Ecology of an Exploited Wolf Population in South-Central Alaska

During April 1975 through April 1982, 151 gray wolves (Canis lupus) in 30 packs were captured and radio-collared in a <tex-math>$61,600\text{-}{\rm km}^{2}$</tex-math> area of south-central Alaska. Area traversed by wolf packs was correlated with number of radiolocations, pack size, and density of ungulate prey. Territory sizes of packs located >60 pack days averaged <tex-math>$1,645\ {\rm km}^{2}$</tex-math>. Pack areas (located <60 pack days) and territories did not normally overlap, but, when overlaps occurred, packs were separated temporally. Wolves did not follow migratory movements of moose (Alces alces) or caribou (Rangifer tarandus granti) outside of their pack areas but did follow elevational movements of moose within their areas. Twenty-eight percent of 135 wolves dispersed from their original area. Dispersal occurred mainly during April through June and October through November. Seventy-four percent of dispersers were males. Twenty-two percent of all wolves that dispersed were accepted into existing packs. Parturition in south-central Alaska occurred during May. Natal dens usually were abandoned between late June and late July. Earlier abandonment resulted from human disturbance. Average distance between dens of neighboring packs was 45 km. Wolf densities ranged from <tex-math>$10.3/1,000\ {\rm km}^{2}$</tex-math> in autumn 1975 to <tex-math>$2.6/1,000\ {\rm km}^{2}$</tex-math> in spring 1982. Mean annual litter sizes in November varied from 3.7 to 7.3 pups. At least 3 packs (7%) produced 2 litters at separate den sites. Intraspecific strife and other natural factors caused 20% of the annual wolf mortalities; the remaining mortalities resulted from legal and illegal human harvest. Harvest by humans >40% or total mortality >50% of autumn wolf numbers resulted in a population decline. During 1976 through summer 1978, 60 wolves were killed in the <tex-math>$7,262\text{-}{\rm km}^{2}$</tex-math> Susitna River Study Area to determine the effects of reduced wolf densities on moose survival. Spring wolf densities were reduced from precontrol levels by 42% to 58% annually. Annual rates of increase (λ) of wolves during years of control ranged from 0.57 to 0.81. When reduction efforts were terminated, wolf densities quickly increased with annual rates of increase ranging from 1.04 to 2.40. Wolf packs were observed at 439 kills; 70% were moose. Wolves preyed upon moose calves slightly less or in proportion to their occurrence in the moose population during late May through October. Proportionately more calves were killed by wolves during winter, but adult moose were overall the most common prey (38% of the kills). Caribou were the second most common prey. The condition of wolf-killed moose, as reflected by bone marrow fat, was similar to that of moose that died from incidental causes; the latter were assumed to represent the average condition of moose in the population. Adult cow moose killed by wolves were relatively old in relation to cow moose live-captured from the population, but were probably healthy. Wolf predation rates during summer (based on biomass equivalent to 1 adult moose) ranged from 1 kill/7 to 16 days/pack, whereas winter rates ranged from 1 kill/5 to 11 days/pack. Large packs killed ungulates more frequently than smaller packs. Kill rates per wolf, however, were greater for smaller packs. Wolf-killed ungulates usually were heavily utilized by wolves. During winter, 7.1 kg of food were available per wolf per day, and the length of time wolves remained at a kill site depended upon pack size and amount of prey. Spring wolf densities were negatively correlated with subsequent autumn moose calf: cow ratios, suggesting that reduced wolf densities improved survival rates of calf moose. Calf moose mortality studies indicated that predation by brown bears was the most important calf mortality factor. Estimates of moose recruitment compared with estimates of annual mortality from wolf predation during 1980-81 and 1983-84 within the Susitna River Study Area suggested that wolves were not preventing moose population growth at that time.