Reproduction Usually only the dominant wolf pair breeds, however in areas where a high ratio of prey per wolf exists, such as in Yellowstone National Park, multiple litters may be born per pack. In the western Great Lakes area wolves breed in February through March and, after a gestation period of 63 days, four to six pups are born in late-April or early-May. However, the higher the latitude, the later the breeding. For instance, wolves in Northern Russia living at a latitude of 71 degrees breed in late March through April.
Pup Survival Pup survival is directly related to prey availability. Prey availability is generally higher in areas that are being newly colonized by wolves, where wolves have been recently reintroduced, or where adult wolves are killed.
Adult Survival and Longevity The overall survival of yearling and adult wolves in the western Great Lakes area has been documented to vary between 60 and 80 percent. Gray wolves are known to live up to 13 years in the wild and 16 years in captivity. However, averages vary based on geographic location.
Pack and Territory Size The number of individuals per pack can be highly variable, but averages four to eight during winter in the western Great Lakes area, with records of up to 16. Pack size can be as high as 30 or more in parts of Canada and Alaska. A wolf pack will roam and defend a territory of between 42 and 100 square miles in the western Great Lakes area. Territories can cover hundreds of square miles where prey densities are low, such as in Alaska.
Dispersal and Ability to Colonize New Areas Dispersal is the primary way wolves colonize new areas and maintain genetic diversity. Wolves have been known to disperse up to 550 miles, but more commonly disperse 50-100 miles from their natal pack. Generally wolves disperse when 1-3 years old as they reach sexual maturity, although some adults disperse also. At any one time 5-20 percent of the wolf population may be dispersing individuals. Usually a wolf disperses to find an individual of the opposite sex, find a territory and start a new pack. Some dispersers join packs that are already formed.
Habitat Requirements Wolves can live wherever they find a sufficient number of large ungulates, such as deer, moose, elk, bison, and musk ox. Wolves were once considered a wilderness animal, however if human-caused mortality is kept below certain levels, wolves can live in most areas. Historically, they once occupied every habitat that had sufficient prey in North America from mid-Mexico to the polar ice pack.
Food Requirements Wolves can survive on 2.5 pounds of food per day, but require about 5 pounds per day to reproduce successfully. Wolves are estimated to eat 10 pounds of food per day on average. Wolves don't actually eat every day, however as they live a feast-or-famine lifestyle. They may go several days without a meal and then gorge on more than 20 pounds of meat when a kill is made. Wolves primarily feed on prey animals larger than themselves, as this provides food for many individuals. However, wolves will prey upon smaller mammals such as beaver and hare. Because wolves inhabit much wider home ranges than their prey species, different populations of wolves prey upon varying species of animals. Wolves located in the Western Great Lakes region typically prey upon whitetail deer, whereas wolves located in central Canada prey primarily on caribou.
Impacts on Prey On average, one wolf eats the equivalent of 15-20 adult-sized deer per year in Minnesota. Based on this average, the 2003-04 estimate of 3,020 wolves in Minnesota, kill the equivalent of 45,300 to 60,400 adult-sized deer each year. However, wolf kill rates vary in relation to winter severity. Young, old and sick or injured prey animals are often nutritionally stressed and have difficulty traveling in deep snow. Wolf kill rates are highest during severe winters and the following spring. Sometimes wolf predation can keep prey populations at low levels for extended periods, but habitat alterations like forest cutting or fire, improved weather conditions, and human management practices allow prey populations to quickly recover.
One example of the predator-prey dynamic is that the reductions in deer herds caused by wolves increases habitat quality and helps rid the herd of genetically unfit and diseased individuals. This results in long term maintenance of a healthier deer herd. Deer and wolves have evolved together, and wolf predation has played a crucial role in making the deer what it is today.
Population Cycles Wolf density often changes with the density of its primary prey. For example, in the northern Great Lakes region, the severe winters of 1995-96 and 1996-97 resulted in substantial numbers of deer being stressed, and many starved or were killed by wolves. This provided a readily available food supply to wolves and increased their survival rate. However, wolf numbers usually decline a year or two following the decline of primary prey. In addition to other factors, the mild winters since 1997 have been favorable to deer populations by increasing the winter survival of deer and in turn increasing the number of fawns being born.
Potential for Population Change With abundant food and low human-caused mortality, wolves have a high capacity for population growth. In fact, in the right conditions, wolf populations can double in two to three years. From 1997 to 2000, the wolf population in the Northern Rocky states doubled from 200 to 400. Wolf populations can decline, however, if human-caused mortality is consistently greater than 28-50 percent of the fall wolf population.
Selected References Carbyn, L.C. 1987. Gray wolf and Red wolf. Pages 361-376 in M. Novak, J.A. Baker, M.E. Obbard, and B Malloch editors. Wild Furbearer Management and Conservation in North America. Ontario Ministry of Natural Resources, Ontario, Canada. 1150 pp.
Fuller, T.K. 1997. Guidelines for gray wolf management in the northern Great Lakes region. International Wolf Center, publication no. IWC97-271. 20pp.
Mech, L.D. 1995. What do we know about wolves and what more do we need to learn? Pages 537-545 in L.N. Carbyn, S.H. Fritts, and D.R. Seip editors. Ecology and conservation of wolves in a changing world. Canadian Circumpolar Institute, occasional publication no. 35. 642 pp.
Nowak, R.M. 1995. Another look at wolf taxonomy. Pages 375-398 in L.N. Carbyn, S.H. Fritts, and D.R. Seip editors. Ecology and conservation of wolves in a changing world. Canadian Circumpolar Institute, occasional publication no. 35. 642 pp.
