The Mexican wolf (Canis lupus baileyi), also known as "El lobo," is the smallest, southernmost, rarest, and most genetically distinct subspecies of gray wolf in North America. Once common throughout its core range, which historically spanned from central Mexico through southeastern Arizona, southern New Mexico, and southwestern Texas, the Mexican wolf faced near extinction due to intensive eradication efforts in the southwestern United States and Mexico. These efforts were spurred by declining populations of native prey, such as deer and elk, which led many wolves to prey on livestock, creating conflict with humans. The U.S. Fish and Wildlife Service listed the Mexican wolf as an endangered species in 1976, prompting recovery efforts to save the species.
General Characteristics of the Mexican Wolf
Mexican wolves typically weigh between 50 and 80 pounds, measure about 5 ½ feet from nose to tail, and stand 28 to 32 inches at the shoulder. Their coats are distinctively colored with buff, gray, rust, and black, often displaying distinguishing facial patterns. Unlike other North American gray wolves, solid black or white variations do not exist in this subspecies.
These wolves are highly social animals, living in extended family groups or packs, consisting of an adult mated pair and their offspring, often from several generations. They have a complex social structure, including the alpha male and female (the breeding pair) and "helpers." The hierarchy of dominant and subordinate individuals enables the pack to function effectively. Wolves usually travel with their pack and establish a territory that could range from 30 square miles to over 500 square miles, which they define with scent markings and vocalizations such as barks, growls, and howls. Mexican gray wolves are monogamous, with only the alpha pair breeding each year.
Hunting and Prey
Mexican wolves hunt cooperatively to bring down prey animals usually much larger than themselves. This is accomplished primarily by chasing their prey, often over large distances. Hunting behavior and strategies likely vary depending on terrain, prey size, and availability. These wolves can survive on 2.5 to 3.7 pounds of meat daily, but they require 5 to 7 pounds per day for successful reproduction. However, they typically do not eat every day, living a feast-or-famine lifestyle.
Primary Food Sources
Based on scat analysis, 80-90% of the Mexican gray wolf's diet consists of elk (Cervus canadensis). On average, one wolf consumes the equivalent of about 16 adult elk per year. Studies have shown that wolves typically take down more elk calves, especially in the summer when the ungulates are still small.
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Secondary Food Sources
Secondary food sources for Mexican gray wolves include:
- Mule deer (Odocoileus hemionus)
- Coues’ white-tail deer (Odocoileus virginianus couesi)
- Bighorn sheep (Ovis canadensis)
- Javelina
- Rabbits
- Other small mammals
Researchers have found that wolves kill mule deer, though not as much as previously assumed. It’s also likely that the wolves kill even smaller prey species that were undetected using certain research techniques, like rabbits and wild turkey (Meleagris gallopavo).
Livestock Depredation
Mexican wolves can and do occasionally kill livestock, particularly young animals. There have been about 25 confirmed depredations per 100 wolves per year. This issue brings them into direct conflict with humans, as wolves compete for the same resources as humans.
Habitat and Distribution
Mexican wolves are found in a variety of southwestern habitats; however, they are not low desert dwellers as once commonly believed. They prefer mountain woodlands, likely because of the favorable combination of cover, water, and available prey.
Historically, the core range of Mexican wolves occurred throughout mountainous regions from central Mexico, through southeastern Arizona, southern New Mexico, and southwestern Texas. Their historic range has shrunk to the mountain range between New Mexico and Arizona. They have now been reintroduced in southeastern Arizona in the Apache National Forest and may move into western New Mexico to the adjacent Gila National Forest as the population grows. These wolves are also being reintroduced in Mexico.
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Wolf-Prey Dynamics
For over half a century, Isle Royale has been the focus of the longest running predator-prey study on wolves. From 1959 to 1980, the moose and wolf populations of Isle Royale tended to reflect each other. When the moose numbers were high, there was more food for the wolves, meaning better nutrition, higher pup survival rates and an increase in the wolf population. More wolves eventually led to a decline in moose and less food for wolves, meaning fewer wolves survived. As wolf numbers declined, they put less pressure on the moose populations, which in turn helped moose numbers rebound, and the cycle repeats.
In areas where more than one prey species is available, wolf-prey relations are even more complex. In multi-prey ecosystems, when the primary prey species goes into decline, two things can happen: the predator population may also go into decline, or the predator population may continue to increase by supplementing its diet with alternate prey.
In the east-central Superior National Forest in northeastern Minnesota, white-tailed deer, moose and beavers are the top menu items for wolves. From 2006 to 2016, the moose population declined by more than half. To determine if wolf numbers also declined, or whether wolves supplemented their diet with an alternate prey, Shannon Barber-Meyer and Dr. L. David Mech compared wolf numbers before and after the moose decline. Their study, which tracked and counted radio-collared wolves, showed that as the moose population declined, the wolf population, instead of decreasing, almost doubled. Wolf scat revealed that wolves supplemented their diets by hunting white-tailed deer. They also continued to prey on moose calves, contributing to the continuing decline of the moose population.
A recent study focused on what the wolves of the Alexander Archipelago and the southeastern mainland of Alaska eat when ungulates became scarce or absent. From 2012 to 2018, researchers from the Alaska Department of Fish and Game and Oregon State University collected 860 wolf scats from twelve study sites. DNA analysis of the wolf scat identified 55 food sources in the wolves’ diet. Although the study confirmed that ungulates represented roughly 65% of the wolves’ diet on a regional level, it also revealed that the kind and proportion of ungulates in their diets varied from one location to another. For instance, on the mainland, wolves’ main prey were moose and mountain goats, while on several of the islands, Sitka black-tailed deer were the main prey. As in other studies, when one of these ungulates went into decline or became scarce, wolves changed the prey that they hunted or scavenged.
In several other locations ungulates were not the main items on the wolf’s menu. For instance, the wolves who inhabit the area near Gustavus, on the shores of mainland Alaska, had the most varied diet. Here, moose comprised only 28% of the wolves’ diet, while sea mammals (mostly sea otters) comprised 22%. Black bears represented another 11% of their food while seasonally salmon made up 10% of their diet. The researchers suggest that the wolves opt for these other species because they are less dangerous and easier to hunt than moose.
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Southeast of Gustavus, in the Icy Straits, lies Pleasant Island where both Sitka black-tail deer and moose are found. Wolves arrived on Pleasant Island in 2013, and moose and deer numbers went into decline. Yet, despite the scarcity of these ungulates, wolves remained on the island. Scat analysis revealed that moose and deer made up only 13% of the wolves’ diet.
Threats and Conservation
Humans are the biggest threat to this species. In the late 1800s, once railroads were built, large numbers of settlers moved to the southwest. There was no protection at that time for wildlife. Many of the prey animals for this species were killed, and wolves were trapped, poisoned, or shot to protect people's livestock.
Despite these challenges, recovery efforts have been underway since the 1970s. After many had been killed by the mid-1970s, and just a handful existed in zoos. Fish and Wildlife Service, under Jamie Rappaport Clark (who became president of Defenders of Wildlife), introduced 11 Mexican gray wolves into the wild in Arizona. As of population monitoring in 2013, at least 83 wolves were counted roaming in Arizona and New Mexico. This is an increase from 75 in 2012 and the highest since the start of the recovery program. According to the U.S. Fish and Wildlife Service, the total population size of the Mexican wolf in 2015 was 97 individuals in the wild. This includes 50 wolves in Arizona, 47 wolves in New Mexico, and 7 breeding pairs in total. and Mexico.
Mexican gray wolf activities are monitored by the Interagency Field Team (IFT). Fish and Wildlife Service, White Mountain Apache Tribe, USDA Animal and Plant Health Inspection Service, and USDA Forest Service. The team includes field team leaders (one per state and tribal lead agency), wildlife biologists and specialists, depredation specialists, conservation education and outreach specialists, field assistants, as well as interns and volunteers. The IFT is responsible for tracking and monitoring the wolves, recording their location and behavior, responding as necessary when issues develop, drafting annual work plans, annual performance reports, and any new or revised Mexican Wolf Recovery Program operating procedures.
Initial Releases and Translocations
Initial releases (wolves born in captivity with no previous wild experience) can only occur in the primary recovery zone in Arizona. Translocations (previously released wolves or wolves born in the wild) can occur in the primary or secondary recovery zones.
After the initial release, the three packs established territories and by the first summer Arizona’s first wild-born wolves in more than 50 years were living in dens in the recovery area. By 2005, the need to release wolves born and raised in captivity had diminished, and by 2010 nearly all wolves in the wild were wild born.