SEXUAL SEGREGATION IN MOOSE: EFFECTS OF HABITAT MANIPULATION

Abstract

We studied effects of mechanical crushing on abundance of forage and quality of feltleaf willow (Salix alaxensis) in winter, 3 years following habitat manipulation in interior Alaska, USA. We also examined differences in snow depth and track counts for Alaskan moose (Alces alces gigas) between the crushed site and an adjacent area containing old-growth stands of willow. Likewise we tested for differences in foraging by moose between areas, and noted differences in use of the 2 sites by adult males, and females and their young. Mechanical crushing resulted in a 5-fold increase in the number of leaders of current annual growth and a 3-fold increase in dry mass for willows subjected to crushing compared with the uncrushed site. The size of individual leaders resprouting from the crushed area was similar to stump sprouts available to moose on the uncrushed area. Moose took larger bites, however, on the crushed compared with the uncrushed. No significant differences occurred in the chemical composition of willows, including concentration of tannins, between crushed and uncrushed areas. Similarly, there were no differences in in vitro dry matter digestibility of willow between sites. Moose sexually segregated in winter. Males occurred predominantly on the more open crushed area, whereas females and young used the uncrushed area where the dense vegetation offered substantial concealment cover. We hypothesized that mechanical manipulation of willow benefited primarily male moose 3 years following crushing, and that females and young faced a tradeoff between feeding on the greater abundance of forage on the crushed area and a reduced risk of predation on the uncrushed site. We see merits in considering the sexes of moose as if they were separate species for purposes of management, and recommend that future management of habitat to benefit moose consider differences in requirements of the sexes, especially factors related to risk of predation.