtain reliable data on sex and 

age composition of sheep located by this method. 
143

In 1981, a helicopter census took place on the low elevation winter ranges of the Mount 

Baxter and Sawmill Canyon herds. It was carried out with simultaneous ground 

observers to produce a double survey estimate (Magnusen et al. 1978) and evaluate the 

utility of such helicopter counts (Wehausen 1981) in the Sierra Nevada, a methodology 

that had been highly successful elsewhere in California (Holl and Bleich 1983, Holl et al. 

2004). This approach was never repeated in the Sierra Nevada, because the results were 

poor compared with data that a single experienced investigator could produce with 

repeated ground surveys. 

Nevertheless, helicopter surveys recently have been useful as a supplement to winter 

ground data. In 2001, under conditions of optimal early March snow cover, a helicopter 

survey of numerous potential winter ranges was particularly effective in finding sheep via 

tracks and in verifying the absence of tracks and, presumably, bighorn sheep. This 

method allowed ground surveys to be focused where sheep were known to be present. 

Helicopter surveys of Wheeler Ridge have been used to look for sheep in areas not 

accessible during winter ground counts. On a couple of occasions, such aerial surveys 

have found no further sheep, which contributed to the evaluation of the completeness of 

winter ground counts. 

For winter range counts, helicopter surveys will frequently be most effective in late 

winter when sheep are likely to be at low elevations. However, a helicopter survey of 

Bubbs Creek on the west side of the Sierra Nevada located a key group of sheep on that 

range in January of 2003 and January 2005. Remote areas like Bubbs Creek that 

currently lack sheep (e.g., Kern Recovery Unit) may prove difficult to access by other 

means when conditions are optimal for counting sheep (e.g., winter). 

Helicopters should continue to be used where they prove to be effective or might add 

some key additional data (e.g., sheep not counted on the ground because of lack of 

access). Moreover, the use of helicopters, in combination with marked animals (see 

below), provides a method of covering large expanses without huge investments of time 

by ground observers. Results may have wide associated confidence intervals, but as the 

distribution of sheep expands, the need to cover more ground may necessitate the use of 

additional methodologies. 

Telemetry Collars 

Radio collars have been used to great effect in the past to aid in monitoring the three 

reintroduced herds in the Sierra Nevada and similarly can aid future population 

monitoring. Radio collars can be added to herds through the capture of existing members 

or by translocating sheep to populations from a larger and more productive herd. Capture 

opportunities will be limited largely to low-elevation winter ranges because of logistical 

constraints. Consequently, the option of translocating sheep to add radio collars will 

have the advantage of not putting members of small herds through the major disturbance 

of capturing them during brief visits to winter ranges that these sheep may be hesitant to 

utilize. If efforts to capture members of such small groups cause winter range avoidance, 

those efforts may trade off population recovery for easier and better information. 
144

Because females are the basis of recovery goals and central to population monitoring, a 

greater return in population monitoring can be expected by radio collaring that sex. 

Radio collars will have the extra benefit of adding data on habitat use patterns and causes 

of mortality where mortality signals can be detected and investigated in a timely manner, 

while quantifying survivorship rates (Pollock et al. 1989). Survivorship statistics will be 

limited by the number of radio collars that can be placed in each herd. However, this 

information can be increased notably by configuring collars to transmit for as long as 

possible. Longer transmitter life will be beneficial to other uses of telemetered animals 

as well and should be a standard consideration. 

While the recovery plan calls for the monitoring of habitat use patterns only relative to 

winter ranges, telemetry collars placed on sheep to aid in population monitoring also can 

provide considerable other important information on home range patterns and changes in 

the distribution of bighorn sheep. That information will be important for proper 

definition of populations and development of sampling strategies. Detailed data on 

movements of bighorn sheep also are important relative to understanding potential for 

disease transmission from contact with domestic sheep and among herd units (Gross et al. 

2000, Zeigenfuss et al. 2000, Singer et al. 2001) and metapopulation questions regarding 

potential for gene flow and natural colonization (Schwartz et al. 1986, Bleich et al. 1990, 

1996, Mills and Allendorf 1996). Monitoring of bighorn movements relative to diseases 

is particularly pertinent to the Northern and Central Recovery Units, which continue to 

have domestic sheep grazing in the vicinity. Data from GPS collars placed on rams in 

those areas will allow a more quantitative assessment of risk of contact with domestic 

sheep. 

Detailed information from GPS collars also can be used to research questions of habitat 

use by sex and season (White and Garrott 1990) at varying levels of detail relative to 

resource selection: home range delineation, habitat selection within home ranges, and use 

of foraging patches (Johnson 1980). Habitat suitability modeling using resource selection 

probability functions (Manly et al. 2002, Johnson et al. 2005) should help refine 

understanding of bighorn habitat in the Sierra Nevada. Those models should be useful in 

identifying important movement corridors, areas where natural range expansions are most 

likely to occur, and more quantitative assessment of areas for translocation, while better 

understanding factors determining carrying capacities (DeYoung et al 2000). 

Capture of animals for placement of telemetry collars can yield additional data not 

directly associated with the collars themselves, such as ultrasonography and serum assays 

to assess pregnancy status (Stephenson et al. 1995, Drew et al. 2001), ultrasonography to 

measure fat deposits (Stephenson et al. 1998, 2002), and serum assays of disease 

exposure. Radio-collared females can be monitored to determine birthing dates, lamb 

production, and lamb survival and recruitment to provide additional data on reproduction. 
145

Mark-Resight Estimation 

Telemetry collars also can be used to generate mark-resight population estimates if an 

adequate percentage of the herd is collared and the herd can be sampled in a random 

manner. The latter requirement precludes the use of telemetry signals from radio collars 

to influence which sheep are sampled. In the Sierra Nevada, this will eliminate the 

primary benefit of radio telemetry for herd monitoring: greater efficiency in finding sheep 

and an aid in finding otherwise missed sheep. This will lead to a difficult tradeoff in the 

allocation of sampling effort, given that the time when the best sampling for mark-resight 

estimates occurs frequently also will coincide with the time when the best minimum 

counts can be obtained. Where minimum counts include essentially all of the population, 

mark-resight estimates will contribute little, if any, additional population information. 

Additionally, Wehausen and Stephenson (2004) reported evidence that random sampling 

of the Wheeler Ridge herd in winter might not be possible, and that somewhat biased 

mark-resight estimates can result. Despite those potential problems, periodic markresight estimates provide important evaluations of minimum counts and should be 

pursued where results will provide estimates of meaningful precision and accuracy. 

There are multiple mark-resight estimators that result in part from different sampling 

approaches (Bailey 1951, Chapman 1951, Caughley 1977, Minta and Mangel 1989, Neal 

et al. 1993), but all have the advantage of providing measures of precision in the form of 

confidence intervals. Mark-resight estimates typically require the capture and marking of 

some proportion (typically 5-20%) of the bighorn herd in question; however, in some 

situations it may be possible to generate such estimates using naturally marked animals. 

Animals may be captured using a combination of methods, including drop net, helicopter 

net gun, drive net, and ground darting (Kock et al. 1987). Animals can receive colored, 

numbered ear tags to facilitate recognition of individuals, and a primary VHF radio 

collar, or a GPS collar that can be remotely downloaded and triggered to drop off. 

Animals that receive a GPS collar that will drop off also should be fitted with a secondary 

VHF collar that will remain with the individual to facilitate longer-term sampling. 

The precision of mark-resight estimates is a function of the percentage of the population 

collared and the total size of the random sample(s). The latter will be critical to estimates 

of sizes of bighorn sheep herds in the Sierra Nevada and may require numerous sampling 

episodes for each estimate to narrow the precision to a meaningful level. Sample sizes 

can be increased using both sampling with and without replacement approaches. The 

joint hypergeometric estimator (Neal et al. 1993) uses the latter and is well suited to the 

development of population estimates in the Sierra Nevada where enough marked sheep 

are present. This approach involves repeated ground surveys within a specified 

geographic region (e.g., winter or summer range) using multiple observers equipped with 

binoculars and spotting scopes to survey the range in a systematic fashion, classifying all 

sheep seen by sex and age categories and marked status. Data can be analyzed using the 

program NOREMARK (White 1996), which offers multiple potential estimators. Two of 

those estimators require reliable individual identification of marked sheep; thus, it is 

important to develop an appropriate visual marking system. 
146

Large sample sizes also can be developed using a sampling with replacement approach 

that approximates binomial sampling. One advantage of this approach is that a Bayesian 

statistical method can be incorporated using the beta distribution as a close approximation 

of the binomial distribution (Gill 2002). Ananda (1997) showed that this approach can 

significantly narrow the confidence intervals for mark-resight estimates of bighorn sheep 

populations. 

Genotyping from Feces 

Individual sheep can be identified genetically from DNA extracted from fecal samples 

(Taberlet et al. 1996, 1997, 1999). This tool has been applied to some bighorn sheep 

herds in the Sierra Nevada to help develop more complete minimum counts. This 

method is particularly useful for small populations like the Mount Williamson herd, 

where neither aerial monitoring nor ground surveys have been very successful. Indeed, 

when populations do not possess sufficient marked animals for mark-resight sampling, a 

combination of directed searches and fecal DNA sampling may be the most reasonable 

way to arrive at minimum herd sizes. With further refinement of fecal DNA technology 

(Wehausen et al. 2004), it has proven to be an important tool for monitoring some 

bighorn sheep herds in the Sierra Nevada. 

Frequency and Intensity of Population Monitoring 

Annual monitoring of all herds is a desired but, perhaps, unrealistic long-term goal. The 

intensity of monitoring applied to the various bighorn herds in the Sierra Nevada will 

depend on a variety of factors including herd size, risk of decline (e.g., from disease, 

predation, or severe weather), use as translocation stock, personnel, and financial 

resources. As long as a population remains small, monitoring should remain intensive so 

that immediate action may be taken to mitigate population declines. As populations 

become self-sustaining, increase in numbers, and are exposed to a lowered risk of 

extinction, the frequency and intensity of monitoring might decline. 

Because survey results can vary across years in their completeness, it is important to 

maximize the probability of getting excellent counts when conditions are favorable. 

Developing an understanding of what factors underlie the completeness of counts (e.g., 

winters of heavy snowfall for low elevation winter ranges) will allow a more focused 

approach that maximizes data return for effort. What follows is a recommendation of 

minimum monitoring frequencies for herds in different categories if available funds do 

not allow annual monitoring of all herds. 

A. Herds considered potential sources of translocation stock. Determine 

minimum numbers of females, yearlings, and lambs yearly to provide data on 

recruitment and herd size. Any population to be used as translocation stock likely 

will make concentrated use of low elevation winter habitat where the best 

population data will probably be obtained. Data on population parameters should 

be developed on winter ranges unless opportunities for better data occur in a 
147

different season. An attempt should be made to develop data on number of males, 

including age distribution, every 1-2 years. 

B. Herds not used as translocation stock containing 1-15 females. Gather 

yearly data on size and recruitment. Attempt to count males every 2-3 years. 

C. Herds not used as translocation stock containing 15-25 females. Attempt 

to assess size and recruitment every 1-2 years for each female group. Count 

males every 2-4 years. 

D. Herds not used as translocation stock containing more than 25 females. 

Attempt to assess size and recruitment every 2-3 years and every 3-5 years for 

males if possible until delisting. After delisting, attempt to develop population 

data every 5 years or more often if severe environmental conditions (e.g., a very 

severe winter) occur that raise concerns about the status of the population. 

 
148

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151

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Wehausen, J. D. 1983. Sierra Nevada bighorn herds: 1983 status. Unpubl. report. 18pp. 

Wehausen, J. D. 1987. Mount Baxter bighorn population: 1987 Status. Unpubl. report. 

8pp. 

 

Wehausen, J. D. 1996. Effects of mountain lion predation on bighorn sheep in the Sierra 

Nevada and Granite Mountains of California. Wildlife Society Bulletin 24:471-

479. 

Wehausen, J. D. 1999. Sierra Nevada bighorn sheep: 1999 population status. Unpubl. 

report. Univ. of Calif., White Mountain Research Station, Bishop. 

Wehausen , J. D. 2001. Sierra Nevada bighorn sheep: population survey results. Unpubl. 

report to the California Department of Fish and Game under Interagency 

Agreement #P9980060. Univ. of Calif., White Mountain Research Station, 

Bishop. 

Wehausen, J. D. 2002. Sierra Nevada bighorn sheep herds: 2002 status. Unpubl. report 

to the California Department of Fish and Game under Interagency Agreement 

#P0260003. Univ. of Calif., White Mountain Research Station, Bishop. 

Wehausen, J. D., and Karl D. Chang. 1995. 1995 status of three bighorn sheep 

populations in the Sierra Nevada. Sierra Nevada Bighorn Sheep Foundation Tech. 

Report No. 1. 

Wehausen, J. D. and Karl D. Chang. 1997. Sierra Nevada bighorn sheep: 1995-97 

status. Sierra Nevada Bighorn Sheep Foundation Tech. Report No. 2. 

Wehausen, J. D., and Karl D. Chang. 1998. Sierra Nevada bighorn sheep: 1998 survey 

results. Sierra Nevada Bighorn Sheep Foundation Tech. Report No. 3. 

Wehausen, J. D., R. R. Ramey II, C. W. Epps. 2004. Experiments in DNA extraction and 

PCR amplification from bighorn sheep feces: the importance of DNA extraction 

method. Journal of Heredity 95:503-509. 

Wehausen, J. D., and T. R. Stephenson. 2004. Sierra Nevada bighorn sheep: 2003 status. 

Unpubl. report, Calif. Dept. of Fish and Game, Bishop, CA. 

White, G. C., and R. A. Garrott. 1990. Analysis of Wildlife Radio-Tracking Data. 

Academic Press, Inc. San Diego, CA. 

White, G. C. 1996. NOREMARK: Population estimation from mark-resighting surveys. 

Wildlife Society Bulletin 24:50-52. 
152

Zeigenfuss, L. C., F. J. Singer, and M. A. Gudorf. 2000. Test of a modified habitat 

suitability model for bighorn sheep. Restoration Ecology 8:38-46. 
153

APPENDIX E CONSIDERATIONS FOR A PREDATOR MANAGEMENT 

PLAN 

Predators are an integral ecological component of the community occupied by Sierra 

Nevada bighorn sheep. Sierra Nevada bighorn sheep will not be recovered until 

population objectives are attained, at which point Sierra Nevada bighorn sheep will be 

able to withstand naturally occurring predation without intervention. Coyotes and 

bobcats are known to prey on bighorn sheep; however, mountain lions, because of their 

larger size, are better adapted to kill larger prey, such as deer and bighorn sheep. 

Predation is a natural component of the system. However, predation, like disease, 

represents another vehicle of bighorn sheep mortality, and all mortality must be 

minimized until full recovery is attained. The goal of the predator management plan is to 

temporarily protect bighorn sheep from adverse effects of predators while preserving an 

intact ecosystem. 

A predator management plan (Task 2.1) should be prepared that ties together the multiple 

tasks concerning predators called for in section II.D of this recovery plan and lays out 

specifics of how they will be accomplished and when they will be ended. These tasks 

include monitoring, research, and selective, humane predator removal where needed. Of 

potential predators, mountain lions have been implicated as the primary predator of Sierra 

Nevada bighorn sheep, and they may affect population dynamics of those bighorn sheep 

through direct losses or by influencing habitat selection by the bighorn sheep. Below is a 

brief discussion of some of the elements that should be included in this plan. 

 

1. Experimental approaches in an ecosystem context. 

The primary objective of the predator management plan should be to protect small herds 

of bighorn sheep to prevent further extirpations and to restore populations to a level at 

which the natural predator-prey interactions can be allowed to occur without human 

intervention. Predators, and their potential direct and indirect effects on these bighorn 

sheep, are part of the ecosystem inhabited by these bighorn sheep, and management of 

predators needs to recognize the role of these species in an ecological system. 

The one sure way of protecting endangered Sierra Nevada bighorn sheep from the 

potential negative effects of predation would involve long-term, indiscriminate removal 

of predators in the vicinity of bighorn sheep herds. There is little question that such a 

control program would also result in the unnecessary removal of some predators that had 

little or no influence on the population dynamics of bighorn sheep. Further, such a 

program would undoubtedly have unforeseen effects on other aspects of the ecosystem 

that might ultimately negatively affect bighorn sheep. Therefore, this approach is 

undesirable in that it has unacceptable consequences. 

Finding a balance in which the minimum of predator management is practiced will take 

creative and experimental approaches. Management prescriptions will evolve as they are 

tried and evaluated and conditions change. Balanced predator management will entail 

using different approaches for different bighorn sheep herds and will take into account 
154

the vulnerability of each herd to extirpation. Finding the optimal prescription(s) for 

minimal predator management while still recovering bighorn sheep will entail risk to 

some individual bighorn sheep. At the same time, though, those risks will be allowed 

only where the bighorn herds are large enough to be able to withstand such a loss. 

2. Protection of bighorn sheep translocation stock. 

The ultimate success of population recovery hinges on the development and use of 

sources of translocation stock. Past reintroduction efforts occurred only because of the 

prior size and productivity of the Mount Baxter and Sawmill Canyon herds. The decline 

and inability of those herds to serve as further sources of translocation stock was 

associated with widespread changes in winter habitat use patterns that Wehausen (1996) 

suggested were linked to increased predation pressure from mountain lions during the 

1980s. Predation pressure from mountain lions that developed in the 1980s may have 

been exceptional, and differed substantially from the current situation of lower lion 

densities. Nevertheless, the predator management plan should address how herds serving 

as sources of translocation stock might be treated, given their key role in the recovery of 

these bighorn sheep. 

3. Protection of translocated bighorn sheep. 

Bighorn sheep may be translocated to augment existing herds or to create new ones. 

Translocation stock has been, and will likely continue to be, a rare and precious resource. 

The predator management plan needs to address questions of how translocated bighorn 

sheep will be treated relative to predators compared with other herds, and why. Among 

the tasks to be considered will be investigations of potential predator conflicts at sites 

considered for reintroductions (Task 6.6). Results of such investigations may influence 

decisions on where available translocation stock will be used. For instance, 

reintroduction sites that have higher potentials for predator problems may be a lower 

priority for translocation projects. Those areas may be stocked later when, presumably, 

greater numbers of bighorn sheep will be available and that will allow larger initial 

releases to compensate for potential losses to predators. 

4. Monitoring of mountain lions in the vicinity of winter ranges (Task 5.2). 

 It is well known that mountain lions vary in their behavior toward different prey species. 

Research in Canada, New Mexico, and California (Ross et al. 1997, Logan and Sweanor 

2001, H. Ernest, unpubl.data) indicates that one or a small number of individual mountain 

lions often are responsible for a disproportionate number of bighorn sheep kills. Radio 

collaring of lions in the vicinity of winter ranges will allow the details of habitat use 

patterns to be elucidated, thereby identifying potential problem animals. 

In the Sierra Nevada, mountain lions range long distances as a response to the availability 

of prey (Pierce et al. 1999). Radio-collaring lions will allow predator management teams 

to monitor their locations precisely in relation to areas used by bighorn sheep. Although 

physical evidence of the presence of mountain lions is important when evaluating degree 
155

of threat to bighorn sheep, tracks of individual lions are not always distinguishable from 

each other (Grigione et al. 1999). Collared lions will remove most guesswork in reading 

sign (i.e., distinguishing individual lions via track measurements), provide more reliable 

data on which lions are of concern, and allow predator management specialists to be most 

efficient in the use of their time. In the absence of the use of radio collars on lions, 

efforts to protect bighorn sheep in the Sierra Nevada will likely result in the deaths of 

some lions that might have been spared if telemetry data were available. It is possible to 

collar most lions near bighorn sheep winter ranges, but it is unlikely that more than a 

small proportion of the bighorn sheep population can be collared. Monitoring of collared 

lions can provide considerable data regarding bighorn sheep and predator dynamics. The 

success of this approach ultimately will lie with the schedule of monitoring of collared 

and uncollared lions in conjunction with monitoring of populations of bighorn sheep. 

Through the collaring of mountain lions, detailed information also can be gathered on 

lion population dynamics, allowing assessment of the impacts of removals of mountain 

lions on their populations and, thereby, helping to put recovery efforts for these sheep in 

a larger ecosystem context. 

5. Attempting to alter habitat use patterns of mountain lions on bighorn sheep 

winter ranges by aversive conditioning (Task 6.5). 

Aversive conditioning has not been attempted before with mountain lions. It is a 

potentially useful tool that, if successful, could afford a reduction of mortality for both 

Sierra Nevada bighorn sheep and mountain lions. Experiments should be carried out 

when and/or where they do not jeopardize bighorn sheep. To be effective, these efforts 

will need to occur during fall and early winter, prior to the usual appearance of bighorn 

sheep on winter ranges. These experiments will require the development of data on 

activity patterns of the subject mountain lions that will allow an adequate evaluation of 

the effectiveness of this intervention. 

6. Development of long-term data to elucidate predator-prey dynamics of this 

ecosystem as they affect bighorn sheep (Task 6.7). 

The predator-prey situation that unfolded in the eastern Sierra Nevada during the 1980s 

was unexpected and is not sufficiently understood. Those dynamics are not likely to be 

adequately explained unless similar circumstances recur and key elements are monitored 

over many years. Of primary interest will be the dynamics of deer herds, which are the 

primary prey of mountain lions, and the distributions and densities of which are important 

factors determining the abundance of lions (Pierce et al. 2000). Monitoring of 

mesopredators, such as coyote or bobcat, to ascertain population fluctuations relative to 

mountain lion populations should also be considered. Careful monitoring of key 

elements of this ecosystem will help elucidate whether the events of the past two decades 

were simply part of a cyclical phenomenon, or whether these events constitute an 

exceptional circumstance that is not likely to be repeated; in either situation, however, 

future efforts to conserve wild sheep will be enhanced through the acquisition of such 

knowledge. 
156

Literature Cited 

Grigione, M. M., P. Burman, V. C. Bleich, and B. M. Pierce. 1999. Identifying 

individual mountain lions (Felis concolor) by their tracks: refinement of an 

innovative technique. Biological Conservation 88:25-32. 

Logan, K., and L. Sweanor. 2001. Desert Puma. Island Press, Covelo, CA. 390pp. 

Pierce, B. M., V. C. Bleich, and R. T. Bowyer. 2000. Social organization of mountain 

lions: does a land-tenure system regulate population size? Ecology 81:1533-

1543. 

Pierce, B. M., V. C. Bleich, J. D. Wehausen, and R. T. Bowyer. 1999. Migratory 

patterns of mountain lions: implications for social regulation and conservation. 

Journal of Mammalogy 80:986-992. 

Ross, P. I., M. G. Jalkotzy, and M. Festa-Bianchet. 1997. Cougar predation on bighorn 

sheep in southwestern Alberta during winter. Canadian Journal of Zoology 

74:771-775. 

Wehausen, J. D. 1996. Effects of mountain lion predation on bighorn sheep in the Sierra 

Nevada and Granite Mountains of California. Wildlife Society Bulletin 24:471-

479. 

 
157

APPENDIX F PUBLIC INFORMATION AND OUTREACH PLAN 

Abstract 

The Sierra Nevada bighorn sheep Public Information and Outreach Program is based on 

the overarching principle that understanding and appreciation of the natural history and 

ecology of the Sierra Nevada bighorn sheep and concern for its future are vital to 

building public support for conservation measures and recovery actions. A number of 

recovery actions will directly affect the public using the eastern Sierra Nevada. 

Conversely, human activities may affect recovery. Knowing how Sierra Nevada bighorn 

sheep live and survive and the threats they face will help people understand the need for 

regulatory actions. 

Delegating Public Information and Outreach Plan responsibilities to one agency and one 

or two individuals within that agency will eliminate confusion and ensure that a uniform 

and timely message gets out to the public. 

An initial survey to assess the present level of public understanding of Sierra Nevada 

bighorn sheep and the situation threatening the survival of the species can be used as a 

tool to create the most effective public information and outreach program. The survey 

data will be used to establish and prioritize the steps that are needed to inform the public 

and build support. The program will not only seek to build an appreciation and 

understanding of the species, but also to make the public aware that the Sierra Nevada 

bighorn sheep recovery effort is a collaborative effort supported by multiple agencies, 

organizations, and individuals. 

A second survey will be taken 1 year later and compared to the initial survey in order to 

measure the success of the program and to identify areas where the program needs to be 

strengthened or otherwise modified. 

Certain information projects should be initiated concurrently with the activities to design 

a Sierra Nevada bighorn sheep Public Information and Outreach Program. The public 

needs to be made aware as soon as possible about required actions and restrictions while 

in Sierra Nevada bighorn sheep habitat. The recovery plan will also be released to the 

public, and wide distribution should be ensured. Funding to support future programs and 

broadened public information campaigns should be sought. 

 

1. INCREASING AWARENESS 

Using Understanding as a Foundation for Support

The public needs to have a foundation upon which to build concern for the situation 

facing the Sierra Nevada bighorn sheep and an interest in its recovery. The words 

"endangered species" frequently carry a negative connotation for a significant segment of 

the public. In the absence of more information, the public may interpret the words to 

mean that a rather hopeless situation exists that will limit human activities in order to 
158

save a remote species of unknown importance. The Public Information and Outreach 

Plan should provide information about the unique qualities of the Sierra Nevada bighorn 

sheep, its historic significance to American Indians, its decline with the settlement of the 

west, its ecology, and its natural history. This information will offer the public an 

alternative picture to conceptualize when hearing about the Sierra Nevada bighorn sheep, 

the threats to the survival of the species, and the recovery program underway. 

Assigning Program Duties

To be optimally effective, an information campaign needs to be coordinated, accurate, 

timely, and consistent in the message it delivers. Deliberate steps need to be taken to 

ensure that a uniform message reaches the public. Numerous agencies have been and 

will continue to be involved in the recovery efforts. The responsibility for overseeing the 

Sierra Nevada bighorn sheep Public Information and Outreach Program should be 

delegated to one agency or organization and a single or small number or persons within 

the organization. Restricting oversight of outreach efforts will ensure that a consistent 

message is delivered to both the public and agency personnel who are not directly 

involved in the recovery effort. It will also ensure that a message is getting out to the 

public, rather than setting up a situation that could lead to misunderstandings and 

confusion about which agency is undertaking a given information or outreach activity. 

Finally, it will provide some assurance that the importance of communicating with the 

public and building public support will not be forgotten or minimized amid the urgent 

and intriguing biological questions attendant to the recovery of Sierra Nevada bighorn 

sheep. 

2. DESIGNING A PUBLIC INFORMATION AND OUTREACH PLAN 

Objectively Assessing Current Public Perceptions

An objective assessment of current public knowledge and attitudes toward the Sierra 

Nevada bighorn sheep needs to be made. Identifying the target audience and a baseline 

use of Sierra Nevada bighorn sheep habitat, key messages, and methods for disseminating 

information can all be achieved using a survey. The survey should be conducted 

simultaneously with the effort currently underway for Peninsular bighorn sheep and 

could be conducted by one of the partner agencies or a university. 

Surveying for Target Audiences

The survey will be used to identify target audiences. Recreationists, commercial packers, 

local residents, range allotment permittees, and domestic sheep and/or goat owners all 

conduct activities that take place in or near Sierra Nevada bighorn sheep habitat. Other 

target audiences need to be identified as part of the process of determining how people 

receive their information (see Methods of Disseminating Information below). The 

identification of target audiences includes information about how these individuals and 

businesses use Sierra Nevada bighorn sheep habitat and important surrounding areas. 
159

Defining and Prioritizing Key Messages

The survey will establish public knowledge of the natural history and ecology of Sierra 

Nevada bighorn sheep. It will also provide insight into the public perception of the 

threats to Sierra Nevada bighorn sheep and the seriousness of the situation, as well as 

attitudes about conservation efforts related to Sierra Nevada bighorn sheep. The data, in 

turn, will provide direction for defining key messages. Specific information should 

include: an overview of the ecology of Sierra Nevada bighorn sheep, current threats to 

population viability, and recovery actions; effects of mountain lion predation on recovery 

of Sierra Nevada bighorn sheep and the larger role of predators in ecosystems; threats to 

Sierra Nevada bighorn sheep due to disease transmission from domestic sheep and goats; 

threats to bighorn sheep recovery from domestic dogs in bighorn sheep habitat; threats to 

bighorn sheep from disturbance by human recreational activities; actions needed to 

achieve recovery objectives; and opportunities to learn more about Sierra Nevada bighorn 

sheep. This approach will encourage the full spectrum of business people, recreationists, 

students, seniors, and local residents to behave in ways that promote the recovery of 

Sierra Nevada bighorn sheep populations. 

Disseminating Information

The survey will provide data that identify the most effective means of conveying 

information. The survey could query individuals about how they receive their 

information, and media outreach efforts could then be channeled through the media that 

are most effective at delivering the message. The survey will also be used to identify 

other target audiences, including opinion leaders such as local elected officials and 

national and local media. The means and methods of distributing information include but 

are not limited to: printed material (press releases, handouts, brochures, newspaper 

articles, signage); electronic media (radio and television interviews, public service 

announcements, web sites); person to person delivery (presentations for service 

organizations, elected officials, as well as school programs and field trips, interpretive 

programs, campfire talks); and the merchandising of consumer goods with an educational 

theme (t-shirts, posters, postcards, notepaper). The information should be updated 

regularly and kept current regarding the status of Sierra Nevada bighorn sheep and 

recovery actions. 

Distributing Information 

Identifying the most effective method of message delivery also guides the identification 

and prioritization of points of distribution. Printed matter could be distributed at a variety 

of locations, including visitor’s centers, agency offices, chambers of commerce, web 

sites, email, and conventional mail. Links to a single web site would assure that the 

information is up-to-date and would eliminate duplicative efforts. 
160

Information should be specifically distributed to members of the general public that are 

directly affected by recovery actions, such as hikers, ranchers, ranchette owners with 

domestic sheep or goats, commercial packers, and off-road vehicle users. 

3. ASSESSING THE EFFECTIVENESS OF AND MODIFYING THE PLAN 

Second Survey

Approximately 1 year after the initial survey is undertaken and a formal Sierra Nevada 

bighorn sheep Public Information and Outreach campaign is launched, a second survey 

should be undertaken. Comparisons of the results with the initial survey would provide 

the basis for modifying the information and outreach efforts. 

Recovery Plan Advisory Team Meeting

A meeting of the Recovery Plan Advisory Team (section II.D.8) should be convened to 

critique the Sierra Nevada bighorn sheep Public Information and Outreach Plan. 

Broadening the outreach should also be considered. Interviews on national radio and 

television should be considered to maximize the number of people reached. Videotapes 

or audio tapes of the programs could be used as tools for further outreach. 

4. USING CONCURRENT INFORMATION PROJECTS 

Disseminating Information on Multiple Fronts

Certain information projects should be initiated concurrently with the activities to design 

a Sierra Nevada bighorn sheep Public Information and Outreach Program. The public 

needs to be made aware as soon as possible about required actions and restrictions while 

in Sierra Nevada bighorn sheep habitat. The recovery plan will also be released to the 

public, and broad distribution should be ensured. Existing outreach programs need to be 

updated to incorporate the most current information. 

During implementation of recovery efforts, the public should be fully informed as early 

as possible regarding actions required or restricted while in Sierra Nevada bighorn sheep 

habitat. For example, signs or flyers explaining trail closures (in such places as the 

Zoological Area) or restrictions (such as areas where dogs or pack goats are not allowed) 

should be located so that users are aware of these restrictions while planning their trip 

and/or when they are still able to modify their visit. 

Affected members of the public should be contacted in other ways, such as through 

presentations to commercial packers or campers. Information regarding restrictions and 

requirements while in Sierra Nevada bighorn sheep habitat should also be included in 

sources of information that attract visitors to the area, such as commercial advertising, 

chamber of commerce publications, and web sites. 
161

A master calendar that lists all specific recovery actions requiring public involvement 

should be developed (such as seasonal trail closures). This calendar should indicate the 

dates that publicity should begin, as well as the outreach message and method. 

Distributing the Recovery Plan

The final recovery plan, along with a cover letter, should be widely distributed to affected 

and interested people, including hikers and other recreationists, ranchers, ranchette 

owners with domestic sheep or goats, commercial packers, environmental groups, 

mountain lion and bighorn sheep advocacy groups, and affected local, State and Federal 

agencies. Distribution of the recovery plan can be facilitated through the Recovery Plan 

Stakeholders Working Group. At a minimum, recovery plans should be distributed to 

everyone on our mailing list of people interested in the Endangered Species Act listing of 

Sierra Nevada bighorn sheep as well as the local news media. 

Updating and Coordinating Existing Informational and Outreach Programs

There is an immediate need to update existing programs to provide an accurate view of 

our current knowledge regarding Sierra Nevada bighorn sheep. Information should strive 

to highlight not only each agency or organization's contributions to the recovery of Sierra 

Nevada bighorn sheep, but how these activities complement those of other agencies and 

organizations. 

The bighorn sheep exhibit at the Mono Basin Scenic Area Visitor's Center should be 

updated and upgraded. 

The California Watchable Wildlife Viewing Guide site at Lee Vining/Tioga Lake should 

include interpretive information on bighorn sheep. 

National Park Service, U.S. Forest Service, Bureau of Land Management, and California 

Department of Fish and Game interpretive talks at visitor centers and campgrounds 

should include segments on bighorn sheep. 

Using Educational Programs for Students

If an educational program targeting local schools is developed, the goals of the program 

should be for students to: understand the ecology of Sierra Nevada bighorn sheep; 

develop a respect, appreciation and concern for this species; become aware of the threats 

this species is currently facing and how recovery actions will reduce these threats; 

understand the role of Sierra Nevada bighorn sheep within the ecosystem and the value of 

bighorn sheep recovery to the ecosystem; become aware of specific actions they must 

take while in Sierra Nevada bighorn sheep habitat and why they are important to 

recovery; and become aware that the Sierra Nevada bighorn sheep recovery effort is a 

collaborative effort supported by multiple agencies, organizations, and individuals. 
162

Existing bighorn sheep curricula should be reviewed and modified as needed to be 

applicable to Sierra Nevada bighorn sheep. Existing activities or curricula include: 

"Murder Ewe Wrote" (level: Grades 6-8) 

(http://www.sd5.k12.mt.us/glaciereft/wild8-12.htm) 

“Bringing bighorn into the classroom” (Cunningham, S. C. 1993. Desert Bighorn 

Council Trans. 37:33-36). 

 

In addition, a variety of educational materials on bighorn sheep exist that target schoolaged children and that could be incorporated into a Sierra Nevada bighorn sheep 

curriculum. They could be incorporated as is or modified to be made specific to Sierra 

Nevada bighorn sheep. These materials include: 

National Bighorn Sheep Center's Traveling Trunk Exhibit 

(http://www.bighorn.org/exhibit.html) 

National Bighorn Sheep Center's A Year in the Life of the Whiskey Creek Bighorn Sheep 

(http://www.bighorn.org/Exhibit.html) 

Foundation for North American Wild Sheep's Wild Sheep Journal 

5. IDENTIFYING FUNDING AND PARTNERSHIPS TO SUSTAIN SIERRA 

NEVADA BIGHORN SHEEP PUBLIC INFORMATION AND 

OUTREACH PROGRAMS 

 

Finding New Partners and New Funding 

An effort should be made to identify new partners in the Sierra Nevada bighorn sheep 

Public Information and Outreach Plan such as the Paiute Shoshone Tribes, The 

Independence Civic Club, the Yosemite Association, and others. Funding to support 

future programs and broaden public outreach campaigns should be sought. In addition to 

grants, a partnership with the Eastern Sierra Interpretive Association might be explored. 

As referred to in section 2 above, marketing t-shirts, posters, and other informational 

consumer goods would not only raise awareness about the Sierra Nevada bighorn sheep 

program but could also provide a source of income to sustain or augment the program. 

Conclusion 

An effective Sierra Nevada bighorn sheep Public Information and Outreach Plan will 

enhance the success of recovery efforts for the Sierra Nevada bighorn sheep. The 

program needs to celebrate the uniqueness and majesty of the species along with 

delivering a message about the threats facing the Sierra Nevada bighorn sheep and how 
163

recovery efforts are addressing those threats. With opportunities for innovative 

partnerships, the Sierra Nevada bighorn sheep campaign can be the source of regional 

pride not only for residents of the eastern Sierra Nevada but also the agencies that are 

collaborating on the recovery plan. 
164
165

APPENDIX G SUMMARY OF THREATS AND RECOMMENDED 

RECOVERY ACTIONS 

Listing 

Factor 

Threat Recovery 

Criteria 

Task Numbers 

A Habitat loss [considered 

a minor threat] 

B4 1.1, 1.2, 6.3 

B Hunting [historical in 

19th century; not 

currently considered a 

substantial threat] 

N/A N/A 

C Disease (pneumonia and 

other epizootics 

contracted from 

domestic sheep) 

A2 2.3.1, 2.3.2, 5.4, 7.1, 7.2, 7.3 

C Disease (lungworm 

infestation) [considered 

a minor threat] 

 5.4 

C Direct mortality from 

predation (by mountain 

lions and other 

predators) 

A1, B1 2.1, 5.2, 6.5, 6.6, 6.8, 7.1, 7.2, 7.3 

C 

Reduced nutritional 

condition and lamb 

survival due to use of 

poor-quality winter 

range at high elevations, 

perhaps indirectly 

resulting from excessive 

predation 

A1, B1 2.1, 2.2.1, 2.2.2, 2.2.3, 5.1, 5.2, 5.3, 

6.3, 6.5, 6.6, 6.7, 6.8, 7.1, 7.2, 7.3 

D Limited effectiveness of 

management by State 

and Federal agencies 

B3 1.2, 2.3.1, 2.3.2, 7.1, 7.2, 7.3, 8 

E Random variation in 

population 

characteristics (e.g., sex 

ratio) due to small 

population size 

A1, B1, 

B2, B3 

2.2.2, 3.1, 3.2.1, 3.2.2, 5.1, 6.6, 6.7 

E Loss of genetic 

variability due to small 

population size 

A1, B1, 

B2, B3 

2.2.2, 3.1, 3.2.1, 3.2.2, 4, 5.1, 6.1, 6.6, 

6.7 
166

E Increased vulnerability 

to naturally occurring 

environmental events 

(avalanches, prolonged 

or severe winters) due 

to small population size 

A1, B1, 

B2, B3 

2.2.2, 3.1, 3.2.1, 3.2.2, 5.1, 6.6, 6.7 

E Competition with elk or 

deer for winter range 

resources [considered a 

minor threat] 

B4 6.8 

E Disturbance from 

recreational use [not 

currently considered a 

substantial threat; may 

be reevaluated if 

warranted in future]† 

B4 1.2, 2.4.1, 2.4.2, 6.4, 7.1, 7.2, 7.3 

E Mortality from 

automobile strikes 

B4 7.3 

E Vegetation succession 

decreasing openness in 

habitat† 

B4 1.2, 2.2.3, 5.3, 6.3 

E Broad environmental 

factors (climate change, 

acid rain, mining 

wastes)[potential threat, 

needs research]† 

B4 1.2, 6.9 

† Not identified as a threat in the original listing rule. 

Listing Factors: 

A: The Present or Threatened Destruction, Modification, or Curtailment Of Its Habitat Range 

B: Overutilization for Commercial, Recreational, Scientific, Educational Purposes (not a factor) 

C: Disease or Predation 

D: The Inadequacy of Existing Regulatory Mechanisms 

E: Other Natural or Manmade Factors Affecting Its Continued Existence 

Recovery Criteria 

Downlisting 

A1: A minimum total of 305 females at least 1 year of age, distributed among the Kern (50), Southern 

(155), Central (50), and Northern (50) Recovery Units 

A2: The measures to prevent contact between domestic sheep/goats and bighorn sheep have been 

implemented and are successful. 

Delisting 

B1: Downlisting population levels maintained for 7 years without intervention. 

B2: Bighorn sheep of both sexes present in 12 herd units, distributed among the Kern (2), Southern (6), 

Central (2), and Northern (2) Recovery Units (Mount Warren and Mount Gibbs for the Northern Recovery 

Unit). 

B3: A population viability analysis projects that all recovery units are viable. 

B4: Regulatory mechanisms and management commitments have been established to protect bighorn 

sheep and their habitat. 
167

APPENDIX H GENETIC MANAGEMENT OF SIERRA NEVADA BIGHORN 

SHEEP 

Abstract 

Genetic diversity develops slowly in populations but can erode rapidly when populations 

decline to and remain at small sizes (population bottlenecks) for numerous generations. 

Bighorn sheep in the Sierra Nevada exhibit strong evidence of a recent population 

bottleneck, which is consistent with their demographic history in the past 150 years. 

Additionally, the three reintroduced herds show the lowest genetic diversity resulting 

from founder effects. However, relative to a variety of bighorn sheep herds whose 

genetic diversity has been sampled in the southwestern states, genetic diversity in the 

Sierra Nevada simply falls at the lower end of natural variation among populations. 

Additionally, recent strong population gains in the Sierra Nevada indicate that existing 

genetic diversity currently is not a limiting factor for the demographic recovery of this 

taxon. Thus, there is no justification for induced gene migration from populations 

outside of the Sierra Nevada. 

Attempts to increase genetic diversity in existing herds by moving sheep between herd 

units within the Sierra Nevada mostly will not be effective because of large population 

sizes and overall similarity in allele frequencies between source and recipient herds. 

Genetic diversity can be influenced most effectively when populations are small. 

Consequently, actions to maximize genetic diversity need to occur during reintroductions 

or when populations go through bottlenecks. Genetic management for bighorn sheep in 

the Sierra Nevada needs to focus on minimizing the loss of existing genetic diversity. 

This will be accomplished by actions that enhance herd sizes and natural gene migration 

among herds in this metapopulation: habitat manipulations in herd units, restoration of 

bighorn sheep to vacant habitat, and conservation/enhancement of habitat in corridors 

connecting herd units. The following actions are recommended: (1) use fire and other 

methods to enhance habitat within herd units to increase carrying capacities where 

appropriate; (2) translocate sheep to vacant habitat within occupied recovery units as 

quickly as possible using the genetically most diverse stock available, and attempt to 

expand habitat use within herd units with translocations; (3) identify key habitat 

connecting herd units and recovery units and take actions to improve and conserve that 

habitat to promote gene flow; (4) where new herds are established in isolated locations 

not likely to receive gene flow from nearby populations, use at least 40 sheep to initiate 

the new herd, and use the genetically most diverse stock available; (5) monitor genetic 

diversity in herds containing fewer than 40 sheep at least every 14 years and every 35 

years for all herds; and (6) where herds undergo population bottlenecks, assess genetic 

diversity and take actions to enhance it where appropriate. 

Dynamics and Importance of Genetic Diversity 

Loss of genetic diversity due to genetic drift in small isolated populations has been a 

concern of conservation biology (Soulé 1980, Hedrick et al. 2001) and has resulted in 

suggested minimum population goals and population structures to minimize this loss 
168

(Franklin 1980, Templeton and Read 1983, 1998). The loss of genetic diversity in small, 

isolated populations may be exacerbated by “cryptic genetic bottlenecks” when few 

individuals contribute to subsequent generations, but census size of the population does 

not signal immediate concern (Luikart et al. 1998, Ramey et al. 2000). In these and very 

small isolated populations, inbreeding (mating between relatives) is a concern. 

Reduced genetic diversity results in higher levels of homozygosity in individual 

organisms. This can lead to increased phenotypic expression of deleterious recessive 

alleles (Soulé 1980). It also can lead to reduced fitness where heterozygosity translates to 

more varied physiological functions that effectively buffer individuals better against 

challenges such as novel pathogens. Extreme inbreeding and loss of genetic diversity can 

lead to overt fitness effects with demographic consequences that may hasten extinction 

(Ralls and Ballou 1983). However, because of different time scales involved in 

demographic and gene pool dynamics, Lande (1988) suggested that demographic 

problems associated with small populations most likely will preempt genetic problems in 

importance. Nevertheless, an important consideration in endangered species 

management is the retention of as much genetic diversity as possible under the 

expectation of recovery of the population in question. In addition to reducing potential 

deleterious effects of inbreeding, this diversity is considered important for populations to 

be able to respond to selection from future environmental changes (Franklin 1980). 

There is growing evidence that genetic diversity manifested as heterozygosity levels of 

individuals can be important for disease resistance, including in sheep (Carrington et al. 

1999; Coltman et al. 1999). Indeed, novel disease pathogens are one form of 

environmental change. However, at what point lowered genetic diversity is detrimental 

to population fitness varies among organisms as a function of demographic history, and 

cannot be predicted (Williams et al. 2004). 

Although not always obvious, endangered species management ultimately concerns 

conservation of diversity of a unique gene pool. Endangered species typically represent 

unique gene pools, and their endangered status implies a significant past population 

decline, which is likely to be associated with loss of genetic diversity (Frankham 1995a, 

1996). In extreme situations, improving genetic diversity requires bringing in outside 

sources of genetic material, and thereby somewhat diluting the uniqueness of the gene 

pool in question (Varvio et al. 1986, Mills and Smouse 1994). Thus, genetic 

management of endangered species can be a balancing act between preserving 

uniqueness and preventing extinction (Hedrick 1995). 

While immigration can be an important source of increased genetic diversity, the initial 

source of all genetic diversity is mutations. New mutations necessarily begin at very low 

frequencies in populations and generally disappear quickly. However, occasionally they 

persist and become established in gene pools, increasing in frequency through genetic 

drift and/or selection. Because mutation rates are generally low, genetic diversity builds 

slowly in populations over hundreds and thousands of generations. While mutations are 

the source of genetic diversity, and genetic drift causes some new mutations to become 

established in gene pools, genetic drift also results in the loss of existing genetic variants. 

In time, equilibrium can be reached between the addition of new genetic variation from 
169

mutations and the loss of variation from genetic drift. When that theoretical equilibrium 

is reached, genetic diversity is a function of population size and mutation rate according 

to the following equation (Hartl and Clark 1997): 

 H = 4Ne μ/(1 + 4Ne μ) (1) 

where H is heterozygosity, a measure of genetic diversity (the probability that two alleles 

randomly drawn from the gene pool are different by state), Ne is the genetically effective 

population size, and μ is the mutation rate. A fundamental conclusion from this equation 

is that at large population sizes mutation rate has the dominating effect on H, while at low 

population sizes, drift dominates and H is lower (Gillespie 1998). Bighorn sheep tend to 

fall at the low end of population sizes. However, gene flow among populations within 

metapopulations will counter the effects of genetic drift on individual populations 

(Schwartz et al. 1986), as will selection that favors more heterozygous individuals. 

While genetic diversity accumulates slowly in populations, it can be lost relatively 

quickly when populations go through bottlenecks. Genetic diversity, as measured by 

heterozygosity, declines at a rate of 1/2Ne per generation, i.e. 

 H′ = (1 – 1⁄2 Ne)H (2) 

where H and HΝ are heterozygosity in successive generations, and Ne is genetically 

effective population size (Gillespie 1998). The effect of a population bottleneck on 

genetic diversity depends on the severity of the bottleneck (Ne) and how many 

generations it lasts. During population bottlenecks, the drift-mutation equilibrium of 

equation (1) is disrupted and leads to a transient heterozygosity excess relative to what 

would be expected at equilibrium from the surviving numbers of alleles per locus. That 

pattern is the basis of a test for recent population bottlenecks (Cornuet and Luikart 1996, 

Luikart and Cornuet 1998, Luikart et al. 1998). 

Genetic Diversity in Sierra Nevada Bighorn Sheep Herds

Wehausen and Ramey (2004) measured genetic diversity on a relative scale for all extant 

bighorn sheep herds in the Sierra Nevada. The recovery plan defines those herds on a 

demographic basis as eight different herd units. From a genetic standpoint it is more 

meaningful to combine herd units that are geographically contiguous with no barriers to 

male-mediated gene flow. Consequently, Wehausen and Ramey (2004) defined five 

different genetic populations (Mount Langley, Mount Williamson, Mount Baxter, 

Wheeler Ridge, and Mono Basin) for analyses, with each separated from others by 

unoccupied habitat. 

Wehausen and Ramey (2004) used twelve microsatellite loci to measure genetic 

diversity. DNA was obtained from fecal samples, blood from captured sheep, and tissue 

from recently dead sheep using silica-based methods (Wehausen et al. 2004) to develop 

large sample sizes (> 35 individuals) for each population, with >200 total different sheep 

sampled. In addition, data were developed for the Mount Baxter population from around 

1980 prior to the recent bottleneck using dried tissue from skulls. Comparative data were 
170

developed also for four bighorn sheep populations immediately east of the southern 

Sierra Nevada (White Mountains, Inyo Mountains, Last Chance Range, and Hunter 

Mountain) using the same methods. Gutierrez-Espeleta et al. (1998, 2000) developed 

data on a variety of bighorn sheep populations in southwestern United States using nine 

of the same microsatellite loci. Those data also were used for further comparisons. 

Historical data summarized in the recovery plan indicate that about fourteen herds of 

bighorn sheep disappeared from the Sierra Nevada between 1850 and 1970, leaving only 

three surviving native herds. That loss alone would be expected to reduce genetic 

diversity. It is probable, however, that the surviving herds also went through significant 

population bottlenecks during that time period that would diminish genetic diversity 

further. During 1979-88, 93 bighorn sheep were captured from the Mount Baxter and 

Sawmill Canyon herd units and used to restock historic ranges in three areas (Bleich et al. 

1990a). The founder effects associated with those reintroductions would be expected to 

produce herds with genetic diversity yet lower than the native source herds. 

Additionally, all bighorn sheep herds in the Sierra Nevada went through population 

bottlenecks lasting about two generations beginning in the 1980s (Wehausen 1996), 

where a generation is about 7 years. The effects of 150 years of demographic 

perturbations are apparent in strong genetic evidence of past bottlenecks in all herds in 

the Sierra Nevada (Wehausen and Ramey 2004; Table H-1). 

The effects of those bottlenecks on genetic diversity also are apparent, with Sierra 

Nevada bighorn sheep exhibiting among the lowest genetic diversity levels for bighorn 

sheep populations sampled (Table H-2). Only a captive herd (Red Rock NM), expected 

by its history to show low genetic diversity, is as low. Within the Sierra Nevada, the 

reintroduced herds exhibit the lowest diversity, as expected (Table H-2). Additionally, 

the relative level of genetic diversity of those reintroduced herds follows expectations 

based on differences in founder size and severity of recent bottlenecks (Wehausen and 

Ramey 2004). 

Similar to other measures of diversity, genetic diversity is determined by the number of 

different states (alleles) and the frequency distribution among those states. Expected 

heterozyogosity similarly reflects those two parameters: the more alleles and the more 

even the frequency distribution among them, the higher the heterozygosity. Genetic 

diversity differences among herds in the Sierra Nevada reflect both parameters. For the 

12 loci examined by Wehausen and Ramey (2004), 27 different alleles were recorded in 

the Sierra Nevada. Only the Mount Williamson herd has all of them. The Mount Baxter, 

Mono Basin, and Wheeler Ridge herds each have 26, while the Mount Langley herd has 

24. 

Comparative results that fit expectations from demographic histories (e.g., Table H-2) 

provide some confidence in the measures of genetic diversity used. However, those 

measures apparently are meaningful only on a comparative basis. Mitton and Pierce 

(1980), Chakraborty (1981), and DeWoody and DeWoody (2005) have pointed out that 

samples of small percentages of loci in the genome will not correlate with genetic 

diversity of the entire genome. For example, microsatellite loci (mostly neutral markers) 
171

in vertebrates yield mean heterozygosities an order of magnitude higher than do 

allozymes (markers under selection; DeWoody and Avise 2000). DeWoody and 

DeWoody (2005) noted that at least 10% of the genome would have to sampled to 

develop a meaningful estimate of average heterozygosity. 

Given (1) inability to predict the level at which inbreeding is important for different 

species, and (2) the inability to develop a genetic diversity measure for the overall 

genome, population performance is the best assessment of whether reduced genetic 

diversity might limit the ability of bighorn in the Sierra Nevada to recovery to sufficient 

numbers. For instance, Kodiak brown bears exhibit extremely low genetic diversity as 

measured by microsatellite loci (Petkau et al. 1998), yet the population is 

demographically healthy with large bodied bears. Large mammals in general appear able 

to recover as populations after severe bottlenecks that greatly reduce genetic diversity 

(McCullough et al. 1996; Amos 1999; Weber et al. 2000, 2004; Williams et al. 2004). 

Sierra Nevada bighorn sheep appear to fit that pattern. Recent strong population gains in 

most herds beginning in the late 1990s indicate that genetic diversity is not hindering 

their potential to recover as a population. Within the Sierra Nevada, the Mount Langley 

herd unit has the lowest measured genetic diversity (Table H-2), yet recently exhibited 

essentially maximum rate of increase (30% per year) while making minimal use of low 

elevation winter ranges. 

While microsatellite heterozyogosity levels in Sierra Nevada bighorn appear reduced 

relative to some other bighorn sheep populations, it is not known from what level they 

have declined. There is considerable variation in genetic diversity among native bighorn 

sheep populations (Table H-2), much of which is probably natural variation reflecting 

differences in long-term population dynamics and gene migration. Other than the captive 

population at Red Rock, New Mexico, the lowest measured genetic diversity outside of 

the Sierra Nevada is the Old Dad Peak population in the eastern Mojave Desert of 

California. . Its level of genetic diversity is comparable to the native herds in the Sierra 

Nevada (Table H-2); it also clearly has not been compromised by lower genetic diversity. 

It appears that the current level of genetic diversity in the Sierra Nevada may simply fall 

at the lower end of natural variation in genetic diversity of bighorn sheep populations. 

Genetic Management

The conclusion that genetic diversity currently is not a limiting factor indicates that there 

is no apparent reason to bring in outside genetic variation; thus, this situation is not a 

balancing act between extinction and uniqueness. Consequently, genetic considerations 

for Sierra Nevada bighorn sheep need to focus on minimizing future losses of genetic 

diversity. 

Equation (2) describes the rate at which genetic diversity will be lost in the absence of 

gene flow between populations. In polygynous (breeding system in which a male mates 

with several females) species like bighorn sheep, Ne is considerably smaller than actual 

population size (N) and may approach N/10 (Frankham 1995b). Wehausen and Ramey 

(2004) noted that the maximum numbers of translocated sheep that could have 
172

contributed genes to the 3 reintroduced populations in the Sierra Nevada ranged from 21 

to 26, thus Ne levels for those founding populations may have been <10. Currently, the 

most isolated population is in the Mono Basin, with the total population recently varying 

between 35 and 40. Assuming an Ne of 20 for this population, it will lose about 2.5% of 

its variation per generation due to genetic drift in the absence of immigration, which 

translates to about a 7.3% loss in 20 years (3 generations). However, if Ne is 10, that loss 

increases to 5% per generation and 14.3% in 3 generations. 

Unfortunately, effecting a change in genetic diversity via induced migration between 

populations may be difficult. In the 1970s a rule of thumb was developed from the 

population genetic model of Wright (1931) that about one migrant per generation (Nm=1, 

where m is migration rate and N is population size) would substantially counteract the 

negative effects of genetic drift on heterozygosity in otherwise isolated populations 

(Spieth 1974, Lewontin 1974). This rule has found its way into conservation biology, 

including for bighorn sheep (Schwartz et al. 1986) and would indicate that few sheep 

may need to be moved between populations in the Sierra Nevada to counteract losses of 

genetic diversity. However, Mills and Allendorf (1996) pointed out that this rule of 

thumb is greatly influenced by a number of unrealistic model assumptions and thereby 

underestimates the number of migrants needed in many situations. One such assumption 

is that migrants originate randomly from any of many widely diverging populations that 

consequently differ considerably in gene frequencies. When the source population 

instead is closely related, with mostly the same alleles, considerably more migrants may 

be needed. That is the current situation in the Sierra Nevada, where reintroduced herds 

are naturally closely related to their source herd in alleles present and their frequencies, 

as are the two native herds to each other, perhaps due to close proximity. 

 The one-way migration model (mainland to island migration model) is 

 pt = p* + (1-m)t

(p0 - p*), (3) 

where pt is allele frequency at generation t, p* is allele frequency of migrants, and p0 is 

the initial allele frequency in the island population receiving migrants (Hartl and Clark 

1997). Under this model, allele frequency in the island population approaches that of the 

mainland over time at a rate equal to the migration rate (m). This model assumes that 

some proportion (m) of the alleles in the island population is replaced by alleles from 

migrants each generation; the higher that proportion, the more rapid the convergence. 

The difficulty of altering allele frequencies in Sierra Nevada populations can be 

illustrated by applying equation (3) to data from existing populations. The Mount 

Langley herd is the only reintroduced population that lacks some alleles present in its 

source herd. One of those is the 106bp allele of microsatellite locus MAF36. That allele 

is present in the Wheeler Ridge herd at a frequency of 0.171. Table H-3 lists expected 

frequencies of the 106bp allele in the Mount Langley herd from equation (3) for different 

levels of induced migrations from the Wheeler Ridge herd under the assumption that the 

Mount Langley herd size is about 100 (a reasonable carrying capacity suggested by 

analysis of its population trajectory). For a migration of 2 sheep per generation, the 
173

frequency of the 106 bp allele would be only 0.016 at 5 generations, and 0.031 at 10 

generations. For 10 sheep moved per generation those frequencies increase to 0.070 and 

0.111 respectively. 

The latter frequency is still well below the frequency of that allele in the Wheeler Ridge 

herd, yet took a total induced sheep migration of 100 over approximately 70 years (7 

years per generation) to reach that frequency. That total induced migration represents the 

number of sheep that successfully replaced themselves in the Mount Langley gene pool 

via reproduction. The actual number of sheep that would have to be moved to achieve 

that might be considerably higher due to animals that died, did not remain in the 

population, or failed to reproduce due to dominance status (males). Given the 

polygynous mating system of bighorn sheep (Geist 1971), a male that achieved 

dominance status would accelerate the rate of gene migration, especially if dominance 

was related to level of heterozygosity. However, given the higher variance in 

reproductive success of male sheep (Coltman et al. 2001), females might be the better 

choice for such an effort to induce gene migration. Females would be especially 

preferable if they also increased the population carrying capacity through expansion of 

the habitat used and thereby increased Ne. 

The numbers of sheep that would need to be moved to effect a notable change in gene 

frequencies essentially preclude consideration of this approach for most situations in the 

Sierra Nevada. For numerous years to come, most sheep available for translocation will 

be needed to increase total population size by restocking vacant herd units and expanding 

habitat use of existing herds. The one exception might be small populations, where 

changes in gene frequencies could be effected with translocation of fewer sheep. 

Management Implications and Recommendations

The most important lesson from the previous section is that the initial reintroduction is 

when genetic diversity best can be maximized. Two variables are important for 

reintroductions: total founding numbers and genetic diversity of the source herd(s) used. 

The former may be less important where reintroductions are contiguous to existing herds 

and will attract male-mediated gene flow from the existing herd (e.g., Taboose Creek). 

Where herds are re-established in more isolated situations, planning should include early 

augmentation(s) to maximize genetic diversity. The Mono Basin herds resulted from a 

total of 38 sheep reintroduced there, but only a maximum of 26 of those might have 

contributed genes (Wehausen and Ramey 2004). Initial mortality rates associated with 

reintroductions are typically somewhat elevated, but were more so in the Mono Basin. 

While that effort has produced the highest level of genetic diversity of the three 

reintroduced populations, despite the lowest current population size, it is nevertheless 

lower than its source herd. Based on analysis of success of numerous reintroductions of 

bighorn sheep in the Rocky Mountain region, Singer et al. (2000) suggested a minimum 

of 41 sheep for reintroductions. A total founding population of 40-50 is a reasonable goal 

to maximize genetic variability where populations are isolated. 
174

With the relative ineffectiveness of using induced migration to alter genetic diversity, it 

will be necessary to rely on natural dispersal to link bighorn sheep herds genetically in 

the Sierra Nevada. What the extent of that gene flow will be is not known. Presumably, 

such linkage between herds once served to connect them sufficiently to counteract losses 

of genetic diversity that otherwise occur in isolated populations of limited sizes. Known 

movements of translocated males that returned to their native herds (Mount Langley to 

Mount Baxter and Sawmill Canyon, and Wheeler Ridge to Mount Baxter) and of males 

not translocated (Mount Warren to Mount Gibbs and to Laurel Mountain in the Convict 

Creek herd unit, Wheeler Ridge to Mount Tom and Mount Izaak Walton in the Convict 

Creek herd unit) suggest a large potential for gene flow among herds. 

Re-establishing herds in habitat gaps is the primary management tool that will conserve 

genetic diversity by enhancing dispersal. This needs to be coupled with the appropriate 

conservation of migration corridors that link herd units and recovery units (Bleich et al

1990b). Additionally, habitat manipulations that will minimize habitat gaps, and thereby 

enhance gene flow, also will be beneficial. Early photographs indicate that taller 

vegetation that obstructs vision increased substantially in the eastern Sierra Nevada 

during the twentieth century, and thereby reduced the quality of some potential bighorn 

sheep habitat. Prior to that vegetation succession, habitat favorable to bighorn sheep 

apparently was considerably more continuous. This would have enhanced genetic 

diversity through more gene flow, as well as through higher overall population size. In 

short, as Lande (1988) concluded, enhancing demographic potential for these sheep will 

enhance retention of genetic diversity. 

Trends in genetic diversity should be monitored periodically where appropriate. Loss of 

genetic diversity from genetic drift is a relatively slow process unless populations 

undergo extreme and prolonged bottlenecks. It would be appropriate to repeat the genetic 

diversity measurements of Wehausen and Ramey (2004) for smaller herds (< 40 sheep) 

every 1-2 generations to develop a measure of the actual rate that genetic diversity is 

declining. As long as larger populations maintain herd sizes, there is no reason to expect 

detectable changes in genetic diversity for numerous generations. This is illustrated by 

the lack of evidence of any loss of genetic diversity in the Mount Baxter population 

between the period around 1980 and 20 years later, despite a short bottleneck in those 

two decades (Table H-2). Because conservation of genetic diversity in this entire 

metapopulation depends on gene flow among populations that is poorly understood, 

genetic diversity of all populations in the Sierra Nevada should be monitored over a time 

scale of 5 generations (35 years) to better understand the extent of gene flow. Finally, 

where major population declines occur, genetic diversity should be reassessed and 

appropriate actions taken to restore it via induced migration if appropriate. As with 

founding populations, small populations offer the best opportunity to effect such changes. 

Specific recommendations are: 

1. Use fire and other methods to enhance habitat within herd units to enhance carrying 

capacity and connectivity with adjacent herd units. 
175

2. Translocate sheep to vacant habitat within occupied recovery units as quickly as 

possible using the most genetically diverse stock available. Also, attempt to expand 

habitat use within herd units with translocations. 

3. Identify key habitat connecting herd units and recovery units and take actions to 

improve and conserve that habitat to promote gene flow. 

4. Where new herds are established in isolated locations not likely to receive gene flow 

from nearby populations, use at least 40 sheep to initiate the new herd, and use the 

most genetically diverse stock available. 

5. Monitor genetic diversity in herds containing fewer than 40 sheep at least every 2 

generations (14 years) to determine the actual rate at which genetic diversity is 

declining and for all herds on a time scale of 5 generations (35 years). 

6. Where herds undergo population bottlenecks, assess genetic diversity and take 

actions to enhance it with translocation where appropriate. 
176

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population bottleneck in the Guadalupe fur seal (Arctocephalus townsendii). 

Journal of Heredity 95:144-153. 

Wehausen, J. D. 1996. Effects of mountain lion predation on bighorn sheep in the Sierra 

Nevada and Granite Mountains of California. Wildlife Society Bulletin 24:471-

479. 

Wehausen, J. D., and R. R. Ramey II. 2004. Microsatellite diversity in Sierra Nevada 

mountain sheep herds. Unpubl. manuscript. 

Wehausen, J. D., R. R. Ramey II, and C. W. Epps. 2004. Experiments in DNA 

extraction and PCR amplification from bighorn sheep feces: the importance of 

DNA extraction method. Journal of Heredity 95:503-509. 

Williams, C. L., B. Lundrigan, and O. E. Rhodes. 2004. Microsatellite DNA variation in 

tule elk. Journal of Wildlife Management 68:109-119. 

Wright, S. 1931. Evolution in Mendelian populations. Genetics 16:97-259. 
180

Table H-1. Bottleneck test results (one-tailed Wilcoxen probabilities that the data came 

from an unbottlenecked population at drift-mutation equilibrium) based on variable 

microsatellite loci for the infinite allele model (IAM), stepwise mutation model (SMM), 

two-phased models (TPM; #1 = 70% SMM, variance=30; #2 = 90% SMM, variance=4). 

MODE is an assessment of the overall allele frequency distribution pattern. Data from 

Wehausen and Ramey (2004). Asterisk identifies Sierra Nevada bighorn sheep populations.

POPULATION LOCI IAM SMM TPM #1 TPM #2 MODE

Last Chance Range 12 0.0104 0.409 0.059 0.402 normal 

Hunter Mountain 12 0.0320 0.661 0.190 0.545 shifted 

Inyo Mountains 12 0.00012 0.604 0.0012 0.102 normal 

White Mountains 12 0.0067 0.339 0.088 0.170 normal 

*Mount Baxter 

(1980) 10 0.00049 0.00049 0.00049 0.00049 shifted 

*Mount Baxter 

(2001) 10 0.00049 0.00049 0.00049 0.00049 shifted 

*Mount Williamson 10 0.00049 0.00049 0.00049 0.00049 shifted 

*Mount Langley 10 0.00146 0.0420 0.00146 0.0420 shifted 

*Wheeler Ridge 10 0.00049 0.00244 0.00098 0.00146 shifted 

*Mono Basin 10 0.00098 0.00146 0.00098 0.00098 shifted 
181

Table H-2. Expected heterozygosity (He; Nei 1987) calculated from data for 12 

microsatellite loci and 9 of those also run by Gutierrez-Espeleta et al. (1998, 2000). 

Sample size (N) is number of sheep. Data from Wehausen and Ramey (2004). Asterisk 

identifies Sierra Nevada bighorn sheep populations. 

POPULATION N He

(12 loci) 

He

(9 loci) 

Eagle Mountains, CA 22 0.612 

Last Chance Range, CA 21 0.629 0.602 

Hunter Mountain, CA 20 0.600 0.586 

Inyo Mountains, CA 31 0.606 0.571 

Castle Dome, AZ 20 0.564 

White Mountains, CA 25 0.485 0.483 

San Ysidro Mountains, CA 22 0.466 

San Gorgonio, CA 22 0.452 

Mount Nutt, AZ 28 0.444 

*Mount Baxter, CA (current) 62 0.468 0.434 

Old Dad Peak, CA 23 0.427 

*Mount Baxter, CA (1980s) 46 0.454 0.412 

*Mount Williamson, CA 37 0.446 0.390 

*Mono Basin, CA 42 0.430 0.384 

*Wheeler Ridge, CA 35 0.420 0.389 

*Mount Langley, CA 40 0.404 0.335 

Red Rock (captive), NM 25 0.324 

Table H-3. Modeled effects of moving sheep from the Wheeler Ridge herd to the Mount 

Langley herd (N = 100) on the frequency of the MAF36 106bp allele using equation (3). 

Migrants per generation represent sheep translocated that were successful in replacing 

themselves genetically through reproduction. 

migration migrants per 106bp allele frequency 

rate (m) Generation generation 5 generation 10 

0.02 2 0.016 0.031 

0.04 4 0.032 0.057 

0.06 6 0.046 0.079 

0.08 8 0.058 0.097 

0.10 10 0.070 0.111 
182
183

APPENDIX I CAPTIVE BREEDING CONTINGENCY PLAN, 

EXECUTIVE SUMMARY 

Prepared by Holly Ernest, DVM, PhD 

The Captive Breeding Contingency Plan (Ernest 2001), contracted by the California 

Department of Fish and Game's Sierra Nevada Bighorn Sheep Population Recovery 

Program, includes several tools to facilitate decisions relating to the captive breeding of 

bighorn sheep. This analysis was also provided to the multi-agency Sierra Nevada 

Bighorn Sheep Recovery Team to assist recovery planning. The concept of captive 

breeding in general, along with past Sierra Nevada bighorn sheep captive breeding 

attempts were reviewed in the Introduction. A model for decision tree analysis was 

presented in a dichotomous format: a series of questions requiring yes or no answers to 

lead to specific recommendations for captive breeding. 

Next, to assess the impact that captive breeding-associated sheep removal and 

augmentation would have on extinction probabilities in populations, population modeling 

was conducted. Preliminary models for the populations at Wheeler Ridge, Mt. Baxter 

region, and a theoretical captive herd were run under three different scenarios 

representing a range of mortality and survival values. Since this pilot set of models 

detailed is very preliminary and simplistic, they should be used only for initial guidance 

decision-making and construction of future models. Perhaps most importantly, these 

models demonstrate the conspicuous need for age- and cause-specific mortality, 

survivorship, and census data. Although the models were run with limited available data, 

they revealed that the potential for Wheeler population to serve as a reliable source of 

transplantation stock may be limited and tenuous due to small population size. Using 

data available at the time of writing from the Sierra Nevada and existing captive bighorn 

sheep facilities, models indicated that a captive herd would produce a more reliable 

source of translocation stock than Wheeler Crest alone. Depending on factors specific to 

the contemporary populations, well planned and conducted captive breeding and 

translocation of animals may facilitate recovery goals by increasing the rate of population 

growth and achieving population numbers to reduce likelihood of extinction. 

Captive breeding site selection guidelines were presented, along with a detailed 

assessment of a site (Paoha Island in Mono Lake) that had been under consideration by 

the California Department of Fish and Game. Preliminary assessments were made for 

potential sites west of Big Pine between Baker and Fuller Creeks. The Plan includes 

information (including strengths and weaknesses) on existing captive breeding facilities 

in southern California and other states collected by site visits and communications with 

facility managers, veterinarians, and biologists. Most of the problems experienced in the 

past would be eliminated or at least greatly reduced with proper facility planning and 

management. Also included are guidelines and recommendations for constructing and 

maintaining a facility for captive breeding, selection of founder breeding stock, 

husbandry, and veterinary care, along with a summary of diseases that may affect a 

captive herd. A preliminary cost estimate worksheet for start-up and first year is 
184

provided. Start-up and first year costs range from $600,000-1,000,000 (roughly 

estimated, since there are many unknowns). 

My general conclusion at the time of writing, from literature review, consultation with 

captive breeding and bighorn sheep experts, and preliminary population modeling was 

that establishment of a well-managed captive herd would reduce the risk of extinction of 

Sierra Nevada bighorn sheep, given the year 2000 population estimates. The captive herd 

should consist of a minimum of 30-40 founder animals, collected over at least fifteen 

years, from the Wheeler population (and other populations, as available) to preserve a 

minimum level of genetic diversity (at least 90-95% of original heterozygosity). Wellplanned breeding, and pedigree and genetic analyses should be conducted under 

consultation of a geneticist experienced in ungulate captive breeding. The captive herd 

would provide a new population (estimated to be 50-100 animals) as a safeguard against 

wild extinctions. Based on models, within 4-7 years, reliable translocation stock should 

be available for translocation and reintroduction to Sierra Nevada populations. 

Simulation models specific to the Sierra Nevada metapopulation should be constructed 

and further modeling with updated population estimates should be conducted. One 

potential problem that needs further research is the translocation success of captive raised 

vs. wild caught sheep (see Thompson et al. 2001; Clark et al. 1988). Other issues for 

further research include detailed examinations of the risks of pathogen exposure and 

infection in a captive herd and transmission to wild sheep. 

The final products of a captive breeding herd should be healthy, behaviorally normal 

individuals capable of surviving and reproducing in the wild. A large enclosure with an 

abundance of natural forage, escape terrain and protection from predation is required. 

Disease may be an unavoidable occurrence in a captive herd, especially an intensively 

managed herd in a small enclosure. Prevention will be the key to minimizing and 

delaying this event. In the case of a disease event in the captive herd, the eventual release 

of captive animals into the wild must be managed very conservatively. It is within the 

realm of possibility that disease could totally prevent the release of any captive animals 

into the wild. A long-term commitment (i.e. greater than 10 years) by California 

Department of Fish and Game, U.S. Fish and Wildlife Service, and the Recovery Team 

for high-quality facility planning, construction, and management will be critical to the 

success of a captive breeding program.

 

Reduced adult survival and high environmental variation in reproduction and lamb 

survival are likely to be important factors driving Sierra Nevada populations toward 

extinction. A captive population can be managed to have optimum reproduction and 

survival without the high environmental variation that is present in wild populations. 

Without the potential stability of captive herd, the Wheeler population, as currently 

modeled, may have a limited potential to supply translocation stock for augmentation of 

existing Sierra Nevada populations and for reintroduction of new populations, and 

therefore, population recovery goals may not be achieved in the desired time frame. 

Finally, as the Sierra Nevada metapopulation of bighorn sheep and their ecosystems are 

dynamic, so should be captive breeding contingency planning. This document is meant 
185

as a starting point, and as a living document it should be revised and supplemented as 

new science becomes available. 

Literature Cited 

Clark, R.K., D.A. Jessup, and R.A. Weaver. 1988. Relocation of bighorn sheep within 

California. Joint Proceedings of the Annual Meeting of the American Association 

of Zoo and Wildlife Veterinarians. Toronto, Canada. November 1988. Pages 

121-129. 

Ernest, H. 2001. Captive breeding contingency plan: A guide for captive breeding of 

Sierra Nevada bighorn sheep. Report for Interagency Agreement # P9980059 

between California Department of Fish and Game and Wildlife Health Center, 

School of Veterinary Medicine, University of California, Davis CA. 147 pages. 

Available online at http://www.vgl.ucdavis.edu/wildlife/sheep_plan.html 

Thompson, J.R., V.C. Bleich, S.G. Torres, and G.P. Mulcahy. 2001. Mountain sheep 

translocation techniques: Does the method matter? Southwestern Naturalist 

46:87-93. 
186
187

APPENDIX J COMMENTS RECEIVED ON THE DRAFT PLAN 

In July 2003, we released the Draft Recovery Plan for the Sierra Nevada bighorn sheep 

(Draft Plan) and initiated a 90-day comment period. This comment period was re-opened 

in October of 2003 for an additional 60 days. During both comment periods, we received 

comments from Federal agencies, State and local governments, and members of the 

public. Marco Festa-Bianchet, Michael Oehler, and Frances Cassirer were asked to 

provide peer review of the draft plan. We received comments from all three peer 

reviewers. 

This section provides a summary of general information including the total number of 

letters received from various affiliations. It also provides a summary of the major 

comments. All letters of comment on the draft plan are kept on file in the Ventura Fish 

and Wildlife Office at 2493 Portola Road, Suite B, Ventura, California 93003. 

We received 47 letters during the two open comment periods. Many of these letters 

simply voiced support or opposition to the recovery plan with no reason provided; these 

letters are on file but have not been specifically addressed. Some letters included new 

information or suggestions for clarity. In these cases, the information has been 

incorporated into the final version of the recovery plan. Some letters requested an 

explanation of the scientific basis for various points made in the draft plan. In these 

cases, the final recovery plan has been revised to include an expansion or clarification of 

the particular section. Most comments resulted in revisions to the draft recovery plan. 

Information and comments not incorporated into the final version of the recovery plan 

were considered, noted, and are on file with the entire package of agency and public 

comments. Major comments that were not incorporated or that require clarification in 

addition to their incorporation are addressed in the summary below. 

The following is a breakdown of the number of letters received from various affiliations: 

Federal agencies 3 

State agencies 2 

Local governments 1 

Environmental/conservation organizations 7 

Academia/professional 5 

Business/industry 13 

Individual citizens 15 

Recreation groups 1 

Summary of comments and our responses 

Comment: One commenter stated that the Forest Service is designated as the lead agency 

responsible for “eliminating the risk of contact between bighorn sheep and domestic 

sheep or goats.” However, the Forest Service has no authority to influence contact 

between bighorn sheep and domestic sheep on lands other than those managed by the 

National Forest System, and this should be clearly explained in the plan. 
188

Response: Although we agree with the commenter that the authority of the Forest 

Service is limited, recovery plans do not obligate cooperating or other parties to 

undertake specific tasks, but delineate reasonable actions required to recover and/or 

protect listed species. The Forest Service was included as the lead agency for this task 

because the vast majority of areas where risk of contact between domestic and Sierra 

Nevada bighorn sheep remains is on lands administered by the Forest Service. Most of 

the tasks listed in the plan will require cooperation among various agencies, but at no 

time would the plan recommend or expect any agency to carry out an action outside of its 

jurisdiction. 

Comment: One commenter recommended that the word “should” in the narrative outline 

of recovery actions (section D) be replaced with “shall" for all necessary protective 

measures. 

Response: Changing the wording of the narrative for recovery actions as recommended 

by the commenter would imply that the tasks are mandatory. Recovery plans are 

guidance documents and are not regulatory documents. No agency or other entity is 

required by the ESA to implement the recovery strategy or specific recommended actions 

in a recovery plan. 

Comment: One commenter believed that the plan is based on the incorrect assumption 

that, since the bulk of Sierra Nevada bighorn sheep habitat is on Federal land, it is 

protected. 

Response: All proposed Federal actions that may affect Sierra Nevada bighorn sheep 

must be analyzed, and consultation must be initiated with the U.S. Fish and Wildlife 

Service. This ensures that Federal projects, projects carried out on Federal land, or 

projects with some type of Federal nexus will not jeopardize bighorn sheep. 

Comment: One commenter recommended that the plan should include measures to 

prevent mortality of bighorn sheep by vehicles. 

Response: Data indicate that the number of bighorn sheep being struck by vehicles is so 

small that it is an insignificant factor affecting population levels. Accordingly, this has 

not been identified as a threat to recovery. As population numbers increase, we anticipate 

there may be a small increase in the number of collisions, but the rate of collisions and 

level of population impacts is not expected to change. 

Comment: One commenter faulted the plan for not including the economic impacts to 

livestock operators. 

Response: Recovery plans are guidance documents only and do not create new 

regulations. No agency or other entity is required by the ESA to implement the recovery 

strategy or specific recommended actions in a recovery plan, and therefore recovery plans 
189

are categorically excluded from NEPA and not required to incorporate economic impact 

analyses. 

Comment: One commenter recommended that existing land and forest management 

plans be reviewed to identify allowed uses that would have an adverse effect on bighorn 

sheep and that the plans be amended as appropriate. 

Response: Under section 7(a)(2) of the Endangered Species Act, Federal agencies are 

required to consult with the Service on any action that may affect a listed species. 

Because the law requires land management agencies to consult on any actions that they 

determine to have an effect on Sierra Nevada bighorn sheep, we felt that identifying the 

review of authorized uses, as a recovery action would be redundant. The Service has not 

reviewed the broad effects of the land and forest management plans for the HumbodltToiyabe National Forest, Inyo National Forest, and BLM-Bishop Field Office. However, 

the land management agencies review all site-specific actions taken under the 

authorization of these plans, and they consult with the Service on any actions that may 

affect the Sierra Nevada bighorn sheep. 

Comment: Some commenters were concerned that the study of human/recreational 

impacts, including impacts from dogs, is only a low priority. 

 

Response: Actions to ameliorate the effects of human/recreational use were not given 

high priority in this plan because we do not currently consider recreational use, including 

the activities of dogs, a significant threat to Sierra Nevada bighorn. If information 

indicating recreational use is having an effect on recovery becomes available, appropriate 

actions will be recommended. 

Comment: Some commenters disagreed with the assumption that the Sierra Nevada 

bighorn sheep were near their historic carrying capacity in the past 25 years and believed 

that the numbers have actually been declining since the mid-1880s. 

 

Response: The overall historic carrying capacity of the Sierra Nevada is not known. The 

plan refers to the specific areas (Mt. Baxter and Sawmill Canyon herds) that were likely 

near their historic carrying capacity in the late 1970s. These two areas are used as a point 

of reference for comparisons with nearby herd units. 

Comment: One commenter believed that the generation time for bighorn sheep is 3 years 

rather than 6 years as given in the plan. 

Response: A generation time is how long it takes the population to replace itself. Given 

the age at which female bighorn sheep reach sexual maturity (2-3 years) in the Sierra 

Nevada, a 3-year generation time would not be sufficient for population replacement via 

natural reproduction. Ramey (1995) also used 7 years for the generation time when 

performing genetic analysis.
190

Comment: One commenter questioned the validity of the "natural breaks" which are used 

to separate the four recovery units. The commenter concluded that the boundaries of the 

Southern Recovery Unit and the Kern Recovery Unit seemed appropriate, but the breaks 

separating the Southern, Central, and Northern Recovery Units appear more arbitrary in 

light of several recent sightings. 

 

Response: The breaks in the recovery units are based on current knowledge of Sierra 

Nevada bighorn sheep distribution and movement. Their distribution consists of a series 

of subpopulations, represented by herd units, which occupy patches of suitable habitat 

within a matrix of unsuitable habitat. These subpopulations interact intermittently 

through the movement of males between them. The recovery units are comprised of 

those herd units that are more likely to be connected by males moving between them to a 

greater degree than those in other recovery units. Males may also move between 

recovery units, but movement between recovery units is much less common that 

movement within them. 

Comment: One commenter believed that, if the Sierra Nevada bighorn sheep is truly a 

separate population from the bighorn sheep to the east, then the plan should include 

techniques to ensure that any sheep traveling from the east are intercepted to prevent 

hybridization. 

Response: Although there have been occasional observations of bighorn rams on the 

floor of Owens Valley, we have no evidence that Sierra Nevada bighorn sheep are mating 

with other bighorn sheep subspecies from ranges to the east. The morphological 

uniqueness of the Sierra Nevada bighorn sheep indicates that gene flow from mountain 

ranges to the east is limited at best. 

Comment: One commenter believed there is no justification for eliminating sheep 

grazing on all areas west of Highway 395 for the recovery of Sierra Nevada bighorn 

sheep. 

Response: Because the transmission of disease from domestic sheep to bighorn sheep is 

the greatest threat to recovery of Sierra Nevada bighorn sheep, preventing contact 

between domestic sheep and Sierra Nevada bighorn is a critical strategy highlighted in 

this plan. However, we are not recommending elimination of domestic sheep grazing in 

all areas west of Highway 395. We are recommending closing certain allotments to 

sheep grazing where the risk of contact between domestic sheep and bighorn sheep is 

high (see also section II.E). 

Comment: One commenter recommended that the California Department of Fish and 

Game should capture any bighorn sheep that wander off or vaccinate them for disease. 

Response: There is currently no vaccine available for the Pastuerella strains that are of 

concern. We have incorporated a strategy for preventing contact between bighorn sheep 

and domestic sheep (Section E) that addresses the concept of removing bighorn sheep if 

they move into the Twin Lakes Herd Units. We have also indicated the need to remove 
191

Sierra Nevada bighorn sheep from areas east of Highway 395. We have addressed these 

areas specifically because current conditions with regard to bighorn population size and 

distance from potential disease sources make this concept logistically feasible. We have 

not included other areas for implementation of this measure because they are too close to 

potential sources of disease transmission, which makes them inappropriate due to the 

logistical difficulties of monitoring and managing bighorn sheep movements. However, 

given the logistical difficulty of monitoring and capturing wild sheep and likelihood of 

expanding populations in the future we cannot provide an absolute guarantee that all 

bighorn sheep that wander away from essential herd units will be captured and removed 

in perpetuity. 

Comment: One commenter recommended that the California Department of Fish and 

Game control bighorn sheep to the south of Lundy Canyon, thereby preventing conflicts 

with domestic sheep and protecting bighorn sheep from the hard winters that occur in 

northern areas. 

Response: We disagree that bighorn sheep would benefit from being protected from hard 

winters in northern areas. The south-facing slopes in Lundy Canyon provide high quality 

winter and spring habitat, which is particularly important during winters with heavy 

snowfall. In addition, there are some areas to the north of Lundy Canyon that are still 

within the Mount Warren Essential Herd Unit. However, the concept of removing 

bighorn sheep from areas in the Twin Lakes region has been incorporated into Section E 

of the recovery plan. Because the Twin Lakes Herd Unit is not needed for recovery, the 

occupation of this area by bighorn sheep would pose a risk due to the presence of active 

domestic sheep grazing allotments to the north. Consequently, we have recommended 

that bighorn sheep be monitored and managed intensively in the Northern Recovery Unit 

to allow removal of any bighorn sheep that wander that far north. However, based on the 

data that we currently have on bighorn sheep locations and movements it is not 

logistically feasible to prevent bighorn sheep from moving into areas that are between 

Lundy Canyon and Twin Lakes. 

Comment: One commenter pointed out that the recovery plan identifies the Forest 

Service and National Park Service as the lead agencies for implementing a habitat 

improvement program, yet fails to outline any specifics. 

Response: In the case of the Forest Service, National Park Service, and other land 

management agencies, the recovery plan prescribes general management concepts only; 

development of specific applications to address the general concepts in the plan are under 

the purview of the responsible agencies. 

 

Comment: One commenter stated that the use of the northern part of the Mono Basin 

area by bighorn sheep should be reevaluated, especially in light of recent sightings and 

high recreational use of the area. 

Response: A spatial model of bighorn sheep habitat suitability in the Sierra Nevada is in 

preparation, and recreational use relative to bighorn sheep will be monitored. 
192

Comment: One commenter stated that the Sierra Nevada bighorn sheep are the same 

species as the desert bighorn and should never have been listed. 

Response: It is correct that Sierra Nevada bighorn sheep are the same species as desert 

bighorn; all bighorn sheep are the same species. However, Sierra Nevada bighorn sheep 

are a separate subspecies that is supported by objective analyses of morphometric and 

genetic data, as published in the scientific literature (Wehausen and Ramey 2000). The 

ESA states that a species is endangered when it is in danger of extinction throughout all 

or a significant portion of its range and that the term species includes any subspecies of 

wildlife and any distinct population segment of any species of vertebrate wildlife that 

interbreeds when mature. Sierra Nevada bighorn sheep were listed as a distinct 

vertebrate population segment. All of this information is reviewed in the recovery plan. 

Comment: One commenter stated that critical habitat should be designated for the Sierra 

Nevada bighorn sheep, including travel corridors. The critical habitat designation would 

then provide the rationale for developing a recovery plan prior to completion of other 

portions of section 4 of ESA. 

 

Response: The designation of critical habitat and the preparation of recovery plans are 

two separate processes, and critical habitat is not necessarily synonymous with recovery 

plans or recovery units. However, we are currently in the process of preparing a 

proposed rule to designate critical habitat for the sheep; we expect to publish this rule in 

2007. 

Comment: One commenter stated that the appropriate distances between bighorn sheep 

and grazing allotments should be determined by section 7 consultations. 

Response: The distances given in the recovery plan are guidelines only. The entity that 

issues grazing permits, such as the Forest Service, determines which allotments will be 

permitted. If an agency determines that a permit it intends to issue is likely to affect a 

listed species, they are subsequently required to consult with the Fish and Wildlife 

Service pursuant to section 7 of the ESA to determine whether that action will jeopardize 

the continued existence of the listed species. The distance allowed for a specific grazing 

permit would be determined through the section 7 consultation process for that permit. It 

should be noted, however, that the agency issuing the permit also has the authority to use 

a greater distance if it believes it is appropriate. 

Comment: One commenter stated that the Fish and Wildlife Service should not tell the 

Forest Service how and where to graze cattle or sheep. 

Response: The U.S. Fish and Wildlife Service does not determine where the Forest 

Service allows cattle or sheep grazing. Congress has outlined procedures for Federal 

interagency cooperation to conserve listed species in section 7 of the Endangered Species 

Act. Section 7 makes it clear that all Federal agencies should participate in the 

conservation and recovery of listed threatened and endangered species and that any action 
193

they authorize, fund, or carry out is not “likely to jeopardize the continued existence of a 

listed species...” The issuance of a grazing permit is a Federal action that must be 

analyzed for any effects to endangered or threatened species. Through that consultation 

process, the Fish and Wildlife Service has an obligation to advise the Forest Service on 

measures it should take to minimize take of a listed species, but the Fish and Wildlife 

Service cannot suggest substantial changes to their proposed action unless that action will 

jeopardize the continued existence of the species. 

Comment: One commenter recommended that the recovery plan include a review of the 

listing of the Sierra Nevada bighorn sheep. 

Response: Under the Endangered Species Act (Act) (16 U.S.C. 1531 et seq.), we 

maintain a List of Endangered and Threatened Wildlife and Plants at 50 CFR 17.11 (for 

animals) and 17.12 (for plants). Section 4(c)(2)(A) of the Act requires that we conduct a 

review of listed species at least once every 5 years. Then, based on such reviews under 

section 4(c)(2)(B), we determine whether or not any species should be removed from the 

List (delisted), or reclassified from endangered to threatened or from threatened to 

endangered. Reviews consider the status of threats to the species, including: 1) the 

present or threatened destruction, modification, or curtailment of its habitat or range; 2) 

overutilization for commercial, recreational, scientific or educational purposes; 3) disease 

or predation; 4) the inadequacy of existing regulatory mechanisms; and 5) other natural 

or manmade factors affecting its continued existence. These reviews are not part of the 

recovery planning process. A recovery plan is a guidance document that includes 

specific actions that, if implemented, should lead to the recovery of the listed species 

(i.e., bring the species to the point where the protections of the ESA are no longer 

necessary). 

Comment: One commenter believed that the plan requires a full economic and 

environmental analysis before it can be considered for approval. 

Response: The development and approval of recovery plans are categorically excluded 

from National Environmental Policy Act (NEPA) requirements and are not required to 

incorporate economic impact analyses because recovery plans are guidance documents 

only. No agency or other entity is required by the ESA to implement the recovery 

strategy or specific recommended actions in a recovery plan. Management tasks 

identified in the plans are subject to NEPA, and therefore a full economic and 

environmental analysis, if they are proposed for implementation. In these cases, public 

involvement would be sought through the development of Environmental Assessments or 

Environmental Impact Statements. 

Comment: One commenter stated that Forest Service permits for domestic sheep grazing 

within the Bloody Creek and Dunderberg allotments are eligible for exemptions in 

accordance with ESA section 7 and that these exemptions should be granted immediately. 

The commenter requested that these exemptions be included in the recovery plan. 
194

Response: Recovery plans are guidance documents only and are not appropriate for 

regulatory issues such as exemptions. Exemption refers to exemption from take 

prohibitions defined in section 9 of the Endangered Species Act. Take is defined as “to 

harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to 

engage in any such conduct.” After formal consultation with the Fish and Wildlife 

Service, an action agency may be allowed exemption from take through the incidental 

take statement of a biological opinion. Incidental take statements exempt action agencies 

and their permittees from the ESA’s section 9 prohibitions if they comply with the 

reasonable and prudent measures and the terms and conditions of the incidental take 

statements. To be considered in an incidental take statement, any taking associated with 

an agency’s action must meet the following three criteria. The taking must not be likely 

to jeopardize the continued existence of listed species or destroy or adversely modify 

designated critical habitat, result from an otherwise lawful activity, and be incidental to 

the purpose of the action. 

Comment: One commenter faulted the plan because it ignores the findings of 

veterinarians who have studied the transmission of disease between domestic and wild 

animals and have documented the presence of disease in bighorn sheep populations that 

have had no contact with domestic sheep. 

Response: We acknowledge in the plan the fact that bighorn sheep have died from 

disease where there was not contact with domestic sheep (Section I.D.3). However, there 

is compelling scientific evidence to support the conclusion that exposure to domestic 

sheep greatly increases the risk of fatal pneumonia in bighorn sheep. 

Comment: One commenter criticized the plan for failing to cite scientific evidence that 

domestic sheep caused the decline in bighorn sheep populations. 

Response: A number of factors may have contributed to the decline of bighorn sheep in 

the western United States. Refer to Section I.C.1 and Section I.D.3 for a full discussion 

of disease die-offs in bighorn sheep. 

Comment: One commenter recommended that the plan include climatological data 

concurrent with existing population information. 

Response: Long-term temperature and precipitation data series from weather stations in 

the region are readily available from a number of sources, including the National Weather 

Service. Similarly, snowpack data are available from the California Snow Survey. 

Where we believe that weather and/or climate are factors in population regulation, these 

are noted. 

Comment: One commenter suggested that more deer be provided for mountain lions. 

Response: Deer population numbers in the eastern Sierra Nevada are determined by 

precipitation and forage. Mountain lion populations are determined by deer populations. 

A large increase in the number of deer would likely cause an increase in the mountain 
195

lion population, an increase in competition between deer and sheep for forage resources, 

and an increase in the use of sheep winter range by deer with a correlated increase in 

mountain lion use of those areas. Therefore, it is doubtful that an increase in the deer 

population would benefit bighorn sheep. 

Comment: One commenter stated that aversive conditioning of mountain lions is 

untested and that it is irresponsible to use on untested methodology with an endangered 

species. 

Response: Aversive conditioning has been tested in a limited manner with some success. 

Allowing mountain lions that do not show a predilection for killing bighorn sheep to 

maintain a home range may be an effective tool for preventing immigration by mountain 

lions that do kill sheep. The use of aversive conditioning to limit use of bighorn sheep 

winter ranges by known mountain lions could be a useful tool for enhancing bighorn 

sheep recovery efforts. 

Comment: One commenter stated that the removal for translocation of 103 individuals 

from 1979-1987 should not be dismissed as a factor in the use of lower quality habitats 

by bighorn in some areas and the subsequent decline in abundance observed in those 

areas. The removal of bighorn for translocation may have resulted in a loss of 

“knowledge,” which in turn may have been one reason for the problems mentioned 

above. 

Response: More than 30 years ago, Valerius Geist proposed the concept that bighorn 

sheep can lose knowledge of important habitats when populations are extirpated. That 

concept emerged from research in Canada where bighorn sheep must cross through 

considerable amounts of forested habitat that separate important seasonal ranges, and for 

various reasons probably does not apply to the Sierra Nevada. First, because of the rain 

shadow and precipitous nature of the eastern slope of the Sierra Nevada, forested barriers 

between summer and winter ranges are not an issue for the herd units in question; the 

sheep can simply follow steep, open ridges that connect the two. Second, the harvesting 

of sheep for translocations in no way approached extirpations. To the contrary, those 

removals were intentionally very conservative. Thus, more than 75% of the population 

remained after each translocation, and the knowledge of different habitats available for 

use was embodied in those individuals, all of whom had used those habitats over the 

previous year. For instance, following the removal of 32 sheep from the Sand Mountain 

winter range in 1986 for translocations, 109 bighorn were observed there 3 weeks later.

Comment: One commenter stated that translocations are not always successful and 

wanted to know what criteria would be used for both conducting translocations and 

determining whether or not they are successful. 

Response: Bighorn sheep are well documented to be relatively slow colonizers because 

of strong philopatry (tendency to remain in home locality), especially among females. 

Therefore, reintroduction has been the primary tool, and will continue to be the primary 

tool, used to re-establish bighorn sheep in areas where they have been extirpated. Each 
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translocation will be evaluated, but criteria have not yet been established. A variety of 

factors, including long-term persistence and genetic diversity, will likely be evaluated for 

all future translocations; these factors will be included in future translocation plans (see 

Appendix C). 

Comment: One commenter recommended that a protocol be developed for sampling live 

and dead bighorn sheep. 

Response: Fecal DNA methodologies have been established. Sampling of live bighorn is 

standardized on field data sheets filled out during collection of samples from live 

animals. Examinations of dead bighorn sheep are conducted by the San Bernardino and 

Davis branches of the California Animal Health and Food Safety Lab System according 

to their standard necropsy protocols for ruminants and with consultation from California 

Department of Fish and Game veterinarians. Formalized sample collection and disease 

testing protocols for live and dead bighorn sheep are currently under development. 

Comment: One commenter noted that the management strategy for domestic sheep has 

always focused on domestic sheep straying into bighorn sheep areas. The commenter 

recommended that there should also be a strategy for bighorn sheep moving onto 

domestic sheep allotments. 

Response: This document incorporates a strategy for preventing contact between 

domestic sheep and bighorn sheep (Section E) that identifies actions that should be taken 

to prevent bighorn sheep from moving onto some domestic sheep grazing allotments in 

areas where such a program is logistically feasible and meets our recovery objectives. 

Comment: One commenter suggested that mountain lion predation should be the focus of 

the recovery plan. 

Response: Although mountain lion predation is one factor in bighorn recovery, we 

disagree that it should be the focus of the plan. Predator control is just one part of a 

strategy for increasing survival of bighorn sheep and meeting recovery objectives, which 

are outlined in the plan. 

Comment: One commenter recommended that the recovery plan should also address 

other predators, including coyotes and golden eagles. 

Response: We are not aware of any data that suggest predators other than mountain lions 

have had a substantial impact on bighorn sheep in the Sierra Nevada. Predation in 

general is discussed in Section I.D.3 of the recovery plan. 

Comment: One commenter was concerned that the recovery plan will negatively affect 

domestic sheep grazing. 

 

Response: Recovery plans do not obligate cooperating or other parties to undertake 

specific tasks, but delineate reasonable actions required to recover and/or protect listed 
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species. We acknowledge that some grazing operations may be modified in response to 

our recommendations. However, if an agency were to undertake a task outlined in the 

plan that would affect domestic sheep grazing, the agency would continue to work with 

all affected parties to accommodate the needs of the permit holders while working to 

achieve the goals outlined in the recovery plan. 

Comment: One commenter was concerned that the plan indicates the potential need for 

future restrictions on recreational users, but fails to specify what those actions might be. 

Response: The recovery plan states that any actions limiting recreational use will take 

place only if research results in a recommendation to limit human use in some areas. At 

present, there appear to be few locations where recreational disturbance has the potential 

to significantly affect sheep. Because the research needed to address this issue has not 

been completed, it would be premature to speculate about these actions. 

Comment: One commenter believed the potential effects of off-trail recreation and 

mountain climbing on new herds that have become established and proposed future herd 

ranges have not been adequately addressed in the plan. 

 

Response: Although we recognize the potential of recreation to impact bighorn sheep, 

these impacts seem to be minor. However, the recovery plan calls for continued 

monitoring of the compatibility between recreational use of bighorn sheep habitat and 

bighorn sheep recovery (see Task 6.4). 

Comment: One commenter recommended that a PVA should be done prior to the 

issuance of the final plan. 

Response: The California Department of Fish and Game’s Sierra Nevada Bighorn Sheep 

Recovery Program is initiating an in-depth, spatially explicit population viability 

analysis. For such an analysis to be meaningful, it is essential that we incorporate 

detailed and accurate values for model parameters. Data for all recovery units are being 

collected and compiled to ensure that modeling is representative across the range of the 

species. Long-term viability will be examined using demographic, habitat, and genetic 

data. To understand population trajectories, our detailed analysis will include factors as 

varied, but interrelated, as vital rates, forage conditions, climate, habitat suitability, and 

inbreeding. 

Comment: One commenter stated that the plan does not provide protection for critical 

migration corridors between proposed recovery units despite the fact that they are 

threatened by development. 

Response: Recovery plans are guidance documents only. Recovery plans do not create 

reserves or restrict development. However, recovery plans are dynamic documents, and 

as more information on migration corridors becomes available, this information will be 

incorporated into the plan. This information may result in additional action items as 

necessary. 
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Comment: One commenter recommended that the plan should include objective, 

measurable criteria for determining whether reasons for avoidance of winter range have 

been addressed. 

Response: We use the best available science in preparing recovery plans. If new 

scientific information on winter range avoidance becomes available, we will incorporate 

that information into the next version of the plan. New information may result in the 

addition of new action items to the plan or changes in existing ones.

Comment: One commenter believed that the Fish and Wildlife Service should 

recommend permanent mineral withdrawal on all lands in bighorn sheep habitat. 

Response: We are not aware of any information that indicates mining activities are 

incompatible with the recovery of the Sierra Nevada bighorn sheep. Those mines on 

Federal lands or that have a Federal nexus are subject to section 7 of the ESA. 

Comment: One commenter suggested periodic sampling of the closest herds of domestic 

sheep and goats to look at changes in time of both wild and domestic populations. These 

data could be important for determining the source of pathogens in the event of a disease 

outbreak in bighorn sheep. 

Response: When captured, Sierra Nevada bighorn sheep receive a physical examination 

and a bank of diagnostic tests. Blood is collected for a complete blood count and 

chemistry panel, trace mineral analysis, and serology for potential viral and bacterial 

sheep pathogens. Pharyngeal swabs are taken for Pasteurella isolation and identification. 

No similar effort is being made at this time for domestic sheep and goats. Currently, 

there are no serology or microbiology techniques that could definitively tie a die-off to a 

specific band of domestic sheep. 

 

Comment: One commenter encouraged a review of what has been done in other areas 

subsequent to a pneumonia outbreak. 

Response: Various responses to ongoing pneumonia outbreaks have proven ineffective. 

During the Hell’s Canyon pneumonia epizootic in 1996, 72 live bighorn sheep were 

removed from the outbreak area and placed into captivity for treatment. All 72 sheep 

developed pneumonia and died. Various strategies for antibiotic treatment of sick 

bighorn sheep have been developed. Single treatments of individual, free-ranging 

bighorn sheep with antibiotics may suppress bacterial growth temporarily, but infection 

will usually run its course despite treatment. Treatment may also prolong the shedding 

period, thus exposing more bighorn sheep. There are currently no vaccines that will 

prevent infection or disease from Pasteurella pneumonias in bighorn sheep. These 

unsuccessful efforts to stop ongoing outbreaks dictate the cautious approach to proximity 

of domestic and bighorn sheep, and lead us to conclude that prevention is more 

appropriate than reaction. 
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Comment: One commenter was concerned with the emphasis of the plan being research. 

With fewer than 250 individuals, this population does not lend itself to being a test bed 

for theoretical management. 

Response: The focus of the recovery program is to conserve the Sierra Nevada bighorn 

sheep. We do not agree with the commenter that the focus of this recovery plan is 

research, but we acknowledge that research is one component of the plan. The California 

Department of Fish and Game’s Sierra Nevada Bighorn Sheep Recovery Program 

collects data on population status and trends and the underlying factors that influence 

them in an effort to ensure the long-term persistence of Sierra Nevada bighorn sheep. We 

believe that gathering information to improve our understanding of Sierra Nevada 

bighorn sheep and the factors that limit them, will contribute to their conservation and 

recovery. 

Literature Cited 

Ramey, R. R. 1995. Mitochondrial DNA variation, population structure and evolution of 

mountain sheep in the southwestern United States and Mexico. Molecular 

Ecology 4:429-439. 

U.S. Fish and Wildlife Service and National Oceanic and Atmospheric Administration. 

1996. Policy regarding the recognition of distinct vertebrate population segments 

under the Endangered Species Act. Federal Register 61:4722-4725. February 7, 

1996.