The interspecific relationships of black rhinoceros (Diceros bicornis) in Hluhluwe-iMfolozi Park
Authors:   , Plotz Roan David 
Published: November 2021

<p>As habitat loss, predators (human and non-human) and disease epidemics threaten species worldwide, protected sanctuaries have become vital to species conservation. Hluhluwe-iMfolozi Park (HiP) in South Africa is at the centre of one of the world’s greatest conservation success stories. The formal proclamation of HiP in 1895 prevented the extinction of the south-central black rhino (Diceros bicornis minor) population. In recent times HiP has been a strategic source population for the D. b. minor range expansion program, facilitating an 18-fold population increase across southern Africa. However, HiP’s own black rhino population appears to be in decline. Evidence for decline is most often attributed to overpopulation and poor habitat quality that is driving apparently significant increases in the average home range sizes, poor growth rates (i.e., low calf recruitment) and poor body condition of black rhino. Other factors such as non-human calf predation and parasitism have also been raised as potential causes of decline but remain untested. HiP does have some of the highest densities of lion (Panthera leo) and spotted hyena (Crocuta crocuta). HiP’s black rhino population also suffers from remarkably severe chronic haemorrhaging lesions caused by a filarial parasite (Stephanofilaria dinniki). Empirical evidence if or indeed why the HiP black rhino population might be in decline is lacking. Investigating this population’s true status and any potential causes of an apparent decline is urgently needed.  This thesis therefore aimed to test three hypotheses for poor performance that included: (1) investigations of the average black rhino home range size, (2) confirmation of black rhino calf predation and (3) the relationship between filarial lesions and black rhino body condition. I inserted horn-implant VHF radio transmitters into 14 adult (i.e., >5 years) female black rhino in HiP and regularly monitored them on-foot over a three-year period. I found that average home range estimates (9.77 km2) were not significantly dissimilar to estimates using a similar technique obtained forty years prior (i.e., 7.5 km²). I also established the first confirmed link between predation attempts and tail amputation during a lion attack on a black rhino calf. Black rhino body condition, while significantly inversely and temporally correlated to lesion severity, did not appear to be driven by lesion severity itself and highlights the need for further research.  An additional research focus for my thesis developed while in the field. I regularly witnessed red-billed oxpeckers (Buphagus erythrorynchus) feeding at black rhino filarial lesions while also alarm calling to alert them to my presence. Studies have found it difficult to empirically show how oxpecker-host interactions have net positive benefits that make it a mutualism. Thus, two chapters were designed to determine if red-billed oxpeckers were predominately mutualistic or parasitic when visiting black rhino. Determining this depended on whether I could identify net positive benefits or net costs to black rhino. Oxpeckers provide rhino with two possible benefits i.e., benefit 1 is cleaning ectoparasites and benefit 2 is increasing vigilance, and one cost i.e., lesion parasitism. More than 50 hours of behavioural observations established that oxpeckers favoured haemorrhaging filarial lesions over sites of tick attachment on black rhino. Moreover, black rhino appeared to be completely tolerant of oxpeckers that fed at lesions. To test whether oxpeckers increased rhino’s anti-predator vigilance, I conducted 84 human approach trials towards black rhino both with and without oxpeckers present. Results showed that rhino were immediately responsive to oxpecker alarm calls and benefitted from more than a two-fold increase in human detection rate and detection distance. Rhino predominately orientated to face towards their sensory blind spot (i.e., downwind) after an oxpecker alarm call. The traditional name (Askari wa kifaru) of the red-billed oxpecker, which translates as the rhino’s guard, appears to be validated. However, future research will need to confirm whether black rhino’s tolerance of parasitic oxpeckers is directly related to vigilance benefits.  In summary, black rhino managers in HiP can be confident that the average home range sizes have not increased significantly. Further, predation of calves might be a greater problem than previously realised and requires further investigation. Monitoring changes in the filarial lesion severity of black rhino might be a useful tool for detecting impending changes in a rhino’s condition. Finally, black rhino are clearly eavesdropping and benefitting from oxpecker alarm calls – a co-evolution that has implications for conserving oxpecker populations as well.</p>