Temporal patterns in the survival of twin and single moose (Alces alces) calves in southcentral Alaska

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, P rior studies established that predation by brown bears (Ursus arctos) was t he primary cause of mortality of moose calves in the region. Our objectives were to characterize vulnerability of moose calves to predation as influen ced by age, date, snow depths, and previous reproductive success of the mot her. We also tested the hypothesis that survival of twin moose calves was i ndependent 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 o f 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 surv ival of the mother's previous calf was not related to neonatal survival. Se lection 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 f irst 15 days after birth and independently thereafter, suggesting that pred ators usually killed both when encountered up to that age.