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| Location: |
Africa - Eastern Africa - Kenya |
| Subject: |
Ecology - Interspecific Relations |
| Species: |
Black Rhino |
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Conservationists have expressed fears that spotted hyenas, Crocuta crocuta, could be killing rhino calves in the Salient. Since the late 1970s the Wildlife Conservation and Management Department (WCMD) has expressed concern about the effect that a high density of spotted hyenas might have on the herbivore species in the ANP forest, in particular on those endangered species such as bongo, Tragelaphus euryceros, and black rhinos whose numbers have decreased rapidly in the last few years. The skyrocketing of hyena sightings at both forest lodges during the 1980s and the extent to which pack hunting became more conspicuous have also been a matter of concern. A field study was undertaken in 1986-87 to estimate the actual population of hyenas in the Salient and its effect on prey species.
Hyenas are the chief predator in the Salient. Although the Salient does not resemble the optimal habitat for hyenas as described in the literature, it harbours a density of 1.34 hyenas per km? second only to that of Ngorongoro. This may be a result of the high concentration of herbivores which itself is probably a consequence of a 'funnel effect' exerted by the physical boundary and the creation of secondary forest by elephants. Hyenas were found to feed mostly on medium sized ungulates. They forage alone or in small groups more often than in packs. However, hunting packs of up to 17 hyenas were observed, which was unexpected in a forest habitat. Lions, Panthera leo, were rare in the ANP forest until 1983 when the lodges' records show a sharp increase in their presence, probably due to range expansion from other parts of the ANP. At least 12 different lions utilized the Salient during our study. Regular use of the area by lions would almost certainly lead to a decrease in the hyena population through interference and exploitation competition.
Predation on Rhino Calves
Rhinos can be killed by lions even when adult. They also appear to be vulnerable to predation by spotted hyena up to the age of four months. Four attempts by hyenas to pull down rhino calves were observed at the Ark salt-lick during this study, all of them unsuccessful (Table). Three attacks were made on male calf A12 when he was approximately one year old. In August 1986, two hyenas grabbed the calf by the flank, inflicting wounds. A12 was attacked twice again in 1986, and on both occasions the mother, who herself is missing half her tail, charged the hyenas after the calf emitted a distress squeal. In April 1987, a very young calf of unknown sex was harassed by two hyenas and presumably wounded. Again, the mother defended the calf by repeatedly charging the hyenas, and then mother and calf fled for cover. Both calves were seen again after the attacks in seemingly good condition .
Four out of nine individually recognizable calves observed in the Salient had scars on flanks or hind legs and one had neither ears nor tail (Table). Earlessness (i.e. lack of pinnae) in the black rhino has been reported from a number of populations in southern and eastern Africa. Although Goddard first suggested that a genetic character could be responsible for a congenital deformity, Hitchins reviewed the subject and attributed the conditions to predation on rhino calves by spotted hyenas.
Table. Known rhino calves in the Salient and evidence of predation attempts. Age estimation follows Hitchins (1970)
Calf Age Sex Evidence of predation
A4 2.5 yr F none
A7 2 yr F none
A12 1 yr M attacked by hyenas 3 times in 1986
A14 2.5 yr F no ears, no tail
A17 1 yr F wound right shoulder
A? <1 yr ? attacked by hyena in April 1987
A19 3.5 yr F none
TT 3 yr F none
MM 2 yr m none
End
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Threats to Aberdare rhinos: predation versus poaching
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