Mexican Wolf Natural History
The Mexican Wolf Recovery Plan, adopted in 1982 under the authority of the Endangered Species Act, has a primary goal of re-establishing at least 100 wild wolves within a portion of the subspecies’ historical range, located in east-central Arizona and western New Mexico. A secondary goal is to manage wolves and their habitat in a manner that will not negatively impact the lifestyles and economy of local residents. Cooperating agencies closely monitor and study wolves in the wild. Full recovery of the Mexican wolf subspecies will require a second population in their historical range in Mexico.
Habitat and Distribution
Mexican wolves were historically found in a variety of vegetation types in Arizona. Some sources indicate that wolves were never abundant in the state. Early naturalists may have often confused coyotes with wolves, making early estimates uncertain. Almost all wolf reports came from the mid- to high-elevation woodlands, including oak, pinyon pine, juniper, ponderosa pine and mixed conifer forests above 4,500 feet in elevation.
Vegetation type influences wolf density and distribution indirectly through the support of large ungulate (hoofed) prey, upon which the wolf is dependent. Early accounts of its range included the Sierra Madre Occidental of Mexico, southern Arizona, southwestern New Mexico, and sometimes western Texas. Such accounts are well supported by ecological, physiographic and morphological data. Recent attempts to show a more extensive northern periphery of historical range have been based entirely on a fragmented geographic sampling of a few genetic markers with no evidence they are diagnostic of this subspecies.
Wolves occurred mostly in Arizona’s mountainous woodlands prior to European settlement, and were gradually eliminated first in the more accessible areas as livestock production became more common and depredations increased. Most wolves were gone from Arizona by the 1940s, but occasional sightings were still reported, mostly along the Mexican border. The last known wolf was killed in Arizona in 1970.
Mexican wolf pack size has averaged between three and five wolves per pack. Historical pack sizes were reported to be from three to eight animals.
Mortality and Lifespan
Wolves die from a variety of causes, ranging from disease, malnutrition, injuries and inter-pack strife to human-caused mortality (shooting and car collisions). In areas with little or no human exploitation, the primary causes of mortality are disease and malnutrition in pups or yearlings.
Fall and winter are critical periods for wolf survival. Beginning in the fall, wolf mortality rates are most influenced by human-caused mortality.
Outreach efforts are intended to inform the public of the presence of wolves and their similarities to coyotes, and will hopefully decrease the number of accidental shootings of wolves. Ongoing telemetry monitoring and analysis helps to reveal specific causes of mortality.
Wolves are primarily monogamous, even though a pack can include more than one sexually mature female. Behavioral and physiological adaptations usually prevent more than one female per pack from breeding, which normally occurs in February. If a breeding wolf, also known as an alpha wolf, dies or is removed from the pack, another wolf from within or outside of the pack can fill this breeder position immediately, prior to the next breeding season. However, removal of an alpha animal can disrupt the pack to the point where it essentially dissolves and pack members begin moving independently. Mexican wolf dens are located under various objects, including rock ledges or logs, or dug into soft soil. Dens can be reused, but it appears that most reintroduced Mexican wolves move their dens annually, even if just a short distance.
After about a 63-day gestation period, a single litter of four to seven pups is usually born in April. The average litter size midwinter in Yellowstone National Park in 2002 was 4.3 animals. Annual pup mortality is normally around 50 percent, but can vary widely depending on prey density, weather, disease and other competitors. Pups are weaned at five to six weeks, and remain totally dependent on adult help until they are at least nine to 10 months old. After about six weeks, the wolves move the pups away from the den site to another area near water called a rendezvous site. Pups and other pack members use these rendezvous sites as their center of activity during the summer months. Pups begin traveling with the adults by October, sometimes sooner on shorter forays. Sex ratios have been found to be nearly equal between males and females, although in some cases there are more males.
Wolves in the wild usually are not sexually mature and do not breed until they are at least two years old, but a female in the wild was bred at 10 months. Mexican wolves in the wild have been known to breed until at least eight years old for males and seven years old for females, but the maximum age for reproduction is not known. Courtship behavior begins during the winter months, with potential mates staying closer to each other and physically interacting more often with each other. Scent marking activity increases, with the breeding alpha female eventually exhibiting raised-leg urinations tinged with pre-estrous blood alongside her mate.
Historically, Mexican wolves were believed to have preyed upon white-tailed deer, mule deer, elk, collared peccaries, pronghorn, bighorn sheep, jackrabbits, cottontails and small rodents. Wolves are highly adaptable prey generalists, and Mexican wolves can efficiently capture a range of ungulate prey species of widely varying size. Elk have comprised the bulk of the biomass in the diet of wolves reintroduced to Arizona and New Mexico. Data from Arizona indicate that elk are the preferred prey, with wolves showing a preference for calf elk over adult elk. Mexican wolves are also feeding on adult and fawn deer, other wild ungulates, cattle, small mammals and occasionally birds.
- Although small in comparison to all available livestock present, depredation is measurable and usually focused on one or two allotments at any given time.
- If a depredation is found, ranchers can be reimbursed by Defenders of Wildlife (DOW).
- Compensation programs for depredations not found are being discussed.
- To date, there have been about 70 possible or confirmed depredations or injuries, with $34,000 paid out by DOW.
Home Range Size
- Most packs utilize about 150-250 square miles.
- Average pack size consists of three to five wolves.
- Large migrations between summer and winter ranges have not been seen, although packs along the Mogollon Rim use areas of high elk density just below the rim in the winter.
Mexican wolves can be monitored through a variety of methods. Techniques include tracking, scent posts, howling, photo traps and other methods. In addition, affixing a radio telemetry collar to one member of the pack will reveal the pack size and other associates due to their communal behaviors.