Letters to the Editor

Dear Editor,

Disassociation between blackrhinoceros mothers and their calves appears to occur when a Black rhinoceros mother visits a watering point without her calf, which remains alone at some distance from the water point.

This behaviour was first highlighted by Berger (1993), based on observations of desert rhino in Namibia. Berger found that this behaviour occurred only for calves less than six months old and further speculated that it may be correlated with the long distances mothers travel to water in desert regions and, possibly, low density of predators reducing the risk of leaving a calf alone.

We recently reported two further instances of disassociation in Black rhino (Law et al. 2019). Although both cases again involved Black rhino in Namibia, both occurred on private game ranches where the distances travelled to water were not great (only one kilometre in one case) and, in any case, comparable to distances the cow-calf pairs were observed to travel together.

Lion and spotted hyaena were also absent from both ranches. It is of course possible that the disassociation behaviour was shaped by conditions that Black rhino on game ranches no longer encounter but that the behaviour nevertheless persists. We speculated that another factor that could contribute to this behaviour, and if so would still be operating, is the risk of accidental injury or mortality to young calves during interactions between their mothers and rhino bulls. It is known that social interactions amongst rhinos frequently occur at water holes, sometimes in large congregations (Cunningham and Berger 1997:102; BBC 2013).

When writing up our observations, we conducted a search of the Rhino Resource Center database (www. rhinoresourcecenter.com) for further literature on disassociation behaviour but found only two other references (Joubert & Elof, 1971:27; Anon., 1997), neither of which, unfortunately, is informative about the behaviour, except that while the older report also comes from Namibia, the more recent one was from Kenya. This observation would appear to undermine Berger’s suggestion that disassociation behaviour evolved only in those parts of the range of the species with more extreme conditions. In any case, we were surprised that no other reports of disassociation have been made in the 26 years since Berger’s article, or the 48 years since the observation of Joubert and Elof.

Although disassociation behaviour is well known in various ungulates (Lent 1974), this behaviour in Black rhino remains mysterious. How are the acts of disassociation and re-association initiated? What is the primary driver? Is the behaviour ecologically restricted? Does this behaviour occur with white rhino? Not only is this behaviour intrinsically interesting but understanding its modus operandi and frequency could be important to conservation and management of the species.

We therefore encourage all those engaged in monitoring black (and white) rhino to look for this behaviour when calf births are detected. We also invite anyone with observations and information on disassociation to communicate with us (to prldb@protonmail.com) as we are interested in collating such data to better understand this behaviour. Questions of interest include: i) Does the behaviour appear to be related to this individual’s history, including its matrilineage? ii) Are there characteristics of the water points where disassociation occurs? For example, evidence of other rhino present? iii) Distance travelled by the mother alone? iv) Behaviours of the mother while in transit, e.g., browsing?

Peter R Law Research Associate, Center for African Conservation Ecology Nelson Mandela University South Africa