A 'pool' of known-aged animals in the Pretoriuskop area has been watched by T. Mostert, and these observations have provided very useful data. For example, of 27 births the sex ratio was skewed to two males to one female.
The black rhino population in the Addo Elephant National Park (of the subspecies Diceros bicornis michaeli) was established from animals introduced from Kenya in 1961 and 1962. In 1977 three bulls of the Zululand subspecies (D. b.minor) were introduced to augment the population. In 1980 the IUCN/SSC African Rhino Specialist Group sent a request to the Board to remove the Zululand bulls and any mixed parentage progeny so that a pure population of the Eastern Kenya subspecies (Diceros bicornis michaeli) could be maintained. Two of the Zululand bulls were removed in May 1981, the third animal which had been castrated in 1979 because of its undesirable congenital one-eared condition was left at Addo. Removal of hybrids The second phase of the removal project, which was the capture of the calves of possible mixed parentage was done during May 1983. The capture operation was preceded by a survey carried out by helicopter during which the black rhino were counted. As all individuals in the Park in 1977 were caught and marked, and all subsequent births had been recorded, it was possible to account for 100% of the known population. Some confusion in the field arose from one unmarked hybrid animal being counted twice. However, subse- quent extensive flying and two repeat counts during which all known individuals were seen eliminated this problem. Eight calves were born after the introduction of the Zululand bulls. One of these was conceived before their arrival, four were conceived after their removal and three were con- ceived while they were at Addo. The Zululand animals look markedly different in the field being smaller and having a smooth skin, as opposed to the larger D. b. michaeli animals with rough and strongly grooved skin. The grooves or folds were particularly conspicuous on the flanks of the D. b. michaeli animals. Of the three animals captured, two males looked like hybrids and a female looked like a D. b. michaeli animal. However, all three were consigned to the National Zoological Gardens in Pretoria. An adult female held by the zoo, which came from eastern Kenya was translocated to Addo during the same operation. Within three months the translocated cow at Addo had died of undefined causes. The female at the zoo died of a respiratory infection which followed on treatment to nasal injuries received during transport. Status of animals at Addo There are at present 14 D. b. michaeli animals at Addo and one castrated D. b. minor bull. Of the fourteen, five are adult cows born at Addo and ranging in age (as at February 1984) from 9-20 years. All of them have calved within the past four years. One cow, originally from Kenya, at least 32 years old has not calved since 1978 and may well be too old to breed again. The immature animals presently at Addo are three females and two males. The overall sex ratio of the D. b. michaeli animals is 5 males, 9 females. Prospects for reproduction and a rapid increase in this population are therefore very good. Management The Addo black rhino are confined to that part of the Park which is enclosed by the elephant proof Armstrong Fence. Since 1977 when the rhino were released from their 210 ha enclosure their available range has been expanded from 4,000 ha to 5,200 ha and in March 1984 this was increased to 6,800 ha. Conclusion Initial management problems discussed in detail by Hall-Martin and Penzhorn (1977) severely limited the population growth potential of the Addo D. b. michaeli population. The unfortunate introduction of D. b. minor animals and its aftermath was a further setback to this population. However, these problems have all been overcome, the available range has been enlarged and the prospects for the future of this population are excellent.
A 'pool' of known-aged animals in the Pretoriuskop area has been watched by T. Mostert, and these observations have provided very useful data. For example, of 27 births the sex ratio was skewed to two males to one female. Over the years, the juveniles have comprised 5,5% - 13,9% of the population, with 8% in 1983 in the southern district of the Kruger National Park. Pienaar 1994b The size of the founder population is also an important factor when establishing new populations, with larger founder populations being more successful. If one introduced 10 white rhino on a 20 km? game farm with suitable habitat, this would generate a density of 0,5 rhino per km?. A suitable sex and age structure for such an introduced population would be: 2 adult males, 3 adult females and their 3 calves, one subadult male and one subadult female.
Addo NP (introduced michaeli from Kenya). The Zululand animals look markedly different in the field being smaller and having a smooth skin, as opposed to the larger D. b. michaeli animals with rough and strongly grooved skin. The grooves or folds were particularly conspicuous on the flanks of the D. b. michaeli animals.
Of the three animals captured [hybrids of michaeli and minor], two males looked like hybrids and a female looked like a D. b. michaeli animal. However, all three were consigned to the National Zoological Gardens in Pretoria. An adult female held by the zoo, which came from eastern Kenya was translocated to Addo during the same operation. Within three months the translocated cow at Addo had died of undefined causes. The female at the zoo died of a respiratory infection which followed on treatment to nasal injuries received during transport.
At Addo NP, in May 1983 three hybrid calves were captured and sent to the National Zoological Gardens (Pretoria).
Animals of the michaeli subspecies were introduced from Kenya in the early 1960's. Unfortunately, there minor bulls were added in 1977 which created the problem of genetic mixing of subspecies. However, it is relatively easy to distinguish rhinos of the two subspecies from the air and from the ground - minor animals are smaller and have a smoother skin than do michaeli animals.
Animals of the michaeli subspecies were introduced from Kenya in the early 1960's. Unfortunately, there minor bulls were added in 1977 which created the problem of genetic mixing of subspecies. However, it is relatively easy to distinguish rhinos of the two subspecies from the air and from the ground - minor animals are smaller and have a smoother skin than do michaeli animals.
