Timing and Synchrony of Parturition in Alaskan Moose: Long-Term Versus Proximal Effects of Climate

Abstract

We studied timing and synchrony of parturition in Alaskan moose CAlces alces) in Denali National Park and Preserve, Alaska, from 1990 to 1994. Mean date of birth was 25 May (SD = 5.7 days) and did not differ significantly among 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, especially 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 the hypothesis that moose timed births to avoid predation. We also measured depth of snow in winter, and precipitation, cloud cover, and temperature in spring; none of these variables was related to timing or synchrony of births. Likewise, quality of willow (Salix pulchra) in 3 springs in which percent nitrogen and in vitro dry-matter digestibility of this important forage varied markedly was unrelated to timing of births. We reject the hypothesis that moose timed parturition in response to proximal changes in their environment. We hypothesize that both timing and synchrony of parturition in moose are adaptations to long-term patterns of climate that provide the most hospitable conditions to bear and rear young. Consequently, moose may be more susceptible to climatic change than other ungulates that are more adapted to climatic variability.

Density-dependent effects on physical condition and reproduction in North American elk: an experimental test

“…Our results are consistent with studies of muskoxen (Ovibos moschatus) and caribou (Rangifer tarandus) in northern environments where body mass, nutritional condition, and lactational status strongly affected reproduction (Cameron et al 1993;Gerhart et al 1997;. Moreover, maternal fat reserves also are related to body mass in neonatal cervids, with subsequent effects on lifehistory characteristics, including survivorship (Gaillard et al 1997;Bowyer et al 1998;Keech et al 1999;Barten et al 2001). Thus, increasing population density, which resulted in lowering of fat reserves and pregnancy in our study also provides a link to survivorship of young (Keech et al 2000).…”

“…We calculated number of degree days >5°C (number of degrees that the mean daily temperature was >5°C, summed across all days; Bowyer et al 1998). This variable was selected because it provided an index of growth for plants in seasonal environments (Chapin 1983;Bowyer et al 1998).…”

Spatial patterns in relative primary productivity and gazelle migration in the Eastern Steppes of Mongolia

“…In the second scenario -effective predators as a major source of mortality for young -females can 'swamp' predators by producing young over a short time span in a constrained area (Estes and Estes, 1979). Although predator swamping has been rejected as a possible explanation for birth synchrony in moose (Alces alces, Bowyer et al, 1998b) and bighorn sheep (Ovis canadensis, Rachlow and Bowyer, 1991), this behavioral response may occur in barren-ground caribou (Rangifer tarandus, Bergerud and Page, 1987) and wildebeests (Connochaetes taurinus, Estes and Estes, 1979). Zeer movements to calving grounds are similar to the movements of open-steppe ungulates, such as caribou and wildebeest, with zeer selecting the most productive habitat available to them during the birthing season.…”

Evaluating the road-effect zone on wildlife distribution in a rural landscape

“…In general, female moose appeared to be more sensitive to disturbance, with no statistically significant positive associations with Routes or Willow 3 Routes. This could be explained possibly by a female's higher levels of vigilance necessary for protecting calves (Bowyer et al 1998, Stankowich 2008.…”