TEMPORAL PATTERNS IN THE SURVIVAL OF TWIN AND SINGLE MOOSE (ALCES ALCES) CALVES IN SOUTHCENTRAL ALASKA

Abstract

We studied survival of 220 calves of radiocollared moose (Alces alces) from parturition to the end of July in southcentral Alaska from 1994 to 1997. Prior studies established that predation by brown bears (Ursus arctos) was the primary cause of mortality of moose calves in the region. Our objectives were to characterize vulnerability of moose calves to predation as influenced by age, date, snow depths, and previous reproductive success of the mother. We also tested the hypothesis that survival of twin moose calves was independent and identical to that of single calves. Survival of moose calves from parturition through July was 0.27 ± 0.03 SE, and their daily rate of mortality declined at a near constant rate with age in that period. Mean annual survival was 0.22 ± 0.03 SE. Previous winter's snow depths or survival of the mother's previous calf was not related to neonatal survival. Selection for early parturition was evidenced in the 4 years of study by a 6.3% increase in the hazard of death with each daily increase in parturition date. Although there was no significant difference in survival of twin and single moose calves, most twins that died disappeared together during the first 15 days after birth and independently thereafter, suggesting that predators usually killed both when encountered up to that age.