Draft Mexican Wolf Conservation Assessment 

U.S. Fish and Wildlife Service 

Southwest Region (Region 2) 

Albuquerque, New Mexico 
Disclaimer

Data from the Mexican Wolf Blue Range Reintroduction Project used in this document spans 

from 1998 to August 1, 2008, or for a range of years within this time period. Some data is 

only available in published form in annual reports, and thus is reported only through 2007. 

After the public comment period, the final conservation assessment will be updated with new 

data as appropriate. 

2
Acknowledgments

The following U.S. Fish and Wildlife Service (Service) staff have been instrumental in 

promoting and supporting the development of this document: Benjamin N. Tuggle, Regional 

Director, Region 2; Wendy Brown, Region 2 Recovery Coordinator; John Morgart, former 

Mexican Wolf Recovery Coordinator; Steve Chambers, Region 2 Senior Scientist; and 

John Slown, Biologist. Maggie Dwire, Assistant Mexican Wolf Recovery Coordinator, and 

John Oakleaf, Mexican Wolf Field Coordinator, contributed tremendous time, information, 

and institutional knowledge of the program without which this document would be 

incomplete. The Mexican Wolf Adaptive Management Oversight Committee (AMOC) 

members also contributed profoundly to the development of the document with their insights 

and critique. In particular, AMOC members Terry Johnson – Arizona Game and Fish 

Department (AGFD), Matt Wunder and former AMOC member Chuck Hayes – New Mexico 

Department of Game and Fish (NMDGF), Dave Bergman - U.S. Department of Agriculture – 

Wildlife Services (USDA-WS), and Cathy Taylor – U.S. Forest Service (USFS) provided 

substantive feedback. 

Most importantly, the Southwest District Population Segment (SWDPS) Recovery Team, 

especially the Technical Subgroup, contributed the ideas that form the foundation of this 

document. This recovery team was convened by the Southwest Region of the Service in 

2003 to revise the 1982 Mexican Wolf Recovery Plan. This document intends to capture the 

scientific concepts and information that they discussed before the planning process was put 

on hold by the Service in 2005 due to litigation. Their work has not been resumed, although 

the agency maintains its intent to develop a revised plan when circumstances permit. 

3
Literature Citation and Availability

Literature citation should read as follows: 

U.S. Fish and Wildlife Service. 2008. Draft Mexican Wolf Conservation Assessment. 

Region 2, Albuquerque, New Mexico, USA. 

Copies of the draft document can be requested from: 

U.S. Fish and Wildlife Service 

New Mexico Ecological Services Field Office 

2105 Osuna Drive NE 

Albuquerque, New Mexico 87113 

Telephone #: 505-346-2525 or 1-800-299-0196 

Fax #: 505-346-2542 

U.S. Fish and Wildlife Service 

Southwest Regional Office 

P.O. Box 1306 

Albuquerque, New Mexico 87103-1306 

Telephone #: 505-248-6920 

Fax #: 505-248-6788 

Copies are also available on-line at: 

http://www.fws.gov/southwest/es/mexicanwolf 

4
FOREWORD 

A conservation assessment, unlike a recovery plan, is not a document required by or defined 

in the Endangered Species Act of 1973 (ESA), as amended (16 U.S.C. 1531 et seq.) or 

related policies. It has no predetermined format or content mandated by law or policy. 

Rather, this is a unique document developed in response to the unique needs of the Service at 

this time. It has been over 20 years since the completion of the 1982 Mexican Wolf 

Recovery Plan, and an up-to-date description and assessment of the gray wolf (Canis lupus) 

recovery effort in the Southwest is needed. 

The purpose of this conservation assessment is to provide information relevant to the 

conservation and recovery of the gray wolf. Specifically, the document may provide 

background information needed for future gray wolf recovery planning or policy decisions 

pertaining to the southwestern region of the country. The scope of the document is limited to 

biological science and related disciplines in order to provide an up-to-date assessment of and 

scientific basis for gray wolf recovery in the Southwest. The social and economic facets of 

gray wolf recovery are recognized as equally important, but are beyond the realm of 

information this document strives to provide. 

The terms used to identify the wolf that is the subject of this conservation assessment are 

subtle but distinct. The generic gray wolf, Canis lupus, is the entity listed on the List of 

Endangered and Threatened Wildlife (50 CFR 17.11(h)) and protected by the ESA; therefore, 

it is appropriate from a policy, and at times biological, standpoint to use the term “gray 

wolf.” Due to the Service’s regional division of gray wolf recovery efforts, it is also useful at 

times to refer to the gray wolf in specific regions of the country. Thus, when the term “gray 

wolf” is used in reference to the Service’s gray wolf recovery programs in the MountainPrairie and Pacific regions or the Great Lakes, Big Rivers Region, it describes the gray 

wolves located there. In the Southwest, the situation becomes more complex. Here, the 

regional gray wolf recovery focus has been on the Mexican gray wolf (Mexican wolf), Canis 

lupus baileyi, a subspecies of gray wolf that historically inhabited the southwestern region of 

the United States and Mexico. Since this program, from a policy standpoint, is a regional 

program for gray wolf recovery, the assessment refers to “gray wolf recovery in the 

Southwest.” The assessment uses the term “Mexican wolf” when providing biological 

information specific to the subspecies, as well as in the context of the agency’s commitment 

to conserve the subspecies, the ongoing Mexican wolf reintroduction and captive breeding 

program, and the subspecific focus of the 1982 Mexican Wolf Recovery Plan. While these 

various terms are used for clarity and adherence to policy, they may unfortunately cause 

confusion. However, the assessment does not change the listed status of, commitment to, 

focus of, or any other aspect of the Service’s existing wolf program in the Southwest Region 

or any other region. 

The Southwest Region of the Service includes the states of Arizona, New Mexico, 

Oklahoma, and Texas. Gray wolf recovery efforts to date have taken place in Arizona and 

New Mexico, namely the reintroduction of the Mexican wolf to the wild. However, southern 

portions of Colorado and Utah have been included in recent Service policy decisions related 

to the Southwest that were overturned by court decisions (see Status and Implications of 

5
National Gray Wolf Recovery for the Mexican Wolf). Thus, the assessment does not attempt 

to define “Southwest” or “southwestern” in recognition that such definitions are context 

dependent, but instead uses these terms broadly as a general reference to this region of the 

country. When precise locations are required for accuracy, they are provided. 

The document is organized in three main sections. “History of the Gray Wolf Recovery 

Program in the Southwest” briefly reviews the decline of the gray wolf in the Southwest and 

the inception of national recovery efforts for the gray wolf pursuant to the ESA, focusing on 

the development of a captive breeding program and reintroduction project for the Mexican 

wolf. “Gray Wolf Biology and Ecology” provides an overview of basic gray wolf biology 

and ecology, with descriptive information on the Mexican wolf where available and 

informative. Synthesized data from the 5-Year Review of the reintroduction project is 

provided throughout this section, in some cases updated with annual data from the years 

following the review (2003-July 2008). “Conservation Assessment” assesses the gray wolf 

recovery effort in the Southwest by conducting a 5-factor analysis to ascertain the security of 

the reintroduced population and by identifying the conservation principles that provide the 

foundation for gray wolf recovery and discussing the degree to which the current recovery 

effort in the Southwest embodies these principles. “Summary statements” throughout the 

document serve as focal points of the assessment. These statements are not 

recommendations, nor do they have any regulatory standing. Rather, they are provided as a 

communication tool. 

6
EXECUTIVE SUMMARY

HISTORY OF THE GRAY WOLF RECOVERY PROGRAM IN THE SOUTHWEST 

The Mexican wolf was listed as an endangered subspecies in 1976 due to near extinction 

resulting from predator extermination programs in the late 1800s and early to mid-1900s. 

This subspecies of gray wolf historically inhabited the southwestern United States and 

Mexico. In 1978, the Service subsumed this and several other gray wolf subspecies listings 

into a species-level listing for the gray wolf in order to protect the species throughout its 

range in the coterminous United States and Mexico. The Service initiated three regional 

recovery programs for the gray wolf; in the Southwest Region, a recovery plan was 

developed for the Mexican wolf, solidifying the regional gray wolf recovery focus on the 

conservation of this subspecies. The 1982 Mexican Wolf Recovery Plan recommended a 

two-pronged approach to recovery (i.e., establishment of a captive breeding program and 

reintroduction of wolves to the wild) but did not establish recovery criteria for the region, as 

did the 1992 Recovery Plan for the Eastern Timber Wolf and the 1987 Northern Rocky 

Mountain Wolf Recovery Plan for their respective regions of the country. A range-wide 

recovery plan for the gray wolf has never been developed. 

Today, an international Mexican wolf captive breeding program has been established and 

Mexican wolves have been reintroduced to the wild in Arizona and New Mexico in a 

nonessential experimental population pursuant to section 10(j) of the ESA. The reintroduced 

Mexican wolf population numbers approximately 50 wolves, the halfway point of the 10(j) 

objective to establish a single population of at least 100 wolves. The growth of this 

population has lagged behind initial projections for achieving the population objective, likely 

due to a combination of biological, sociological, and regulatory factors. 

Although substantial progress in implementing the 1982 Mexican Wolf Recovery Plan has 

been achieved, a revised recovery plan has never been developed to establish recovery 

criteria for the region. Thus, other than the population objective for the reintroduced 

Mexican wolf population in Arizona and New Mexico, the gray wolf recovery effort in the 

Southwest operates without any guidance in terms of the number and distribution of wolves 

considered adequate for recovery and delisting. 

 

GRAY WOLF BIOLOGY AND ECOLOGY 

The gray wolf, Canis lupus, is a member of the dog family (Canidae; Order Carnivora). 

Five subspecies of gray wolf are currently recognized in North America, including the 

Mexican wolf. 

Gray wolves are typically a mottled gray, but pelt color can range from white, cream, brown 

and red, to dark gray and black. Mexican wolves tend to be patchy black, brown to 

cinnamon, and cream in color. Gray wolves typically weigh between 80-120 lbs, are 5-6.5 ft 

long from tip of nose to tip of tail, and 2-2.5 ft high at the shoulder. The Mexican wolf is 

somewhat smaller; adults weigh 50-90 lbs with a length of 5-6 ft and height at shoulder 2-2.5 

ft. 

7
Wolves typically live 4 to 5 years in the wild, reaching sexual maturity at 2 years of age. 

Female wolves produce a litter of several pups each spring. Offspring remain with their 

family until they disperse to establish a new territory. These hierarchical family units are 

referred to as packs. 

Wolves are top predators that have flexibility in using different prey and habitats. 

Historically, wolves occupied every habitat in the northern hemisphere that supported 

populations of large hoofed mammals (ungulates). Wolf packs establish territories in which 

they hunt for prey, primarily pursuing medium to large hoofed mammals. Historically, 

Mexican wolves were associated with montane woodlands characterized by sparsely- to 

densely-forested mountainous terrain and adjacent grasslands in habitats found at elevations 

of 4000-5000 ft where ungulate prey were numerous. 

Wolves may interact with other predators, including coyotes (C. latrans), mountain lions 

(Puma concolor), and black bears (Ursus americanus). Wolves may also interact with 

humans, although wild, unhabituated wolves are generally not considered a threat to humans. 

CONSERVATION ASSESSMENT 

Threats to the Gray Wolf in the Southwest

Species are listed as threatened or endangered if it is determined that one or more of the 

following five factors in section 4(a)(1) of the ESA are responsible for their condition. These 

five factors are reassessed periodically while the species is listed to evaluate its status and 

ensure that conservation actions are appropriately tailored to address current threats to the 

species. 

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

or range 

The three fundamental ecological conditions necessary for wolf habitat include large area 

size, adequate prey, and security from human-caused mortality. Threats related to the 

destruction, modification, or curtailment of these conditions do not likely threaten the 

Mexican wolf at the current time, based on an increase in the area available to reintroduced 

wolves since the project began, lack of indication that wolves are food-limited, and a 

relatively small number of vehicular-related wolf deaths each year (other sources of humancaused mortality are considered under Factor D and Factor E). Future habitat availability for 

wolves may decrease over time due to human population growth and resultant development 

on public and private lands. 

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

Overutilization for commercial, recreational, scientific, or educational purposes is not 

considered a threat to the Mexican wolf because the Service does not authorize legal killing 

or removal of wolves from the wild for commercial, recreational (i.e., hunting), scientific, or 

educational purposes, illegal killing or trafficking for pelts is not know to occur, and nonlethal techniques are used during Mexican wolf research in the reintroduced and captive 

populations. 

8
(C) disease or predation 

A number of viral, fungal, and bacterial diseases and endo- and ectoparasites have been 

documented in gray wolf populations. There is little research specific to disease or 

contaminant issues in Mexican wolves, and only one wolf death due to disease (distemper) 

has been documented in the wild population. Mexican wolves are routinely vaccinated for 

rabies, distemper, parvovirus, and corona virus before release to the wild from captive 

facilities. Disease is not considered a threat to the Mexican wolf based on known 

occurrences in the reintroduced population and the active vaccination program. 

Predation is not considered a threat to the Mexican wolf because no wild predator regularly 

preys on wolves and only a small number of predator-related wolf mortalities have been 

documented in the reintroduced population. 

(D) the inadequacy of existing regulatory mechanisms 

A number of concerns have been raised regarding the adequacy or appropriate 

implementation of regulatory mechanisms being applied to the Mexican wolf reintroduction 

project, including: 1) the internal and external boundaries of the Blue Range Wolf Recovery 

Area (BRWRA), including the configuration of the Primary and Secondary Recovery Zones 

and the regulations governing removal of wolves due to boundary violations; 2) regulations 

or management procedures for livestock management (e.g., carcass removal); 3) management 

procedures related to livestock depredation (i.e., Standard Operating Procedure 13 (SOP 13)); 

4) implementation of conservation actions by Federal agencies pursuant to section 7(a)(1) of 

the ESA; and, 5) the alleged transfer of management authority of the reintroduction project 

from Service to the AMOC; and 6) failure to complete a revision of the 1982 Mexican Wolf 

Recovery Plan with objective and measurable delisting criteria, as required by the ESA. 

Modifications in implementation of ESA regulatory mechanisms that will support the 

reintroduction and recovery effort are being evaluated by the Service. 

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

In the Southwest, illegal killing of wolves is the single greatest source of wolf mortality in 

the reintroduced population. However, human-caused mortality in the Blue Range 

population is in line with FEIS mortality-rate projections and is therefore not considered a 

threat to the population at the current time. Public opinion has long been recognized as a 

significant factor in the success of gray wolf recovery efforts and illegal killing of wolves by 

those opposed to wolf reintroduction and recovery efforts is proof of its importance. In the 

Southwest, extremes of public opinion vary between those who strongly support or object to 

the recovery effort. Illegal take of wolves provides an indication of the level of social 

tolerance of the Mexican wolf reintroduction. In the BRWRA, illegal shooting of wolves has 

been the biggest single source of mortality since the reintroduction began in 1998. Although 

combined sources of human-caused mortality are in line with project projections and are less 

than that observed in other gray wolf populations, the Mexican wolf could be more 

susceptible to population decline at a given mortality rate than other gray wolf populations, 

based on lower reproductive rates, smaller litter sizes, and combined sources of mortality. 

9
When wolf mortalities are combined with wolf removals (which may function as the 

equivalent to mortality if the wolf is permanently removed), the combined mortality/removal 

rate is higher than projections and is occurring at a level inconsistent with natural population 

growth. Human-caused mortality of Mexican wolves, of which illegal shooting is a 

significant proportion, in combination with removal actions, are hindering the population’s 

growth toward the population objective of at least 100 wolves. 

The Conservation Principles of Resiliency, Redundancy, and Representation

The principles of resiliency, redundancy, and representation represent a recently popularized 

conceptualization of key elements of biological diversity conservation and provide a useful 

framework for discussing scientific concepts relevant to gray wolf conservation and recovery 

in the Southwest, including demography, environmental variability, and genetics. The 

Service has invoked these principles to describe recovery efforts for the gray wolf in the 

Northern Rockies and Great Lakes, and for consistency, the conservation assessment uses 

these principles in similar fashion. 

Resiliency 

The principle of resiliency suggests that species that are more numerous and widespread are 

more likely to persist than those that are not. That is, a species represented by a small 

population faces a higher risk of extinction than a species that is widely and abundantly 

distributed due to the sensitivity of small populations to stochastic (that is, uncertain) 

demographic events. In small populations, including those with a positive growth rate, it is 

more likely that a wide deviation from average birth or survival results could result in a 

decline toward extinction from which the population would not be able to recover. Thus, as a 

population grows larger and individual events tend to average out, the population becomes 

less susceptible to demographic stochasticity. There is not a single population size that will 

ensure persistence. Rather, populations of various sizes, vital rates, and biological and 

ecological characteristics will simply have different risks of extinction. 

A variety of methods are available for estimating a species’ likelihood of 

persistence/extinction risk, ranging from complex theoretical or simulation models to simple 

observation of existing populations or best professional judgment. Viable wolf populations 

have been estimated in the scientific literature and previous gray wolf recovery plans as those 

that number in the hundreds to the thousands, depending on a number of factors. A current, 

complete, peer-reviewed viability analysis of the objective to establish a population of at 

least 100 wolves in the Southwest has not been conducted to determine the extinction risk 

faced by this population. No other population objective (i.e., recovery criteria) has been 

determined for the Southwest Region upon which to evaluate the degree to which the current 

reintroduced population establishes or contributes to regional resiliency. 

Redundancy 

Redundancy refers to the existence of redundant, or multiple, populations spread throughout 

a species’ range. It advances the notion that a species’ likelihood of persistence generally 

increases with an increase in the number of sites it inhabits because it allows for populations 

10
to exist under different abiotic and biotic conditions, thereby providing a margin of safety 

that random perturbation (or, variation) affects only one, or a few, but not all, populations. 

Random variations in the environment that in turn affect the demography of a population are 

referred to as environmental stochasticity. Environmental stochasticity may take the form of 

variation in available resources (e.g., prey base), or in direct mortality (e.g., a disease 

epidemic). Extreme environmental events, referred to as catastrophic, including events such 

as wildfire, drought, or a disease epidemic, may result in drastic, rapid population declines. 

The scientific literature does not recommend a specific number or range of populations 

appropriate for conservation efforts, although rule of thumb guidelines for the reintroduction 

of a species from captivity recommends that at least two populations be established that are 

demographically and environmentally independent. 

 

When a species is distributed in redundant populations, there are two possible relationships 

between the populations: they can be completely isolated from each other, or they can be 

connected with one another through the dispersal of individual animals. If connectivity 

between populations is desired, conservation efforts must ensure that the distance between 

populations is compatible with wolf dispersal abilities and that the habitat through which 

individuals will be dispersing is of sufficient quality and quantity to support immigration. 

Alternatively, artificial immigration between populations must be accomplished through the 

translocation of wolves by management. For a species that has been extirpated from so much 

of its historic range, explicit effort must be made to recreate redundancy. 

Numerous habitat assessments have been conducted to identify possible areas for 

reestablishment of the gray wolf in Arizona, New Mexico, Utah, Colorado, and Mexico. 

However, the number of redundant populations and related connectivity appropriate for 

recovery in the Southwest has not been specified. The establishment of a single population 

provides the least amount of redundancy, and therefore the least possible security against 

extinction risk from environmental variation. 

Representation 

Representation refers to the genetic diversity represented by members of a population or 

species, specifying that higher levels of diversity better support ecological and evolutionary 

processes than low levels. Representation also suggests that a species should be conserved in 

a variety of habitats in order to conserve ecosystem structure and function. 

Attention to genetic structure and diversity may be a critical component of conservation 

efforts for small populations due to the likelihood for genetic drift to occur. Genetic drift 

refers to genetic changes in populations due to random fluctuations in allele frequency. It 

can influence the persistence of a population through several outcomes, including loss of 

phenotypic variation, loss of adaptive potential, and the buildup of harmful mutations, 

including mitochondrial mutations. Small populations are also at greater risk of inbreeding 

depression (a reduction of fitness due to inbreeding) due to the smaller pool of unrelated 

potential mates available as compared to a larger population. 

11
Effective population size can be defined as the size of the ideal population that will result in 

the same amount of genetic drift as the population being considered. Effective population 

size, rather than the census population size, provides a measuring stick for determining a 

population’s risk of genetic drift and inbreeding. For the gray wolf, social structure greatly 

affects which wolves mate. The effective population size of a census population of 100 

Mexican wolves has been estimated at approximately 28 wolves. 

Several general (non-species specific) rules of thumb have been presented in the scientific 

literature to inform efforts for conservation of a species’ or populations’ genetic diversity, 

ranging from effective population sizes of several dozens of animals to avoid immediate 

fitness-related issues, to effective population sizes of hundreds to thousands of animals to 

preserve long-term adaptive potential. 

Intensive management of genetic diversity has been an integral component of the Mexican 

wolf captive breeding program and reintroduction project due to the small number of 

founders upon which the captive breeding program was established. Management has 

focused on ensuring the representation of genes from each of the three founding lineages in 

both the captive and wild populations and on the continued maximization of overall gene 

diversity retention. Inbreeding depression has been observed in captive and reintroduced 

wolves. Determination of an effective population size for regional gray wolf recovery in the 

Southwest has not been made, and thus the degree to which the reintroduced population 

contributes to representation cannot be evaluated. 

CONCLUSION 

The gray wolf recovery effort in the Southwest Region consists of a Mexican wolf captive 

breeding program and a reintroduction project to reestablish a population of at least 100 

wolves in the wild. As envisioned by the 1982 Mexican Wolf Recovery Plan, these efforts 

have ensured the survival of the Mexican wolf. Although lagging behind population growth 

projections, the current reintroduced population is relatively secure from threats. 

However, recovery criteria have not been developed to provide a broader perspective for the 

significance of the reintroduced population. Consideration of the principles of resiliency, 

redundancy, and representation suggest that larger populations have less extinction risk than 

smaller populations, multiple populations enhance the likelihood of species’ persistence more 

than a single population, and short-term fitness and long-term adaptive potential of 

populations is best supported by establishing larger, rather than smaller, effective population 

sizes. Although the degree to which the Blue Range population contributes to resiliency, 

redundancy, and representation is precluded by a lack of recovery criteria against which the 

population objective to establish a single population of at least 100 wolves can be evaluated, 

it is clear that the establishment of this population does not achieve resiliency, redundancy, 

or representation. 

12
ABBREVIATIONS AND ACRONYMS 

AGFD Arizona Game and Fish Department 

AMOC Adaptive Management Oversight Committee 

AMWG Adaptive Management Working Group 

APA Administrative Procedures Act of 1946 

AZA Association of Zoos and Aquariums 

Blue Range population Wolves in the BRWRA, FAIR, and surrounding areas 

BRWRA Blue Range Wolf Recovery Area 

DPS Distinct Population Segment 

EIS Environmental Impact Statement 

ESA Endangered Species Act of 1973, as amended 

FAIR Fort Apache Indian Reservation 

FEIS Final Environmental Impact Statement of 1996 (for proposed 

reintroduction of Mexican wolves 

Final Rule Final “nonessential experimental population” or “10(j)” rule of 

1998 for Mexican wolf reintroduction in Arizona and New 

Mexico 

Great Lakes USFWS gray wolf recovery program administered out of the 

Great Lakes, Big Rivers Region (Region 3) 

IFT Interagency Field Team (for the Reintroduction Project, see 

below) 

MVP Minimum Viable Population 

MWEPA Mexican Wolf Experimental Population Area 

NEPA National Environmental Policy Act of 1969 

NMDGF New Mexico Department of Game and Fish 

Northern Rockies USFWS gray wolf recovery program administered out of the 

Mountain-Prairie Region (Region 6) and Pacific Region 

(Region 1) 

PVA Population Viability Analysis 

SOP Standard Operating Procedure for the Reintroduction Project 

SSP Species Survival Program 

SWDPS Southwestern Gray Wolf Distinct Population Segment 

USDA-WA US Department of Agriculture-Animal Plant Health Inspection 

Service Wildlife Services 

USFWS US Fish and Wildlife Service 

USFS USDA Forest Service 

WMAT White Mountain Apache Tribe 

13
TABLE OF CONTENTS 

FOREWORD .................................................................................................................... 5

EXECUTIVE SUMMARY .............................................................................................. 7 

ABBREVIATIONS AND ACRONYMS ......................................................................... 13 

HISTORY OF THE GRAY WOLF RECOVERY PROGRAM IN THE 

SOUTHWEST .................................................................................................................. 15

The Decline of the Gray Wolf in the Southwestern United States ................................... 15 

The Road to Recovery for the Gray Wolf ......................................................................... 16 

Status and Implications of National Gray Wolf Recovery for the Mexican Wolf ............ 22 

State and International Regulatory Protection in the Southwestern United States 

and Mexico........................................................................................................................ 24 

GRAY WOLF BIOLOGY AND ECOLOGY .................................................................. 25 

Taxonomy and Range ....................................................................................................... 25 

Physical Description and Life History .............................................................................. 27 

Pack Formations and Movements ..................................................................................... 29 

Ecology and Habitat Description ...................................................................................... 30 

Wolves and Non-prey ....................................................................................................... 33 

Wolf-Human Interactions ................................................................................................. 33 

CONSERVATION ASSESSMENT ................................................................................. 35 

Threats to the Gray Wolf in the Southwest ....................................................................... 35 

Factor A ................................................................................................................ 36 

Factor B ................................................................................................................ 39 

 Factor C ................................................................................................................ 40 

 Factor D ................................................................................................................ 42 

 Factor E ................................................................................................................ 46 

The Conservation Principles of Resiliency, Redundancy, and Representation ................ 49 

Resiliency .............................................................................................................. 49 

Redundancy ........................................................................................................... 54 

Representation ...................................................................................................... 58 

CONCLUSION ................................................................................................................. 64

LITERATURE CITED ..................................................................................................... 66 

APPENDIX A: FIGURES ............................................................................................... 81 

Figure 1: Mexican Wolf Blue Range Recovery Area ...................................................... 81 

Figure 2: Photo of Mexican Wolf .................................................................................... 82

14
HISTORY OF THE GRAY WOLF RECOVERY PROGRAM IN THE SOUTHWEST 

The Decline of the Gray Wolf in the Southwestern United States 

Gray wolves were once abundant and widespread in North America; presettlement, the gray 

wolf ranged from the Canadian high arctic through the United States to central Mexico 

(Wayne and Vilá 2003, Mech 1970). Prior to the late 1800s, gray wolves ranged across the 

landscape of the southwestern United States in montane forests and woodlands (Young and 

Goldman 1944). Mexican wolves were abundant in the Sierra Madre and outlying mountain 

ranges in Mexico, and frequented the borderlands between Mexico and the United States 

(Brown 1983). In southern Arizona, Mexican wolves inhabited the Santa Rita, Tumacacori, 

Atascosa-Pajarito, Patagonia, Chiricahua, Huachuca, Pinaleno, and Catalina mountains, west 

to the Baboquivaris and east into New Mexico (Brown 1983). In central and northern 

Arizona, Mexican wolves and several other formerly recognized subspecies of gray wolf 

were interspersed (Brown 1983). Mexican wolves and up to four formerly recognized 

subspecies were present throughout New Mexico, with the exception of low desert areas, and 

were documented as numerous or persisting in areas including the Mogollon, Elk, Tularosa, 

Diablo and Pinos Altos mountains, the Black Range, Datil, Gallinas, San Mateo, Mount 

Taylor, Animas, and Sacramento mountains (Brown 1983). The gray wolf was found 

eastward into the Trans-Pecos region of Texas, Oklahoma, and northward into the Rocky 

Mountains, including the states of Montana, Idaho, Wyoming, and Colorado (Young and 

Goldman 1944). In Colorado, gray wolves inhabited both sides of the Continental Divide, 

including the eastern plains (Young and Goldman 1944). In Utah, gray wolves were 

restricted to the southern and eastern portions of the state. 

Population estimates of gray wolves, and specifically Mexican wolves, prior to control 

actions in the late 1800s and early to mid 1900s are not available for the Southwest or 

Mexico. This is due primarily to a lack of available data on wolf abundance, but also to 

difficulty in interpreting anecdotal accounts of wolf abundance in light of evolving gray wolf 

taxonomy (see Taxonomy and Range). Anecdotal pre-colonization estimates for 

New Mexico suggested a state-wide population of about 1500 gray wolves (Bednarz 1988). 

It has been hypothesized that close to 400,000 gray wolves likely inhabited the western 

United States (Leonard et al. 2005). 

As human settlement intensified across the Southwest in the 1800s, the conflict between 

wolves and humans, primarily due to wolf depredation of livestock, also intensified. 

Individual wolves gained infamy for purported levels of depredation, although the validity of 

some of these accounts is questionable (Gipson et al. 1998, Gipson and Ballard 1998). 

Federal control programs and extermination campaigns, coupled with habitat alteration 

resulting from the intensification of agriculture and livestock operations, led to the near 

extinction of the gray wolf in the Southwest by the early 1900s (Brown 1983). By 1925, 

poisoning, hunting, and trapping efforts had drastically reduced wolf populations in all but a 

few remote areas of the southwestern United States, and control efforts shifted to wolves in 

the borderlands between the United States and Mexico (Brown 1983). Bednarz (1988) 

estimated that breeding populations of Mexican wolves were extirpated from the United 

States by 1942. The use of increasingly effective poisons and trapping techniques during the 

15
1950s and 1960s eliminated remaining wolves north of the border. Occasional reports of 

wolves crossing into the United States from Mexico persisted to the 1960s, and small pockets 

of wolves likely persisted in Mexico until the 1980s. McBride (1980) estimated that fewer 

than fifty breeding pairs of Mexican wolves inhabited Mexico by 1978. 

The Road to Recovery 

With the passage of the ESA, the legal relationship of the Service to the gray wolf changed 

dramatically. Formerly a proponent of efforts to exterminate the wolf, the agency became 

responsible for the conservation and recovery of species protected by the ESA, including the 

gray wolf. The Service originally added the Mexican wolf to the list of threatened and 

endangered species as a subspecies (41 FR 17736-17740, April 28, 1976), but soon 

subsumed this and several other gray wolf subspecies listings into a species-level listing for 

the gray wolf in order to protect the species throughout its range in the coterminous United 

States and Mexico (43 FR 9607-9615, March 9, 1978). This reclassification provided a 

commitment that the Service would maintain a conservation focus on recognized gray wolf 

subspecies in the future although it simultaneously recognized that some of the gray wolf 

taxonomy used in previous subspecies listings was out of date. 

Soon after the range-wide listing of the gray wolf in 1978, the Service initiated several 

independent regional recovery programs to recover the gray wolf. These recovery programs 

were centered in three core geographic areas: Minnesota, Michigan, and Minnesota (“Great 

Lakes”, administered by the Service’s Great Lakes, Big Rivers Region); Idaho, Montana, and 

Wyoming (“Northern Rockies”, administered by the Service’s Mountain-Prairie Region and 

Pacific Region); and Arizona and New Mexico, with coordination with Mexico (administered 

by the Service’s Southwest Region). Recovery plans were developed by the three recovery 

programs to organize and prioritize recovery actions appropriate to the unique circumstances 

of the gray wolf in each area. The Mexican Wolf Recovery Plan was finalized in 1982, 

solidifying the focus of gray wolf recovery efforts in the southwestern United States on the 

Mexican wolf subspecies (USFWS 1982). The recovery plan was binational, signed by the 

Service in the United States and the Dirección General de la Fauna Silvestre in Mexico. 

The development of the 1982 Mexican Wolf Recovery Plan marked the beginning of a 

2-pronged approach to recovery that included establishment of a captive breeding program 

and reintroduction of Mexican wolves to the wild. The prime objective of the 1982 recovery 

plan was to “conserve and ensure and survival of Canis lupus baileyi by maintaining a 

captive breeding program and re-establishing a viable, self-sustaining population of at least 

100 Mexican wolves in the middle to high elevations of a 5,000-square-mile area within the 

Mexican wolf’s historic range (USFWS 1982:23).” This “prime objective” of the recovery 

plan was not considered an objective and measurable recovery criterion for delisting as 

required by section 4(f)(1) of the ESA, but instead was a recommendation to ensure the 

immediate survival of the Mexican wolf. The recovery team could not foresee full recovery 

and eventual delisting of the Mexican wolf due to its dire status in the wild and the increasing 

encroachment of humans into wolf habitat, and therefore stopped short of providing recovery 

criteria. 

16
A captive breeding program, founded by three of the last six Mexican wolves removed from 

the wild, was underway at this time in the United States, with the first pups born in captivity 

in 1981 (Parsons 1996, Hedrick et al. 1997, Lindsey and Siminski 2007). In 1987, several 

facilities in Mexico joined the captive breeding effort (SEMARNAP 2000). By 1994, 

breeding of the three founding wolves and their offspring (initially referred to as the Certified 

lineage, later as the McBride lineage) had resulted in a captive population of 92 wolves. 

However, concern began to surface over the limited genetic diversity of the captive 

population and the potential for inbreeding depression to hinder its success (Parsons 1996, 

Hedrick et al. 1997). Thus, in 1995, after definitive genetic testing methods became 

available and were applied, two additional lineages of pure Mexican wolves, the Ghost 

Ranch lineage, founded by two wolves, and the Aragon lineage, founded by two wolves, 

were integrated into the captive breeding program to increase the genetic diversity of the 

founder population. This raised the founding base of the captive population from three to 

seven pure Mexican wolves (Hedrick et al. 1997). The Association of Zoos and Aquariums 

(AZA) developed a Species Survival Program (SSP) for the captive population to establish 

breeding protocols and genetic goals to guide wolf pairings, with the ultimate objective of 

providing healthy offspring for release to the wild (Parsons 1996, Lindsey and Siminski 

2007). 

In 1994, Mexico formally recognized the Mexican wolf as an endangered subspecies under 

the Norma Oficial Mexicana NOM-059-ECOL-1994, a Mexican Federal law protecting 

wildlife, followed by development of a recovery plan for the Mexican wolf, Programa de 

Recuperación del Lobo Mexicano, in 1999 (SEMARNAP 2000). Mexico’s recovery plan 

supported reintroduction on both sides of the Mexico-United States border, but stated that it 

would be difficult to find appropriate habitat for reintroduction in Mexico and suggested that 

the best habitat may exist within the Sierra Madre Occidental and the Sierra Madre Oriental 

mountain ranges (SEMARNAP 2000). 

Plans for the reintroduction of the Mexican wolf in the southwestern United States began to 

develop in the mid-1990s, stimulated in part by a suit filed against Service by seven 

environmental organizations for failure to implement provisions of the ESA (Wolf Action 

Group, et al. vs. United States, Civil Action CIV-90-0390-HB, U.S. District Court, 

New Mexico). During this time, the Service formed a new recovery team to revise the 1982 

Mexican Wolf Recovery Plan with updated scientific information and recovery criteria. The 

draft recovery plan developed by the new recovery team was not finalized, and the prime 

objective of the 1982 recovery plan to establish a population of at least 100 wolves in the 

wild was maintained as a guiding recommendation for the upcoming reintroduction. Several 

analyses were conducted to assess locations for the reintroduction (Johnson et al. 1992, 

USFWS 1993), culminating with the Final Environmental Impact Statement, “Reintroduction 

of the Mexican Wolf within its Historic Range in the Southwestern United States,” (FEIS) 

(USFWS 1996). By 1998, the plans for the reintroduction were solidified in the final rule, 

“Establishment of a Nonessential Experimental Population of the Mexican Gray Wolf in 

Arizona and New Mexico” (Final Rule) (63 FR 1752-1772, January 12, 1998), and in March 

of that year, 11 Mexican wolves from the captive breeding program were released to the 

wild. The Mexican wolf was one of only three carnivores (the Mexican wolf, the black17
footed ferret (Mustela nigripes), and red wolf (Canis rufus)) in North America to have been 

eliminated in the wild, bred in captivity, and reintroduced to the wild (Brown and Parsons 

2001). 

The Final Rule established the Mexican Wolf Experimental Population Area (MWEPA) in 

central Arizona and New Mexico, which designated the reintroduction effort as a nonessential experimental population under section 10(j) of the ESA (Figure 1). This 

designation was made because wolves released to the wild would represent excess genetic 

material produced from the captive breeding program and because it allowed for regulatory 

flexibility in managing released wolves and their progeny, an important consideration at the 

time for public support of the reintroduction (Brown and Parsons 2001; 63 FR 1752-1772, 

January 12, 1998). The entire MWEPA was not considered reintroduction and recovery 

habitat for the Mexican wolf, but rather much of the MWEPA provided a transition zone 

between the Blue Range Wolf Recovery Area (BRWRA) designated within the MWEPA and 

the endangered designation of the surrounding landscape (i.e., wolves outside of the 

MWEPA have full endangered status under the classification provided by the 1978 gray wolf 

listing) (63 FR 1752-1772, January 12, 1998). The rule stipulated that the reintroduction of 

wolves would take place within the BRWRA, a 17,775 km2 (6,845 mi2) area that included the 

Apache National Forest in east-central Arizona and the Gila National Forest in west-central 

New Mexico. Within the BRWRA, a Primary Recovery Zone in the Apache National Forest 

was designated for release (initial release and translocation) of Mexican wolves, with a 

Secondary Recovery Zone in the Gila National Forest providing dispersal habitat for released 

wolves (Figure 1). The Final Rule defined a Secondary Recovery Zone as “...an area 

adjacent to a primary recovery zone in which the Service allows released wolves to disperse, 

where wolves captured in the wild for authorized management purposes may be translocated 

and released, and where managers will actively support recovery of the reintroduced 

population” (63 FR 1752-1772, January 12, 1998). The FEIS, however, made no specific 

analysis of translocating wolves into the Secondary Recovery Zone (USFWS 1996). The 

Service prepared an environmental assessment in 2000, analyzing translocation of wolves 

into the Secondary Recovery Zone. This analysis determined that such translocation of 

wolves into the Secondary Recovery Zone of the BRWRA would not create significant new 

impacts beyond those analyzed in the EIS (USFWS 2000). The strategy for the 

reintroduction was to release 14 family groups of wolves over a period of 5 years in order to 

establish the population (63 FR 1752-1772, January 12, 1998). The FEIS projected that the 

population target of at least 100 wild wolves would be reached in nine years (USFWS 1996). 

Today, the Mexican Wolf Blue Range Reintroduction Project (reintroduction project) is an 

interagency effort governed by a Memorandum of Understanding that assigns state and tribal 

leadership of the reintroduction to the Arizona Game and Fish Department (AGFD), New 

Mexico Department of Game and Fish (NMDGF), and the White Mountain Apache Tribe 

(WMAT) (see AMOC and IFT 2005: AC-Appendix 2). Together with the Service, U.S. 

Department of Agriculture-Animal and Plant Health Inspection Service Wildlife Services 

(USDA-WS), and U.S. Department of Agriculture Forest Service (USFS), these lead 

agencies have primary regulatory jurisdiction and management authority of the Mexican wolf 

in Arizona and New Mexico. Graham, Greenlee, and Navajo counties in Arizona, and 

Catron and Sierra counties in New Mexico, as well as the New Mexico Department of 

18
Agriculture, are designated as cooperators to the reintroduction project with an interest in 

Mexican wolf management. The adjoining Fort Apache Indian Reservation (FAIR) tribal 

lands of the WMAT provide an additional 6,475 km2 (2,500 mi2) for direct release of wolves, 

pursuant to an agreement signed between Service and WMAT in 2002. (“Blue Range 

population” refers to wolves in the BRWRA, as well as those on FAIR and surrounding 

lands). 

Turner Endangered Species Fund and Wolf Haven International support the reintroduction 

project by providing pre-release captive facilities where wolves from the captive breeding 

program are acclimated prior to release to the wild. The Defenders of Wildlife administers a 

compensation trust that provides economic compensation to ranchers for wolf depredation of 

cattle, sheep, and other livestock. The AZA SSP captive breeding program, which has 

expanded to 47 facilities and has received national commendation for its commitment to the 

conservation of the Mexican wolf (AZA 2008), continues to support the reintroduction by 

producing wolves for release to the wild and conducting research. 

On a daily basis, management of the wolf reintroduction project may include wolf releases 

and translocations, monitoring, depredation response, outreach and education, research and 

information collecting, and other fieldwork (Brown and Parsons 2001). An Interagency Field 

Team (IFT), consisting of field staff from the six lead agencies, carries out the majority of the 

daily on-the-ground activities, with oversight and planning carried out by AMOC, a 

committee of management-level staff from the six lead agencies. 

As of December 2007 the Blue Range wolf population consisted of approximately 52 wolves 

and a minimum of 4 breeding pairs (USFWS 2008: Population Statistics). Although the 

population has grown steadily since 1998 from both the direct release of wolves and natural 

reproduction (AMOC and IFT: TC-11), the population target of at least 100 wolves has not 

been reached. The highest annual minimum population count since 1998 was 59 wolves 

(minimum of 7 breeding pairs) in 2006, the year in which the FEIS predicted the population 

target would be met USFWS 2008: Population Statistics). 

One of the initial hypotheses for the moderate progress of the reintroduction was the reliance 

on naïve, captive wolves (Brown and Parsons 2001), which had been considered one of the 

biggest possible impediments to successful reintroduction (Brown 1983). In this regard, the 

Mexican wolf reintroduction is more similar to the Service red wolf reintroduction and 

recovery program in the eastern United States than to the Service gray wolf programs in the 

Northern Rockies and Great Lakes, both of which relied on translocation of wild wolves, 

natural population growth, and/or natural recolonization from wolf dispersal from adjacent 

wolf populations rather than captive-bred wolves. Specifically, it has been hypothesized that 

naïve Mexican wolves may be less capable of exploiting prey and therefore have fewer 

surviving pups than other gray wolf populations (AMOC and IFT 2005: TC-17-18), with data 

suggesting that the success (breeding and production of pups after release to the wild) of 

Mexican wolves in the wild may be positively influenced when the greater proportion of its 

life is spent in the wild. Success of Mexican wolves has been more comparable to the 

success of red wolves than the Northern Rockies gray wolves (AMOC and IFT 2005: TC18). 

19
In addition to the potential implications of using naïve, captive wolves to establish a 

reintroduction project, two biological evaluations of the Mexican wolf reintroduction project 

have suggested that regulatory mechanisms may also be contributing to the moderate growth 

of the population (Paquet et al. 2001, AMOC and IFT 2005, and see Threats to the Gray 

Wolf in the Southwest, below). These evaluations were conducted pursuant to the Final 

Rule, which stipulated that the progress of the reintroduction be assessed 3 years and 5 years 

after its inception to determine whether the reintroduction should continue, and if so, whether 

it should be modified in any way (63 FR 1752-1772, January 12, 1998). Both reviews also 

included extensive socio-economic components (Kelly et al. 2001, Unsworth et al. 2005). 

The 3-Year Review, which included a technical component and a stakeholder’s component, 

assessed the progress of the reintroduction from its inception to 2001. The technical 

component of the 3-Year Review, commonly referred to as the Paquet Report, was conducted 

by four independent (non-agency) gray wolf experts. They analyzed the establishment of 

home ranges in the recovery area, wild reproduction, wolf mortality levels, wolf population 

growth, prey adequacy, livestock depredation control, and threats to human safety. They 

concluded that the project was proceeding reasonably well from a biological standpoint and 

that continued application of existing management would eventually result in the 

establishment of a wild, self-sustaining population of wolves. Lower than predicted survival 

rates and reproduction levels, however, would likely result in slower progress in achieving 

population targets than estimated during the planning of the reintroduction. They further 

concluded that several factors were ultimately hindering the biological success of the project: 

1) the small size of the primary recovery zone, which limited the establishment phase of the 

project; 2) the requirement that wolves stay within the BRWRA, which did not allow for 

natural dispersal movements; and, 3) the Service’s objective to establish a population of at 

least 100 wolves, which was not deemed an adequate size for long-term viability (Paquet et 

al. 2001:60-61). To address these issues, they recommended that the Service initiate a 

recovery team to revise the 1982 Mexican Wolf Recovery Plan and modify the Final Rule to 

allow initial releases into the Gila National Forest and allow wolves to establish territories 

outside of the BRWRA. They also made several additional recommendations relating to 

management, outreach, and education to improve the efficacy of the project. 

In the few years between the 3- and 5-Year reviews, the Service and its State, Federal, and 

tribal partners sought to implement the recommendations of the 3-Year Review. However, 

due to a variety of circumstances that are detailed in the 5-Year Review, many of the 

recommendations were not implemented, or not to the degree desired and expected by 

interested parties (AMOC and IFT 2005: AC). The purpose of the 5-Year Review was again 

to evaluate the progress of all aspects of the reintroduction, this time from 1998 to 2003 

(some aspects of the project were analyzed through 2005), specifically providing follow-up 

to questions identified in the 1998 Mexican Wolf Interagency Management Plan (Parsons 

1998), recommendations from the 3-Year Review, recommendations from the Arizona-New 

Mexico independent review of the 3-Year Review that was directed by Congress (AGFD and 

NMDGF 2002), “Commission Directives” to the State Wildlife Agencies of Arizona and 

New Mexico and NM (see AMOC and IFT 2005, Attachment 1), and public comments 

received during the 5-Year Review process in 2005. 

20
The 5-Year Review was conducted by AMOC, the IFT, and a socioeconomic consulting 

firm, and incorporated extensive public input. In the Technical Component of the Review, 

which addressed the biological progress of the project, AMOC concluded that progress 

toward establishment of a population of at least 100 wolves was generally proceeding in line 

with projections from the FEIS. However, they also recognized that guidelines in the Final 

Rule that require removal of wolves that establish home ranges outside of the recovery 

BRWRA or at landowners request are contrary to normal wolf movements and are resulting 

in higher levels of wolf releases and removals than projected in the FEIS. Further, they 

found that wolves spending a greater proportion of their lives in the wild are more likely to 

be successful, and therefore wolves ought to be translocated, rather than permanently 

removed, after their first removal event except in extreme situations (AMOC and IFT: TC24). 

The 5-Year Review culminated with a list of 37 recommendations. Fourteen of the 

recommendations addressed the need for further analysis of potential modification of the 

MWEPA, including expansion of external boundaries, expansion of a recovery zone 

designated for release of wolves, additional provisions for harassment and take of wolves, 

creation of an incentives program to mitigate wolf nuisance and livestock issues, analysis of 

social and economic impacts associated with any MWEPA modifications under 

consideration, and provisions for another review of the reintroduction project in 2009-2010. 

The remaining recommendations dealt with management issues related to information 

gathering, techniques, and public access to data; ongoing advisory needs; annual planning, 

including staffing, training, and budgeting; field techniques; law enforcement; outreach, 

public involvement, and education; and private property incentives (AMOC and IFT: ARC). 

Following the completion of the 5-Year Review in 2005, the Service determined that the 

reintroduction should continue, and agreed that modifications to the Final Rule may be 

necessary (USFWS 2006b). Since that time, the lead agencies have acknowledged that the 

population is lagging behind the projections of the FEIS (USFWS 2005:27) and that 

management action is needed to support population growth (AGFD 2007: 13). Recently, the 

Service conducted a public scoping process to seek additional public input on possible 

modifications to the reintroduction project that will address biological, social, and economic 

issues related to its progress (72 FR 44065-44069, August 7, 2007). Analysis of these 

comments is currently underway (USFWS 2008: Rule Modification). 

Summary statement: A two-pronged gray wolf recovery effort in the Southwest includes 

an international network of Mexican wolf captive breeding facilities and an interagency 

Mexican wolf reintroduction project in Arizona and New Mexico. 

Summary statement: Following completion of the 5-Year Program Review in 2005, the 

Service determined that reintroduction should continue, and agreed that modification to the 

Final Rule may be necessary. 

Summary statement: Progress in achieving the Mexican wolf population target of at least 

100 wolves in the BRWRA has fallen short of initial expectations by several years, likely due 

to a combination of biological and regulatory factors. 

21
Status and Implications of National Gray Wolf Recovery for the Mexican Wolf 

It is reasonable to expect that the progress of gray wolf recovery efforts in the Great Lakes, 

Northern Rockies, and Southwest would differ due to the variety of circumstances and policy 

decisions affecting each program. In both the Great Lakes and Northern Rockies, the gray 

wolf has rebounded rapidly in the wild due to a combination of factors, including the 

reintroduction of wild wolves from Canada into the Northern Rockies, natural population 

growth, and natural recolonization by wolves from nearby populations. Both programs have 

been guided by recovery plans with recovery criteria that were revised and refined over time 

as relevant new information was gathered (see USFWS 1987 and 72 FR 6051-6103, 

February 8, 2007, for the Great Lakes, and USFWS 1992 and 73 FR 10514-10560, 

February 27, 2008, for the Northern Rockies). In the Great Lakes, a population of over 3,000 

wolves inhabits Minnesota, with a second population of close to 1,000 wolves inhabiting the 

two-state area of Michigan and Wisconsin (72 FR 6051-6103, February 8, 2007). Prior to 

listing, wolves had been effectively exterminated from Wisconsin and Michigan, with the 

exception of a small population on Isle Royale, and less than 1,000 wolves inhabited 

Minnesota (72 FR 6051-6103, February 8, 2007). With the protections of the ESA in the late 

1970’s, gray wolves began to rebound in abundance and distribution. Today, population 

growth in the three-state area has leveled off, and these populations maintain connectivity to 

healthy gray wolf populations in Manitoba (~4,000 wolves) and Ontario (~8,000 wolves), 

Canada (72 FR 6051-6103, February 8, 2007). 

In the Northern Rockies, a population of over 1,500 gray wolves inhabits core recovery areas 

in Montana, Idaho, and Wyoming (USFWS et al. 2008). Gray wolves had also been 

decimated in these states prior to protection under the ESA. In the mid 1980s, natural 

reproduction was documented in a small population of wolves that had dispersed to 

northwestern Montana from Canada; this population continued to grow to its current size of 

around 200 wolves. In central Idaho and the Greater Yellowstone Area (which includes 

portions of Idaho, Montana, and Wyoming surrounding Yellowstone National Park), gray 

wolves were reintroduced from Canada in the mid-1990s into nonessential experimental 

populations (59 FR 60266-60281, November 22, 1994; 59 FR 60252). In 2008, the 

Yellowstone population was estimated at close to 200 wolves, and the Idaho population was 

close to 900. Routine dispersal has been documented between the northwestern Montana 

population, Idaho population, and Canadian populations (73 FR 10514-10560, February 27, 

2008). 

In the Great Lakes and Northern Rockies, the Service determined that the gray wolf is 

recovered, and reclassified and delisted these portions of the species’ range as distinct 

population segments (DPS) in 2007-2008 (72 FR 6051-6103, February 8, 2007; 73 FR 

10513-10560, February 27, 2008). However these designations and delistings were reversed 

in legal challenge against each (Humane Society of the United States, et al. v. Kempthorne, 

et al., Civil No. 1:07-cv-00677-PLF (D. D.C.), Defenders of Wildlife, et al. v. Hall, et al., 

Civil No. 9:08-cv-00056-DWM (D. Mont.)). While the Service will attempt to address the 

legal issues in future delisting rules for these populations, as of this writing, gray wolves 

remain threatened in the Great Lakes and endangered throughout the rest of the coterminous 

United States, except where designated as nonessential experimental populations. 

22
The ongoing struggle between the Service’s delisting actions and related legal challenges in 

the Great Lakes and Northern Rockies has been ongoing for several years and has delayed 

efforts to develop an up-to-date gray wolf recovery plan in the Southwest to replace the 1982 

Mexican Wolf Recovery Plan. In 2003, the Service reclassified the gray wolf into three 

distinct population segments in order to divide the gray wolf’s listed range from the 1978 

listing (the coterminous United States and Mexico) into three separate entities for which 

policy action, such as delisting, could be pursued for each independent of the others (68 FR 

15804-15875, April 1, 2003; and see “Policy Regarding the Recognition of Distinct 

Vertebrate Population Segments Under the Endangered Species Act”, 61 FR 4721-4725, 

February 7, 1996). Specifically, the Service wanted to recognize the progress made toward 

recovery of the gray wolf in the Great Lakes and Northern Rockies but concurrently 

recognized that commensurate progress toward recovery had not been made in the gray wolf 

recovery program in the Southwest (68 FR 15804-15875:15811, April 1, 2003). Thus, under 

the 1978 gray wolf listing, neither range-wide downlisting of the gray wolf from endangered 

to threatened nor range-wide delisting could be pursued due to the imbalance of recovery 

achieved between the regional programs. 

Soon after the 2003 reclassification, the Southwest Region of the Service convened a 

recovery team to develop a recovery plan and recovery criteria for the newly designated 

Southwestern Distinct Population Segment (SWDPS), which included the southern portions 

of Utah and Colorado, western portions of Oklahoma and Texas, all of Arizona and 

New Mexico, and the wolf’s historic range in Mexico. The recovery planning effort was 

intended to provide a regional gray wolf recovery plan that would supercede the 1982 

Mexican Wolf Recovery Plan and provide context for the Blue Range reintroduction in terms 

of the wolf abundance and distribution necessary for recovery in the Southwest. However, 

the 2003 reclassification rule was vacated and remanded to the Service in 2005 (see 

Defenders of Wildlife v. Norton, 03-1348-JO; National Wildlife Federation v. Norton, 1:03-

CV-340, D. VT. 2005). As a result of this litigation, which invalidated the team’s charge to 

develop a plan for the SWDPS because the SWDPS was no longer a listed entity, the Service 

put the recovery planning process on hold while the agency determined how to respond. The 

planning effort has not been resumed, and the Southwest Region remains without the 

guidance of an up-to-date gray wolf recovery plan, specifically as it relates to the future of 

the subspecific Mexican wolf reintroduction and recovery effort currently underway. 

Meanwhile, the DPSs for the Great Lakes and Northern Rockies have been redesignated and 

delisted later to be overturned in litigation. 

If future reclassification and delisting of the gray wolf distinct population segments in the 

Northern Rockies and Great Lakes are successful, the species will remain delisted in these 

areas but listed as endangered in all or portions of 42 states based on the remaining gray wolf 

range designated in the 1978 listing. Thus, gray wolves dispersing from delisted areas may 

travel into areas designated as endangered, where they receive the full protections of the 

ESA. However, other than the potential for small numbers of dispersals from delisted areas 

into areas designated as endangered, gray wolves do not currently inhabit any of the 

remaining listed states in substantial number other than Arizona and New Mexico, where the 

Mexican wolf nonessential experimental population reintroduction is conducted. The gray 

wolf recovery program in the Southwest is the only remaining of the original three, and the 

23
agency has not indicated whether additional gray wolf recovery efforts will be pursued in 

other regions of the country. 

Summary statement: A shifting policy landscape for gray wolf recovery and recovery 

planning in the Southwest continues to be created by the fluctuating status of gray wolf 

recovery and delisting actions in the Northern Rockies and Great Lakes. 

Summary statement: The gray wolf recovery program in the Southwest operates in absence 

of an up-to-date recovery plan that contains recovery criteria and conservation actions that 

would situate the BRWRA population as an integral component of regional and national gray 

wolf recovery. 

State and International Regulatory Protection in the Southwestern United States and Mexico

In addition to its listed status under the ESA, the gray wolf is also protected under State 

wildlife statutes in the Southwest and Mexico. The gray wolf is classified as endangered in 

Arizona (Wildlife of Special Concern/Threatened native wildlife in Arizona, and listed as 

endangered in New Mexico (Wildlife Conservation Act, 17-2-37 through 17-2-46 NMSA 

1978) and Texas (Texas Statute 31 T.A.P). Wolves are considered “protected wildlife” in 

Utah; they cannot be harvested unless the Wildlife Board establishes an open season for 

harvest (Utah Code Annotated, Title 23). The gray wolf is not included on Utah’s Sensitive 

Species List, as the species is not considered resident in Utah at this time and because the 

ESA provides protection. Wolves are listed as endangered by Colorado (Colorado Revised 

Statues 33-2-105, “Nongame, Endangered, or Threatened Species Conservation Act”, Title 

33. In Mexico, the Mexican wolf subspecies continues to be protected under the Ley de Vida 

Silvestre (2000), Norma Oficial Mexicana NOM-059-ECOL-2001 (2002). The gray wolf is 

not listed or protected by State law in Oklahoma. 

24
GRAY WOLF BIOLOGY AND ECOLOGY 

Taxonomy and Range

The gray wolf, Canis lupus, is a member of the dog family (Canidae; Order Carnivora). 

The genus Canis also includes the red wolf (C. rufus), dog (C. familiaris), coyote (C. 

latrans), several species of jackal (C. aureus, C. mesomelas, C. adustus) and the dingo (C. 

dingo) (Mech 1970). Type localities of previously recognized subspecies are documented in 

Young and Goldman (1944); the type locality of Canis lupus baileyi Nelson and Goldman is 

Colonia Garcia, Chihuahua, Mexico. 

It is likely that, with the possible exception of the wolf of southeastern Canada and 

northeastern United States (Wilson et al. 2003), all gray wolves evolved from the small, early 

canids that were widespread in North America and the Old World during the Pliocene, some 

2 to 4.5 million years ago (Nowak 2003). The gray wolf likely evolved in Eurasia from 

wolves that crossed into Eurasia from North America. A branch of these wolves (that is, 

Canis lupus) then reinvaded the New World during the middle Pleistocene (around 300,000 

years ago), via the Bering Strait land bridge (Wayne et al. 1992, Nowak 1995, Nowak 2003: 

Table 9.2, Brewster and Fritts 1995, Parsons 1996). It is hypothesized that waves of gray 

wolf migration likely occurred in response to changing glacial ice patterns and openings in 

the Bering Sea (Nowak 1995, Nowak 2003, Wayne and Vilá 2003). Once in the New World, 

wolves dispersed southward and eastward, gradually spreading across the continent (Nowak 

2003, Parsons 1996). 

Twenty-four subspecies of gray wolf have been described in North America (Hall and 

Kelson 1959). Five of these subspecies occurred in the southwestern United States and 

Mexico: C. l. baileyi, C. l. mogollonensis, C. l. monstrabilis, C. l. nubilus, and C. l. youngi. 

Hall (1981) described C.l. baileyi’s range as including only a small portion of extreme 

southwestern New Mexico and southeastern Arizona. However, a taxonomic revision 

proposed by Bogan and Mehlhop (1980, 1983) lumped C. l. mogollonensis and C. l. 

monstrabilis with C. l. baileyi, thereby extending C.l. baileyi’s range to northern Arizona and 

central New Mexico, and recognizing only three southwestern subspecies, C.l. baileyi, C.l. 

youngi, and C.l. nubilis. The Service adopted the findings of Bogan and Mehlhop in the 

1982 Mexican Wolf Recovery Plan, thus supporting reintroduction of C.l. baileyi north of 

C.l. baileyi’s range as originally conceived by Young and Goldman (1944) and Hall and 

Kelson (1959). 

In a subsequent reclassification of North American gray wolves, Nowak (1995) proposed 

reduction of the number of recognized subspecies from 24 to 5, recognizing C.l. arctos, C.l. 

baileyi, C.l. lycaon, C.l. nubilus, and C.l. occidentalis as subspecies. In this classification, C. 

l. baileyi was recognized as a subspecies, but C. l. mogollonensis and C. l. monstrabilis were 

grouped with C. l. nubilus. The classifications proposed by Hall and Kelson (1959), Bogan 

and Mehlhop (1983), and Nowak (1995) were based on comparisons of morphological 

characteristics, primarily skull measurements. Parsons (1996) added knowledge of dispersal 

patterns to the historic range of C.l. baileyi proposed by Nowak (1995) and concluded that 

historically Mexican wolves ranged as far north as central New Mexico and east-central 

25
Arizona. The Service adopted the historic range proposed by Parsons (1996) for C.l. baileyi, 

a 200-mile northward extension of Nowak’s range for C.l. baileyi, and included it in the FEIS 

(USFWS 1996). 

This history highlights the disagreement in North America over the use of sub-specific 

nomenclature to describe geographic variation among gray wolf populations across their 

historically vast range (Brewster and Fritts 1995, Nowak 2003). As Brewster and Fritts 

(1995:355) explained, “Inherent in most recent thinking [of subspecies definition] is the idea 

that members of a subspecies should be more closely related to one another than to 

individuals of another subspecies, and further, that geographic or ecological isolation (e.g., 

islands, mountain ranges separated by deserts, plains separated by mountain ranges) has 

caused gene flow between populations to be restricted and allowed differentiation of 

characteristics.” Difficulty in grouping wolves into subspecies arises due to the tendency of 

gray wolves to move significant distances across the landscape: during these movements, 

dispersing wolves may come into contact with near or distant wolf populations, potentially 

resulting in high rates of gene flow between populations and limited genetic differentiation 

among populations (Wayne et al. 1992, Roy et al. 1994, Vilá et al. 1999). 

Wolves’ dispersal behavior led to the conclusion that wolves existed historically in 

intergradations across the North American landscape (Young and Goldman 1944, Mech 

1970, Brewster and Fritts 1995, Leonard et al. 2005). Mech (1970:30) commented that, 

“Wherever subspecies meet, their characters tend to blend as a result of interbreeding, or 

intergradation...”. Under optimal conditions wolves’ dispersal capabilities exceed 500 miles 

(Fritts 1983, Boyd et al. 1995), thus these zones of subspecies intergradation were likely 

hundreds of miles wide (Brewster and Fritts 1995). Given this information, the difficulty in 

describing where one subspecies’ boundary begins and ends becomes apparent. As Wayne 

and Vilá (2003:223) recently stated, “the division of wolves into discrete subspecies and 

other genetic units may be somewhat arbitrary and overly typological (conforming to a 

specific ideal type). In reality, wolves are better viewed as a series of intergrading 

populations having subtle or undetectable patterns of clinal [continuous gradation in any 

trait] genetic change.” 

In recent decades, the emergence of the field of conservation genetics has contributed 

significantly to understanding the gray wolf. Recent molecular genetic evidence indicates 

that there was considerable gene flow across the subspecies’ boundaries postulated by 

Nowak (1995, 2003) (Leonard et al. 2004), in keeping with the previous understanding that 

wolves naturally existed in intergradations across the landscape. More specifically, there is 

evidence of gene flow across the recognized boundary of C.l. baileyi; analyses of historic 

specimens demonstrate that the gray wolves that inhabited northern Arizona, southern and 

central Utah, northern New Mexico, and southern and central Colorado had genetic markers 

now associated with the Mexican wolf. In other words, Mexican wolves likely intergraded 

with other gray wolves at the northern extent of their range. This intergradation of northern 

and Mexican wolf-related haplotypes has recently been conceptualized as a southern clade 

(i.e., group that originated from and includes all descendents from a common ancestor) 

(Leonard et al. 2005). This research has also shown that there are some genetic markers 

26
more typical of Canadian and Alaskan wolves in Mexican wolves, providing evidence of 

some historical contact between Mexican wolves and northern subspecies (Leonard et al. 

2004). 

Based on genetic analyses, it has also been determined that the genetic makeup, or genotype, 

of all gray wolves is very similar (Wayne et al. 1992). Mitochondrial DNA analysis has 

suggested that, with a few exceptions, a genetic basis for the previous sub-specific 

designations of gray wolf may not exist (Wayne et al. 1995). Molecular genetic analyses, 

however, provide indisputable evidence that the Mexican wolf has distinct genetic attributes 

differing by 2.2 percent from other North American gray wolves (Wayne and Vilá 2003), 

thus supporting earlier morphological characterization of the Mexican wolf as a distinct 

subspecies (García-Moreno et al. 1996, Hedrick et al. 1997, Wayne et al. 1992, and see 

Nowak 2003). 

The origins of the distinct genetic traits and morphological features of the Mexican wolf are 

uncertain, but it is hypothesized that C.l. baileyi represents one of the earliest waves of 

migration of the gray wolf onto the continent (Wayne and Vilá 2003) after which C.l. baileyi

may have experienced random genetic drift during a period of isolation from other wolf 

populations as expansion and retraction of glacial ice patterns caused ephemeral boundaries 

to dispersal and continent-wide population flux in gray wolf abundance (Vilá et al. 1999, Roy 

et al. 1994, Wayne et al. 1995). Another possible explanation is based on the knowledge that 

morphological differences are not necessarily indicative of long periods of geographic 

isolation and may only indicate intense natural selection on particular physical features 

(Wayne et al. 1992). Geographic variations in body size and pelage, therefore, could be a 

result of selection for differences in habitat or prey type, resulting in differentiation despite 

otherwise high levels of gene flow (Wayne et al. 2004). There is no scientific certainty 

whether drift or selection caused C.l. baileyi’s distinctiveness. 

Summary statement: Integration of ecological, morphological, and genetic evidence 

supports several conclusions relevant to the southwestern United States regarding gray wolf 

taxonomy and range. First, there is agreement that the Mexican wolf is distinguishable from 

other gray wolves based on morphological and genetic evidence. Second, recent genetic 

evidence continues to support the observation that historic gray wolf populations existed in 

intergradations across the landscape due to gene flow as a result of their dispersal ability. 

Third, evidence suggests that the southwestern United States (southern Colorado and Utah, 

Arizona and New Mexico) included multiple wolf populations distributed across a zone of 

intergradation and interbreeding, although only C.l. baileyi inhabited the southernmost 

extent. 

Physical Description and Life History 

Gray wolves often vary considerably in size, although males typically weigh between 36-55 

kg (80-120 lbs), are 1.5 to 2 m (5-6.5 ft) long from tip of nose to tip of tail, and 66 to 81 cm 

(26-32 in) high at the shoulder. Males are typically 15-20 percent larger than females in 

weight and length. Gray wolves exhibit significant variety in pelt color: the most commonly 

27
observed pelt is a mottled charcoal gray, but pelt color can range from white, cream, brown 

and red, to dark gray and black (Mech 1970). Individual wolves may exhibit any or all of 

these colors (Fuller 2004). 

The Mexican wolf (Figure 2) is the smallest extant gray wolf in North America; adults weigh 

23-41 kg (50-90 lbs) with a length of 1.5-1.8 m (5-6 ft) and height at shoulder of 63-81 cm 

(25-32 in) (Young and Goldman 1944, Brown 1983). Mexican wolves are typically a patchy 

black, brown to cinnamon, and cream color, with primarily light underparts (Brown 1983); 

solid black or white Mexican wolves do not exist as seen in other North American gray 

wolves (USFWS 2008). 

Basic descriptive life history information is well documented for gray wolves, although less 

so for the Mexican wolf. In the wild, wolves typically live 4 to 5 years, although they can 

reach 13 years (Mech 1988). They reach sexual maturity at 2 years of age (Mech 1970). 

Wolves have one reproductive cycle per year, and females are capable of producing a litter of 

pups, usually four to six, each year (Mech 1970). Litters are born in spring in a den or 

burrow that the pack digs (Mech 1970, Packard 2003). Pups weigh about 1 lb (0.5 kg) at 

birth (Mech 1991), and remain inside the den for at least 4 weeks, during which time their 

eyes open and the animals learn to walk (Packard 2003). Pup mortality during the denning 

period is difficult to document due to lack of access to den sites (Fuller et al. 2003). 

In the Blue Range population, Mexican wolf pups are generally born between early April and 

early May (AMOC and IFT 2005: TC-6). Average litter size (2.1 pups) following the 

denning period is smaller than Mexican wolf litters in captivity (4.6 pups/litter) (AMOC and 

IFT: TC-17), gray wolf litters elsewhere (AMOC and IFT: TC-12, see Fuller et al. 2003), or 

the historical litter sizes of wild Mexican wolves reported by McBride (4.5 pups) (1980), but 

is similar to red wolf litter sizes (2.8 pups/litter) (Phillips et al. 2003). Several hypotheses to 

explain the small litter sizes in Blue Range population have been suggested: 1) wolves may 

be limited by the amount of vulnerable prey due to winter snow patterns; 2) litter sizes may 

be a historical adaptation to the environment; or, 3) wolves released from captivity may be 

less capable of exploiting vulnerable prey, potentially further affected by frequent 

management that decreases their ability to fully exploit their home ranges (AMOC and IFT: 

TC-18). Moreover, it is likely that more Mexican wolf pups are born than are observed in 

the wild when counts are conducted, but actual litter size at birth and early pup mortality is 

unknown (AMOC and IFT 2005: TC-18). Mexican wolf pups are difficult to distinguish 

from adults by early fall, therefore pup counts are conducted opportunistically after the 

denning period, but prior to October (AMOC and IFT 2005: TC-6). Documentation in the 

BRWRA of wild-born wolves breeding and raising pups has been made for six years in a row 

(2001-2007), and in 2007 approximately 90 percent of wolves in the Blue Range population 

were wild-born (AGFD et al. 2007). 

 

During the first few months of life, gray wolf pups are gradually weaned from their parents, 

transitioning from nursing to feeding on semi-liquid regurgitated food provided by adult 

wolves at the den site, to consuming solid food. During this period, pups grow rapidly, likely 

due to high prey availability during summer months. Pup survival is typically highest in 

28
those areas of high prey availability (Fuller et al. 2003). Wolves are referred to as pups up to 

1 year of age when they reach adult size and yearlings when 1-2 years of age (Packard 2003). 

Juveniles begin hunting with adults when 4-10 months old (Packard 2003), remaining with 

their family until they disperse to establish a new territory. Wolves exploit their prey by 

hunting in packs. Adult wolves typically experience a feast or famine existence, gorging on 

freshly killed prey after successful hunts and subsequently able to survive for days with low 

food intake (Peterson and Ciucci 2003). Wolves buffer these extremes of food availability 

by burying food for later consumption (Peterson and Ciucci 2003). Food biomass intake 

rates of individual wolves vary significantly, from 0.5 to 24.8 kg/wolf/day, based on a variety 

of factors such as prey selection, availability and vulnerability of prey, and the effects of 

season or weather on hunting success (Mech and Peterson 2003, see Table 5.5). Minimum 

daily food requirements of an adult gray wolf have been estimated at 1.4 kg/wolf, or about 13 

adult-sized deer per wolf per year, with the highest kill rate of deer reported as 6.8 

kg/wolf/day (Mech and Peterson 2003). Prior to the Blue Range reintroduction, it was 

estimated that Mexican wolves would need to kill 1 mule deer every 12-13 days or one 

white-tailed deer every 8-9 days (Johnson et al. 1992). Wolves also scavenge on carcasses 

when available (Peterson and Ciucci 2003). 

Wolf survival rates vary seasonally, as shifts in prey availability occur (Fuller et al. 2003). 

Annual survival rate of yearling and adult gray wolves is estimated at 0.55 to 0.86 (Fuller et 

al. 2003: Table 6.6). Documented causes of death include starvation, disease, human-caused 

mortality, and interactions with other wolves or predators (Fuller et al. 2003, Ballard et al. 

2003). In the Blue Range population, causes of mortality have been largely human-related, 

including vehicle collision, illegal gunshot, lethal control, and capture complications, 

although dehydration, brain tumor, infection, snakebite, disease, mountain lion attack, and 

unknown causes have also been documented (AMOC and IFT 2005: TC-12). Between 1998 

and 2007, illegal gunshot (28 of 62 deaths) and vehicle collision (12 of 62 deaths) were the 2 

most prevalent causes of death (USFWS 2008: Population Statistics). In 2007, the annual 

survival rate was 0.53 (or a corresponding failure rate of 0.47, which includes both mortality 

and management removal of wolves) (AGFD et al. 2007).

Pack Formation and Movements

Wolves are social animals that live in hierarchical families, referred to as packs. Wolf packs 

consist of a breeding pair (formerly “alpha” (Packard 2003)) and their subordinate pup and 

yearling offspring (Mech 1970) although many variations of this typical pack structure have 

been observed (Mech and Boitani 2003). Pack size in the Blue Range population between 

1998 and 2003 ranged from 2-11 (mean = 4.8) wolves (AMOC and IFT 2005: TC-12). 

Bednarz (1988) estimated historic Mexican wolf pack size as 2-8 animals. 

To secure food, water, and shelter, a pack establishes an area, or territory, that is maintained 

by the breeding pair through scent-marking (Peters and Mech 1975), howling (Harrington 

and Mech 1983), and direct defense (Mech and Boitani 2003). Minimum territory size is the 

area in which sufficient prey exist to support the pack (Fuller et al. 2003), so territories vary 

in size depending on prey density or biomass and pack size. Average wolf pack territory size 

29
documented for 19 monitored packs in the Blue Range population between 1988 and 2003 

averaged 462 km2

 +/- 63 km2 (182 mi2 +/- 24 mi2) (AMOC and IFT 2005: TC-10). Bednarz 

(1988) predicted that reintroduced Mexican wolves would likely occupy territories ranging 

from 200-400 km2

 (approximately 125 to 250 mi2), and hypothesized that Mexican wolf 

territories were historically comparable in size to those of small packs of northern gray 

wolves, but possibly larger, due to habitat patchiness (that is, mountainous terrain that 

included areas of unsuitable lowland habitat) and lower prey densities associated with the 

arid environment. 

Wolf packs move within their respective territories as they forage and defend their territories 

(Mech and Boitani 2003). Wolves’ daily movements vary in response to the distribution, 

abundance, and availability of prey. Seasonal movements vary as well: while rearing pups, 

adult wolves leave the den, returning throughout the day to care for their young. When pups 

are old enough to travel with adults, packs become nomadic, traveling throughout the 

territory, sometimes returning to rendezvous sites (Mech and Boitani 2003). Daily pack 

movements of less than 10 miles per day to over 40 miles in a 24-hour period have been 

documented in different wolf populations in different seasons (see Mech and Boitani 

2003:32). 

In addition to movements within territories, wolf travels typically include dispersal 

movements (Mech and Boitani 2003). An individual wolf, or rarely a group, will disperse 

from its natal pack in search of vacant habitat or a mate; dispersers are typically younger 

wolves of 9 to 36 months of age (Packard 2003). A yearling might make several dispersal 

forays before completely disassociating from the family (Messier 1985). These dispersals 

may be short to a neighboring territory, or may be long to find a mate and establish a 

territory. Dispersal of more than 1092 km (655 mi) has been documented in northern 

populations (Wabakken et al. 2007). Between 1998 and 2003, 45 wolf dispersals (natural 

dispersals and post-release movements) were documented in the Blue Range population, with 

an average distance of 87 km +/- 10 km (54 mi +/- 6 mi). This is likely an underrepresentation of true movement distances, due to management response required by the 

nonessential experimental-population designation when wolves disperse outside of the 

BRWRA. Wolves in the BRWRA primarily dispersed northwestward or southeastward, in 

the direction that mountain ranges lie within the area (AMOC and IFT 2005: TC-13). 

Dispersing gray wolves usually travel alone and tend to have a high risk of mortality (Fuller 

et al. 2003). In the Blue Range population, 12 known mortalities were documented in 

association with dispersal between 1998-2003 (including natural dispersal and movements 

directly after release to the wild) (AMOC and IFT 2005: TC-14). Wolves that disperse and 

locate a mate and an unoccupied patch of suitable habitat usually establish a territory 

(Rothman and Mech 1979, Fritts and Mech 1981). 

Ecology and Habitat Description 

Wolves are top predators. They are generally not habitat specific and are considered to have 

fairly broad ecological capabilities (Wayne et al. 2004) and flexibility in using different prey 

and habitats (Mech 1991). Historically, wolves occupied every habitat in the northern 

30
hemisphere that supported populations of large ungulates (Mech 1991). The gray wolf hunts 

in packs, primarily pursuing medium to large hoofed mammals, potentially supplementing its 

diet with small mammals (Mech 1970). It is well documented that wolf density is directly 

related to the amount of ungulate biomass available and the vulnerability of ungulates to 

predation (see Fuller et al. 2003). 

Wolves may play a variable role in ungulate population dynamics depending on the predatorprey interaction and the relative importance of other ecosystem factors (Messier 1994, 

Gasaway et al. 1993, Boutin 1992). Ungulates employ a variety of defenses against 

predation (e.g., aggression, migration), and wolves are frequently unsuccessful in their 

attempts to capture prey (Mech and Peterson 2003). Generally, wolves tend to kill less-fit 

prey (e.g., young, old, injured) that are predisposed to predation (Mech and Peterson 2003). 

Wolves may reduce prey numbers, especially during adverse conditions, but only in extreme 

circumstances have they been documented exterminating a prey population, and then only in 

a relatively small area (Mech and Peterson 2003). 

Wolves may also impact ecosystem diversity beyond that of their immediate prey source in 

areas where their abundance is numerous enough to affect the distribution and abundance of 

other species (sometimes referred to as “ecologically effective densities” (Soule et al. 2003)) 

(Soule et al. 2005). This may occur through two mechanisms: 1) wolf predation may 

decrease the population of an herbivore that otherwise would competitively exclude other 

herbivores; and, 2) wolf predation on an herbivore may result in increases or decreases to 

lower tropic levels, cascading to the autotrophs at the bottom of the food web (i.e., “trophic 

cascade”) (Terbough et al. 1999). Such effects have been attributed to gray wolf 

reintroduction in Yellowstone National Park (e.g., Ripple and Bescheta 2003, Ripple and 

Bescheta 2004). 

Historically, Mexican wolves were associated with montane woodlands characterized by 

sparsely- to densely-forested mountainous terrain and adjacent grasslands in habitats found at 

elevations of 1219-1524 (4000-5000 ft) (Brown 1983). Wolves were known to occupy 

habitats ranging from foothills characterized by evergreen oaks (Quercus spp.) or pinyon 

(Pinus edulus) and juniper (Juniperus spp.) to higher elevation pine (Pinus spp.) and mixed 

conifer forests. Factors making these habitats attractive to Mexican wolves likely included 

an abundance of ungulate prey, availability of water, and the presence of hiding cover and 

suitable den sites. Early investigators reported that Mexican wolves probably avoided desert 

scrub and semidesert grasslands that provided little cover, food, or water (Brown 1983). 

Wolves traveled between suitable habitats using riparian corridors, and later, roads or trails 

(Brown 1983). Elevation in the BRWRA ranges from 1219-3353 m (4000-11000 ft), ranging 

from semi-desert grasslands to conifer forests, with ponderosa forests dominating the area in 

between (USFWS 1996). 

Historically, Mexican wolves were believed to have preyed upon white-tailed deer 

(Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus elaphus), collared 

peccaries (javelina) (Tayassu tajacu), pronghorn (Antilocapra Americana), bighorn sheep 

(Ovis Canadensis) jackrabbits (Lepus spp.), cottontails (Sylvilagus spp.), and small rodents 

31
(Parsons and Nicholoupolos 1995); white-tailed deer and mule deer were believed to be the 

primary sources of prey (Brown 1983, Bednarz 1988, Bailey 1931, Leopold 1959). 

Data from the Blue Range indicates that elk are the preferred prey (Brown and Parsons 2001, 

Reed et al. 2006), with wolves showing a preference for calf elk over adult elk (AMOC and 

IFT 2005: TC-14). Mexican wolves are also feeding on adult and fawn deer, unknown wild 

ungulates, cattle, small mammals, and occasionally birds (Reed et al. 2006). Scat analysis 

suggests that Mexican wolves in the Blue Range are concentrating on the largest prey 

available (elk), which is atypical given that wolves typically concentrate on the smallest or 

easiest prey available if two or more sources of prey are present. One hypothesis for this is 

that during the initial stages of the reintroduction, elk were naïve to predation by wolves and 

were the most numerous ungulate species; a second is that study methodology may have 

skewed data collection in order to minimize the probability of including coyote scat (Reed et 

al. 2006, Carrera et al. 2008). 

The FEIS estimated that a population of 15,800 elk (average density 3.7/km2), and 57,170 

mule deer and white-tailed deer (average density 13.36/ km2) were present in the BRWRA 

prior to the reintroduction of Mexican wolves (USFWS 1996). Although prey densities for 

the entire BRWRA are not available, wolf activity in the BRWRA appears to be located in 

areas of high elk density, as defined by state game management units (AMOC and IFT 2005: 

TC-14), and no evidence of food shortage has been observed (AMOC and IFT 2005: TC-21). 

The difference in historic versus current prey preference may in part be due to varying 

interpretations of Mexican wolf range; historic accounts which considered Mexican wolf 

range as southern Arizona and New Mexico into Mexico reflect the prevalence of deer (and 

relative absence of elk) in these areas, whereas elk are common, and sometimes more 

numerous than white-tailed or mule deer, in the current Mexican wolf range in the BRWRA 

(AMOC and IFT: TC-1). 

 

Livestock are another widely available potential source of prey for Mexican wolves in the 

BRWRA. Historically, records of Mexican wolf exploitation of livestock were prominent 

(Young and Goldman 1944, McBride 1980, Brown 1983, Bednarz 1988); this is not 

surprising given that such reports were made by government and private wolf control agents 

whose jobs focused on depredating animals (and see Gipson and Ballard 1998, Gipson et al. 

1998). When the reintroduction began, sheep and cattle grazing was permitted on 

approximately 69 percent of the BRWRA, with about half of the allotments being grazed 

year-round (USFWS 1996). Program projections predicted that at the reintroduction goal of 

at least 100 Mexican wolves, depredation levels of 1-34 cattle per year would occur (USFWS 

1996). Between 1998 and 2007, 117 confirmed cattle depredations were documented 

(AMOC and IFT 2005: TC-15; USFWS 2006a, USFWS 2005; USFWS 2004; AGFD et al. 

2007), or an average depredation rate of 25 cattle per 100 wolves per year. This depredation 

rate may represent an underestimate due to incomplete detection of wolf-killed cattle 

(Oakleaf et al. 2003). Between 1998 and 2007, 70 wolves were removed as a result of 

confirmed depredations (USFWS 2008: Reintroduction Project Statistics), or one wolf 

removal per 1.67 confirmed depredations. 

32
Wolves and Non-prey

Wolves also interact with non-prey species. Although these interactions are generally not 

well documented, competition and coexistence may occur between wolves and other large, 

medium, or small carnivores (Ballard et al. 2003). 

In the Southwest, wolves may interact with other wolves, coyotes, mountain lions (Puma 

concolor), and black bears (Ursus americanus) (AMOC and IFT 2005: TC-3). Aggression 

among wolves is typically associated with food shortages as wolves venture into neighboring 

territories to locate prey (Mech and Boitani 2003). Observation of wolf and coyote 

interactions in other regions have documented decreased coyote density in areas of high wolf 

density and that wolves occasionally kill or eliminate coyotes (Ballard et al. 2003). Bednarz 

(1988) suggested that prior to wolf extirpation, Mexican wolves excluded coyotes from many 

areas. A current study of Mexican wolf and coyote diets in the BRWRA shows that wolves 

and coyotes have similar diets consisting mainly of elk (Carrera et al. 2008). It is not known 

whether coyotes are scavenging elk carcasses from wolf kills or preying on elk directly, 

although both behaviors have been documented in other areas. It is hypothesized that this 

shared source of prey may cause competition between wolves and coyotes that will result in 

wolves killing coyotes (Carrera et al. 2008). 

Bednarz (1988) also hypothesized that wolves and mountain lions interacted historically, 

given their overlapping habitats and shared prey source of mule deer, but suggested that 

wolves may have exploited gentler sloping terrain, with mountain lions hunting in steeper 

craggy mountainous terrain. The potential for competition between wolves and lions 

certainly exists in areas where spatial overlap is extensive and prey selection patterns are 

similar (see Kunkel et al. 1999), although differences in hunting behavior and prey 

vulnerability to wolves and mountain lions have been observed (see Husseman et al. 2003). 

One Mexican wolf death from a mountain lion attack has been recorded in the BRWRA 

(AMOC and IFT 2005: TC-12). Gray wolves have been known to kill black bears near their 

dens and to take over kill sites occupied by black bears (Ballard and Gipson 2000, Ballard et 

al. 2003), but interactions between Mexican wolves and black bears have not been 

documented. Two other Mexican wolf deaths have been attributed to predators, but 

identification of specific predators were not provided (USFWS 2008: Population Statistics, 

USFWS 2004, USFWS 2006a). 

Wolf – Human Interactions

Wolves’ reactions to humans include a range of non-aggressive to aggressive behaviors, and 

may depend on their prior experience with people. For example, wolves that have been fed 

by humans, habituated, or reared in captivity may be more apt to show fearless behavior 

towards humans than wild wolves; diseased wolves may also demonstrate fearless behavior 

(McNay 2002, Fritts et al. 2003). In North America, wolf-human interactions have increased 

in the last three decades, likely due to increasing wolf populations and increasing visitor use 

of parks and other remote areas (Fritts et al. 2003). Generally, wild, unhabituated wolves are 

not considered a threat to human safety (McNay 2002). However, one recent human death in 

Canada has been attributed to wolves (International Wolf Center 2008). 

33
In the BRWRA, wolf-human interactions have been documented. For example, between 

1998 and 2003, 33 cases of wolf-human interaction were documented in the BRWRA; the 

majority of these (64 percent) were considered investigative searches in which wolves 

ignored human presence. In several cases (27 percent), wolves approached humans in a nonthreatening manner, and in three reports wolves displayed aggressive behavior (charging) 

toward humans (AMOC and IFT 2005: TC-15). A majority of the interactions involved 

wolves recently released from captivity, suggesting that wolves released from captivity may 

be more prone to initial fearless behavior toward humans, despite appropriate captive 

management and selection criteria for release candidates (AMOC and IFT 2005: TC-22). 

Wolves are known to kill dogs virtually everywhere the two coexist (Fritts et al. 2003), thus 

the presence of dogs may provoke investigative or aggressive behavior. Dogs were present 

in many of the cases (including the three charges, in which the aggression appeared to focus 

on the dogs rather than the humans) (AMOC and IFT 2005: 22). Aversive conditioning or 

removal of the wolf was applied in all cases of wolf-human interaction. 

Humans may also be a significant source of mortality for wolves. Human-caused mortality is 

a function of human densities in and near occupied wolf habitat and human attitudes toward 

wolves (Kellert 1985, Fritts and Carbyn 1995, Mladenoff et al. 1995). Sources of mortality 

may include accidental incidents such as vehicle collision, or intentional incidents such as 

illegal shooting of protected wolves. In areas where humans are tolerant to the presence of 

wolves, wolves demonstrate an ability to persist in the presence of a wide range of human 

activities (e.g., near cities and congested areas) (Fritts et al. 2003). In the BRWRA, vehicular 

collision and illegal shooting are the two biggest mortality sources of Mexican wolves 

(USFWS 2008: Population Statistics) (and see “Physical Description and Life History”, 

above). 

34
CONSERVATION ASSESSMENT 

Threats to the Gray Wolf in the Southwest

The ESA defines an “endangered species” as “any species which is in danger of extinction 

throughout all or a significant portion of its range” 16 U.S.C 1532(6). Similarly, a 

“threatened species” is “any species which is likely to become an endangered species within 

the foreseeable future throughout all or a significant portion of its range” 16 U.S.C 1532(20). 

Species are listed as threatened or endangered if it is determined that one or more of the 

following five factors in section 4(a)(1) of the ESA are responsible for their condition: 

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

 or range; 

 (B) Overutilization for commercial, recreational, scientific, or educational purposes; 

 (C) Disease or predation; 

 (D) The inadequacy of existing regulatory mechanisms; or, 

 (E) Other natural or manmade factors affecting its continued existence. 

Subsequent 5-factor analyses are conducted periodically while a species is listed to assess its 

status and ensure that conservation actions are addressing current threats. Finally, a 5-factor 

analysis is conducted when a species is proposed for delisting due to recovery to ensure that 

none of the factors continue to threaten or endanger the species. 

Several 5-factor analyses have been conducted for the Mexican wolf. In the initial proposal 

to list the Mexican wolf as endangered in 1975, the Service found that threats from habitat 

loss (Factor A), sport hunting (Factor B), and inadequate regulatory protection from human 

persecution (Factor D) were responsible for the subspecies’ decline and near extinction (40 

FR 17590-17591, April 21, 1975). In the 1978 listing of the entire gray wolf species as 

endangered throughout the coterminous United States and Mexico (except for Minnesota 

where it was classified as threatened), the Service identified the same threats (43 FR 9607-

9615, March 9, 1978). 

In 2003, when the Service reclassified the gray wolf into three distinct population segments, 

the agency assessed threats to the Mexican wolf as a part of the SWDPS (68 FR 15804-

15875, April 1, 2003). The reclassification rule stated that habitat destruction or 

modification (Factor A) was not currently considered a threat or deterrent for restoration of 

southwestern (Mexican) gray wolves based on the 1982 Mexican Wolf Recovery Plan which 

stated that sufficient habitat existed at that time to support current recovery plan objectives. 

“Take” for commercial or recreational purposes (Factor B) was not considered a threat. 16 

U.S.C 1532(19). Diseases and parasites (Factor C), which are known to be an important 

consideration in wolf conservation, were not known to be significant factors in the decline of 

the Mexican wolf, and there was no reason to believe they would hinder recovery. Illegal 

killing (“human predation”, considered Factor C in the rule) was recognized as a factor that 

may slow, but not likely preclude, recovery in the Southwest. Regulatory protection of 

reintroduced Mexican wolves was deemed adequate (Factor D). Finally, public attitudes 

35
toward gray wolves were cited as a primary determinant in the long-term recovery status of 

wolves (Factor E), and the rule anticipated that the potential for human-wolf conflicts would 

increase as the number of wolves increased. 

A current 5-factor analysis provides an opportunity to assess threats to the Blue Range 

population based on information available since the 2003 reclassification. 

 

Factor A 

Factor A considers whether habitat alteration threatens the species in either the present or the 

future (i.e., “present or threatened destruction, modification, or curtailment of its habitat or 

range”). While knowledge of current and ongoing habitat alteration informs an assessment 

of threats to the present Blue Range population, the degree to which habitat alteration may 

hinder future recovery would be made by considering projections of future events and 

landscape trends in relation to recovery criteria that specify the abundance or distribution of 

wolves needed for recovery and by considering any future modifications to the boundaries of 

the BRWRA/MWEPA. Lack of an up-to-date recovery plan containing such criteria and lack 

of a determination of how the BRWRA/MWEPA may be modified preclude such an analysis 

(see Road to Recovery and Status of National Gray Wolf Recovery and Implications for the 

Mexican Wolf, above). However, available results from simulations of future wolf habitat 

will be briefly discussed for insight into development trends that may warrant attention as 

decisions affecting the future of the reintroduction and recovery effort are made. 

The three fundamental ecological conditions necessary for wolf habitat include large area 

size, adequate prey, and security from human exploitation (Carbyn and Fritts 1995, and see 

“Gray Wolf Biology and Ecology”, above). Factor A considers roads as an element of 

habitat suitability, specifically as they relate to wolf mortalities due to vehicle collision (e.g., 

a form of human exploitation). Other sources of human-caused mortality will be discussed 

under Factors D and E, below. 

The BRWRA was selected for the reintroduction effort based on its size and its abundance of 

native prey species, as well as its topography, water availability, Federal land status, human 

density, road density, and historic inhabitance by wolves (USFWS 1996: 2-2 - 2-4). Since 

the designation of the BRWRA in 1998, the recovery area has not been curtailed in size, and 

thus continues to provide 17,775 km2 (6,845 mi2) of ecologically suitable wolf habitat, 95% 

of which occurs on Forest Service lands (63 FR: 1752-1772). The 1982 Mexican Wolf 

Recovery Plan suggested that a population of 100 wolves could likely be supported in an area 

of 5000 mi2 (USFWS1982), and the FEIS found that the BRWRA was large enough to 

support the recovery’s plan recommendation to establish a population of at least 100 wolves 

(USFWS 1996: 2-5). In 2000, WMAT agreed to allow wolves to inhabit FAIR, and in 2002 

signed an agreement allowing direct release of wolves onto FAIR, providing an additional 

6,475 km2 (2,500 mi2) of wolf habitat. Thus, since the reintroduction project began, the size 

of the reintroduction area has effectively increased. 

Initial projections in the FEIS estimated that the BRWRA contained adequate prey to support 

a population of 100 wolves; prior to the reintroduction, a population of 15,800 elk (average 

density 3.7/km2), and 57,170 mule deer and white-tailed deer (average density 13.36/ km2) 

36
were estimated to be present in the BRWRA (USFWS 1996). The 3-Year Review 

hypothesized that based on the author’s estimation of prey base, the BRWRA could support a 

minimum of over 200 wolves (Paquet et al. 2001). In the 5-Year Review, AMOC recognized 

that although AGFD, NMDGF, and WMAT collect data on prey abundance, data are not 

available or comparable for the entire BRWRA. However, AMOC concluded that adequate 

prey exists based on lack of indication that wolves are food limited. That is, starvation and 

interspecific strife have not been documented in the Blue Range population, and only two 

cases of significant weight loss have been documented (AMOC and IFT: TC-21). However, 

the 5-Year Review also hypothesized that inadequate prey vulnerability (as opposed to 

biomass) due to ephemeral snow pack in winter months may contribute to small litter sizes 

(AMOC and IFT: TC-18), although conclusive data has not been gathered to support or 

negate this hypothesis and other hypotheses for litter size are offered. The 5-Year review 

also stated that no detectable changes in big game availability have occurred as a result of 

wolf reintroduction (AMOC and IFT: TC- 21). In recognition of their need for information 

related to prey abundance and distribution, AMOC recommended that an advisory group be 

convened to provide technical expertise on native ungulate populations, prey base dynamics, 

and relevant monitoring techniques (AMOC and IFT 2005: ARC – 6). There is no indication 

from annual project reports conducted since the 5-Year Review that prey availability is a 

limiting factor for the Blue Range wolf population USFWS 2006a; AGFD et al. 2007). 

Based on this information, it seems likely that the BRWRA contains adequate prey to support 

the reintroduced population, but adequate information is unavailable to provide a firm 

conclusion. 

Roads are a significant form of habitat modification to wolves because they are known to 

facilitate human access to areas occupied by wolves. Specifically, roads are a source of 

vehicular traffic and wolf mortality due to vehicle collision, as well as providing numerous 

access points for hunters and trappers, and supporting more residences, farms, and domestic 

animals, which increase the likelihood of wolf interactions with humans and livestock. Thus, 

it has been recommended that areas targeted for wolf recovery have low road density of 

approximately 1 mile of road per square mile of area, or 1.6 km of road per 2.56 square 

kilometer (Thiel 1985). Road density in the BRWRA was estimated at 0.8mi road/mi2

 area 

prior to the reintroduction (Johnson et al. 1992: 48). Roads in the BRWRA primarily exist to 

support forest management, livestock grazing, recreational access, and transport of forest 

products (USFWS 1996: 3-13). In the decade since the reintroduction has been underway, 

calculation of road density in the Gila and Apache National Forests has not been conducted, 

and a formal comparison between prior and current road density in the BRWRA is not 

possible without that information. 

Vehicular collision has been the second biggest source of mortality for wolves in the Blue 

Range population between 1998 and July 2008 (12 out of 62 total documented Mexican wolf 

deaths) (USFWS 2008: Population Statistics). With the exception of a high of four 

vehicular-related wolf deaths in 2003, annual vehicular-related deaths have ranged from zero 

to two per year (USFWS 2008: Population Statistics). The loss of any animal, particularly a 

breeding adult, tends to be more important when a population is small in size and has a 

limited number of breeding adults. However, although this cause of death is notable in that it 

ranks as the second leading cause of mortality in the Blue Range population, it does not seem 

37
to be occurring at a level significant to hinder population growth toward the population 

objective of 100 and has not been identified in previous project evaluations (e.g., Paquet et 

al. 2001, AMOC and IFT 2005) as a significant threat. In lieu of information on changes in 

road density (or traffic patterns, for which a baseline was not provided in the FEIS) in the 

BRWRA and in areas outside of the BRWRA through which wolves may try to disperse, the 

annual number of mortalities from vehicle collision is relied upon as an indication of the 

severity of this threat, which seems to be minimal at current levels. 

Habitat necessary for wolves in the future will entail the same ecological conditions as it 

does today, namely adequate prey, large areas, and security from excessive mortality (Fritts 

and Carbyn 1995). Several regional spatially-explicit population habitat viability analyses 

have been conducted in recent years to identify suitable gray wolf habitat in the Southwest, 

southern Rockies, and Mexico, and assess how suitability may change over time. Given that 

site-specific assessment of future habitat threats is precluded by lack of recovery criteria and 

potential modification to the BRWRA/MWEPA (see “The Road to Recovery”, above) 

consideration of these analyses can at least provide an indication of trends that may affect 

recovery and should be monitored. 

According to Carroll et al. (2003, 2005, 2006), there are a number of adequately-sized, 

ecologically suitable blocks of habitat in the Southwest, southern Rockies, and Mexico for 

establishment of wolf populations. However, model simulations suggest that these sites are 

impacted in the future by human population growth and associated road development on 

public and private lands surrounding core wolf habitat (Carroll et al. 2003, Carroll et al. 

2005, Carroll et al. 2006). 

For example, simulations of gray wolf establishment at sites in the Southwest (Utah, 

Colorado, Arizona, New Mexico, and Trans-Pecos Texas) and Mexico (Sonora, Chihuahua, 

Coahuila, Nuevo Leon, Durango, Tamaulipas, and portions of Zacatecas and San Luis 

Potosí) suggest that habitat that is currently suitable for reintroduction and persistence of 

gray wolf populations will be less able to support wolf populations in the year 2025 (Carroll 

et al. 2005). Development (i.e., roads) on public and private land resulted in a 25 percent 

decline in carrying capacity of the United States portion of the region by the year 2025, with 

private land development accounting for two-thirds of this decline. Extinction risk at 

individual reintroduction sites for current scenarios was generally low, but increased in future 

scenarios by as much as 20 percent. The increase in extinction risk was in part based on a 

metric used to estimate wolf mortality that captures the association between wolf mortality 

and proximity to roads and areas of high human density. (This metric captures a suite of 

human-caused mortality sources related to roads, e.g., vehicle collisions as well as poaching, 

therefore it is impossible to tease out effects solely from vehicle collision and simulation 

results are perhaps equally applicable to considerations of social tolerance and illegal killing, 

Factor E). Simulations of New Mexico and Colorado reintroduction sites showed the 

greatest vulnerability to landscape development, as compared to larger core habitat blocks in 

Arizona. Connectivity between reintroduction sites also diminished substantially by 2025, 

leaving some sites relatively isolated (Carroll et al. 2005). 

38
In addition to the trends of increasing human population growth and resultant development 

on public and private lands explored in these analyses, other potentially significant sources of 

habitat modification that may impact future recovery efforts in the region could include the 

United States-Mexico border fence or climatic factors, depending on the location of future 

reintroduction and recovery efforts. 

Summary statement: Threats related to habitat destruction, modification, or curtailment do 

not likely threaten the Blue Range Population at the current time, based on an increase in the 

area available to reintroduced wolves since the project began, lack of indication that wolves 

are food-limited, and a relatively small number of vehicular-related wolf deaths each year. 

Continued attention to habitat-related threats, particularly those that affect area size, prey 

availability, and road-related mortality, will be necessary as the BRWRA population expands 

toward the population objective of 100, if modification to the BRWRA/MWEPA occurs, and 

when recovery criteria are developed. 

In spite of this finding, there are several issues closely related to habitat curtailment that 

warrant mention: the regulations associated with the internal and external boundaries of the 

BRWRA, and management procedures related to livestock depredation in the BRWRA. 

These issues are discussed under Factor D, below, because they are viewed as management 

constraints placed on habitat that otherwise is of sufficient size and ecological condition to 

support the existing population.

Factor B

Since the inception of the Mexican wolf reintroduction, the Service has not authorized legal 

killing or removal of wolves from the wild for commercial, recreational (i.e., hunting), 

scientific, or educational purposes. Illegal killing of wolves for their pelts is not known to 

occur in the Southwest, nor is illegal trafficking in wolf pelts or parts known to occur. 

Mexican wolf pelts and parts from wolves that die in captivity or in the wild are used for 

educational purposes, such as taxidermy mounts for display, when permission is granted 

from the Service; most wolf parts are sent to a curatorial facility at the University of 

New Mexico to be preserved, catalogued, and stored. A recreational season for wolf hunting 

is not currently authorized in the Southwest, and would only become so in conjunction with 

post-delisting monitoring and applicable state regulations. Several ongoing Mexican wolf 

research projects occur in the BRWRA or adjacent tribal lands by independent researchers or 

project personnel, but these studies have utilized radio-telemetry, scat analysis, and other 

non-invasive methods that do not entail direct handling of, or impact to, wolves. Non-lethal 

research for the purpose of conservation is also conducted on Mexican wolves in the SSP 

captive breeding program; current projects include research on reproduction, artificial 

insemination, and semen collection (USFWS 2006a). 

Interagency Field Team and other agency personnel handle and confine wolves during the 

administration of vaccines and medical treatment, and during non-lethal control or capture 

actions in the field and captive pre-release facilities, but these activities are not considered 

scientific in purpose; rather they are regular management activities necessary for 

implementation of the reintroduction project. These activities have rarely resulted in the 

39
unintended death of a wolf (two capture-related wolf deaths in the wild (USFWS 2006a, 

USFWS 2001) and one capture-related wolf death in a captive pre-release facility (Siminski 

2005). 

Summary statement: Overutilization for commercial, recreational, scientific, or educational 

purposes is not considered a threat to the Mexican wolf because the Service does not 

authorize legal killing or removal of wolves from the wild for commercial, recreational (i.e., 

hunting), scientific, or educational purposes, illegal killing or trafficking for pelts is not know 

to occur, and non-lethal techniques are used during Mexican wolf research. 

Factor C

A number of viral, fungal, and bacterial diseases and endo- and ectoparasites have been 

documented in gray wolf populations (Kreeger 2003). Typically, diseases are transmitted 

through direct contact (e.g., feces, urine, or saliva) with an infected animal, or by aerosol 

routes. Parasites are picked up through water, food sources, or direct contact; wolves are 

able to tolerate a number of parasites, such as tapeworms or ticks, but at times such 

organisms are lethal (Kreeger 2003). 

There is little research specific to disease or contaminant issues in Mexican wolves, and little 

documentation of disease prevalence in wild wolves in the Blue Range population. 

Information from studies of other wild North American gray wolf populations is summarized 

in the threat analyses conducted for the delisting of the Great Lakes and Northern Rockies 

populations based on disease occurrences in those geographic regions, and can be referenced 

for a broader list of diseases than those described below (see 72 FR 6051-6103, February 8, 

2007 and 73 FR 10513-10560, February 27, 2008). Contaminants that occur in the 

environment may have the potential to affect wolves through transfer in the food chain, but 

little data has been published on pollutant or pesticide levels in wolves (e.g., see Shore et al. 

2001). 

Mexican wolves are routinely vaccinated for rabies, distemper, parvovirus, and corona virus 

before release to the BRWRA from captive facilities USFWS 2006a). Wolves that are 

captured in the wild are vaccinated for the same suite of diseases. The following descriptions 

of these diseases have been summarized based on Kreeger 2003 unless otherwise noted. 

Rabies, caused by a rhabdovirus, is an infectious disease of the central nervous system 

typically transmitted by the bite of an infectious animal. Fox variants of rabies have been the 

primary vectors when the disease is reported in wolves. An animal infected by rabies may 

exhibit a variety of symptoms as it proceeds through several stages of infection; the animal 

may experience paralysis of the throat and excessive salivation, advancing to a state of 

agitation in which the animal may bite at inanimate objects, people, or other animals, to an 

advanced paralysis that leads to death. Rabies can spread between infected wolves in a 

population (e.g., among and between packs), or between populations, resulting in severe 

population declines. Once an animal is infected, it is untreatable. 

A rabies outbreak in and near the BRWRA began in 2006 in eastern Arizona and continues 

through 2008, with positive rabies diagnoses (fox variant) in both foxes and bobcats. No 

40
wolves in the Blue Range population have been diagnosed with rabies during this outbreak 

(AZDHS 2008: Rabies Statistics and Maps) or throughout the history of the reintroduction 

(USFWS 2008: Population Statistics). 

Canine distemper, caused by a paramyxovirus, is a febrile disease typically transmitted by 

aerosol routes or direct contact with urine, feces, and nasal exudates. Symptoms of 

distemper may include fever, loss of appetite, loss of coordination (ataxia), shortness of 

breath (dyspnea), swollen feet, and eye and nose discharge. Death from distemper is usually 

caused by neurological complications (e.g., paralysis, seizures). Once an animal is infected, 

distemper is untreatable. Although wolf populations are known to be exposed to the virus in 

the wild, mortality from distemper in wild wolves is uncommon. 

Two Mexican wolf pups brought to a wolf management facility in 2000 from the wild were 

diagnosed with distemper, indicating they were exposed to the disease in the wild, and died 

in captivity (AMOC and IFT: TC-12). These are the only known mortalities due to 

distemper documented in relation to the Blue Range population, and are considered captive 

deaths rather than wild mortalities (USFWS 2008: Population Statistics). 

Canine parvovirus is an infectious disease caused by a virus that results in severe 

gastrointestinal and myocardial (heart disease) symptoms. Canine parvovirus can be 

transmitted between canids (e.g., wolves, coyotes, dogs), but not to other hosts such as 

humans or cats (although there are other strains of parvovirus that can infect both). Canine 

parvovirus is typically transmitted through contact with feces or vomit, where it can survive 

for months. Symptoms of an infected adult animal may include severe vomiting and 

diarrhea, resulting in death due to dehydration or electrolyte imbalance. Pups may die from 

myocardial (heart) disease if infected with canine parvovirus while in utero or soon after 

birth from cardiac arrhythmias. Although canine parvovirus has been documented in wild 

wolf populations, there are few documented mortalities due to parvovirus; it is hypothesized 

that parvovirus is a survivable disease, although less so in pups. Captive wolves have been 

successfully treated with fluid therapy until symptoms abated. 

Three Mexican wolf pups brought to wolf management facilities from the wild died from 

canine parvovirus in 1999, indicating that they had been exposed to the disease in the wild 

(AMOC and IFT 2005: TC-12). Mortality from canine parvovirus has otherwise not been 

documented in the Blue Range population (USFWS 2008: Population Statistics). (Note: one 

pup died in the pen in the wild and is the one disease-related mortality documented for the 

wild population, the other two pups died at a pre-release captive facility and are considered 

captive mortalities.) 

Corona virus is an infectious disease transmitted primarily through feces (Zarnke et. al. 

2001). Symptoms in canids (dogs, wolves, coyotes) include diarrhea and dehydration. 

Infection of dogs and coyotes by both corona virus and canine parvovirus has been 

documented, resulting in symptoms similar to canine parvovirus but more severe (Zarnke et 

al. 2001). Mortality due to corona virus has not been documented in the Blue Range 

population (USFWS 2008: Population Statistics). 

41
Monitoring of collared wolves in the Blue Range population has not documented significant 

levels of wolf mortality due to disease. Neither the 5-Year Review nor annual reports in the 

following years indicate that disease is a concern or is significantly impacting population 

growth rate. Of 62 total documented wolf deaths between 1998 and July 2008, one death 

was attributed to disease (canine parvovirus) (USFWS 2008: Population Statistics). Some 

diseases are more likely to spread as wolf-to-wolf contact increases (Kreeger 2003), thus the 

potential for disease outbreaks may increase as the population expands in numbers or density. 

Even if disease occurrences increase in number, disease may not threaten the population 

when considered as an isolated threat; however, as with any mortality source, its significance 

may increase when considered in conjunction with other demographic factors, such as low 

recruitment. 

Summary statement: Disease is not considered a threat to the Mexican wolf based on 

known occurrences in the Blue Range population and the active vaccination program. 

In addition to disease, Factor C also requires consideration of threats due to predation. No 

wild predator regularly preys on wolves (Ballard et al. 2003). Although large prey may 

occasionally kill wolves during self-defense (Mech and Peterson 2003), this is rare and not 

considered predation on the wolf. Between 1998 and 2007, three documented Mexican wolf 

mortalities were due to predators (USFWS 2006a, AGFD et al. 2007). Monitoring of 

Northern Rockies wolf populations demonstrated that wolf-to-wolf conflicts may be the 

biggest source of predation among gray wolves, but this typically occurs from territorial 

conflicts and has not occurred at a level sufficient to affect these populations’ viability (73 

FR 10513-10560, February 27, 2008). As the Mexican wolf population begins to saturate 

available habitat, wolf mortalities resulting from territorial conflicts may become more 

prevalent. However, information does not indicate that wolf-to-wolf or other sources of 

predation are a threat to the current or future Mexican wolf recovery effort. 

Intentional human-caused mortality of wolves has sometimes been considered “human 

predation” by the Service and assessed under Factor C, but this assessment places intentional 

human-caused mortality under Factor E, as it is an indication of social tolerance of wolves. 

Summary statement: Predation is not considered a threat to the Mexican wolf because no 

wild predator regularly preys on wolves and only a small number of predator-related wolf 

mortalities have been documented in the Blue Range population. 

Factor D

A number of concerns have been raised regarding the adequacy of regulatory mechanisms 

being applied to the Mexican wolf recovery program and reintroduction project pursuant to 

the ESA. To some degree, it is normal to expect that significant concerns will be raised by 

different factions of society during the implementation of a complex program such as wolf 

recovery. The fact that such concerns exist does not necessarily mean that regulatory 

mechanisms are inadequate for the conservation and recovery of the species. Rather, it may 

indicate that there are several methods for achieving objectives, with pros and cons inherent 

in each. For example, some who support wolf recovery may want wolves to have 

endangered status across their entire range, whereas others may support the flexibility offered 

42
by a non-essential experimental designation in certain locations. However, when both the 

public and the implementing agencies indicate that regulatory mechanisms are not fully 

supporting stated objectives (i.e., establishment of a wild population of at least 100 wolves), 

a mid-course correction in strategy may be necessary. 

The adequacy, or appropriate implementation of the following regulatory mechanisms have 

been raised in the 3-Year Review, 5-Year Review, annual reports of the reintroduction 

project, or active litigation: 1) the internal and external boundaries of the BRWRA, 

including the configuration of the Primary and Secondary Recovery Zones and the 

regulations governing removal of wolves due to boundary violations; 2) regulations or 

management procedures for livestock management (e.g., carcass removal); 3) management 

procedures related to livestock depredation (SOP 13); 4) implementation of conservation 

actions by Federal agencies pursuant to section 7(a)(1) of the ESA; 5) the transfer of 

management authority of the reintroduction project from Service to AMOC; and, 6) revision 

of the 1982 Mexican Wolf Recovery Plan. 

The efficacy of the configuration of the internal and external boundaries of the BRWRA has 

been questioned in both the 3-Year and 5-Year reviews, as well as internally within the 

agencies responsible for the reintroduction and recovery effort. Paquet et al. (2001:61) stated 

that the small size of the Primary Recovery Zone (the Apache National Forest, the zone 

designated for release of wolves) was hindering rapid establishment of the wild population 

and recommended that the Final Rule be modified to allow releases in the Secondary 

Recovery Zone (the Gila National Forest). In a follow-up to this recommendation, AMOC 

provided a detailed explanation in the 5-Year Review of why modification of the internal 

boundaries of the BRWRA had not yet occurred by 2005. In short, initial progress toward 

revising the Final Rule between 2001 and 2003 was eclipsed by the Service’s subsequent 

intent to revise the 1982 Mexican Wolf Recovery Plan to provide big picture guidance for the 

recovery program before proceeding with revision to the reintroduction project. After the 

SWDPS recovery team was put on hold due to litigation in 2005, the Service indicated that 

AMOC should resume consideration of necessary modifications to the reintroduction project, 

including boundary modifications (AMOC and IFT 2005: AC-14-17). AMOC concluded in 

the 5-Year Review that the provision governing release of wolves solely into the Primary 

Recovery Zone restricts the pool of available release candidates, restricts release of wolves 

for management purposes such as genetic augmentation, and causes public perception issues 

between the states of Arizona and New Mexico (AMOC and IFT 2005: AC-14-15). Thus, 

the 5-Year Review recommended that the Final Rule be modified to expand the area in which 

wolves could be released and translocated. 

In the 3-Year Review, Paquet et al. (2003: 23, 65) also noted that wolves were dispersing 

outside of the external boundaries of the BRWRA into the MWEPA and would continue to 

do so, given the long-distance movements of normal wolf activity. They concluded that the 

provision in the Final Rule requiring removal of wolves that establish territories wholly 

outside of the BRWRA boundaries was contrary to normal wolf movement patterns and 

recommended that the Final Rule be modified to allow wolves to establish territories outside 

of the BRWRA. In the 5-Year Review, AMOC again explained why action had not been 

taken toward this recommendation by 2005, referencing the previous explanation of progress 

43
toward revising the internal boundaries, as well as acknowledgement that the requirement for 

removal of wolves due to boundary violations had been carefully developed during the 

planning of the reintroduction based on public comment (AMOC and IFT 2005: AC-17-19). 

AMOC concluded, based on several additional years of project implementation since the 3-

Year Review, that boundary removals were hindering natural dispersal and colonization, 

creating unrealistic public expectations that wolves could be successfully captured when they 

left the BRWRA, and creating staffing and logistical concerns related to the effort required to 

attempt such removals (AMOC and IFT: AC-18). Calculations in the 5-Year Review 

demonstrated that a hypothetical wolf dispersing the average lone-movement distance (i.e., 

87 km) in a random direction from the center of the BRWRA and FAIR would end up 

outside the BRWRA 66 percent of the time, and indeed project data was showing that the 

majority of single dispersers were ending up outside of the BRWRA (AMOC and IFT: TC20). Between 1998 and December 2007, removal of wolves from the wild for boundary 

violations was the second leading cause of management removal in the BRWRA (39 

boundary removals out of 142 total removals) (USFWS 2008: Population Statistics). Thus, 

AMOC recommended that the Final Rule be modified to allow wolves to expand into the 

MWEPA in order to reduce removals associated with boundary violations (AMOC and IFT: 

TC-24) and committed to further analysis of the extent to which boundaries should be 

modified (AMOC and IFT: ARC-3). 

During the planning of the reintroduction project, the amount of permitted public lands 

grazing in the BRWRA was identified as a likely source of conflict for the reintroduction due 

to the potential for wolf depredation of livestock and related social and economic issues 

(USFWS 1996: 2-4). In the 3-Year Review, Paquet et al. (2001: 52-54) concluded that 

livestock depredation by wolves was occurring and that wolf-livestock interaction would 

continue due to the spatial and temporal occurrence of livestock in the recovery area. They 

stated that sufficient information was not provided for a detailed analysis of the adequacy of 

the depredation control program. They followed this with a recommendation that 

implementation of specific livestock husbandry techniques, particularly removal of carcasses, 

could lessen the potential of wolves becoming habituated and subsequently depredating 

livestock and therefore should be required for livestock operators on public lands (p. 67). 

In the 5-Year Review, AMOC analyzed available data to determine the extent to which a 

carcass feeding issue exists. They concluded that the number of depredations committed 

after wolves were known to have fed on a carcass was too small of a sample size to 

determine whether a “depredation predisposition” exists (AMOC and IFT: AC-31). They 

also investigated Federal and State authority to regulate carcass removal and related 

husbandry practices and determined that Federal agencies (Forest Service and Bureau of 

Land Management) do not have the authority to require lease and permit holders to remove 

carcasses from public land, and that State statutes further constrain carcass removal (AMOC 

and IFT 2005: AC-30 – 31). Thus, AMOC committed to development of a conceptual 

incentives program that would address this and related wolf nuisance and depredation issues 

(AMOC and IFT 2005: AC-32). Two recent studies of factors affecting wolf depredation of 

cattle in the Northern Rockies and the Great Lakes provide inconclusive results as to whether 

wolves display a depredation predisposition (Mech et al. 2000, Bradley and Pletscher 2005). 

44
A second facet of conflict that has arisen between wolves and livestock in the BRWRA 

relates to management response to depredation events. Adaptive Management Oversight 

Committee developed Standard SOP 13 in 2005 to specify criteria for determining the status 

of depredating and non-depredating wolves and provide guidelines for conducting control 

actions in response to depredation events (USFWS 2008: Blue Range Reintroduction Project 

– Standard Operating Procedures). In particular, SOP 13 requires the removal of wolves 

involved in three depredation incidents in a 365-day period. Between 1998 and December 

2007, wolf-livestock conflict was the leading cause of management removal of wolves in the 

Blue Range population (70 livestock-related wolf removals out of 142 total removals); 

removals in 2006 and 2007, the years in which SOP 13 was actively implemented, had the 

highest number of removals of all years (16 and 19 removals, respectively) (USFWS 2008: 

Population Statistics). At the end of 2007, the lead agencies acknowledged that the 

aggressive removal rate of wolves by management due to depredation, nuisance, and 

boundary issues was hindering population growth, although they also reiterated the 

importance of demonstrating a high level of responsiveness to conflicts (AGFD et al. 2007). 

Two lawsuits currently challenge the Service’s adoption of SOP 13 for failure to comply with 

NEPA (Defenders of Wildlife et al. v. Tuggle et al., Civil No. 4:08-cv-280-DCB (D. Ariz.)) 

and on the grounds that SOP13 does not “further the conservation of” the Mexican wolf as 

required by section 10(j) of the ESA and is therefore arbitrary and capricious under the 

Administrative Procedures Act (APA) (WildEarth Guardians et al. v. USFWS et al., Civil 

No. 2:08-cv-820-DCB (D. Ariz.)). These challenges have not yet been resolved, but 

resolution of the second case in particular will provide insight into whether SOP 13 

contributes to the adequacy of existing regulatory mechanisms for the Mexican wolf. 

These two lawsuits also challenge the adequacy of regulatory mechanisms for the Mexican 

wolf on two other counts. The WildEarth Guardians et al. v. USFWS et al. lawsuit alleges 

the failure of the Forest Service to develop and carry out a program for the conservation of 

the Mexican wolf pursuant to section 7(a)(1) of the ESA, while the Defenders of Wildlife et 

al. v. Tuggle et al. lawsuit alleges the Service has delegated authority to AMOC for the 

reintroduction project (see Road to Recovery, above) in violation of both the ESA and the 

APA. Resolution of these challenges will likewise provide insight into whether these 

regulatory provisions are contributing to the conservation and recovery of the Mexican wolf. 

Last, both the 3-Year and 5-Year reviews reiterate that the 1982 Mexican Wolf Recovery 

Plan fails to provide current guidance to the reintroduction, particularly regarding 

establishment of objective and measurable recovery criteria, and recommend that a revised 

plan be developed (Paquet et al. 2001:64, AMOC and IFT 2005: AC-13). A revised recovery 

plan has still not been finalized, for complex logical reasons (see Status and Implications of 

National Gray Wolf Recovery for the Mexican Wolf, above, as well as AMOC and IFT 

2005: AC-10). 

 

While a number of substantial concerns have been raised related to the adequacy of the 

ESA’s regulatory mechanisms for the Mexican wolf reintroduction project and gray wolf 

recovery program in the Southwest, the concerns (including those being resolved through 

litigation) are aimed at the interpretation and implementation of available mechanisms by the 

Service and its interagency partners rather than the adequacy of the mechanisms themselves. 

45
Reintroduction and recovery programs can be, by their very nature, management-intensive 

and subject to trial and error. While the conservation assessment reiterates prior findings that 

several of the ESA’s provisions have not been implemented in a manner or to the degree that 

information now suggests is necessary, the assessment acknowledges the ongoing efforts of 

the Service and the lead agencies to address these inadequacies. Specifically, these efforts 

include the quarterly meetings of the Adaptive Management Working Group, which includes 

AMOC and other State and county governments, to gather input and address issues of 

concern (AGFD 2008); the intent of the Service to modify the Final Rule as demonstrated by 

a recent public scoping process, including a series of public meetings held in November and 

December 2007 to consider modifications to the Final Rule (72 FR 44065-44069, August 7, 

2007; and see USFWS 2008: Rule Modification); multiple attempted revisions of the 1982 

Mexican Wolf Recovery Plan; and the development of a Mexican-wolf-specific incentives 

program and application of existing incentives available through State programs to address 

socioeconomic issues related to wolf conflicts. 

Summary statement: Current interpretation and implementation of several regulatory 

mechanisms are not adequately supporting the reintroduction and recovery effort. 

Modifications to the implementation of these mechanisms that will support the reintroduction 

and recovery effort have been identified and are actively being pursued. 

Factor E

Public opinion has long been recognized as a significant factor in the success of gray wolf 

recovery efforts (considerable literature exists on this topic, e.g., see Fritts et al. 2003, 

Boitani 2003, Primm and Clark 1996, Rodriquez et al. 2003, Bangs et al. 2004) and illegal 

killing of wolves by those opposed to wolf reintroduction and recovery efforts is proof of its 

importance. 

In the Southwest, extremes of public opinion vary between those who strongly support or 

object to the recovery effort. Support stems from such feelings as an appreciation of the wolf 

as an important part of nature and an interest in endangered species restoration, while 

opposition may stem from negative social or economic consequences of wolf reintroduction, 

general fear and dislike of wolves, or Federal land-use conflicts (Unsworth et al. 2005, Duda 

and Young 1995, Research and Polling 2008). Some ranchers, hunters and outfitters, and 

tribes in and near the BRWRA have experienced, and may continue to experience, negative 

social and economic impacts due to wolves, such as loss of revenue due to livestock 

depredation, fear for the safety of family members that may come into contact with wolves, 

stress due to the uncertainty of future economic losses wolves may cause, and anger at the 

government (Unsworth et al. 2005). 

Given the recognition of the potential for social intolerance of wolves and human-caused 

sources of wolf mortality, past recommendations for Mexican wolves estimated suitable 

habitat to occur when human density is less than 12 people per square mile (2.56 km2

), with 

an optimum density of less than six people per square mile (Johnson et al. 1992). In keeping 

with these guidelines, the BRWRA was selected in part due to its low human population 

density (estimated at 0.8/mi2

 prior to the reintroduction) (USFWS 1996: Table 3-3). 

46
Illegal take of wolves provides an indication of the level of social tolerance of the Mexican 

wolf reintroduction. In the BRWRA, illegal shooting of wolves has been the biggest single 

source of mortality since the reintroduction began in 1998. Illegal shootings have ranged 

from zero to seven per year between 1998 and July 2008 (USFWS 2008: Population 

Statistics). Out of 62 wild wolf mortalities documented in that timeframe, 28 deaths are 

attributed to illegal shooting (USFWS 2008: Population Statistics). Although AMOC 

attempts to address concerns about the reintroduction through outreach with affected citizens, 

management responsiveness, and education, these efforts have not been sufficient to alleviate 

some negative attitudes toward the Mexican wolf in the Southwest, nor has the independent 

depredation compensation program administered by Defenders of Wildlife, as evident by 

continued illegal shooting of wolves. 

Individual sources of human-caused mortality are not independently evaluated in project 

statistics (AMOC and IFT: TC-6), thus the significance of all cases of human-caused 

mortality (illegal shooting, vehicle collision, capture-related deaths, legal shooting, lethal 

control) are evaluated as a whole. The loss rates (mortality and missing wolves) for the Blue 

Range population between 1998 and 2003 were similar to those predicted during planning 

stages (25 percent overall), and notably, have been lower than those documented in other 

wolf populations (AMOC and IFT 2005: TC-12, 17). Given that combined sources of 

mortality are in-line with project projections, this suggests that mortality from a single source 

(i.e., illegal take) is not a significant threat at its current levels. 

However, the degree to which a wolf population is able to withstand a given level mortality 

depends on the population’s productivity, including factors such as the level of reproduction, 

and whether breeding animals are killed (Fuller 1989, Fuller et al. 2003, Ballard et al. 1987, 

Ballard et al. 1997). A large range of values for the mean annual percentage of wolves killed 

by humans at levels that did not suppress population growth has been documented for wolf 

populations (Fuller et al. 2003). For example, in populations where habitat has been 

saturated and territorial conflicts between wolves result in wolf mortality, human-caused 

mortality may take the place of such conflicts (i.e., compensatory mortality). In these 

situations, wolves may be quite resilient to levels of human-caused mortality that are 

comparable to levels of mortality that would otherwise occur (Fuller et al. 2003). In the 

Great Lakes, illegal killing and vehicular collisions were significant sources of mortality for 

wolves, but were ultimately not deemed to be threats to recovery, as the populations 

continued to expand in number and range over time (72 FR 6051-6103, February 8, 2007). 

Similarly, human-caused mortality of over 20 percent per year of collared wolves in the 

Northern Rockies did not preclude the populations’ abilities to expand in number and range 

(73 FR 10513-10560, February 27, 2008). A mortality rate of 0.34 has been estimated as the 

inflection point for wolf populations, with populations increasingly naturally when mortality 

rates are below this average and decreasing when mortality rates are above it (Fuller et al. 

2003). The Mexican wolf could be more susceptible to population decline at a given 

mortality rate than other gray wolf populations, however, based on lower reproductive rates, 

smaller litter sizes, and combined sources of mortality (AMOC and IFT 2005: TC-17). 

For example, the level of human-caused wolf mortality observed in the BRWRA becomes 

more significant when combined with removal of wolves for management purposes (e.g., 

47
boundary issues, cattle depredation, human nuisance, relocation, or pairing with another 

wolf), as these removals may have the same practical effect on the wolf population as 

mortality if the wolf is permanently removed (as opposed to translocated) -- that is, the 

population has one less wolf (see Paquet et al. 2001). Removal rates in the Blue Range 

population have been higher than projected in the FEIS, as have combined mortality/removal 

rates; from 1998-2003 the combined mortality/removal rate was 64 percent, as compared to a 

projection of 47% (AMOC and IFT 2005: 12-13). The number of wolf removals since the 5-

Year Review has persisted at high levels, primarily due to livestock depredation response 

(USFWS 2008: Population Statistics). In 2007, the combined mortality/removal rate (i.e., 

failure rate) was 0.47, a level likely too high for unassisted population growth (AGFD et al. 

2007). 

Summary statement: Human-caused mortality of Mexican wolves, of which illegal 

shooting is a significant proportion, in combination with removal actions deemed necessary 

by management to address wolf conflicts, are hindering the population’s growth toward the 

population objective of at least 100 wolves. 

48
The Conservation Principles of Resiliency, Redundancy, and Representation

With several factors hindering the progress of the Blue Range population in achieving the 

objective of at least 100 wolves in the wild, the population is not as secure or self-sustaining 

as it could be. However, none of the threats are so significant as to put the population at 

immediate risk of extirpation. Even with a current assessment of the security of the Blue 

Range population in relation to the five factors, the degree to which this population 

contributes to gray wolf recovery is still unclear. 

Consideration of the principles of resiliency, redundancy, and representation can help assess 

the contributions of the Blue Range population to recovery, although such an assessment is 

ultimately limited by the region’s lack of objective and measurable recovery criteria. These 

principles represent a recently popularized conceptualization of key elements of biological 

diversity conservation (Shaffer and Stein 2000) and provide a useful framework for 

discussing scientific concepts relevant to gray wolf conservation, including demography, 

environmental variability, and genetics. The Service has invoked the principles of resiliency, 

redundancy, and representation to describe recovery efforts for the gray wolf in the Northern 

Rockies and Great Lakes (see 72 FR 6051-6103, February 8, 2007; 73 FR 10513-10560, 

February 27, 2008), and for consistency, the conservation assessment will use these 

principles in similar fashion. These principles were not originally coined for the purpose of 

guiding recovery efforts under the ESA, nor as a collective do they represent formal, peerreviewed principles that establish any particular standard for conservation. 

Summary statement: The Service has invoked the conservation principles of resiliency, 

redundancy, and representation to guide and communicate the fundamental components of 

wolf conservation and recovery. 

Resiliency

Resiliency refers to a species’ (or population’s) ability to recover from disturbance and 

persist over time (Holling 1973). Gray wolves, as a species, have several characteristics that 

confer resiliency. First, their ability to use a variety of prey and habitat types helps to 

ameliorate fluctuations in food availability (Mech 1991, Weaver et al. 1996). Second, 

wolves are sometimes able to compensate for high levels of mortality with high levels of 

reproduction (although this has not necessarily been demonstrated by the Mexican wolf, see 

“Gray Wolf Biology and Ecology” and “Threats to the Gray Wolf in the Southwest: Factor 

E”, above) (Weaver et al. 1996). Finally, wolves’ ability to disperse long distances can result 

in demographic rescue; that is, a small or declining population can be bolstered by the arrival 

of immigrants (Brown and Kodric-Brown 1977). 

As a principle for guiding general conservation efforts across taxa, resiliency suggests that 

species that are more numerous and widespread are more resilient than those that are not 

(Shaffer and Stein 2000). Thus, the resiliency of a species or population can be measured by 

its persistence (also referred to as viability, or conversely, extinction risk, thus these terms 

are used somewhat interchangeably depending on context). Because population size has a 

49
significant bearing on population persistence, consideration of resiliency can provide context 

for assessing the current reintroduction objective to establish a population of at least 100 

wolves. 

Scientific theory and practice generally agree that a species represented by a small population 

faces a higher risk of extinction than a species that is widely and abundantly distributed 

(Goodman 1987, Pimm et al. 1988). The primary cause of this susceptibility to extinction is 

the sensitivity of small populations to stochastic (that is, uncertain) demographic events 

(Shaffer 1987). That is, “The dynamics of a small population are governed by the specific 

fortunes of each of its few individuals. In contrast, the dynamics of a large population are 

governed by the law of averages (Caughley 1994:217).” Sex ratios, survival, and 

reproduction may all be affected by demographic stochasticity. For example, in a given year 

or series of years, offspring could be predominantly one gender or the other, fewer 

individuals may survive, or reproduction may be below average, causing random population 

fluctations. Even in a constant environment, the population trajectory for a small population 

will vary from year to year due to these events. In small populations, including those with a 

positive growth rate, it is more likely that a wide deviation from average birth or survival 

results could result in a decline toward extinction from which the population would not be 

able to recover (Mills 2007). Thus, as a population grows larger and individual events tend 

to average out, the population becomes less susceptible to demographic stochasticity. And, 

the higher the population growth rate, the more quickly persistence times will increase with 

increases in population size (Shaffer 1987). Population sizes considered “small” (that is, 

susceptible to demographic stochasticity) have been described as those that are less than 30 

individuals, depending on age structure (Boyce 1992: 487), “on the order of 10s to 100s” 

(Shaffer 1987: 73), and over 100 (Mills 2007: 101). This being said, there is not a single 

population size that will ensure persistence (Thomas 1990). Rather, populations of various 

sizes, vital rates, and biological and ecological characteristics will simply have different risks 

of extinction. 

A variety of methods are available for estimating a species’ likelihood of persistence, ranging 

from complex theoretical or simulation models to simple observation of existing populations 

(Shaffer 1981) or best professional judgment (Mills 2007). Population viability analysis 

(PVA) and minimum viable population (MVP) analysis are tools that have been used in the 

past to develop numerical population targets for ESA recovery efforts (Clark et al. 2002). 

Both typically entail the use of complex theoretical or simulation models. Minimum viable 

population can be defined as the smallest population size required for a population to have a 

predetermined probability of persistence for a given length of time (Shaffer 1981). Minimum 

viable population has fallen out of favor in recent years, having been replaced with the 

closely related probabilistic approach of PVA (see Gilpin and Soule 1986, Beissinger and 

McCullough 2002). Population viability analysis is similar to MVP but simply does not 

require specification of a minimum population size to maintain the species’ viability (Boyce 

1992); rather, model output will describe the species’ likelihood of persistence over a given 

timeframe, for example, that at a population size of 500, a species has a 12 percent risk of 

extinction over the next 50 years (Beissinger and McCoullough 2002). 

50
The specification of extinction risk and timeframe are typically subjective in viability 

modeling efforts; there is no single set of values generally deemed acceptable within the 

scientific community to describe a (minimally) viable population (Allendorf and Luikart 

2007), nor does the ESA equate any such numeric values with endangerment or recovery 

(Vucetich et al. 2006). Rather, individual bias, or perhaps situational limitations, influences 

whether a 5 or 10 percent level of risk or a 50 or 500-year timeframe is appropriate for a 

given viability exercise. For example, Shaffer (1981:132) defined a minimum viable 

population for any species as “the smallest isolated population having a 99 percent chance of 

remaining extant for 1,000 years despite the foreseeable effects of demographic, 

environmental, and genetic stochasticity, and natural catastrophes.” 

Viability models can be tailored to consider questions about persistence based on information 

related to demography, genetics, management scenarios, or a host of other factors. Viability 

models developed to explore genetic issues (e.g., loss of diversity) may be quite different in 

structure and assumptions from models developed to explore demographic viability; for 

example, genetic PVAs may provide an effective population size opposed to a census (total) 

population size (see Representation, below). In some cases, models attempt to combine 

multiple kinds of information, such as genetics and demography, further contributing to their 

complexity. Although population viability analysis can provide powerful information when 

used appropriately, it is an intensive process with a number of shortcomings, including the 

subjective nature of determining appropriate extinction risk and time frame, time and cost 

necessary to gather adequate data, and the potential for results to be inappropriately applied 

in decision-making (Boyce 1992, Mills 2007: 252-265, Ewens et al. 1987, e.g., Patterson and 

Murray 2008). 

 

Based on the above, it is not surprising that a brief literature review of wolf-specific 

population viability analyses and other estimations of wolf viability generate a range of 

results that can be difficult to compare. For example, Reed et al. (2003) incorporated agestructure, catastrophes, demographic stochasticity, environmental stochasticity, and 

inbreeding depression in an MVP analysis (99 percent probability of persistence for 40 

generations) for a number of vertebrate species and recommended that minimum viable adult 

population size for the gray wolf was between approximately 1,400 and 6,300 wolves. Soule 

(1980) estimated an appropriate population size and area for short-term conservation for the 

gray wolf by incorporating data on wolf density, breeding structure, and carrying capacity, 

and recommended an absolute minimum effective population size of 100-200 wolves, or a 

census population size of at least 600 wolves and an area requirement of approximately 

12,000 km2

, an area larger than Yellowstone National Park (Soule 1980:163). Viability 

analysis of the gray wolf on Isle Royale predicted a population of 50 wolves would have a 

mean time to extinction of 73 years, with a 30 percent chance of surviving over 100 years 

(Vucetich et al. 1997). Theoretical analysis of this population demonstrated that an increase 

in the number of breeding units increased the mean time to extinction due to demographic 

stochasticity more strongly than an increase in population size, suggesting that the social 

structure of wolves may increase their susceptibility to demographic stochasticity compared 

with species in which breeding units are not limited to the number of social (breeding) 

groups in the population. 

51
Two viability analyses were conducted specific to the Mexican wolf prior to the 

reintroduction in 1990 and 1996, but neither was completed after being subject to peer 

review (IUCN 1996, Seal 1990). In both cases, data from extant Mexican wolf populations 

in the wild was unavailable, so information from other wild and captive wolf populations and 

the Mexican wolf captive population was used in modeling simulations to assess the effects 

of various reintroduction and management scenarios. The 1990 Mexican wolf PVA 

incorporated life history data, carrying capacity, environmental stochasticity, and inbreeding 

depression. Summary results found that populations of fewer than 50 wolves had a high risk 

of extinction but that populations of 100 or more wolves had a less than 5 percent 

probability of extinction over a 100-year time span (Seal 1990). The 1996 PVA, which 

incorporated similar types of information as the 1990 analysis, was specifically targeted 

toward the upcoming reintroduction of Mexican wolves into the Blue Range. This analysis 

found that the simulated Blue Range population experienced negative growth rates in 

scenarios with catastrophic events (i.e., drought) and had decreased viability in scenarios 

with inbreeding depression. Supplementation of the population of one adult pair of wolves 

and their offspring every 5 years virtually eliminated the risk of extinction during the 100-

year time span, resulted in maintenance of population size around 100 wolves, and resulted in 

higher retention of genetic variation than in scenarios without management supplementation 

(although the model assumed that new individuals added to the population were unrelated to 

members of the existing population, which is unrealistic given the founding base of the 

captive population) (IUCN 1996). 

Empirical observation of several wolf populations in North America and Europe 

demonstrates that populations of several dozen to several hundred animals are able to persist 

for several decades (Fritts and Carbyn 1995). This may lead to the conclusion that empirical 

data demonstrates persistence of wolf populations at sizes considerably smaller than those 

suggested viable by modeling efforts. However, the drawbacks of basing viability 

estimations strictly on empirical data are several, mainly that persistence in the past does not 

guarantee or provide a future time horizon for persistence, and that site-specific 

circumstances (such as environmental variability) may not be applicable to other situations. 

Several approaches, often in combination, have been used by the Service to assess viability 

and extinction risk in listing and recovery efforts for the gray wolf, including utilization of 

formal population viability analyses (IUCN 1996), literature survey (USFWS 1994: 

Appendix 9), expert-panels and best professional judgment (USFWS 1994: Appendix 9; 

USFWS 2002a), and threat analysis (e.g., 72 FR 6051-6103, February 8, 2007; 73 FR 10513-

10560, February 27, 2008). 

For the gray wolf recovery program in the Northern Rockies, the Service developed and 

repeatedly reassessed recovery criteria based on best professional judgment. In the 1987 

Northern Rocky Mountain Recovery Plan, which was developed by a recovery team, 

recovery criteria recommended establishment of a minimum of 10 breeding pairs for a 

minimum of 3 successive years in each of 3 core recovery areas, with connectivity between 

populations encouraged (USFWS 1987). These criteria were later revised based on literature 

survey, expert opinion, and best professional judgment, to 30 or more breeding pairs 

comprising some 300+ wolves in a metapopulation (a population that exists as partially 

52
isolated sets of subpopulations) with genetic exchange between subpopulations (USFWS 

1994), in order to emphasize the importance of connectivity between populations. In the 

delisting of the Northern Rockies gray wolf distinct population segment, the Service 

acknowledged that the recovery criteria were likely a minimum standard for viability, 

supporting their position by pointing out that empirical evidence of wolf persistence 

demonstrates greater persistence than theory suggests (73 FR 10513-10560, February 27, 

2008, and see Fritts and Carbyn 1995). In the Great Lakes gray wolf recovery program, 

recovery criteria specified the establishment of a Minnesota wolf population of 1,250-1,400 

wolves, with establishment of a second population of either 100 wolves if located within 100 

miles of the Minnesota population, or 200 wolves if located more than 100 miles from the 

Minnesota population demonstrating persistence for at least 5 years (USFWS 1992: 28). 

These criteria were also developed based on best professional judgment of viability by 

members of a recovery team. The only population target established in the Southwest is the 

reintroduction objective of establishing a population of more than 100 wolves, which 

although has not been considered a recovery criterion, was an estimation of viability based 

on the best professional judgment of the recovery team that wrote the 1982 Mexican Wolf 

Recovery Plan (USFWS 1982). 

Noticeably, estimations of viability vary not only between previous gray wolf recovery plans 

but also between those recovery plans and the scientific literature. There may be several 

reasons for this variability, including site-specific considerations, advances in analytical 

techniques and data availability used to explore viability over the last 3 decades, and the 

range of perceived notions of viability that exist within the professional community relative 

to wolf conservation and the ESA. 

Due to the large area requirements of wolves, area size is a feature of resiliency that is 

necessary to support viability. The area required to support a viable population depends on 

how a viable population is defined; clearly the area needed to support a population of several 

hundred wolves for several generations would be different than the area needed to support 

several thousand wolves for 100 or more years. Of equal importance, the area required to 

support a viable population would depend on the quality and configuration of habitat, with 

high quality habitat likely supporting a higher density of wolves than low quality habitat. 

Area requirements for the wolf have been estimated to be in the range of 10,000-13,000 km2

(4,000 to 5,000 mi2) if the area is isolated from other populations (Mech, in Henshaw 

1979:430 and Soulé 1980:163). The 1982 Mexican Wolf Recovery Plan estimated that a 

5000 mi2

 area would be necessary to support a reintroduction objective of 100 wolves 

(USFWS 1982:23), which suggests that populations larger than 100 wolves may require 

areas in excess of 5,000 mi2

. In contrast, Isle Royale National Park in Lake Superior has 

supported a population of 12-50 wolves for 50 years in an area of just 210 mi2 (538 km2) 

(Wayne et al. 1991). Following a review of pertinent literature and wolf population case 

histories, Fritts and Carbyn (1995) concluded that areas as small as 3,000 km2

 (1158 mi2), or 

even smaller, may be adequate to support a wolf population under near ideal circumstances 

(that is, abundant prey, a high level of tolerance for wolves by humans living in or using the 

area or adjacent areas, and effective legal protection); the wolf population that served as 

support for their conclusion ranged from 40-120 wolves over a 60 year period. Ideal 

53
conditions are rare, however, and population requirements extrapolated from demographic 

and genetic estimates of MVPs often require areas larger than available reserves (e.g., parks 

or designated wilderness areas) (Soule 1980:164). In such cases, it may be necessary to 

establish a network of habitat sites with interchange of wolves between areas to achieve an 

overall population target or degree of resiliency (Fritts and Carbyn 1995). 

Effective recovery strategies in the Northern Rockies and Great Lakes gray wolf recovery 

programs have focused on establishing wolf populations in high quality core habitats 

surrounded by lower quality habitat supporting lower densities of prey and wolves. In the 

Southwest, lower prey densities due to the arid environment (Bednarz 1988) may necessitate 

larger areas to support a population of a given size compared with more productive habitat in 

the Northern Rockies or Great Lakes. 

Summary statement: Results from existing gray wolf viability modeling efforts provide a 

wide range of population sizes, extinction probabilities, and time frames that do not 

collectively suggest a scientific consensus on what constitutes an appropriate degree of 

viability for gray wolf recovery pursuant to the ESA. Prior Service gray wolf recovery plans 

in the Great Lakes and Northern Rockies have estimated viable wolf populations as those that 

range from several hundred to over a thousand wolves. 

Summary statement: The extinction risk of the current Blue Range population or the 

population target of at least 100 wolves is unknown because a current, complete, peerreviewed viability analysis based on Mexican wolf data from the captive or Blue Range 

populations has not been conducted. Furthermore, the Service has not specified the viability 

(typically in the form of recovery criteria) that should be achieved for the gray wolf recovery 

program in the Southwest, including population size and area, acceptable probabilities of 

extinction risk, or time frame for persistence. Without these two pieces of information, it is 

not possible to evaluate the degree to which the current reintroduction establishes or 

contributes to resiliency for the Southwest. 

Redundancy 

Redundancy refers to the existence of redundant, or multiple, populations spread throughout 

a species’ range. It addresses the adage, “Don’t put all your eggs in one basket” and 

advances the notion that a species’ likelihood of persistence generally increases with an 

increase in the number of sites it inhabits (Shaffer and Stein 2000). The need for redundancy 

is not a statement in support of the trade-off between establishing multiple, small populations 

over a single large population; rather it supports establishment and maintenance of multiple 

resilient populations as preferable to establishment and maintenance of one resilient 

population. That is, maintenance of multiple populations, rather than a single population, 

confers a benefit to the ability of a species to persist because it allows for populations to exist 

under different abiotic and biotic conditions, thereby providing a margin of safety that 

random perturbation (or, variation) affects only one, or a few, but not all, populations 

(Shaffer and Stein 2000). Thus, the principle of redundancy can be used to provide context 

for the establishment of a single wolf population in the Southwest. 

54
Random variations in the environment that in turn affect the demography of a population are 

referred to as environmental stochasticity (Shaffer 1987). Environmental stochasticity, 

unlike demographic stochasticity, is not dependent on small population size and operates on 

populations of all sizes (Shaffer 1987, Mills 2007:103). Environmental stochasticity may 

take the form of variation in available resources (e.g., prey base), or in direct mortality (e.g., 

a disease epidemic), but either way results in variation in population growth rate (Shaffer 

1987, Caughley 1994). Extreme environmental events, referred to as catastrophic, including 

events such as wildfire, drought, or a disease epidemic, may result in drastic, rapid 

population declines (Shaffer 1987). Consideration of environmental stochasticity would 

suggest that as the number of populations established increases, extinction risk of the species 

decreases. 

The scientific literature does not recommend a specific number or range of populations 

appropriate for conservation efforts, although rule of thumb guidelines for the reintroduction 

of a species from captivity recommends that at least two populations be established that are 

demographically and environmentally independent (Allendorf and Luikart 2007: 472). 

Beyond this instruction, the need for redundancy is probably best described as a case-specific 

determination based on the conservation goal and the species’ characteristics (e.g., longevity, 

dispersal behavior, mating structure). For a goal of recovering a species under the ESA, 

redundancy contributes to the recovery of a species such that it is no longer in danger of 

extinction throughout all or a significant portion of its range. 

When a species is distributed in redundant populations, there are two possible relationships 

between the populations: they can be completely isolated from each other, or they can be 

connected with one another through the dispersal (also referred to as “migration” in the 

genetic literature) of individual animals. There are benefits and drawbacks to either 

relationship. For example, disease transmission will not occur between populations that are 

completely isolated from one another. However, immigration can bolster population size 

through arrival of new individuals (Brown and Kodric-Brown 1977), and if individuals 

successfully mate, can affect the genetic fitness of a population (Allendorf and Luikart 2007). 

If connectivity between populations is desired, conservation efforts must ensure that the 

distance between populations is compatible with wolf dispersal abilities and that the habitat 

through which individuals will be dispersing is of sufficient quality and quantity to support 

immigration. Alternatively, artificial immigration between populations must be 

accomplished through the translocation of wolves by management. Wolves generally have 

good dispersal ability through a variety of habitats, including heavily modified habitat (Fritts 

et al. 2003). 

Support for redundancy as a feature of gray wolf recovery is provided by knowledge of 

historical gray wolf distribution patterns. Although some species are naturally distributed as 

endemics in a single or few localized populations, the gray wolf was historically widespread 

in North America in numerous populations connected by dispersal (including Mexican 

wolves in the Southwest and Mexico), supporting the conclusion that redundancy is a 

fundamental component of natural wolf distribution. 

55
The necessity of establishing multiple populations has been central to the Service’s gray wolf 

recovery programs in the Northern Rockies and Great Lakes. In both areas, the need for 

redundancy was examined within local circumstances, including habitat availability and 

connectivity, existing and desired levels of genetic diversity, and estimations of necessary 

demographic viability. In the Great Lakes, recovery criteria for delisting called for the 

establishment of two populations, explaining that: 

The requirement for more than a single recovery population stems from the basic 

concept of conservation biology that a species can never be assumed to be secure 

from extinction if only a single population exists...The only satisfactory means of 

reducing the threat of extinction...is to ensure that more than a single population is 

established prior to declaring the species recovered (USFWS 1992: 24). 

Two populations, in this case, was considered minimally acceptable by the Eastern Timber 

Wolf recovery team at the time, although there was general agreement that additional 

populations would have provided increased security (USFWS 1992:24). In the Northern 

Rockies, gray wolf recovery criteria initially called for the establishment of three 

populations, later revised to require establishment of a metapopulation with genetic exchange 

between subpopulations. (USFWS 1987:10, USFWS 1994, USFWS 2002a). 

In both the Great Lakes and Northern Rockies, connectivity between redundant populations 

has been an important consideration (USFWS 2002a, USFWS 1994). In the Great Lakes, the 

distance between the two populations, which determined the likelihood of (demographic and 

genetic) connectivity, influenced the population size deemed adequate for viability of the 

smaller population (USFWS 1992: 25). In the Northern Rockies, revised recovery criteria 

recommended connectivity via wolf dispersal between the three (sub)populations to ensure 

maintenance of genetic diversity in each subpopulation as well as the overall metapopulation 

(USFWS 1994, USFWS 2002a). 

Numerous habitat assessments have been conducted to identify possible areas for 

reestablishment of the gray wolf in Arizona, New Mexico, Utah, Colorado, and Mexico. 

These studies, which are listed in chronological order, encompass a range of techniques and 

types of data and therefore as a collective provide only general insight as to the potential for 

redundancy in the Southwest. 

Summary of Information on Four Potential Mexican Wolf Reintroduction Areas in Arizona 

Johnson et al. (1992) compiled information on land area and ownership, precipitation, 

topography and vegetation, prey density, livestock use, competitors and predators, threatened 

and endangered species, human density, road density, future habitat alterations, and potential 

locations for pre-release acclimation enclosures in their analysis of four areas under 

consideration for Mexican wolf reintroduction in Arizona: the Blue Range Primitive Area, 

Chiricahua Mountains, Galiuro and Pinaleno Mountains, and Atascosa and Patagonia 

Mountains. 

56
Colorado gray wolf recovery: a biological feasibility study 

Bennett (1994) analyzed lands in Colorado designated as National Forests by the USDAForest Service, utilizing information on Forest area, percentage of public land of adjoining 

counties, mule deer and elk biomass, human density in adjoining county block, percentage of 

wilderness area in relation to National Forest area, road density, cattle density, level of 

recreational use, annual snowfall, and projected carrying capacity of wolves based on 

ungulate biomass. Seven areas were identified as “Potential Wolf Recovery Areas”: AraphoRoosevelt PWRA, Grand Mesa-Uncompahgre-Gunnison PWRA, Pike-San Isabel PWRA, 

Rio Grande PWRA, Routt PWRA, San Juan PWRA, and White River PWRA. Of these sites, 

all or portions of five sites were identified as good or satisfactory for wolf establishment, 

with issues related to livestock and human density being cited as primary deterrents in all or 

portions of four sites that would need to be addressed before reintroduction could be 

recommended. 

Wolves in the Southern Rockies: report from the population and habitat viability workshop

Workshop participants assessed the suitability of 10 subregions within the Southern Rockies 

ecoregion for the reestablishment of wolf populations. Subregions were identified based on 

habitat factors such as prey abundance and availability, topography, land ownership, and 

road density. Viability predictions for each region were not finalized (Phillips et al. 2000). 

The feasibility of gray wolf reintroduction to the Grand Canyon ecoregion 

Sneed (2001) analyzed six biophysical and human-related factors to determine the feasibility 

of gray wolf reintroduction to the Arizona portion of the Grand Canyon: vegetation cover, 

surface water, ungulate prey abundance, human population density, road density, and land 

status. T he North Kaibab and the South Colorado Plateau were identified as potentially 

appropriate for establishment of the (Mexican) gray wolf. 

Impacts of landscape change on wolf restoration success 

Carroll et al. (2003) identified four potential reintroduction sites in the Southern Rocky 

Mountains Ecoregion (southern Wyoming, Colorado, and Northern New Mexico) with the 

ability to support gray wolf populations of varying sizes and extinction risk, based on habitat 

variables including vegetation, satellite imagery metrics, topography, climate, and humanimpact and life history data. The sites included northern New Mexico, southwest Colorado, 

west-central Colorado, and northwestern Colorado. Projections for the year 2025, which 

took into account human population growth and resultant road development, generally 

demonstrated decreased carrying capacity of habitat and higher extinction risk of populations 

than current conditions. 

Spatial analysis of restoration potential and population viability of the wolf (Canis lupus) in 

the southwestern United States and northern Mexico 

Carroll et al. (2005) used life history data and habitat variables associated with vegetation, 

satellite imagery metrics, topography, climate, and human-impact to analyze five potential 

sites for gray wolf reestablishment in the southwestern United States (BRWRA in 

Arizona/New Mexico, Grand Canyon in Arizona, Mogollon Rim in Arizona, San Juans in 

Colorado, and Vermejo/Carson in northern New Mexico) and potential sites in Mexico (the 

Austin Ranch area located in Chihuahua/Sonora near the United States border, Carmen in 

57
northern Coahuila, northwestern Durango, and the Tutuaca reserve area in westcentral 

Chihuahua) in order to predict the vulnerability of sites to landscape change. Scenarios 

included current conditions, future conditions in the year 2025 based on human population 

growth and landscape development. Results for the United States portion of the analysis 

demonstrated decreased carrying capacity of sites, decreased connectivity, and increased 

extinction risk over time due to landscape development. 

Defining recovery goals and strategies for endangered species: the wolf as a case study 

Carroll et al. (2006) analyzed potential wolf habitat across the western United States from the 

western edge of the Great Plains to the Pacific Ocean, using information on wolf life history, 

demography, and habitat variables (see Carroll et al. 2003). They specifically simulated 

reintroduction scenarios for the SWDPS (Arizona, New Mexico, western portions of Texas 

and Oklahoma, and southern portions of Colorado and Utah; see Status and Implications of 

National Gray Wolf Recovery for the Mexican Wolf, above) to identify and compare 

potential reintroduction sites now and projected for the year 2025. Four potential 

reintroduction sites were identified: Carson (Northern New Mexico), the Grand Canyon 

(Northern Arizona), the Mogollon Rim (central Arizona), and the San Juan Mountains 

(southwestern Colorado). 

Summary statement: The number of redundant populations and related connectivity 

appropriate for recovery in the Southwest has not been specified; therefore the degree to 

which the Blue Range population contributes to redundancy cannot be determined. 

Summary statement: Establishment of only a single Mexican wolf population in the 

Southwest provides the least amount of redundancy, and therefore the least amount of 

security from environmental perturbation, possible. 

Summary statement: For a species that has been extirpated from so much of its historic 

range, explicit effort must be made to recreate redundancy. 

Representation 

Representation refers to the genetic diversity represented by members of a population or 

species, specifying that higher levels of diversity better support ecological and evolutionary 

processes than low (Shaffer and Stein 2000). Representation asserts that a species should be 

able to persist within the range of future habitat conditions that it may encounter (Shaffer and 

Stein 2000). Thus, representation allows for consideration of the short-term maintenance of 

fitness and vigor of individuals, and long-term maintenance of the species’ adaptive potential 

(Soule 1980). Representation therefore provides context for considering the short and longterm genetic health of the captive and reintroduced Mexican wolf populations. On a much 

broader scale, representation also suggests that a species should be conserved in the variety 

of habitats in which it occurs in order to maintain the structure and function of ecosystems, 

i.e., ecosystem representation (Shaffer and Stein 2000). Although most conservation efforts 

under the ESA are directed at single-species, this level of representation aligns with one of 

the primary purposes of the statute, “to provide a means whereby the ecosystems upon which 

endangered species and threatened species may be conserved” 16 U.S.C 1531(b). Thus, both 

genetic and ecosystem representation will be considered. 

58
Support for the appropriateness of genetic representation as a component of recovery stems 

from consideration of genetic stochasticity. Genetic stochasticity, commonly known as 

genetic drift, refers to the change in allele frequencies represented in a population from one 

generation to the next due to random mating events; genetic drift occurs in all natural 

populations (Allendorf and Luikart 2007). The degree of genetic drift experienced by a 

population is inversely related to its size; that is, greater changes in allele frequencies occur 

in small populations over time than in large, simply due to chance (Mills 2007). In small 

populations, attention to genetic structure and diversity may be a critical component of 

conservation efforts, although it has been argued that demographic events are likely to cause 

extinction before genetic concerns surface (Lande 1988). 

Genetic drift results in a decrease in heterozygosity and an increase in homozygosity 

(Allendorf and Luikart 2007: 122), which can result in decreased individual fitness and 

decreased adaptive potential of the population (Allendorf and Luikart 2007, Franklin 1980, 

Soule 1980, Lande and Barrowclough 1987). Thus, the genetic effects of small population 

size can influence the persistence of a population through several outcomes, including loss of 

phenotypic variation, loss of adaptive potential, and the buildup of harmful mutations, 

including mitochondrial mutations (Allendorf and Ryman 2002). Small populations are also 

at greater risk of inbreeding depression (reduced fitness and vigor due to increased 

homozygosity or reduced heterozygosity resulting from the mating of related individuals) 

due to the smaller pool of unrelated potential mates available as compared to a larger 

population. Inbreeding depression may in some cases, but not all, affect traits that reduce 

population viability, such as reproduction, (Fredrickson et al. 2007) survival (Allendorf and 

Ryman 2002), or disease resistance (Hedrick et al. 2003). For animals such as the Mexican 

wolf for which complete pedigree information is available, the relationship between the 

degree of inbreeding and specific fitness traits can be analyzed to determine the severity of 

inbreeding (Asa et al. 2007, Fredrickson et al. 2007). 

Importantly, it is the effective population size, rather than the census population size (as for 

demographic stochasticity), that primarily determines the rate of loss of heterozygosity, 

change in allele frequencies, and rate of inbreeding increase over time in a population 

(Waples 2002, and see Lande and Barrowclaugh 1987), and thus is a useful measure of 

representation. Effective population size is defined as “the size of the ideal population (N) 

that will result in the same amount of genetic drift as in the actual population being 

considered” (Allendorf and Luikart 2007: 148, also see Waples 2002: 149). Effective 

population size takes into account that not all members of a population reproduce every year; 

some may be too old, too young, not find a mate, or myriad other possibilities. Of those 

individuals that do mate, contributions to the next generation may differ due to an unequal 

sex ratio, number of offspring produced, survival of offspring, or other factors. To decrease 

the rate of genetic drift or likelihood of inbreeding (i.e., genetic stochasticity) experienced by 

a population, effective population size would have to increase (Mills 2007: 180). 

For the gray wolf, social structure greatly affects which wolves mate. That is, in a population 

of 100 wolves, not all 100 wolves are reproductively active; rather, some proportion of those 

wolves will breed from year to year. Effective population size for the Mexican gray wolf has 

been estimated at 0.28 times the census population (range of 0.19 to 0.34) (USFWS 2002b, 

59
USFWS 2003, USFWS 2004, USFWS 2005, USFWS 2006a, AGFD et al. 2007), which falls 

within the range of general estimates of effective population size for wildlife populations 

(0.2-0.3, see Mills 2007: 185). With a census population size of 100, effective population 

size would be about 28 wolves. 

Several general (non-species specific) rules of thumb have been presented in the scientific 

literature to inform efforts for conservation of a species’ or populations’ genetic diversity. 

As with other estimations and recommendations of viability, these rules of thumb are not 

intended for verbatim application. The ESA does not require any particular level of genetic 

diversity as a component of recovery, rather genetic diversity is typically considered by 

Service in relation to threats or extinction risk depending on each species’ circumstances. 

Perhaps the most commonly cited genetically-based minimum viable population estimate is 

the 50/500 “rule” (Franklin 1980, Soule 1980), where the “50” represents a recommendation 

of the effective population size deemed adequate to maintain short-term fitness loss due to 

inbreeding (1 percent level of inbreeding per generation), and the “500” is the effective 

population size deemed adequate for the long-term maintenance of adaptive potential. These 

guidelines were developed as a general conservation recommendation for captive efforts 

based solely on genetic information without regard to other factors that may impact a 

species’ long-term persistence (Mills 2007: 250). Lande and Barrowclaugh (1987) revisited 

the “500” recommendation, and concluded more generally that an effective population size 

of at least several hundred individuals would likely be necessary to maintain adaptive 

potential in most wildlife populations. Thomas (1990) suggested that a (census) population 

between 100 and 1,000 individuals would likely be adequate. Subsequently, Lande (1995) 

suggested that effective population sizes should be in the thousands based on the potential 

effects of mutation on population viability. 

Determination of an appropriate effective population size (and extrapolation of a census 

population size) for conservation efforts may identify a population size that is too large for 

any one contiguous area to support. Thus, effective population size could adequately be 

achieved by establishing multiple populations that collectively total the necessary effective 

population size (Allendorf and Luikart 2007: 374). This situation would require specification 

of the level of connectivity needed between (sub)populations to ensure that genetic migration 

occurs. In other wolf populations, one migrant per generation (successfully reproducing) 

connectivity has been recommended (Allendorf 1983, Lande and Barrowclaugh 1987, Lacy 

1987). This connectivity may present an opposing force to the potential for divergence of 

otherwise isolated populations stemming from natural selection and mutation (Allendorf and 

Luikart 2007:206). 

The small number of wolves (seven animals, representing three lineages) the Mexican wolf 

captive breeding program was founded by has necessitated intensive management of genetic 

diversity as an integral component of the recovery effort. Management has focused on 

ensuring the representation of genes from each of the three founding lineages in both the 

captive and wild populations for both short-term and long-term genetic fitness. And, because 

there are no known remaining wild Mexican wolves that can be brought into captivity to 

60
increase the genetic diversity of the captive population, the continued maximization of 

overall gene diversity retention (avoidance of genetic drift) is critical for the future of the 

recovery program (Siminski and Spevak 2007). 

The potential for inbreeding depression to occur in the Mexican wolf captive population has 

been a central concern of the breeding program. This concern led to the combination of the 

three founding lineages (McBride, Ghost Ranch, and Aragon) in 1995 following 

confirmation of the taxonomic standing of the lineages and recommendations that combining 

them would increase genetic variation (and thus, fitness) in the captive population (Hedrick 

et al. 1997). Representation of genes from the McBride lineage of wolves, which had been 

managed the longest under the SSP and were thought to be less heavily inbred than Ghost 

Ranch and Aragon wolves, was set at 80 percent for the captive population, with the 

remaining 20 percent being split evenly between the Ghost Ranch and Aragon lineages. 

Assuming positive results of merging the lineages became apparent, an increase to 25 percent 

representation for both the Ghost Range and Aragon lineages was deemed appropriate 

(Hedrick et al. 1997). 

Several studies have been conducted to determine whether inbreeding depression exists 

and/or is resulting in decreased fitness in the captive and wild population of Mexican wolves. 

Initial study of the captive population found weak evidence of inbreeding depression 

(Kalinowski et al. 1999), but subsequent research documented inbreeding depression 

affecting body size (Fredrickson and Hedrick 2002). More recently, it has been found that 

inbreeding had little or no effect on captive wolves from the founding lineages as measured 

by the probability of producing live pups, litter size, and pup survival. However, crosses 

between pure-lineage captive wolves resulted in fitness increases in these traits, 

demonstrating genetic rescue due to the masking of deleterious alleles (Fredrickson et al. 

2007). Inbreeding depression was observed in inbred cross-lineage captive wolves, 

suggesting the accumulation of deleterious or lethal alleles affecting these same traits 

(Fredrickson et al. 2007). In the reintroduced population, inbreeding depression has 

negatively affected litter sizes (Fredrickson et al. 2007). Fitness in these traits was affected 

in both male and female breeding wolves and pups. Lack of mating success in male wolves 

may be explained by subsequent documentation of inbreeding depression on sperm quality in 

pure-lineage Mexican wolves (Asa et al. 2007). 

In addition to the management of the lineages, the SSP has focused on maintaining as much 

of the original gene diversity from the founding wolves as possible. The current gene 

diversity (83.05 percent of the founding population) in the Mexican wolf captive population 

is lower than similar captive breeding programs due to the small number of founders and a 

significant loss of genetic diversity from the management of the lineages prior to SSP 

involvement (Siminski and Spevak 2007). Conservation breeding programs typically strive 

to maintain at least 90 percent of the genetic diversity at the time of establishment to avoid 

the potential for lower birth weights, smaller litter sites, and greater neonatal mortality 

(Allendorf and Luikart 2007). According to the 2007 Species Survival Plan Population 

Analysis and Breeding Plan, the captive population will retain approximately 75 percent of 

its diversity over the next 44 years. Diversity will decrease to 66.12 percent after 100 years, 

unless carrying capacity of the captive facilities can be increased to allow for an increase in 

61
annual population growth rates of the population, which will improve genetic retention. 

Currently, the carrying capacity of the captive facilities is about 300 captive wolves, which 

has been reached by the existing population (Sivinski and Spevak 2007). 

From a strict genetics perspective, the wild population should contain as much of the genetic 

diversity represented in the captive population as possible to avoid the potential for 

inbreeding and to maximize the ability of the Mexican wolf to adapt over time to changing 

environmental conditions. The goal of 80-10-10 ancestry of McBride, Aragon, and Ghost 

Ranch wolves in the captive population has been applied to the reintroduced population 

(Siminski and Spevak 2007), with the representation of the three lineages at 77.13 percent 

McBride, 12.9 percent Aragon, and 9.96 percent Ghost Ranch (as of July 28, 2007) (Siminski 

and Spevak 2007). In addition to the immediate fitness concerns related to inbreeding 

depression addressed by the merging of the founding lineages, it is also hoped that this 

strategy will maintain genetic diversity in support of the long-term adaptive potential of the 

Mexican wolf (Fredrickson et al. 2007). Results from genetic research demonstrate that 

additional release of cross-lineage wolves has the potential to increase the growth rate of the 

population and add genetic diversity to the current Blue Range population (Fredrickson et al. 

2007); these releases have the greatest potential for effect at smaller population sizes, as the 

addition of just a few wolves into a small population will more significantly alter the ancestry 

represented than will those few releases into a large population. The overall genetic diversity 

of the Blue Range population of Mexican wolves (78.66 percent and 2.34 Founder Genome 

Equivalents, as of July 28, 2007) is lower than that of the captive population, which is 

expected given that the wild population was started using wolves that were well-represented 

in the captive population (Siminski and Spevak 2007). 

 

Although genetic issues are recognized as a critically important component of the 

reintroduction, such issues must be balanced with other logistical considerations when 

wolves are being considered for release to the BRWRA. Wolves from the captive population 

are selected for release to the wild based on several factors, including their genetic makeup, 

reproductive performance, behavior, physical suitability, and overall response to the 

adaptation process in pre-release facilities (USFWS 2006a). Management of released wolves 

may not always fully support genetic considerations; for example, standard operating 

procedures may stipulate removal of a wolf because of its behavior, regardless of its genetic 

value to the population. 

The recovery programs for the gray wolf in the Great Lakes and Northern Rockies provide 

minimal instruction for the application of genetic representation in the Southwest because 

their circumstances differ sufficiently from the Southwest. In both programs, connectivity 

among regional (sub)populations was an important consideration in the development of 

recovery criteria for the maintenance of genetic diversity (see USFWS 1992, USFWS 1994, 

USFWS 2002a). However, neither program has maintained a strict conservation focus on a 

subspecies of gray wolf as has the Southwest on the Mexican wolf, neither program has been 

dependent on a captive breeding program for reestablishment of wild populations, and both 

programs continue to depend in part on connectivity to large, healthy wolf populations in 

Canada for establishment, infusion, and maintenance of genetic diversity (72 FR 6051-6103, 

February 8, 2007; 73 FR 10513-10560, February 27, 2008). 

62
There is some possibility in the future of immigration of wolves between regional recovery 

areas (e.g., a Northern Rockies wolf dispersing to the Southwest and breeding with a 

Mexican wolf), although this will depend in large part on future decisions related to delisting 

of the Great Lakes and Northern Rockies, modification of BRWRA boundaries, expansion of 

the Southwest’s gray wolf recovery effort, state management, and future habitat conditions. 

This would present a new set of genetic considerations for the Southwest related to the purity 

of the Mexican wolf, inbreeding, and adaptive potential. 

At the ecosystem level of representation, the Mexican wolf currently inhabits only the 

BRWRA, and therefore is not conserved in a variety of habitats. From the broader species 

perspective (rather than the subspecific Mexican wolf), gray wolves used to inhabit much of 

the Southwest, from its southern-most extent (and down into Mexico), up through the 

Southern Rockies, an area that included a variety of habitat types ranging from semi-desert 

grasslands to coniferous forests. Although the ESA does not mandate that a species be 

reestablished throughout its historic range or in all of the habitat types in which it historically 

occurred in order to achieve recovery, it does promote the conservation of ecosystems that 

support listed species. This factor, in combination with the potential for gray wolves to 

significantly alter the ecosystem structure of the areas they inhabit (see “Gray Wolf Biology 

and Ecology: Ecology and Habitat Description”, above), lends credence to the consideration 

of ecosystem representation as a component of conservation and recovery efforts. 

Collectively, the three regional gray wolf recovery programs achieve some degree of 

ecosystem representation, as they have resulted in the reestablishment of the gray wolf in a 

variety of significantly differing habitats in North America. However, given that the Service 

has not pursued gray wolf recovery at the national level, but rather at the regional level, the 

significance of this is difficult to evaluate. Prior gray wolf recovery plans in the Great Lakes 

and Northern Rockies did not include consideration of ecosystem representation as a 

component of recovery criteria, although the Service indirectly addressed ecosystem 

representation through the analysis of significance for delineation of both DPSs (72 FR 

6059-6060, February 8, 2007; 73 FR 10520, February 27, 2008). 

Summary statement: Short-term objectives for the appropriate balance of representation by 

each of the three founding lineages in the captive and reintroduced Mexican wolf populations 

have been determined and are actively being implemented through captive wolf pairings and 

selection of wolves for release to the wild. Maximization of long-term (several generations) 

genetic retention is a priority for the captive breeding program. 

Summary statement: Determination of an effective population size or other genetic-related 

objectives appropriate for regional gray wolf recovery in the Southwest has not been made. 

Summary statement: The degree to which ecosystem representation should be a component 

of conservation and recovery efforts in the Southwest is unclear based on minimal 

consideration of the concept by the Service in other gray wolf recovery efforts, nor has any 

determination of ecosystem representation been made for the Southwest. Without this 

information, the degree to which the Blue Range population contributes to regional 

representation cannot be evaluated. 

63
CONCLUSION 

The gray wolf recovery effort in the Southwest consists of an extensive international network 

of Mexican wolf captive breeding facilities and a single nonessential experimental population 

of Mexican wolves in Arizona and New Mexico. This two-pronged recovery strategy was 

the vision of the 1982 Mexican Wolf Recovery Plan, which has been the only gray wolf 

recovery plan developed for this region of the country. Although the 1982 recovery plan was 

instrumental in guiding the inception of the recovery effort, it no longer provides long-range 

guidance for the region. In particular, it established only a preliminary population objective 

for a single wolf population and does not contain recovery criteria. 

Although the progress of the Blue Range population in achieving the population objective of 

at least 100 wolves has been more moderate than expected and has not yet been achieved, the 

population has steadily increased in size since wolves were initially released in 1998. 

Intensive management provides considerable security that any specific threat as discussed 

herein does not likely pose an immediate extinction risk to the population due to the 

existence of over 300 wolves in captivity and the ability of management to bolster the Blue 

Range population with captive wolves in response to a major population decline or 

noticeable decline in fitness. However, individual threats (including aspects of the current 

management regime), and more so the combination of threats, still have the potential to 

decrease population size and growth rate, causing it to remain at a level at which it is more 

susceptible to stochastic events and to further hinder progress toward the population 

objective to establish a population of at least 100 wolves. 

Without a current recovery plan that addresses gray wolf recovery in the Southwest, the role 

of the Blue Range population in the regional recovery effort is unstated, although clearly 

significant. The intent of the ESA is to recover species such that they are able to sustain 

themselves in the wild. A “recovered” species is not one that has a zero chance of extinction; 

rather, it has a risk of extinction that is deemed acceptable for Federal protections to be 

removed with a high degree of certainty that the species is and will continue to be selfsustaining in the wild. Although some degree of management intervention may be necessary 

after delisting for a wide-ranging, socially controversial predator such as the wolf, such 

intervention should serve to make minor adjustments when necessary within a reasonable 

range of population fluctuation, not serve as a major hedge against extinction. 

Application of the conservation principles of resiliency, redundancy, and representation

provide insight into the contributions of the Blue Range reintroduction project to gray wolf 

recovery in the Southwest. Exploration of demographic stochasticity (resiliency) suggests 

that a population of more than 100 wolves will have less extinction risk than a population of 

less than 100 wolves, exploration of environmental stochasticity (redundancy) suggests that 

establishment of more than one population further lessens extinction risk for the Mexican 

wolf by providing safety from environmental perturbations, and exploration of genetic 

stochasticity (representation) suggests that short-term fitness and long-term adaptive 

potential of a population is best supported by establishing larger, rather than smaller, 

effective population sizes. Ecosystem representation suggests that the distribution of the 

gray wolf in a variety of habitats in the Southwest is an important consideration for 

64
ecosystem diversity. Thus, although the contributions of the Blue Range population to 

resiliency, redundancy, and representation are ultimately limited by a lack of objective and 

measurable recovery criteria against which the population objective to establish a single 

population of at least 100 wolves can be evaluated, it is clear that establishment of a single 

population of at least 100 wolves does not achieve resiliency, redundancy, or representation. 

These principles have provided guidance for the agency’s gray wolf recovery efforts in the 

Great Lakes and Northern Rockies, and as such provide a useful framework for structuring 

continuing gray wolf recovery efforts in the Southwest. Resiliency, redundancy, and 

representation are somewhat interdependent, meaning that the degree to which one is 

realized may affect and in turn be affected by the degree to which the others are realized. For 

example, representation may be affected by the number and connectivity of disjunct 

populations (redundancy), thus redundancy may be necessary not only to address 

environmental variability, but also to achieve appropriate levels of representation. This 

flexibility may be beneficial for application to recovery efforts because it allows for tradeoffs to be made based on site-specific considerations to ensure effective implementation of 

conservation actions. Simply put, these principles support a range of appropriate 

formulations for gray wolf recovery. 

The ecological, social, and economic landscape of the Southwest creates a unique backdrop 

for gray wolf recovery efforts, and certainly scientific determinations of resiliency, 

redundancy, and representation will be accompanied by considerations of social and 

economic factors. Moreover, resolution of litigation and policy decisions will continue to 

shape recovery efforts at the regional and national level. However, given the substantial 

progress in securing the Mexican wolf from extinction that has been made over the last 30 

years, it is time to shift the focus of the recovery program from “brink of extinction” toward a 

program in pursuit of recovery. 

65
LITERATURE CITED 

Adaptive Management Oversight Committee and Interagency Field Team [AMOC and IFT]. 

2005. Mexican wolf Blue Range reintroduction project 5-year review. Unpublished 

report to U.S. Fish and Wildlife Service, Region 2, Albuquerque, New Mexico, USA. 

http://www.fws.gov/southwest/es/mexicanwolf/MWNR_FYRD.shtml

Allendorf, F.W., and G. Luikart, editors. 2007. Conservation and the genetics of 

populations. Blackwell, Malden, Massachusetts, USA. 

Allendorf, F.W., and N. Ryman. 2007. The role of genetics in population viability analysis. 

Pages 50-85 in Allendorf F.W., and G. Luikart, editors. Conservation and the 

genetics of populations. Blackwell, Malden, Massachusetts, USA. 

Allendorf, F.W. 1983. Isolation, gene flow, and genetic differentiation among populations. 

Pages 51-65 in Schonewald-Cox C.M., S.M. Chambers, B. MacBryde, L. Thomas, 

editors. Genetics and conservation. Benjaim/Cummings, Menlo Park, California, 

USA. 

Arizona Department of Health Services [AZDHS]. 2008. Rabies statistics and maps 

website. < http://azdhs.gov/phs/oids/vector/rabies/stats.htm>. Accessed August 18, 

2008. 

 

Arizona Game and Fish Department [AGFD]. 2008. Mexican wolf reintroduction and 

management website. < http://www.azgfd.gov/w_c/es/wolf_reintroduction.shtml>. 

Accessed July 29, 2008. 

Arizona Game and Fish Department [AGFD], and New Mexico Department of Game and 

Fish [NMDGF]. 2002. Arizona-New Mexico review of the U.S. Fish and Wildlife 

Service’s 3-year review of the Mexican wolf reintroduction project. Final, September 

30, 2002. 

Arizona Game and Fish Department [AGFD], New Mexico Department of Game and Fish, 

U.S. Department of Agriculture - Animal and Plant Health Inspection Service - 

Wildlife Services, U.S. Fish and Wildlife Service, and White Mountain Apache Tribe. 

2007. Mexican wolf Blue Range reintroduction project: interagency field team report 

(reporting period January 1-December 31, 2007). 

Asa, C., P. Miller, M. Agnew, J.A.R. Rebolledo, S.L. Lindsey, M. Callahan, and K. Bauman. 

2007. Relationship of inbreeding with sperm quality and reproductive success in 

Mexican wolves. Animal Conservation 10:326-331. 

Association of Zoos and Aquariums [AZA]. 2008. AZA website. 

<http://www.aza.org/HonorsAwards/NA_Multiple/index.html>. Accessed May 20, 

2008. 

 

66
Ballard, W.B., L.A. Ayers, P.R. Krausman, D.J. Reed, and S.G. Fancy. 1997. Ecology of 

wolves in relation to a migratory caribou herd in northwest Alaska. Wildlife 

Monographs 135:1-47. 

Ballard, W.B., L.N. Carbyn, and D.W. Smith. 2003. Wolf interactions with non-prey. 

Pages 259-271 in Mech L.D., L. Boitani, editors. Wolves: behavior, ecology, and 

conservation. The University of Chicago Press, Chicago, Illinois, USA. 

Ballard, W.B., and P.S. Gipson. 2000. Wolf. Pages 321-346 in Demarais S., and P.R. 

Krausman, editors. Ecology and management of large mammals in North America. 

Prentice Hall, Upper Saddle River, New Jersey, USA. 

Ballard, W.B., J.S. Whitman, and C.L. Gardner. Ecology of an exploited wolf population in 

south-central Alaska. 1987. Wildlife Monographs 98:1-54. 

Bangs, E. 2002. Wolf population viability peer review – draft summary. Unpublished 

report to U.S. Fish and Wildlife Service, Region 6, Helena, Montana, USA. 

Bangs, E.E., J. Fontaine, T. Meier, C. Niemeyer, M. Jimenez, D. Smith, C. Mack, and V. 

Asher, L. Handegard, M. Collinge, R. Krischke, C. Sime, S. Nadeau, and D. Moody. 

2004. Restoration and conflict management of the gray wolf in Montana, Idaho and 

Wyoming. Transactions of the North American Wildlife and Natural Resources 

Conference 69:89-105. 

Bednarz, J.C. 1988. The Mexican wolf: biology, history, and prospects for reestablishment 

in New Mexico. Endangered Species Report Number 18. U.S. Fish and Wildlife 

Service, Region 2, Albuquerque, New Mexico, USA. 

Beissinger, S.R., and D.R. McCoullough. 2002. Population viability analysis. University of 

Chicago Press, Chicago, Illinois, USA. 

Bennet, L.E. 1994. Colorado gray wolf recovery: a biological feasibility study. Final report 

– March 31, 1994. U.S Fish and Wildlife Service, Region 6, Denver, Colorado, and 

University of Wyoming Fish and Wildlife Cooperative Research Unit, Laramie, 

Wyoming, USA. 

Bogan, M.A., P. Mehlhop. 1980. Systematic relationship of gray wolves (Canis lupus) in 

Southwestern North America. National Fish and Wildlife Laboratory, Washington, 

and University of New Mexico, Albuquerque, New Mexico, USA. 

Bogan, M.A., and P. Mehlhop. 1983. Systematic relationships of gray wolves (Canis lupus) 

in southwestern North America. Occasional Papers of the Museum of Southwestern 

Biology 1:1-20. 

67
Boitani, L. 2003. Wolf conservation and recovery. Pages 317-340 in Mech L.D., and L. 

Boitani, editors. Wolves: behavior, ecology, and conservation. The University of 

Chicago Press, Chicago, Illinois, USA. 

Boutin, S. 1992. Predation and moose population dynamics: a critique. Journal of Wildlife 

Management 56:116-127. 

Boyce, M.S. 1992. Population viability analysis. Annual Review of Ecology and 

Systematics 23:481-506. 

Bradley, E.H., and D.H. Pletscher. 2005. Assessing factors related to wolf depredation of 

cattle in fenced pastures in Montana and Idaho. Wildlife Society Bulletin 33(4): 

1256-1265. 

Brewster, W.G., and S.H. Fritts. 1995. Taxonomy and genetics of the gray wolf in Western 

North America: a review. Pages 353-373 in Carbyn, L.N., S.H. Fritts, and D.R. Seip. 

Ecology and conservation of wolves in a changing world. Canadian Circumpolar 

Institute, Occasional Publication No. 35. University of Alberta, Edmonton, Alberta, 

Canada. 

Brook, B.W., L.W. Traill, and C.A.J. Bradshaw. 2006. Minimum viable population sizes 

and global extinction risk are unrelated. Ecology Letters 9:375-382. 

Brown, D.E. 1983. The wolf in the Southwest: the making of an endangered species. The 

University of Arizona Press, Tucson, Arizona, USA. 

Brown, J.H., and A. Kodric-Brown. 1977. Turnover rates in insular biogeography: effect of 

immigration on extinction. Ecology 58:445-449. 

Brown, W.M., and D.R. Parsons. 2001. Restoring the Mexican gray wolf to the mountains 

of the Southwest. Pages 169-186 in Maehr, D.S., R.F. Noss, and J.L. Larkin, eds. 

Large mammal restoration, ecological and sociological challenges in the 21st Century. 

Island Press, Washington, D.C. 

Carrera, R., W. Ballard, P. Gipson, B.T. Kelly, P.R. Krausman, M.C. Wallace, C. Villalobos, 

D.B. Wester. 2008. Comparison of Mexican wolf and coyote diets in Arizona and 

New Mexico. Journal of Wildlife Management 72(2):376-381. 

Carroll, C., M.K. Phillips, and C.A. Lopez-Gonzalez. 2005. Spatial analysis of restoration 

potential and population viability of the wolf (Canis lupus) in the southwestern 

United States and northern Mexico. Klamath Center for Conservation Research, 

Orleans, California, USA. (2 December 2005; www.klamathconservation.org) 

Carroll, C., M.K. Phillips, C.A. Lopez-Gonzalez, and N.A. Schumaker. 2006. Defining 

recovery goals and strategies for endangered species: the wolf as a case study. 

Bioscience 56(1):25-37. 

68
Carroll, C., M.K. Phillips, N.H. Schumaker, and D.W. Smith. 2003. Impacts of landscape 

change on wolf restoration success: planning a reintroduction program based on static 

and dynamic spatial models. Conservation Biology 17:536-548. 

Carroll, C., R.F. Noss, and P.C. Paquet. 2001. Carnivores as focal species for conservation 

planning in the Rocky Mountain region. Ecological Applications 11:961-980. 

Caughley, G. 1994. Directions in conservation biology. The Journal of Animal Ecology 

63:215-244. 

Clark, J.A., J.M. Hoekstra, P.D. Boersma, and P. Kareiva. 2002. Improving U.S. 

Endangered Species Act recovery plans: key findings and recommendations of the 

SCB recovery plan project. Conservation Biology 16:1510-1519. 

Duda, M.D., and K.C. Young. 1995. Public opinion on and attitudes toward fish and 

wildlife management: New Mexico residents’ opinions toward Mexican wolf 

reintroduction. Responsive Management, Harrisonburg, Virginia, USA. 

Ewens, W.J., P.J. Brockwell, J.M. Gani, and S.I. Resnick. 1987. Minimum viable 

population size in the presence of catastrophes. Pages 59-68 in Soule, M.E., editor. 

Viable populations for conservation. Cambridge University Press, Cambridge, UK. 

 Franklin, I.R. 1980. Evolutionary change in small populations. Pages 135-149 in Soule, 

M.E., and B.A Wilcox, editors. Conservation biology: an evolutionary-ecological 

perspective. Sinauer Associates, Sunderland, Massachusetts, USA. 

Fredrickson, R.J., and P.W. Hedrick. 2002. Body size in endangered Mexican wolves: 

effects of inbreeding and cross-lineage matings. Animal Conservation 5:39-43. 

Fredrickson, R.J., P. Siminski, M. Woolf, and P.W. Hedrick. 2007. Genetic rescue and 

inbreeding depression in Mexican wolves. Proceedings of the Royal Society B 274: 

2365-2371. 

Fritts, S.H., and L.N. Carbyn. 1995. Population viability, nature reserves, and the outlook 

for gray wolf conservation in North America. Restoration Ecology 3:26-28. 

Fritts, S.H., and L.D. Mech. 1981. Dynamics, movements and feeding ecology of a newly 

 protected wolf population in northwestern Minnesota. Wildlife Monographs 80:1-79. 

Fritts, S.H., W.J. Paul, and L.D. Mech. 1984. Movements of translocated wolves in 

Minnesota. Journal of Wildlife Management 48(3):709-721. 

Fritts, S.H., R.O. Stephenson, R.D. Hayes, and L. Boitani. 2003. Wolves and humans. 

Pages 289-316 in Mech, L.D., and L. Boitani, editors. Wolves: behavior, ecology, 

and conservation. The University of Chicago Press, Chicago, Illinois, USA. 

69
Fuller, T.K. 1989. Population dynamics of wolves in north-central Minnesota. Wildlife 

Monographs 105:1-41. 

Fuller, T.K. 2004. Wolves of the world. Voyageur Press, Stillwater, Minnesota, USA. 

Fuller, T.K. 2003. Wolf population dynamics. Pages 161-191 in Mech, L.D., and L. 

Boitani, editors. Wolves: behavior, ecology, and conservation. The University of 

Chicago Press, Chicago, Illinois, USA. 

García-Moreno, J., M.D. Matocq, M.S. Roy, E. Geffen, and R.K. Wayne. 1996. 

Relationships and genetic purity of the endangered Mexican wolf based on analysis of 

microsatellite loci. Conservation Biology 10(2): 376-387. 

Gasaway, W.E., R.D. Boertje, D.V. Grangaard, D.B. Kelleyhouse, R.O. Stephenson, and 

D.G. Larsen. 1992. The role of predation in limiting moose at low densities in 

Alaska and Yukon and implications for conservation. Wildlife Monographs, Number 

120. The Wildlife Society, Bethesda, Maryland, USA. 

Gilpin, M.E., and M.E. Soule. 1986. Minimum viable populations: processes of species 

extinction. Pages 19-34 in Soule, M.E., editor. Conservation biology: the science of 

scarcity and diversity. Sinauer Associates, Sunderland, Massachusetts, USA. 

Gipson, P.S., and W.B. Ballard. 1998. Accounts of famous North American wolves, Canis 

lupus. The Canadian Field Naturalist 112:724-739. 

Gipson, P.S., W.B. Ballard, and R.M. Nowak. 1998. Famous North American wolves and 

the credibility of early wildlife literature. Wildlife Society Bulletin 26(4):808-816. 

Goodman, D. 1987. The demography of chance extinction. Pages 11-31 in Soule, M.E. 

editor. Viable populations for conservation. Cambridge University Press, 

Cambridge, UK. 

Hall, E.R., and K.R. Kelson. 1959. The mammals of North America, Volume II. The 

Ronald Press, New York, New York, USA. 

Hall, E.R. 1981. The mammals of North America. 2 volumes. John Wiley and Sons, New 

York, New York, USA. 

Harrington, F.H., and L.D. Mech. 1983. Wolf pack spacing: howling as a territoryindependent spacing mechanism in a territorial population. Behavioral Ecology and 

Sociobiology 12:161-168. 

Hedrick, P.W., and S.T. Kalinowski. 2000. Inbreeding depression in conservation biology. 

Annual Review of Ecology and Systematics 31:139-216. 

70
Hedrick, P.W., R.N. Lee, and K.M. Parker. 2000. Major histocompatibility complex (MHC) 

in the endangered Mexican wolf and related canids. Heredity 85(6):617-624. 

Hedrick, P.W., P.S. Miller, E. Geffen, and R.K. Wayne. 1997. Genetic evaluation of the 

three captive Mexican wolf lineages. Zoo Biology 16:47-69. 

Hedrick, P.W., R.N. Lee, and C. Buchanan. 2003. Canine parvovirus enteritis, canine 

distemper, and Major Histocompatibility Complex genetic variation in Mexican 

wolves. Journal of Wildlife Diseases 39(4):909-913. 

Holling, C.S. 1973. Resilience and stability of ecological systems. Annual Review Ecology 

and Systematics 4:1-23. 

Husseman, J.S., D.L. Murray, G. Power, C. Mack, C.R. Wenger, and H. Quigley. 2003. 

Assessing differential prey selection patterns between two sympatric large carnivores. 

OIKOS 101:591-601. 

International Union for Conservation of Nature [IUCN]. 1996. Mexican wolf population 

viability analysis draft report. Sponsored by the Conservation Breeding Specialist 

Group, Apple Valley, Minnesota, USA. 

International Wolf Center [IWC]. 2008. IWC website. 

<http://www.wolf.org/wolves/news/live_news_detail.asp?id=1340>. Accessed 

March 24, 2008. 

Johnson, T.B., D.C. Noel, and L.Z. Ward. 1992. Summary of information on four potential 

Mexican wolf reintroduction areas in Arizona. Technical Report 23. Arizona Game 

and Fish Department, Phoenix, Arizona, USA. 

Kalinowski, S.T., P.W. Hedrick, and P.S. Miller. 1999. No inbreeding depression observed 

in Mexican and red wolf captive breeding programs. Conservation Biology 13: 1371-

1377. 

Kellert, S.R. 1985. Public perceptions of predators, particularly the wolf and coyote. 

Biological Conservation 31:167-189. 

Kelly, B., M. Brown, and O. Byers (eds). 2001. Mexican wolf reintroduction program threeyear review workshop: final report. IUCN/SSC Conservation Breeding Specialist 

Group, Apple Valley, MN. 

Kreeger, T.J. 2003. The internal wolf: physiology, pathology, and pharmacology. Pages 

192-217 in Mech, L.D., and L. Boitani, editors. Wolves: behavior, ecology, and 

conservation. The University of Chicago Press, Chicago, Illinois, USA. 

71
Kunkel, K.E., T.K. Ruth, D.H. Pletscher, M.G. Hornocker. 1999. Winter prey selection by 

wolves and cougars in and near Glacier National Park, Montana. Journal of Wildlife 

Management 63(3):901-910. 

Lacy, R.C. 1987. Loss of genetic diversity from managed populations: interacting effects of 

drift, mutation, immigration, selection, and population subdivision. Conservation 

Biology 1: 143-158. 

Laikre, L., and N. Ryman. 1991. Inbreeding depression in a captive wolf (Canis lupus) 

population. Conservation Biology 5:33-40. 

Lande, R.L. 1988. Genetics and demography in biological conservation. Science 241:1455- 

1460. 

Lande, R.L. 1995. Mutation and Conservation. Conservation Biology 9:782-791. 

Lande, R.L. and G.F. Barrowclough. 1987. Effective population size and genetic variation. 

Pages 87-123 in, Soule, M.E., editor. Viable populations for conservation. 

Cambridge University Press, Cambridge, UK. 

Leonard, J.A., C. Vilá , and R.K. Wayne. 2005. Legacy lost: genetic variability and 

population size of extirpated US grey wolves (Canis lupus). Molecular Ecology 

14:9-17.

Lindsey, S.L., and P. Siminski. 2007. The return of the lobo: a binational success story. 

Association of Zoos and Aquariums [AZA] Publication. January 2007. AZA 

website. <http://www.aza.org/Publications/2007/01/return_lobo.pdf>. 

McBride, R.T. 1980. The Mexican wolf (Canis lupus baileyi): a historical review and 

observations on its status and distribution. Endangered Species Report 8: U.S. Fish 

and Wildlife Service, Region 2, Albuquerque, New Mexico, USA. 

McNay, M.E. 2002. Wolf-human interactions in Alaska and Canada: a review of the case 

history. Wildlife Society Bulletin 30(3):831-843. 

Mech, L.D. 1991. The Way of the Wolf. Voyageur Press, Stillwater, Minnesota, USA. 

Mech, L.D. 1989. Wolf population survival in an area of high road density. American 

Midland Naturalist 121:387-389. 

Mech, L.D. 1988. Longevity in wild wolves. Journal of Mammology 69:197-198. 

Mech, L.D. 1970. The wolf: the ecology and behavior of an endangered species. The 

Natural History Press, Garden City, New York, USA. 

72
Mech, L.D, and L. Boitani. 2003. Wolf social ecology. Pages 1-34 in Mech, L.D., L. 

Boitani, editors. Wolves: behavior, ecology, and conservation. The University of 

Chicago Press, Chicago, Illinois, USA. 

Mech, L.D., S.H. Fritts, G.L. Radde, W.J. Paul. 1988. Wolf distribution and road density in 

Minnesota. Wildlife Society Bulletin 16(1):85-87. 

Mech, L.D., E.K. Harper, T.J. Meier, and W.J. Paul. 2000. Assessing factors that may 

predispose Minnesota farms to wolf depredations on cattle. Wildlife Society Bulletin 

28(3): 623-629. 

 

Mech, L.D., and R.O. Peterson. 2003. Wolf-Prey Relations. Pages 131-160 in Mech, L.D., 

Boitani L, editors. Wolves: behavior, ecology, and conservation. The University of 

Chicago Press, Chicago, Illinois, USA. 

Mech, L.D., and U.S. Seal. 1987. Premature reproductive activity in wild wolves. Journal 

of Mammology 68(4):871-873. 

Messier F. 1985. Solitary living and extra-territorial movements of wolves in relation to 

social status and prey abundance. Canadian Journal of Zoology 63:239-45. 

Messier, F. 1994. Ungulate population models with predation: a case study with the North 

American moose. Ecology 75:478-88. 

 

Mills, L.C. 2007. Conservation of wildlife populations: demography, genetics, and 

management. Blackwell Publishing, Malden, Massachusetts, USA. 

Mladenoff, D.J., T.A. Sickley, R.G. Haight, and A.P. Wydeven. 1995. A regional landscape 

analysis and prediction of favorable gray wolf habitat in the northern Great Lakes 

region. Conservation Biology 9: 279-294. 

Nowak, R.M. 1995. Another look at wolf taxonomy. Pages 375-397 in Carbyn, L.N., S.H. 

Fritts, and D.R. Seip. Ecology and conservation of wolves in a changing world. 

Occasional Publication No. 35. Canadian Circumpolar Institute, Univeristy of 

Alberta, Edmonton, Alberta, Canada. 

Nowak, R.M. 2003. Wolf evolution and taxonomy. Pages 239-258 in Mech, L.D., and L. 

Boitani, editors. Wolves: behavior, ecology, and conservation. The University of 

Chicago Press, Chicago, Illinois, USA. 

O’Grady, J.J., B.W. Brook, D.H. Reed, J.D. Ballou, D.W. Tonkyn, and R. Frankham. 2006. 

Realisitic levels of inbreeding depression strongly affect extinction risk in wild 

populations. Biological Conservation 133:42-51. 

Oakleaf, J.K., C. Mack, and D.L. Murray. 2003. Effects of wolves on livestock calf survival 

and movements in central Idaho. Journal of Wildlife Management 67(2):299-306. 

73
Packard, J.M. 2003. Wolf behavior: reproductive, social, and intelligent. Pages 35-65 in 

Mech, L.D., L. Boitani, editors. Wolves: behavior, ecology, and conservation. The 

University of Chicago Press, Chicago, Illinois, USA. 

Packard, J.M., L.D. Mech, U.S. Seal. 1995. Social influences on reproduction in wolves. 

Pages 78-85 in Carbyn, L.N., S.H. Fritts, and D.R. Seip. Ecology and conservation of 

wolves in a changing world. Occasional Publication No. 35. Canadian Circumpolar 

Institute, University of Alberta, Edmonton, Alberta, Canada. 

Paquet, P.C., J.A.Vucetich, M.K. Phillips, and L.M. Vucetich. 2001. Mexican wolf 

recovery: three-year program review and assessment. Prepared by the Conservation 

Breeding Specialist Group for the United States Fish and Wildlife Service, 

Albuquerque, New Mexico. Apple Valley, Minnesota, USA. 

Parsons, D. 1996. Case study: the Mexican wolf. Pages 101-123 in Herrera, E.A., L.F. 

Huenneke, editors. New Mexico’s natural heritage: biological diversity in the Land 

of Enchantment. New Mexico Journal of Science 36.

Parsons, D.R. 1998. 1998 Mexican wolf interagency management plan. U.S. Fish and 

Wildlife Service, Albuquerque, New Mexico, USA. 

Parsons, D.R., and J.E. Nicholopoulos. Status of the Mexican wolf recovery program in the 

United States. Pages 141-146 in Carbyn, L.N., S.H. Fritts, and D.R. Seip. Ecology 

and conservation of wolves in a changing world. Occasional Publication No. 35. 

Canadian Circumpolar Institute, University of Alberta, Edmonton, Alberta, Canada. 

Patterson, B.R. and D.L. Murray. 2008 in press. Flawed population viability analysis can 

result in misleading population assessment: a case study for wolves in Algonquin 

park, Canada. Biological Conservation. doi:10.1016/j.biocon.2007.12.010. 

Peters, R.P., and L.D. Mech. 1975. Scent-marking in wolves. American Scientist 63:628- 

637. 

Peterson, R.O., and P. Ciucci. 2003. The wolf as a carnivore. Pages 104-130 in Mech, L.D., 

and L. Boitani, editors. Wolves: behavior, ecology, and conservation. The 

University of Chicago Press, Chicago, Illinois, USA. 

Phillips, M.K., N. Fasicione, P. Miller, and O. Byers. 2000. Wolves in the Southern 

Rockies. A population and habitat viability assessment: final report. International 

Union of Concerned Scientists, Conservation Breeding Specialist Group, Apple 

Valley, Minnesota, USA. 

Phillips, M.K, V.G. Henry, B.T. Kelly. 2003. Restoration of the red wolf. Pages 272-288 in 

Mech, L.D., and L. Boitani, editors. Wolves: behavior, ecology, and conservation. 

The University of Chicago Press, Chicago, Illinois, USA. 

74
Pimm, S.L., H.L. Jones, and J. Diamond. 1988. On the risk of extinction. The American 

Naturalist 132:757-785. 

Primm, S.A., and T.W. Clark. 1996. Making sense of the policy process for carnivore 

 conservation. Conservation Biology 10(4):1036-1045. 

Reed, D.H., J.J. O’Grady, B.W. Brook, J.D. Ballou, R. Frankham. 2003. Estimates of 

minimum viable population sizes for vertebrates and factors influencing those 

estimates. Biological Conservation 111:23-34. 

Reed, J.E., W.B. Ballard, P.S. Gipson, B.T. Kelly, P.R. Krausman, M.C. Wallace, D. B. 

Wester. 2006. Diets of free-ranging Mexican gray wolves in Arizona and New 

Mexico. Wildlife Society Bulletin 34(4):1127-1133. 

Reed, D.H., J.J. O’Grady, B.W. Brook, J.D. Ballou, and R. Frankham. 2003. Estimates of 

minimum viable population sizes for vertebrates and factors influencing those 

estimates. Biological Conservation 113: 23-34. 

Research and Polling, Incorporated. 2008. Wolf recovery survey: Arizona and New Mexico. 

Albuquerque, New Mexico, USA. http://www.rpinc.com/wb/pages/rpi.php. 

Rodriquez, M., P.R. Krausman, W.B. Ballard, C. Villalobos, and W.W. Shaw. 2003. 

Attitudes of Mexican citizens about wolf translocation in Mexico. Wildlife Society 

Bulletin 31(4):971-979. 

Ripple, W.J., and R.L. Becsheta. 2004. Wolves, elk, willows, and trophic cascade in the 

upper Galatin Range of southwestern Montana. Forest Ecology and Management 

200:161-181. 

Ripple, W.J., and R.L. Becsheta. 2003. Wolf reintroduction, predation risk, and cottonwood 

recovery in Yellowstone National Park. Forest Ecology and Management 184: 299-

313. 

 

Rothman, R.J., and L.D. Mech. 1979. Scent-marking in lone wolves and newly formed pairs. 

Animal Behavior 27:750-760. 

Roy, M.S., E. Geffen, D. Smith, E.A. Ostrander, R.K. Wayne. 1994. Patterns of 

differentiation and hybridization in North American wolflike canids, revealed by 

analysis of microsatellite loci. Molecular Biology and Evolution 11(4):553-570. 

Seal, U.S. 1990. Mexican wolf population viability assessment: Review draft report of 

workshop. 22-24 October 1990. Sponsored by International Union for Conservation 

of Nature, Conservation Breeding Specialist Group. Fossil Rim Wildlife Center, 

Glen Rose, Texas, USA. 

75
Secretaría de Medio Ambiente, Recursos Naturales y Pesca [SEMARNAP]. 2000. Proyecto 

de recuperación del lobo mexicano (Canis lupus baileyi). Instituto Nacional de 

Ecología. Tlacopac, San Ángel, México, D.F. 

Shaffer, M.L. 1981. Minimum population sizes for species conservation. BioScience 

31:131-134. 

Shaffer, M.L. 1987. Minimum viable populations: coping with uncertainty. Pages 69-86 in 

Soule, M.E. editor. Viable populations for conservation. Cambridge University 

Press, New York, New York, USA. 

Shaffer, M.L., and B.A. Stein. 2000. Safeguarding our precious heritage. Pages 301-321 in 

Stein, B.A., L.S. Kutner, J.S. Adams. Precious heritage: the status of biodiversity in 

the United States. Oxford University Press, City, State/Country. 

Siminski, D.P. 2005. Mexican wolf, Canis lupus baileyi, international studbook. The 

Living Desert, Palm Desert, California, USA. 

Siminski, D.P., and E.M. Spevak. 2007. Mexican wolf (Canis lupus baileyi) species 

survival plan: population analysis and breeding plan. Technical Report. The Living 

Desert, Palm Desert, California, USA. 

Sneed, P.G. 2001. The feasibility of gray wolf reintroduction to the Grand Canyon 

ecoregion. Endangered Species Update:18(4):153-158. 

Soule, M.E. 1980. Thresholds for survival: maintaining fitness and evolutionary potential. 

Pages 151-169 in Soule, M.E., and B.A. Wilcox BA, editors. Conservation biology: 

an evolutionary-ecological perspective. Sinauer Associates, Sunderland, 

Massachusetts, USA. 

Soule, M.E., editor. 1987. Viable populations for conservation. Cambridge University 

Press, Cambridge, UK. 

Soule, M.E., J.A. Estes, J. Berger, and C. Martinez del Rio. 2003. Ecological effectiveness: 

conservation goals for interactive species. Conservation Biology 17(5):1238-1250. 

Soule, M.E., J.A. Estes, B. Miller, D.L. Honnold. 2005. Strongly interacting species: 

conservation policy, management, and ethics. BioScience 55(2):168-176. 

Soule, M.E., and D. Simberloff. 1986. What do genetics and ecology tell us about the 

design of nature reserves? Biological Conservation 35:19-40. 

Soule, M.E., and B.A. Wilcox, editors. 1980. Conservation biology: an evolutionaryecological perspective. Sinauer Associates, Sunderland, Massachusetts, USA. 

76
Terborgh, J., J.A. Estes, P.C. Paquet, K. Ralls, D. Boyd-Heger, B. Miller, R. Noss. 1999. 

Role of top carnivores in regulating terrestrial ecosystems. Pages 39-64 in Soule, 

M.E., and J. Terborgh, editors. Continental conservation: design and management 

principles for long-term, regional conservation networks. Island Press, Washington, 

D.C. 

Thiel, R.P. 1985. Relationship between road densities and wolf habitat suitability in 

Wisconsin. American Midland Naturalist 113(2):404-407. 

Thomas, C.D. 1990. What do real population dynamics tell us about minimum viable 

poulation sizes? Conservation Biology 4:324-327. 

U.S. Fish and Wildlife Service [USFWS]. 1982. Mexican wolf recovery plan. Region 2, 

Albuquerque, New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 1987. Northern Rocky Mountain wolf recovery 

plan. Region 6, Denver, Colorado, USA. 

U.S. Fish and Wildlife Service [USFWS]. 1992. Recovery plan for the eastern timber wolf. 

Region 3, Twin Cities, Minnesota, USA. 

U.S. Fish and Wildlife Service [USFWS]. 1993. Comparison of habitat suitability attributes 

of five areas being considered for the reintroduction of Mexican wolves. 

Unpublished report, U.S. Fish and Wildlife Service, Albuquerque, New Mexico, 

USA. 

U.S. Fish and Wildlife Service [USFWS]. 1994. Appendix 9: Memorandum regarding a 

viable wolf population in the Northern Rocky Mountains. In The reintroduction of 

gray wolves to Yellowstone National Park and Central Idaho. Region 6, Helena, 

Montana, USA. http://www.fws.gov/mountainprairie/species/mammals/wolf/EIS_1994.pdf 

U.S. Fish and Wildlife Service [USFWS]. 1996. Reintroduction of the Mexican wolf within 

its historic range in the southwestern United States: Final Environmental Impact 

Statement. Region 2, Albuquerque, New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2002. Environmental Assessment for the 

translocation of Mexican wolves throughout the Blue Range Wolf Recovery Area in 

Arizona and New Mexico. Region 2, Albuquerque, New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2001. Mexican wolf recovery program: Mexican 

wolf reintroduction progress report 4. Technical Report. Region 2, Albuquerque, 

New Mexico, USA. 

77
U.S. Fish and Wildlife Service [USFWS]. 2002a. Draft wolf population viability peer 

review. Draft summary prepared by Ed Bangs, Wolf Recovery Coordinator. Region 

6, Helena, Montana, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2002b. Mexican wolf recovery program: 

Mexican wolf reintroduction progress report 5. Technical Report. Region 2, 

Albuquerque, New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2003. Mexican wolf recovery program: Mexican 

wolf reintroduction progress report 6. Technical Report. Region 2, Albuquerque, 

New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2004. Mexican wolf recovery program: Mexican 

wolf reintroduction progress report 7. Technical Report. Region 2, Albuquerque, 

New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2005. Mexican wolf recovery program: Mexican 

wolf reintroduction progress report 8. Technical Report. Region 2, Albuquerque, 

New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2006a. Mexican wolf recovery program: 

 Mexican wolf reintroduction progress report 9. Technical Report. Region 2, 

 Albuquerque, New Mexico, USA. 

U.S. Fish and Wildlife Service [USFWS]. 2006b. Letter from Acting Regional Director 

Benjamin Tuggle, Southwest Region, USFWS, to Terry B. Johnson, Chair, Adaptive 

Management Oversight Committee, regarding 5-Year Review. Signed July 24, 2006. 

U.S. Fish and Wildlife Service [USFWS]. 2008. Mexican gray wolf recovery program 

website. <http://www.fws.gov/southwest/es/mexicanwolf/>. Accessed March 1 – 

August 29, 2008. 

U.S. Fish and Widlife Service [USFWS]. 2008a. Region 6 homepage. 

<http://www.fws.gov/mountain-prairie/pressrel/08-16.htm>. Accessed March 9, 

2008. 

U.S. Fish and Wildlife Service [USFWS], Nez Perce Tribe, National Park Service, Montana 

Fish, Wildlife and Parks, Blackfeet Nation, Confederated Salish and Kootenai Tribes, 

Idaho Fish and Game, and U.S. Department of Agriculture Wildlife Services. 2008. 

Rocky Mountain wolf recovery 2007 annual report. Sime, C.A., and E. E. Bangs, 

editors. U.S. Fish and Wildlife Service, Region 6, Helena, Montana, USA. 

78
Unsworth, R., L. Genova, K. Wallace, A. Harp. 2005. Mexican wolf Blue Range 

reintroduction project 5-year review: socioeconomic component. Final Report. 

Prepared for Division of Economics, U.S. Fish and Wildlife Service, Arlington, 

Virginia, USA. 

http://www.fws.gov/southwest/es/mexicanwolf/pdf/MW5YRSocioeconomicsFinal20

051231.pdf 

Vilá, C., I.R. Amorim, J.A. Leonard, D. Posada, J. Castroviejo, F. Petrucci-Fonseca, K.A. 

Crandall, H. Ellegren, and R.K. Wayne. 1999. Mitochondrial DNA phylogeography 

and population history of the grey wolf, Canis lupus. Molecular Ecology 8:2089-

2103. 

Vucetich, J.A., M.P. Nelson, M.K. Phillips. 2006. The normative dimension and legal 

meaning of endangered and recovery in the U.S. Endangered Species Act. 

Conservation Biology 20:1383-1390. 

Vucetich, J.A., R.O. Peterson, and T.A. Waite. 1997. Effects of social structure and prey 

dynamics on extinction risk in gray wolves. Conservation Biology 11:957-965. 

Wabakken, P, H. Sand, I. Kojola, B. Zimmermann, J. M. Arnemo, H. C. Pedersen, and O. 

Liberg. 2007. Multistage, long-range natal dispersal by a global positioning systemcollared Scandinavian wolf. Journal of Wildlife Management 71:1631-1634. 

Waples, R.S. 2002. Definition and estimation of effective population size in the conservation 

of endangered species. Pages147-168 in Beissinger, S.R., and D.R. McCoullough, 

editors. Population viability analysis. University of Chicago Press, Chicago, Illinois, 

USA. 

Waples, R.S., P.B. Adams, J. Bohnsack, and B.L. Taylor. 2007. A biological framework for 

evaluating whether a species is threatened or endangered in a significant portion of its 

range. Conservation Biology 21(4):964-974. 

Wayne, R.K., E. Geffen, and C. Vilá. 2004. Population and conservation genetics of canids. 

Pages 55-84 in MacDonald, D.W., and C. Sillero-Zubiri, editors. Biology and 

conservation of wild canids. University Press, Oxford, UK. 

Wayne, R.K., N. Lehman, M.W. Allard, R.L. Honeycutt. 1992. Mitochondrial DNA 

variability of the gray wolf: genetic consequences of population decline and habitat 

fragmentation. Conservation Biology 6(4):165-175. 

Wayne, R.K., N. Lehman, and T.K. Fuller. 1995. Conservation genetics of the gray wolf. 

Pages 55-84 in Carbyn, L.N., S.H. Fritts, and D.R. Seip. Ecology and conservation of 

wolves in a changing world. Occasional Publication No. 35. Canadian Circumpolar 

Institute, University of Alberta, Edmonton, Alberta, Canada. 

79
Wayne, R.K., N. Lehman, D. Gorman, D.A. Gilbert, K. Hansen, R.O. Peterson, U.S. Seal, A. 

Eisenhawer, L.D. Mech, and J. Krumenaker. 1991. Conservation genetics of the 

endangered Isle Royale gray wolf. Conservation Biology 5:41-51. 

Wayne, R.K., and C. Vilá. 2003. Molecular genetic studies of wolves. Pages 218-238 in 

Mech, L.D., and L. Boitani, editors. Wolves: behavior, ecology, and conservation. 

The University of Chicago Press, Chicago, Illinois, USA. 

Weaver JL, PC Paquet, and LF Ruggiero. 1996. Resilience and conservation of large 

carnivores in the Rocky Mountains. Conservation Biology 10: 964-976. 

 

Wilson, P.J., S. Grewal, T. McFadden, R.C. Chambers, and B.N. White. 2003. 

Mitochondrial DNA extracted from eastern North American wolves killed in the 

1800s is not of gray wolf origin. Canadian Journal of Zoology 81:936-940. 

Young, S.P., and E.A. Goldman. 1944. The Wolves of North America. The American 

Wildlife Institute, Washington, D.C., USA. 

Zarnke, R.L., J. Evermann, J.M. Ver Hoef, M.E. McNay, R.D. Boertje, C.L. Gardner, L.G. 

Adams, B.W. Dale, J. Burch. 2001. Serological survey for canine coronavirus in 

wolves from Alaska. Journal of Wildlife Diseases 34(4):740-745. 

80
APPENDIX A: FIGURES 

Figure 1: Mexican Wolf Blue Range Wolf Recovery Area. USFWS. 

81
Figure 2. Photo of Mexican wolf. USFWS. 

82