Breeding Phenology of Black Rhinoceros in Southern Africa

Black rhinoceros (Diceros bicornis) are typically regarded as aseasonal breeders, despite field reports of wet-season birth peaks, especially in southern Africa. I use 60 births from Law, Fike & Lent (2013) to investigate seasonality in breeding. The model of observed frequencies of births was favoured over the null model of expected frequencies across calendar months (P = 0.024) and for the periods Dec–Apr versus May–Nov (P = 0.027). Comparisons of births across explicitly defined wet and dry seasons did not strongly favour one model over the other in AIC comparisons, with the simplest interpretation that more births occurred in the wet season due its greater length (seven months versus five months), but with evidence for concentration in the mid–late wet season. Analysis of conceptions provided weak evidence for a wet-season peak, distributed according to expectations within the wet season, and stronger evidence for a late dry to early wet seasons peak. As with previous studies, the results are provisional due to limited sample size but also exclusion of births with poorly known birth dates. It is suggested that the benefits to both mother and neonate of a wet season birth could contribute to a peak in wet season births beyond expectation by resulting in short inter-birth intervals (IBIs) of about two years and thus ending in another wet-season birth. Thirty-five IBIs were investigated and weak evidence from analysis of medians suggests this possibility is worth further investigation. Much more data are required to adequately address the issue of breeding phenology and would also permit calving histories to play a role that has previously been neglected. Although challenging to collect, such data are required to understand what conditions might favour conception and the subsequent birth, whether peaks occur, and if so, whether they result circumstantially or from adaptive propensities.