Breeding success may be enhanced by separating males from females as little as possible. Specific information about male and female introduction is described below. This followed by a description of behaviour for female and male in relation with mating.
Introducing a male to a female: It is often easier to introduce a male to a female when she is in oestrus. Some collections have reported that for some pairs it is better to introduce them before the female is in oestrous as the male may get too excited when introduced when the female is in oestrus. This is very dependent on the individuals involved. Some females do not express clear behavioural signs of oestrus, even if they are cycling regularly and so should in fact be receptive. This has been reported to be a particular problem in previously non-proven females (Edwards et al. 2013), where females may be cycling based on hormone data, but often do not express overt behavioural signs of oestrus. Hormone analysis can then prove useful by allowing prediction of the period of female receptivity, even if behavioural signs are relatively absent. When introducing a male to a female both animals should be familiarised with the enclosure. The introduction should occur in the largest paddock available, following the general introduction steps. If a single large paddock is not available, adjoining paddocks should be opened to form a large area for the introduction. If the latter strategy is used, care should be taken to modify any resulting dead ends in the exhibit where a rhino may become trapped during an aggressive interaction. This method is proven to be successful. If it is not the usual enclosure of the male, he should have been given time to mark the enclosure. This should not be cleaned out. Before the introduction the contact through bars (indoors) must be sufficiently long until no more aggression is shown. Observation should continue when needed. In any case but especially when aggressive situations arise, preferred feed should widely be distributed throughout the enclosure (fresh greens, browse, carrots, etc).
Introducing a postpartum female to a male: The reintroduction of a male to a female immediately postpartum is not recommended. If the calf is still born or does not survive it is recommended that after four months, reproductive hormone monitoring is resumed to determine the next oestrus. This combined with a judgement of the female’s health dependant on the difficulty of the birth, can be used to decide when to reintroduce the male for mating. If the calf survives, it is recommended that reproductive hormone monitoring resumes by seven months to determine the next oestrus.
It has been reported in the wild female Black rhinos that cyclicity resumes as early as three months after parturition. There has been one report from a captive female at Hannover zoo who was observed to be in oestrus 20 days following giving birth, she was then reported as cycling regularly every 25 – 30 days until conception approximately twelve months after giving birth. Hormone analysis on captive females by Brown et al. (2001) has confirmed that females generally resumed cyclicity within three to ten months post-partum.
If cycling occurs, and it is possible to separate the mother from the calf for a long enough period of time, the male can be reintroduced for mating when the calf is separated. The possibility of training the calf to be separated from the female after the age of seven months, to allow re-mating of the female, depends highly on the character and behaviour of both adult and calf, but can help to reduce the interbirthing period.
Studies have shown interbirthing periods in wild Black rhinos to be highly variable; from as short as 20 months, to 89 months, the mean interbirthing period of Black rhinos was 44 months in Hluhluwe National Park and 30 months at Umfolozi National Park (Bertschinger, 1994). In captivity the shortest interbirthing period reported is 16 months (Smith and Read 1992), indicating potential conception during first post-partum oestrus, however this is relatively rare.
The average interbirthing period in the current living EEP (Oct 2013) is 46 months (calculated from 40 separate cases where the female’s previous calf survived more than four years). This is longer than seen in the wild. In almost half of these cases (48%) the interbirthing period was less than 40 months meaning the calf was separated at less than two years old to allow re-mating of the female. In 13% of these cases, the calf was less than 18 months when separated from the female to allow her to be re-mated. The shortest interbirthing period from these 40 cases was 26 months. The female in this case was ‘Nane.’ If Krefeld zoo, and if the gestation period was fully served, her calf must have been separated from her at ten months old to allow mating to occur. In Nane’s case, short interbirthing periods are common; she has four surviving offspring born at intervals of 27, 26 and 36 months. This may be due to a combination of factors including her confident character, dominance over the male, and very peaceful mating (always the same male). Nane gives clear behavioural indicators that she has come back into oestrus between three and four months after parturition allowing the keepers to decide the best time to re-introduce the male.
Female behaviour: At the peak of oestrus the female shows the following behaviour: positive male solicitation, presentation of hindquarters, aggression towards the male, running from the male, ignoring the male, copulation as well as refusing to copulate. Vulva changes include: squirting of white or cloudy urine, vulva swelling with occasional mucosal discharge prior to mating. At least two collections have succesfully used the hormone treatment Regumate to induce ovulation.
Male behaviour: Although, males in captivity may show interest in females outside of peak oestrus, greatest interest is seen during the peak of oestrus. At the peak of oestrus the male frequently exhibits the following behaviour: erection, genital inspection and flehmen response, head resting, chasing, mounting, copulation, failing copulation attempts.
Ideally a male will show interest in a female one to three days prior to oestrus. The couple may need to be separated for the night. Copulation normally occurs the next day. Copulation will last 20 to 45 minutes with multiple ejaculations. Mating may occur for 24 hours (Fouraker and Wagener, 1996).