CARIBOU CALF MORTALITY IN DENALI-NATIONAL-PARK, ALASKA

Calf mortality is a major component of caribou (Rangifer tarandus) pop ulation dynamics, but little is known about the timing or causes of ca lf losses, or of characteristics that predispose calves to mortality. During 1984-87, we radiocollared 226 calves (less than or equal to 3 d ays old) in the Denali Caribou Herd (DCH), an unhunted population util ized by a natural complement of predators, to determine the extent, ti ming, and causes of calf mortality and to evaluate influences of year, sex, birthdate, and birth mass on those losses. Overall, 39% of radio -collared calves died as neonates (less than or equal to 15 days old), and 98% of those deaths were attributed to predation. Most neonatal d eaths (85%) occurred within 8 days of birth. Few deaths occurred after the neonatal period (5, 10, and 0% of calves instrumented died during 16-30, 31-150, and >150 days of age, respectively). Survival of neona tes was lower (P = 0.038) in 1985, following a severe winter, than dur ing the other 3 years. In years other than 1985, calves born during th e peak of calving (approx 50% of the total, born 5-8 days after calvin g onset) experienced higher (P < 0.001) neonatal survival than did oth er calves. Grizzly bears (Ursus arctos), wolves (Canis lupus), and unk nown large predators (i.e., grizzly bears or wolves) accounted for 49, 29, and 16% of the neonatal. deaths, respectively. The rate of bear-c aused mortalities declined (P < 0.001) with calf age, and bears killed few calves > 10 days old. Wolf predation was not related (P > 0.05) t o calf age and peaked 10 days after onset of carving. Grizzly bear and wolf predation on neonates during the calving season was a limiting f actor for the Denali Caribou Herd.