Age-related fecundity of free-ranging mule deer Odocoileus hemionus Cervidae in south-central, New Mexico, USA

Abstract

Abstract Mule deer Odocoileus hemionus (Rafinesque 1817) populations in southern New Mexico have declined significantly since the 1980s, similar to trends across the arid Southwestern USA. Because production of fawns is critical to population growth, we evaluated factors influencing fecundity in two mule deer populations in southern New Mexico. Conception, litter size and survival of ≥1 fawn to weaning were all affected by maternal age, with older (age 8 and older) females exhibiting reproductive senescence as compared to prime-aged (age 2–7) females for the latter two traits despite achieving similar condition as did prime-aged females. Litter size and survival to weaning were also positively affected by increasing spring precipitation and survival to weaning was also positively affected by increased maternal condition, and size during late gestation. Unlike most previous work, reproductive senescence was evident in mule deer in our study populations, possibly because deer in both populations were in poor condition and older females produced on average 0.24 (95% CI=0.10–0.42) fawns through weaning compared to 0.76 (95% CI=0.60–0.94) for prime-aged females. The positive effect of precipitation during gestation on litter size and fawn survival also indicated that both income (i.e. nutritional intake) and capital (i.e. body reserves) were important determinants of fecundity in our arid Southwestern populations. The relatively early onset of senescence compared to the lifespan of female mule deer indicates that more intensive management of female age structure may be necessary to enhance population-level productivity.