Ex situ populations of endangered species such as the black rhinoceros play an important role in global
conservation strategies. However, the European captive population of eastern black rhinoceros is per-forming sub-optimally, with growth rates and genetic viability limited by low birth rates and high repro-ductive skew. We investigated several intrinsic differences between parous and nulliparou s females that
may underlie differences in reproductiv e success, including ovarian cyclicity, adrenal activity, behaviour
and body condition. Faecal samples were collected from 39 females (17 parous, 15 nulliparous and 7
pre-reproductive) at 11 zoological institutions, every other day for between 4 months and 6 years. Pro-gestagen metabolite concentration indicated that although all non-pregnant females exhibited ovarian
activity, irregular cyclicity was common. Longer cycles (>40 days) were more common in nulliparou s
females and periods of acyclici ty observed more often in females that had not bred for at least 7 years.
Even when endocrine data indicated clear ovarian activity, overt behavioural signs of oestrus were not
always apparent, particularly among nulliparous females. Faecal glucocorticoids did not differ between
parous and nulliparous females, although did differ accordin g to individual temperament. More unpre-dictable temperamen ts were associated with higher glucocortic oids, and nulliparou s females tended to
be rated as more unpredictable. Finally, nulliparous females had higher body condition scores than par-ous females. This is the first comprehensive survey of the reproductive physiology of this European cap-tive population, and highlights a number of intrinsic differences related to parity, which may underlie
differences in reproductive success among captive female black rhinoceros