Birth-Site Selection by Alaskan Moose: Maternal Strategies for Coping with a Risky Environment

We studied birth-site selection in Alaskan moose (Alces alces gigas) from 1990 to 1994 in Denali National Park and Preserve in interior Alaska. Twenty percent of preparturient females made extensive movements (≥5 km) immediately before giving birth. Females selected (use was greater than availability) sites for giving birth (n = 39) that were on southerly exposures with low soil moisture and high variability in overstory cover. Moose selected birth sites based on micro-site characteristics rather than on broad types of habitat, which were used in proportion to their availability. Spatial distribution of birth sites did not differ significantly from random locations. We hypothesize that such unpredictable behavior by females is a strategy to avoid predators. Parturient females also selected sites with high visibility that were located at high elevation, which ostensibly allowed them to see and then hide from approaching predators. We rejected the hypothesis, however, that moose in this population spaced themselves away from predators or avoided habitat types favored by large carnivores. Likewise, we rejected the hypothesis that moose gave birth close to human developments to avoid predators; random sites were >100 m closer to human developments than were birth sites. Cover of forage, especially willows (Salix), was more than twice as abundant at birth sites than random sites. Forage quality, as indexed by nitrogen content and in vitro dry matter digestibility, was slightly but significantly higher at birth sites. An inverse relationship between visibility and availability of forage indicated that female moose made tradeoffs between risk of predation and food in selecting sites to give birth. Thus, maternal females coped with a risky environment; they gave birth at sites that helped them minimize risk of predation but exhibited risk-averse behavior with respect to the forage necessary to support the high cost of lactation. We hypothesize that risk of predation prevented moose from seeking birth sites with more forage and, hence, a greater nutritional reward, which reduced the variance in forage availability at birth sites.