The Natural History of the Mexican Wolf

"We reached the old wolf in time to watch a fierce green fire dying in her eyes. I realized then and have known ever since, that there was something new to me in those eyes-something known only to her and to the mountain. I was young then, and full of trigger itch; I thought that because fewer wolves meant more deer, and that no wolves would mean a hunter's paradise. But after seeing the green fire die, I sensed that neither the wolf nor the mountain agreed with such a view."
Aldo Leopold, 1944

Photo © 1990 Laurence Parent

The Mexican gray wolf (Canis lupus baileyi) or lobo is one of five sub-species of the gray wolf (Canis lupus) found in the Southwest areas of North America. Their habitat ranges from 3,000 to 12,000 ft. in elevation and includes Madrean pine-clad mountains, oak woodlands, pinyon-juniper forests, and intervening or adjacent grasslands within mountainous terrain through Mexico, southeast Arizona, and extreme southwest New Mexico. Because of their natural hunting method, running deer to the ground, southwestern wolves probably avoid rough, precipitous, and bushy terrain. Most reports indicate that they frequent high mountain ridges, rounded hills, mesas, bajadas, and wooded stringers extending into grassland valleys. Free water also must be available within close range and therefore the wolves will cross desert areas but will not remain there.

The gray wolf was once considered to be one of the most successful and widely distributed terrestrial mammal. Although their native prey is primarily the Coues white-tailed deer (Odocoileus virginianus couesi) their natural prey also includes elk, javelina, and occasionally pronghorn, big horn sheep, rabbits, hares, turkeys, and small rodents. They can also easily switch their prey depending on what is available and in some areas they have also been known to take domestic livestock. Once Gray wolves ranged over most of the entire North American continent in every habitat where large ungulates were found. They saturated most of the region between 20N latitude (i.e. Mid-Mexico and India) and the North Pole, in temperatures from -40 to +40 degrees C.

The Mexican subspecies' former geographic range included the United States in central and southeastern Arizona, southern New Mexico, and western Texas and Mexico in the Sierra Madre and surrounding highlands. Historically wolves have been present in the Southwest since at least the late Pleistocene. Their remains are well represented in the fossil record in Arizona and New Mexico, and wolf bones have also been identified from a number of pre-Columbian archaeological sites.

Mexican wolves usually live between 8-16 years in the wild (up to 20 years in captivity) and become sexually mature at around the age of two. They are the smallest subspecies of Gray wolves with an average weight of 89 lb. for males and 77 lb. for females while the wolf species as a whole can range from 60-175 lbs. North American Gray wolves vary greatly in color, from pure white Arctic wolves to the soot black wolves of Glacier and the surrounding areas. As well there are many in between, like silky gray wolves the color of wood ash, and creamy tan wolves with gray splotched backs. Brown mixes are the most common colors for the Mexican Gray wolf, but they can still be diversely colored animals, most with dark gray, brown, cinnamon and buff over light underparts. The Mexican wolves also have an impressive head with a short, thick muzzle and a large nose pad. Their deep chest contours, thick necks, heavy forequarters and long forelegs give them a heavier appearance in the shoulders than in the hindquarters. The tail is generally dark-tipped. A long mane, or hackles, is raised when the animal assumes a threatening posture.

Since wild populations of Mexican Gray wolves have disappeared there is very little data on their social organization. The only scientific data available were collected on a nearly extinct and persecuted, stock-killing population. Their basic ecology is thought to be similar to that of other Gray wolves, although some biologists speculate that pack sizes were smaller then the Gray wolf average of 2-13. A Mexican wolf pack usually consists of 3-8 individuals which depend on each other for survival and therefore have strong bonds between them. It is also not uncommon for packs to join together for a time, for hunting reasons or possible mating opportunities. Within a wolf pack, there is a complex social organization, with a top (alpha) male and female, who are largely responsible for patrolling the territorial boundaries, settling disputes between pack members, deciding where and when to hunt, and controlling the movements of the pack. They may also be the only breeding pair. Other males may try to mate with the alpha female earlier in the season, but as she becomes fertile, she will secrete a pheromone that causes the alpha male to become possessive and to guard her from subordinate males. A significant amount of tension and fighting occurs between the males at this time; competition for a higher ranking position in the pack gets fierce as younger wolves have matured, and other adult wolves try to obtain the mating rights. This tension is thought to be the reason why subordinate females belonging to a pack do not go into estrus. Below the two alpha animals in status are the other wolves, usually arranged in two linear hierarchies. At the very bottom of the social order is often an outcast who lives on the edge of the pack and exists by eating the scraps left by the group. Some young wolves leave the pack and move into new areas when they attain physiological breeding age at about 22 months. New packs form when subordinate pack members disperse from the pack territory, find an animal of the opposite sex, claim and defend a territory, and eventually breed and produce offspring themselves.

Female wolves come into estrus only once a year, and therefore will have only one litter a year. Mating takes place in winter usually around February. A Mexican wolf female often digs her den under rock ledges, under roots of an upturned tree, or under a bush if in open country. She will then line the den with dead leaves, and hairs from her belly. There dens are kept remarkably clean and odorless, with no scat or bones. Around April, after a 63 day gestation period, an average of 5-7 pups are born. The newborn wolves are blind and helpless and therefore will need to be nursed for approximately 5-6 weeks. All pack members may help feed the female and young. The adults either carry food to the den in their mouths, or they swallow it at the kill and later regurgitate it for the young. At about 2 months of age, the pups emerge from the den and are moved to an open area near some form of dense coverage, which biologists call the "rendezvous site". Here, the subordinate adults watch over the young while the rest set out on hunts. By the end of the summer, the young are able to go out hunting with the adults, and the pack is on the move as a group again.

This social system is established and maintained among the wolves by a very complicated sign language, consisting of many movements of the tail, ears, mouth, and body, as well as vocalizations that indicate the status and mood of each pack member. Individual wolves may have distinctive howls. Howls are used to assemble packs and possibly advertise territory. They also bark, growl, whine, and whimper. As well, wolves have acute hearing and sight; but they hunt mainly by their well developed use of scent. Since packs live in territories that are marked and defended, territories are demarcated by scent marks placed on conspicuous trees, rocks, and bushes along the wolves' trail. Territory size depends upon the density of wolves and on the density and distribution of prey. Sizes of individual wolf pack territories reported from the Great Lakes area ranged from 30 to 260 square miles but average approximately 100 square miles. Wolves usually obtain their prey by swift and open chases and therefore when hunting, they can cover up to 40 miles in a day.

BACK to Mexican Wolf
Genetic Conservation
Home Page