Range-body mass interactions of a northern ungulate - a test of hypothesis

Summer diet, summer temperature, length of the growth season and animal den sity appeared to best explain annual and regional differences in calf and y earling body mass in moose from southeastern Norway, in general animals inh abiting steep, alpine landscapes had less body mass than animal using flat, low-altitude habitats. Autumn body mass of calves and yearlings decreased with increasing snow depth during the preceding winter and spring. However, calf body mass was more influenced bq the summer range and less by the win ter range than was body mass of yearlings. There was no indication that the effect of snow depth on autumn bud!: mass was greater in moose living on p oor than on good summer ranges. Body mass decreased with increasing competi tion for summer forage, while the winter range mainly had an density-indepe ndent effect. Habitat quality, expressed as regression lines between calf a nd yearling body mass and animal density (hunting yield) differed between r egions, On ranges of medium and high altitude where birch (Betula spp.) row an (Sorbus aucuparia) and bilberry (Vaccinium myrtillus) dominated moose su mmer diet, body mass decreased at a rapid rate with increasing animal densi ty. Body mass decreased at a slower rate at low-altitude ranges and at high -altitude ranges where willow (Salix spp.) and forbs dominated the diet, Bo dy mass of lactating cows decreased with increasing animal density, bur ani mal density did not affect body mass of non-lactating cows. There was no in dication that the decrease in autumn body mass with increasing moose densit y over the last 25 years has caused a decrease in animal condition (ability to survive the winter). The results are discussed in relation to the effec t of summer and winter range on population regulation in moose. It is concl uded that a density-dependent effect is apparent on the summer range even a t low and intermediate population densities. On the winter range, on the ot her hand, density-dependence is likely to occur only at high levels of popu lation density.