TIMING AND SYNCHRONY OF PARTURITION IN ALASKAN CARIBOU

Timing of parturition of caribou (Rangifer tarandus) varies within pop ulations, but the relative influences of nutritional condition of fema les during the autumn breeding season and during gestation on that var iation is not known. We determined timing of parturition of caribou in Denali National Park, Alaska, during 1984 - 1995, which had wide vari ation in snowfall that influenced nutritional condition and productivi ty of females. The first young were observed each year between 4 and 1 5 May. Annual median dates of parturition for radiocollared females du ring 1987 - 1995 varied from 13 to 21 May. Synchrony of births (i.e., proportion of births during 7 days centered on the median date) did no t vary significantly among years (P > 0.05). Females less than or equa l to 4 years old were more likely to give birth after the annual media n date than older females (P = 0.005). Dates of parturition were signi ficantly correlated with masses of females in the previous autumn (P = 0.034) but not in late winter (P = 0.155). Births tended to be earlie r for parous females that were not lactating during the previous breed ing season compared to those that were lactating (P = 0.030). Annual o nsets of parturition-varied significantly with snowfall in late winter prior to conception (P = 0.012) but not with snowfall during gestatio n. Timing of parturition in our study appeared to be a function of phy sical condition of breeding females in autumn.