Dynamics of Moose Aggregations in Alaska, Minnesota, and Montana

Distributions of annual aggregation patterns in three populations of moose (Alces alces) occupying different habitats are evaluated. Aggregation sizes were related to breeding activities, mother-young relationships, the male social system, sex ratio of the population, and habitat characteristics including forage sources, topography, and cover distribution. Group sizes were highest and most variable in the population of Kenai, Alaska, which was most dense of the three, and lowest and least variable in southwestern Montana, the least dense population. The highest group sizes occurred in fall and winter, and were lowest in summer. Cows were most gregarious in the Kenai population where the sex ratio favored females. Bulls appeared to aggregate following the rut, perhaps for establishment or reaffirmation of a rank order. Largest group sizes occurred when moose were primarily on the most open parts of their habitat: alpine tundra on the Kenai; recent cutover areas in northeastern Minnesota; and willow bottoms in Montana. This tendency may have a psychological basis, wherein the larger group replaces the role of cover in providing security for the individual, but in mountainous terrain animals were concentrated on forage sources at low elevations where snows were least likely to hinder movement and foraging. In contrast, on the relatively even terrain in northeastern Minnesota, successful occupation of late winter cover where forage was sparse was facilitated by dispersal of the population. The highly solitary and aggressive nature of the cow which escorts a calf may serve as a strategy for defense against predation.