Population Dynamics of Moose in South-Central Alaska

Ballard, Warren; Whitman, Jackson; Reed, Daniel

Demography, movements, and habitat use of moose (Alces alces) were studied in south-central Alaska from 1976 through early 1986 and historical data were reviewed. Initially this study tested the hypothesis that predation by wolves (Canis lupus) was limiting moose population growth. When reductions in wolf densities failed to greatly increase calf moose survival, we attempted to directly identify and quantify causes of calf and adult moose mortality. Concurrently, we sought to quantify movements, habitat use, productivity, and the effects of severe winters. Lastly, we tested the hypothesis that predation by brown bears (Ursus arctos) was limiting moose population growth. During 1976 through 1985, 218 neonates, 61 calves 5-10 months of age, and 184 adults were captured and either radio collared or equipped with visual collars. The moose population was estimated at 710 moose/1,000 km¨ in 1980, and at 844 moose/1,000 km¨ in 1963 (lambda = 1.06). Average age of adult cow moose was 7.7 years. Pregnancy rate averaged 81%. Twinning rates averaged 38%. Parturition occurred between 18 May and mid-June. Overall, calf sex ratios were not different from 1:1 except in 1977 when males predominated. Survival through 5 months of age averaged 39% with twin and single calves having similar survival rates. Predation accounted for 83% of total mortality among neonates. Ninety-six percent of natural mortality occurred during the first 6 weeks of life with brown bears accounting for 73% of the mortality. During severe winters, males 6-12 months of age had lower survival rates than females of similar ages. Annual calf survival rates averages 34% and 31% for females and males, respectively. Yearling and adult female annual survival rates averaged 94 and 95%, respectively. Bulls >2 years of age had low rates of natural (excluding hunting) mortality. Average size of moose groups containing radio-collared individuals was greatest in October and lowest in August. Major periods of moose movement occurred during autumn and spring migration and during rut (late Sep-Oct). Total home range sizes for migratory moose averaged 505 km¨, whereas those for resident moose averaged 290 km¨. Nine of 15 radio-collared offspring (mean age = 14 months) partially or fully dispersed from the cow's home range. Males dispersed more frequently and had larger home ranges than females. Spruce (Picea spp.) and willow (Salix spp.) vegetation types were used disproportionately more than their availability. During winter, areas with relatively low browse biomass were heavily used by moose, because browse was more available due to shallow snow depths.

Population Dynamics of Moose in South-Central Alaska

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