Recovering an endangered species - the re-establishment and growth of Mexican wolves in the southwestern United States

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2022-08

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Abstract

The Mexican wolf (Canis lupus baileyi) was on the edge of extinction in the late 1970s when the U.S. Fish and Wildlife Service (USFWS) contracted with a trapper to catch wolves in Mexico in order to start a captive breeding program. Seven wolves (three were considered founders (one female and two males that were unrelated) of the population) were ultimately captured and used as the foundation for this captive breeding program. The captive breeding program was successful, however Mexican wolves in the wild appeared to be extinct by the late 1980s. The success of the captive breeding program allowed the USFWS to consider reintroduction of surplus animals back into the historical range of Mexican wolves within the southwestern United States. The reintroduction of Mexican wolves in 1998 extended the southern distribution of gray wolves by ~1,100 km and reestablished unique genetics (i.e., a different subspecies) that were not present in other gray wolf populations in the wild. While the conservation benefit of the reintroduction of Mexican wolves is clearly important, some of the data available have yet to be published as this was a secondary priority relative to management and growth of the population. In the following chapters, I present information on the status of Mexican wolf conservation and original investigations into the questions related to the efficacy of reintroductions, factors that relate to pup production, recruitment numbers, and predation by Mexican wolves.

In my first core chapter (Chapter II: Gray Wolves in the Southwestern United States: History and Reintroduction Efforts), I provided a general description of gray wolf distribution, habitat, and life history both historically and following the reintroduction of Mexican wolves. I also address the status and management of Mexican wolves and adaptive management of wolves in the southwestern United States. Indeed, the successful reintroduction and growth of the wolf population in the southwest is astounding given the obstacles that Mexican wolves had to overcome. This chapter establishes the background and general information for research focused chapters.

In Chapter III (Efficacy of Initial Releases and Translocations of Endangered Mexican Wolves in the Southwest), I tested the relative success (whether an animal bred and successfully reproduced in the wild) compared to a variety of release, pack, and timing characteristics. These findings are important to future releases of social carnivores and important to examine early in reintroduction efforts to reduce expenditures of failed releases (e.g., maximize the success of each individual effort). Although these data were relied on early in reintroduction efforts and were an important first step towards establishing a population from captivity, they were never published or peer reviewed.

In Chapter IV (Influence of Genetic Versus Environmental Factors on Mexican Wolf Production and Recruitment), I compared a series of a priori models for genetic versus environmental factors via Poisson and logistic regression to determine which set of models had the most support. Genetic factors are important considerations in a population that was started by only 7 independent founders (3 originally captured in Mexico, and 4 other founders that were present in captivity and incorporated into the captive population in the 90’s). The influence of genetic factors relative to pup production in the wild has been debated through time with additional data (more litters added to the database) appearing to reduce the impact of genetics. I attempted to structurally define models and more clearly distinguish hypotheses and perhaps resolve or at least add information to the debate. Investigations of natural reproduction and recruitment are important to the second phase of reintroduction (i.e., moving from a population dependent on releases to a naturally growing population). Natural reproduction and recruitment has been the primary source of growth for this population of wolves since 2002 and is important to understanding the eventual success or failure of a reintroduced population.

The previous chapters primarily address the reestablishment of Mexican wolves and growth concerns in the future. In Chapter V (Kill Rates on Native Ungulates by Mexican Gray Wolves in Arizona and New Mexico) addresses the potential impact of this reintroduction on ungulate prey, I used global positioning system (GPS) cluster analyses to examined species, age, and sex structure of ungulates killed by Mexican wolves. The extension of this type of research to southern populations of wolves allows for comparisons with the greater amount of data collected in more northern systems. In addition, I provide a novel approach to modeling kills based on GPS cluster data alone by using training data in two initial study years to predict kills and classifications in future years, which may reduce expenses and field efforts in an area without substantial variation in snow levels.

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Keywords

Arizona, Canis Lupus Baileyi, Elk, Fertility, Food Caches, Genetic Fitness, Mexican Wolves, New Mexico, Predation, Recruitment, Releases, Reproduction, Survival, Translocations

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