Reproductive non-seasonality in rhinoceroses: A review of the in-situ literature and birth records of ex-situ institutions

Mammals whose breeding activity is triggered by seasonal photoperiodic cues typically maintain seasonal reproduction in zoos, with births accumulating to various degrees in spring. For zoo-kept rhinoceroses, accumulation of births in autumn has been suggested, which would make this group unusual. We compare birthing (and hence conception) patterns of free-ranging rhinoceros populations from the scientific literature with those of the global zoo populations based on birth data available from Species360, to facilitate deductions on the cues that trigger rhinoceros reproduction. The patterns do not indicate a photoperiodic element in rhinoceros reproduction but suggest suppression of conception in free-ranging populations at times of resource scarcity. This is not evident in zoos. However, a slight accumulation of autumn births, due to a slight reduction in births in spring, is visible in the zoo populations. Given rhinoceros gestation periods, this is linked to reduced conceptions in November-December. The most parsimonious interpretation is management-related, as has been suggested (Roth 2006, Int. Zoo Yb. 40(1): 130-143): not all facilities are prepared to allow mating at times when outdoor husbandry is reduced due to weather restrictions. Given the long interbirth intervals of rhinoceroses, missed conception opportunities of 1-2 months are unlikely to affect population demographics. Nevertheless, detailed recording of approaches to facilitate mating during winter months by those zoos that achieve this may increase the general skill of rhinoceros management.