Hitchins, P.M., 1986. Earlessness in the black rhinoceros - a warning. Pachyderm 7: 8-10, figs. 1-5, table 1
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| Subject: |
Morphology |
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Black Rhino |
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Absence of ear pinna in Diceros bicornis, South Africa. Unilateral or bilateral earlessness (i.e. lack of pinnae) in the black rhinoceros has been recorded from a number of populations in eastern and southern Africa (Goddard, 1969; Hitchins and Anderson, 1 983). These authors have attributed the condition to predation on black rhinoceros calves by spotted hyaena Crocuta crocuta whilst Goddard (1969) suggests that a genetic character, a sex influenced or sex-linked gene could also be responsible fora congenital deformity. The black rhinoceros population in the Hluhluwe/ Corridor/ Umfolozi Game Reserve complex, has been monitored at various intervals between 1961 and 1985 by the author. Physical characteristics of all individuals seen were recorded over this period, which resulted in comprehensive data on missing ears and/ or tails or parts of tails of various individuals. Prior to 1961 earlessness was f irst observed in early 1955 (N. Deare, pers. comm.) in the north of Hiuhluwe Came Reserve: an adult female with its left pinna missing. Later during 1955 a male calf was born with both pinnae missing and with no external openings. From 1955 to1985 a total of 23 individuals in Hluhluwe Game Reserve and Corridor showed the earless condition (one or both pinnae absent) and an additional 15 individuals had either a portion of the tail or the whole tail missing
In the earless condition (n =23), 21 animals were examined in the field in detail and showed the following characteristics:
both pinnae absent with no external opening: 1 (no scars);
both pinnae absent with external opening: 3 (scars present);
one pinna absent with no external opening: 1 (scar present);
one pinna absent with external opening: 16 (scars present).
Where tails were missing or damaged (n = 15) obvious scars were always visible.
Of the 36 animals examined with missing ears and/or damaged tails, one showed a congenital deformity. If one considers this single case in relation to the whole black rhinoceros population in the Hluhluwe/Corridor/ Umfolozi Game Reserve complex over a 30-year period (1955 to 1985) the incidence of a genetic character being responsible for earlessness is indeed rare. The impact of hyaena predation on the black rhinoceros population is unknown but is considered to be fairly high in Hiuhluwe, low in the Corridor and very low in Umfolozi. Kruuk (1 972) observed hyaenas grabbing black rhinoceros calves preferentially by the ears and tail at Serengeti which supports the observations in Table 1.
It is of interest to note that in the square-lipped rhinoceros Ceratotherium simum simum there has been no record of any ear or tail losses in the reserve complex from thousands of observations made by the author. There is little doubt that the reason for this is related to predation by spotted hyaenas on black and not square-lipped rhinoceros. This preference is in turn related to the mother-calf relationship when the animals are disturbed: with the square-lipped rhinoceros, a calf always runs in front of the mother (Figure 4) which has total contact with its calf, whereas the black rhinoceros calf follows the mother with very little contact and therefore less protection (Figure 5). Both these relationships are related to the different habitat requirements of these two species.
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Earlessness in the black rhinoceros - a warning
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