Timing and synchrony of parturition in Alaskan moose: Long-term versus proximal effects of climate

We studied timing and synchrony of parturition in Alaskan moose (Alces alce s) in Denali National Park and Preserve, Alaska, from 1990 to 1994. Mean da te of birth was 25 May (SD = 5.7 days) and did not differ significantly amo ng years. Although moose did not congregate to give birth, parturition was highly synchronized (95% of births occurred in 16 days) with no significant differences among years. Most young moose were killed by predators, especi ally grizzly bears (Ursus arctos), but timing of reproduction had no effect on survivorship of young, which was low (ca. 0.2 by 16 June). We reject th e hypothesis that moose timed births to avoid predation. We also measured d epth of snow in winter, and precipitation, cloud cover, and temperature in spring; none of these variables was related to timing or synchrony of birth s. Likewise, quality of willow (Salix pulchra) in 3 springs in which percen t nitrogen and in vitro dry-matter digestibility of this important forage v aried markedly was unrelated to timing of births. We reject the hypothesis that moose timed parturition in response to proximal changes in their envir onment. We hypothesize that both timing and synchrony of parturition in moo se are adaptations to long-term patterns of climate that provide the most h ospitable conditions to bear and rear young. Consequently, moose may be mor e susceptible to climatic change than other ungulates that are more adapted to climatic variability.