 Reference Base  Feeding trials on captive black rhinoceros Diceros bicorn... |
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| Location: |
Africa - Southern Africa - South Africa |
| Subject: |
Ecology - Food |
| Species: |
Black Rhino |
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Food preference of introduced rhino - South Africa. The Andries Vosloo Kudu Reserve/Sam Knott Nature Reserve complex (AVKR/SKNR) in the eastern Cape has received translocated black rhinoceroses Diceros bicornis minor (Linnaeus 1758) as part of the national conservation plan for this species (Brooks 1988).
Black rhinoceroses in Natal feed on a range of browse (Emslie & Adcock 1993) which does not occur in the eastern Cape (pers. obs.). Animals are therefore confronted with unknown food plants to which their gut microflora are not adapted. This problem is not unique and similar food availability differences exist during translocation excersises in South Africa. Translocated rhinos are held in receiving bomas prior to release thus providing a chance to introduce animals to 'new' plants.
The aim of this study was, therefore, to determine how best, and which plants in the eastern Cape, to feed translocated rhinos in future. Given the threatened status of black rhinos in Africa (Brooks 1993), this procedure will contribute towards ensuring that translocated rhinos attain good condition before release. It is thus argued that animals in good condition at release, and having sampled some local plant foods, will have an increased chance of survival.
The AVKR/SKNR complex is approximately 35 km northeast of Grahamstown (33.8 S, 26.39 E). Dominant vegetation is xeric succulent thicket, a suborder of subtropical tran- sitional thicket (Everard 1987), which encompasses Acocks's (1988) Fish River Scrub of the valley bushveld. It is a low (2 to 2,5 m), relatively sparse thicket with larger trees reaching 5 m (Everard 1987). Black rhinoceroses were common in this area in the past (Skead 1987).
One sub-adult male and two adult female black rhinoceroses were kept in separate bomas for three weeks. During a six-day acclimatization period a variety of shrub and tree species were given ad libitum including plants selected for the feeding trials. Fresh lucerne and water were available ad libitum throughout the boma period.
For the trial, twelve plant species were placed in three groups; a thorny group (Acacia karroo, Azima tetracantha, Grewia robusta, Maytenus capitata), other woody plants (Euclea tindulata, Ozoroa mucronata, Pappea capensis, Schotia afra) and succulents (Aloe ferox, Euphorbia bothae, E. triangularis, Portulacaria afra). Each group was separately tested in a three-day trial. Food was weighed to the nearest 200 g on a Salter 50-kg balance and each species randomly allocated a corner of the boma. Animals were fed twice daily and each morning and afternoon food remains were collected and reweighed. Food acceptability was estimated by ranking the total wet mass of food ineested over each three-day trial. Evapo-transpiration was measured by weighing plant samples before and after each feeding period. Excluding the succulent plants, evapo-transpiration was relatively low and ranged from 3 to 10% (Table 1).
We decided a priori that if the animals refused to feed the trial would be cancelled. For this reason the succulent feeding trial was cancelled after the first morning feeding period. Also, the sub-adult male was taken off the woody diet after two days. The rhinoceroses were released in good condition after boma confinement and one gave birth in the wild.
Fresh lucerne was available ad libitum but was eaten by one animal only. Individual acceptability of the plants wa similar for all three trials (Spearman's rank correlation; rv = 0,8; p = 0,1) and the amount of food presented did not differ from an even distribution (Wilcoxon signed rank test; n =4; Z = 0,18; p = 0,86). Consequently, data from all three animal were combined.
Excluding the succulents, which were avoided by all three animals (Table 1), the rhinoceroses ate an average of 37,8 ? 9,0 kg wet weight/day of thorny and woody plants (n = 14 days). This comprised an average of 41,0 ? 9,0 kg thorny and 32.0 ? 5.9 kg woody plants. By comparison, Emslie & Adcock (19930 recorded that a captive black rhino ate an average of 28,2 kg of food per day, similar to the 30 kg/day recorded by Hillman (1982; op. cit.).
A. tetracantha, P. capensis, M. capitata and A. karroo represented the largest mass of individual plant species eaten and over the three days exceeded 50 % of the total amount given (Table 1) . G. robusta and E. undulata were also eaten readily but less than the previous four species (Table 1). Eticlea undulata was rejected by wild rhinoceroses in Zululand as were Maytenus spp. (Emslie & Adcock 1993).
Although only twelve plant species were used in this study, the results are clear; all species offered, except succulents, were eaten. Of the twelve plant species, nine do not occur (including three of the four succuleris) or occur infrequently in the Zululand reserve and hence were unfamiliar to the rhinoceroses. However, the rhinoceroses appeared to quickly accept some of these 'new' foods.
In Hluhluwe Umfolozi Park, black rhinoceroses feed mainly on Spriostachys africana and a wide range of Acacia species (Emslie & Adcock 1993). The importance of Acacias in the diet of black rhinoceroses, has been well documented (Goddard 1968; Loutit, Louw & Seely 1987; Emslie & Adcock 1990, 1993) and large amounts of A. karroo were eaten in this trial. However, A. karroo is the only Acacia in the eastern Cape.
Tree euphorbias (Euphorbia spp.) are eaten by D. b. michaeli (Goddard 1968; Hall-Martin, Erasmus & Botha 1982) and D. b. bicornis (Loutit, Louse & Seely 1987) and are occasionally pushed over by black rhinoceroses in AVKR/ SKNR (pers. obs.). But these plants are usually eaten during dry seasons, implying that they are used as a source of water (Goddard 1968). Since the rhinoceroses in the present study had water provided ad libitum, it may have been unnecessary for them to cat succulents, particularly since Euphorbias are scarce in Zululand Reserves, the source area for the rhinoceroses.
Ample water may only partly explain the rejection of Portulacaria afra which is eaten in relatively large amounts by black rhinoceroses (D. b. michaeli) during the dry season in Addo Elephant National Park (Hall-Martin et al 1982). P. afra is the dominant in xeric succulent thicket and important for many wild and domestic browsers (Aucamp 1979; Aucamp & Tainton 1984) and there seems no reason. why P. afra was not eaten in the trials. P. afra is uncommon in Zululand and its rejection in these trials may have been simply that it was unknown to the animals. Further studies are required to determine the extent to which released black rhinoceroses eat this plant.
It is possible that insufficient time was given for the animals to familiarize themselves with the succulents. Also, presentation of succulents only, rather than a mixture of food types, may have biased the results. However, evaluation of all combinations of the twelve species was impracticable.
Conclusions
When introducing black rhinoceroses to areas where much of the browse may be unknown, the catholic diet of this species (Goddard 1968; Emslic & Adcock 1993) must be exploited. A wide range of food species, includin. about 40-45 kg wet weight of plants that the rhinoceroses will eat, should be presented daily. Potential new foods should be introduced regularly and repeatedly and checked daily for evidence of browsing. Given the rejection of P. afra in these trials, introducing captive rhinoceroses to local, potential foods during the boma period may be important in the post-release survival of translocated rhinoceroses.
Table 1 Overall amount of different plant species eaten by three captive black rhinoceroses during the three day feeding trial. Evapo-transpiration recorded for each plant is also indicated
% of total Kg % Evapo- Kg
Plant species N eaten eaten transpiration per day SD
Thorny (3 days)
Azima tetracantha 18 62.2 155.4 10,3 16,1 3,8
Maytenus capitata 18 54.2 73.0 3.0 7,8 2,3
Acacica karroo 18 52.3 110,4 8,0 11,2 3,4
Grewia robusta 18 43.9 55,9 3,1 5,9 3,2
Woody -3 days
Pappea capensis 10 65,9 81,8 5,1 15,7 4,5
Euclea undulata 10 40,3 42,8 9,0 7,6 5,5
Schotia afra 10 33,4 29,2 9,5 4,4 2,2
0zoroa mucronata 10 28,2 27,4 5,7 4,3 1,9
Succulent (1 day)
Euphorbia bothae 1 6,1 6,8 0,3 1,6 0.4
E. triangularis 1 10,3 5,4 0,7
Aloe ferox 1 8,0 5,6 0,3 1.4 1.7
Portulacaria afra 1 7,6 6,5 0,8
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