Age-specific fertility and fecundity in northern free-ranging white-tailed deer: Evidence for reproductive senescence?

Abstract

Population performance of white-tailed deer (Odocoileus virginianus) is driven largely by survival and reproduction. Knowledge of age-specific reproduction would enhance our understanding of population performance and dynamics relative to intrinsic factors, regulatory mechanisms, and their interaction with extrinsic factors. From 1991 to 2002, we examined serum progesterone as an indicator of pregnancy in free-ranging white-tailed deer (0.5-15.5 years old), age-specific fertility and fecundity, and the potential effect of reproductive senescence on population change. We did not detect relationships between serum progesterone concentrations and Julian date, age, or body mass at capture in 41 confirmed-pregnant, adult (≥ 1.0-year-old) does. Serum progesterone concentrations of 284 females ranging in age from 0.5 to 15.5 years were distributed bimodally with a narrow peak at 0.0-0.4 ng/ml (composed of samples from 46 of 50 fawns) and a broad peak centered at about 3.6 ng/ml. Only 1 (1.8%) of 55 fawns was pregnant, whereas pregnancy rates were 96.6% (112 of 116) for 2.5-7.5 year olds and 98.5% (64 of 65) for 8.5-15.5 year olds. Among adults, the lowest pregnancy rates occurred in yearlings (87.5%), not in the oldest does. Mean estimated fecundity was 1.3 fetuses per doe in yearlings and was 1.8 fetuses per doe in 2.5-15.5 year olds. We observed no evidence of senescence relative to fertility and fecundity in adult female white-tailed deer up to 15.5 years old. Because older does comprise a relatively small proportion of the population, fecundity rates of these females have little impact on population change (λ); however, their ultimate value to the population may be in their life-long reproductive success and associated genetic contribution. © 2007 American Society of Mammalogists.