Male behaviours signal the female’s reproductive state in a pair of black rhinoceros housed at Lincoln Park Zoo

Abstract

The black rhinoceros (rhino; Diceros bicornis) is a Critically Endangered species due to habitat loss and poaching. Zoological institutions’ breeding programs have been minimally successful over the years. Our goal was to introduce and breed an eastern black rhino (Diceros bicornis michaeli) pair at Lincoln Park Zoo (LPZ; Chicago, IL USA). The specific objectives were to: 1) use faecal hormone metabolite and serum analyses to monitor the female’s reproductive state (via progesterone) and male’s testosterone production; 2) determine the behaviours that signalled the female was in oestrus; and 3) use these data to determine the optimal time to introduce the pair. Faecal samples and behavioural observations were collected daily. Sera were collected without restraint during routine veterinary procedures. Results demonstrated that the male’s faecal and serum testosterone concentrations changed with the female’s reproductive state. Specifically, testosterone increased when the female became sexually mature but there were no physical introductions and during her pregnancy. The behaviours most indicative of the female’s oestrous state were the male investigation of female faeces and urine and erect penis. Using these behavioural signals, the staff introduced the rhinos 77% of the time during her follicular phase, when oestrus would occur, versus luteal phase. After 52 days of introduction spanning 1 year and 16 oestrous cycles, the pair successfully bred and a male calf was born approximately 15 months later. This study is an example of how zoo science and management collaborations can improve the breeding success of zoo-housed endangered species.