Behavioral and ecologic effects of differential predation pressure on moose in Alaska

We studied behavioral and ecologic effects of differential predation pressu re on moose (Alces alces gigas) in the eastern Talkeetna Mountains, Alaska, during 1996-1998. Annual mortality from grizzly bear (Ursus arctos) and wo lf (Canis lupus) predation was higher for solitary yearling moose than for dependent yearlings (those with adults) and solitary adults. We tested hypo theses that solitary yearlings have heightened levels of vigilance and grea ter variation in vigilance responses and spend more time near protective co ver than do dependent yearlings or adults. Proportion of time spent vigilan t did not differ between solitary and dependent yearlings, and no differenc es were found between solitary yearlings and adults. However, variation in vigilance increased with distance to protective cover for yearlings but not for adults. Only at distances greater than or equal to 20 m from Protectiv e cover did variation in vigilance differ between solitary yearlings and ad ults. increased variation in vigilance at distances far from protective cov er, locations where putative vulnerability to predators is greatest, may ac count for increased mortality among solitary yearlings, Mean distance to pr otective cover was not different between solitary and dependent yearlings o r between solitary yearlings and adults. Because hypotheses regarding diffe rences in vigilance and use of protective cover between age and social stat us categories generally were not supported, other factors may be involved i n promoting high vulnerability of independent yearlings to predation. Small er body size and maternal defense are unexplored alternatives for explainin g differential mortality between yearling with and without mothers.