The Saga of the Mexican Gray Wolf (el Lobo)

Overzealous predator eradication programs initiated by the federal government in the early 1900s were effective in killing all Mexican gray wolves (Canis lupus baileyi; aka Lobos) in the wild throughout their entire historic range in the southwestern United States by the mid-1900s and in Mexico around 1980. The Endangered Species Act was passed in the nick of time (1973) to save the Lobos, the southernmost and most genetically distinct subspecies of gray wolf (Canis lupus) in North America, from certain extinction.

Thousands of Mexican wolves once roamed the US Southwest and northern Mexico. An exact population estimate is impossible. Wherever there was prey, there were Mexican wolves. Wherever there was adequate moisture and available forage and water sources, there was prey. The best habitat was generally the mid to high elevations in the mountainous regions and the riparian zones along rivers and streams.

Mexican wolves are the smallest subspecies of gray wolves in North America, rarely exceeding 80 pounds for large males. Females are 15 to 20 pounds lighter. Some scientists believe that the epicenter of evolution for the Mexican wolf subspecies was in the Sierra Madres of northern Mexico and Sky Island region of the southwestern United States in southern Arizona and New Mexico. The principal prey in this region was the diminutive Coues whitetail deer—rarely exceeding 100 pounds—and other prey species were likely javelina (collared peccary), beavers, jackrabbits, cottontails, and other small mammals.

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WATCH: Mexican Wolf recovery update interview with Dave Parsons by Executive Director John Davis in the Gila Wilderness, March 2018

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A prevailing hypothesis is that Mexican wolves evolved to have smaller body size than gray wolves in more northern climes because of the smaller size of prey available and because of the need to shed more heat in the warm climate of the region. This phenomenon is known as Bergmann’s Rule. Nineteenth-century German biologist Carl Bergmann observed that within species with broad distributions over a north-south gradient, those in the colder climes had larger bodies than those in the warmer climes. The theory holds that a warm-blooded animal’s body surface-to-volume ratio is important in regulating body temperature by either retaining (smaller surface-to-volume ratio in large-bodied animals) or dissipating (larger surface-to-volume ratio in small-bodied animals) heat. This phenomenon holds true for many widely distributed species.

As gray wolves radiated across North America from their entry point at the eastern end of Beringia to their southernmost distribution near the latitude of Mexico City, they evolved and adapted to the variety of climatic and ecological conditions they encountered. Historically, gray wolves were contiguously distributed from the Arctic to Mesoamerica. Variations among subspecies were subtle rather than abrupt, with fuzzy boundaries between the subspecies taxonomists described. But wolves living substantial distances apart along this clinal distribution exhibited measurable physical, genetic, and ecological differences.

Mexican wolves at the northern end of their distribution blended into wolf populations that were somewhat larger and preyed on the abundant Merriam’s elk and even bison in adjacent regions. That Mexican wolves reintroduced into the Gila region prey primarily on the transplanted Rocky Mountain elk—the native Merriam’s elk having been shot to extinction in the early 20th century—is a testament to their evolutionary plasticity.

As European settlers moved west with their large herds of livestock beginning in the late 1800s, two problems occurred simultaneously to permanently alter our Southwestern ecosystems. One: unregulated hunting and trapping for sport and markets decimated previously abundant wildlife populations, such as bison, elk, deer, pronghorn, and beavers—the preferred prey of large carnivores. And two: unregulated grazing by cattle and sheep degraded fragile grasslands and riparian ecosystems. Watersheds were severely over-grazed, and erosion was unleashed with a vengeance, blighting landscapes to a condition that the ecologically unenlightened now perceive as the normal “look” of the West.

Decimation of native prey populations caused large predators to switch to domestic livestock for subsistence. Early western cattle barons were politically connected and convinced Congress to pass legislation to establish a federal agency in 1915 with a mission of eradicating large predators from the land.

Mexican wolves narrowly escaped extinction with the passage of the Endangered Species Act in 1973 and their placement on the list of endangered species in 1976. A few wild Mexican wolves remained in the remote Sierra Madres in the Mexican states of Chihuahua, Sonora, and Durango. Renowned Texas trapper, Roy McBride, was hired by the U.S. Fish and Wildlife Service (USFWS) in 1977 to live-trap as many wild Lobos as possible in Mexico. Between 1977 and 1980 he live-trapped five wild Mexican wolves—four males and one pregnant female. These wolves were placed in captive breeding facilities in the United States and became the “certified” lineage of Mexican wolves for purposes of captive breeding for future reintroduction to their former wild habitats.

Concerns over the limited gene pool led to the genetic testing of two additional captive lineages of putative Mexican wolves, called the Ghost Ranch and Aragon lines. A team of canid geneticists using new molecular genetics and traditional morphological methods determined in 1995 that both lines were pure Mexican wolves. This increased the number of certified pure founders for the captive population to seven wolves—three females and four males. All ~600 Mexican wolves alive today, in both captivity and the wild, can be traced to these seven founders.

Following many years of captive breeding, lengthy analyses of suitable release sites, development of reintroduction proposals, and public reviews, the first eleven Lobos were released into the Apache National Forest in eastern Arizona in 1998. Over 220 Mexican wolves have been released up to the present day, and the current wild population inhabiting suitable habitats in Arizona and New Mexico is estimated to be a minimum of 257 Lobos. Releases of more than 70 wolves in Mexico have been largely unsuccessful, with wolves surviving an average of only 2.5 months following release. The number of wild wolves surviving in Mexico is currently unknown but thought to be fewer than 20, if any. None have radio collars so monitoring is difficult.

Wild populations of Mexican wolves face serious threats to their long-term survival. The two main threats are severely limited genetic diversity and excessive human-caused mortality, primarily from known and unknown (cryptic) poaching.  Responsible wildlife agencies must confront these threats for Lobos to achieve population levels that would allow them to be removed from the list of endangered species. State wildlife agencies have pressured the USFWS to limit releases of genetically valuable animals from the captive population. The current wild population has a very high inbreeding coefficient (average relatedness is similar to that of siblings), which can lead to genetic problems potentially affecting the Lobos’ long-term survival. And the combination of illegal killing and management-related removal of wolves has further slowed recovery. Few poachers have been prosecuted for illegally killing Mexican wolves because of a U.S. Justice Department policy (called the McKittrick Policy), which requires prosecutors to prove that the wolf-killer knew he was killing a Mexican wolf and knew that Mexican wolves were on the list of endangered species. Those accused of killing a Mexican wolf are quick to claim they thought it was a coyote. The Rewilding Institute continues to work with other partners and federal elected officials to overturn this policy.

Revisions of the US federal rules for managing the wild population and of the official Mexican Wolf Recovery Plan, both adopted in 2017, reflect political influences driven by state wildlife agencies whose policies are disproportionately influenced by hunters and ranchers. Pressure from the Four Corners states’ governors, their governor-appointed game commissions, and New Mexico and Arizona agency wildlife managers has resulted in the USFWS requiring a dangerously low number of Mexican wolves for removal from the list of endangered species; limited options for releasing wolves from the more genetically diverse captive population; and set a northern limit for Mexican wolf occupation at Interstate 40 in Arizona and New Mexico. The Endangered Species Act requires recovery decisions to be based on the best available science, not politics. Yet politics continues to drive Mexican wolf recovery policies that will likely lead to their ultimate extinction.

The current federal regulations and the most recently revised Mexican Wolf Recovery Plan (2017) limit the US population to no more than 320 wolves. The regulation authorizes the removal of all wolves in excess of this threshold and all wolves that cross to the north side of I-40. There is no credible scientific justification for these numerical and geographic restrictions. The USFWS admits that a single population of this size leaves Mexican wolves highly vulnerable to extinction. Their solution in the recovery plan is to encourage the country of Mexico to establish a second population of at least 200 Mexican wolves. Independent and academic scientists believe that 525 wolves in two separate and functionally disconnected populations are insufficient to ensure recovery. Another critical concern is that the UFWS has no authority over recovery actions in Mexico. And we have seen no meaningful recovery results in Mexico so far. The population caps in the US and Mexico were established by agency wildlife managers as “management targets” based on perceived limits of “social tolerance” for wolves, presumably by hunters and ranchers. These politically motivated limits have no defensible scientific basis.

Previous recommendations of independent scientists appointed by the USFWS to a formally established Mexican Wolf Recovery Team in late 2010 called for three separate populations, connected by corridors of suitable habitat, in the US Southwest totaling at least 750 wolves, with each subpopulation having at least 200 wolves. Locations of two of the three recommended populations were north of I-40, dipping into southern Utah and Colorado. These science-based recovery recommendations elucidated in a 268-page draft recovery plan prepared by the independent scientists were rejected by the states and subsequently by the USFWS. The USFWS has ceased even mentioning that this draft plan exists, despite having commissioned its development and facilitating the recovery team meetings for two years.

Conservation plaintiffs won a lawsuit when a federal district court judge ruled that decisions made in the 2015 Mexican wolf management rule were “arbitrary and capricious” and not based on the best available science. The Judge ordered the USFWS to revise the rule in accordance with the requirements of the Endangered Species Act. The revised rule (2017) failed to substantially address the judge’s order and remains inadequate to achieve sustainable long-term recovery of Lobos in the Southwest.

Subsequently, two lawsuits were filed on behalf of conservation plaintiffs challenging the legal and scientific sufficiency of the 2017 revised Mexican Wolf Recovery Plan. That plan was developed in closed sessions among representatives of the four southwestern states, wildlife agencies in Mexico, and the USFWS. Non-governmental scientists and conservation advocates were cut out of the process.

It can be fairly stated that every major advance in the recovery of Mexican wolves was forced by lawsuits filed by conservation groups; and every decision made by the USFWS has been adversely influenced by the politics of special interests antithetical to the recovery of the Lobos, especially by the southwestern states, their game and fish departments and commissions.

The future of Lobos in the Southwest depends on relentless pressure applied to responsible state and federal agencies and elected officials by dedicated citizen activists, conservation organizations, independent scientists, and conservation lawyers. The Rewilding Institute remains actively engaged with our conservation partners to ensure the eventual recovery of Mexican wolves at ecologically effective distributions and abundance throughout the wildlands of the Southwest. Winning conservation battles is hard, but giving up ensures that wild Nature loses.

For suggestions on what you can do to help save the iconic Lobo of the Southwest please visit the website: www.mexicanwolves.org.

You can also learn more about their story by watching “The Right to be Wild: A Mexican Gray Wolf Documentary.”

Note: A previous version of “The Saga of the Mexican Gray Wolf (el Lobo)” was published in Rewilding Earth on June 1, 2018. This version includes information up-to-date as of November 2024.