REPRODUCTIVE-PERFORMANCE OF FEMALE ALASKAN CARIBOU

We examined the reproductive performance of female caribou (Rangjfer t arandus granti) in relation to age, physical condition, and reproducti ve experience for 9 consecutive years (1987-95) at Denali National Par k, Alaska, during a period of wide variation in winter snowfall. Carib ou in Denali differed from other cervid populations where reproductive performance has been investigated, because they occur at low densitie s (less than or equal to 0.3/km(2)) and experience high losses of youn g to predation. Females first gave birth at 2-6 years old; 56% of thes e females were 3 years old. Average annual natality rates increased fr om 27% for 2-year-olds to 100% for 7-year-olds, remained high for 7-13 -year-olds (98%), and then declined for females greater than or equal to 14 years old. Females greater than or equal to 2 years old that fai led to reproduce were primarily sexually immature (76%). Reproductive pauses of sexually mature females occurred predominantly in young (3-6 yr old) and old (greater than or equal to 14 yr old) females. Natalit y increased with body mass for 10-month-old females weighed 6 months p rior to the autumn breeding season (P = 0.007), and for females >1 yea r old and weighed during autumn (late Sep-early Nov; P = 0.003). Natal ity for 2-, 3-, 4-, and 6-year-olds declined with increasing late-wint er snowfall (Feb-May; P less than or equal to 0.039) during the winter prior to breeding. In most years, a high percentage of sexually matur e females reproduced, and lactation status at die time of breeding did not influence productivity the following year. However, following par ticularly high snowfall during February-September 1992, productivity w as reduced in 1993 for cows successfully rearing calves to autumn the precious year. High losses of calves to predators in 1992 may have inc reased productivity in 1993. Losses of young-of-the year to predation prior to the annual breeding season can be an important influence on s ubsequent productivity for ungulate populations where productivity var ies with lactation status of females at die time of breeding.