135 D.b. minor in Kruger
There are 5 D. b. bicornis in the Augrabies Falls National Park (this assumes that these animals are recognised as belonging to this subspecies as suggested by Hall-Martin, 1985).
During 1987 a further group of 7 D.b. bicornis are due to be introduced to the Vaalbos National Park.
Increase in introduced population, Addo NP. For the purpose of this calculation the performance of the population at Addo from 1977 to 1986 was assessed. The hybrid animals (removed in 1 983) were considered to be partof the population in the model, but the Natal bulls not. The population growth overthe 9 years is described by the equation: Log e population = 2.11 + 0.0917t (where t is years) This observed rate of increase r=0.091 7 (giving a finite rate of increase of 9.6% per annum) is slightly higher than the rateof 9.0 % calculated for the Kruger National Park population (Hall-Martin, 1982), and is considerably higher than that of Hluhluwe Came Reserve in Natal (5.3%) (Hitchins and Anderson, 1983), or, historically, the 7.0 % at Ngorongoro and 7.2 % at Olduvai in Tanzania (Goddard, 1967). Other Natal populations such as Umfolozi have a higher rateof increaseof 11.0 % (Hitchins and Anderson, 1983).
Because of the nature of the vegetation at Addo - which is a dense thicket of mainly evergreen and succulent shrubs and small trees (HallMartin,etal. 1982), in which visibility is limited, and access restricted to a few roads and elephant paths - it is difficult to keep records of the rhino. All animals were, therefore, darted in May 1977 when they were still held in a relatively small fenced paddock, and were marked by ear tags ('Lone Star' type) and had notches cut in their ears. The tags lasted a few years and then fell out. The notches, however, have allowed observations of known individuals to continue. A helicopter census of the Park (now carried out annually) during which all rhino are identified and photographed, is the major meansof recording data on the reproductive performance of the populations. When calves reach the age of 2-3 years, before they leave their mothers, they are darted and marked by ear notches. Three young animals were caught and marked in 1986 and more will be marked in 1987. The ultimate objective is to have all animals marked.
Animals introduced from Namibia. This assumes that these animals are recognised as belonging to this subspecies as suggested by Hall-Martin, 1985
Introduced population Addo NP. There is little evidence of the age of bulls at full 'sexual' maturity and first mating. One bull was killed by an older bull at the age of 8 years 5 months which suggests that he was regarded as a rival at that age. One successful mating, according to strong circumstantial evidence, occurred when another bull was 6 years old.
Population introduced in Addo NP. Six cows born in the Park have calved and the ages of first conception and calving are shown. Cow Age Conception First Calving Lucky Star 7 yrs 2 mo 8 - 5 Doreen 6 - 9 8 - 0 Blom 9 - 1 10 - 4 Salttery 3 - 10 5 - 1 Ida 6 - 3 7 - 6 Vega 4 - 10 6 - 1 The ages at first calving are higher than those given in the literature for wild blackrhino (Goddard, 1970) but of the order reported for captives (Mentis, 1972). The records for the first three cows given above (mean age at first calving 8 years 11 months) were derived from the period when the animals were living at an unnaturally high density and when only one adult bull, or no adult bull was available. The age at first calving for the second group of three cows is 6 years 3 months. Four adult bulls were available at the time when the first two of these cows conceived, and three when the third conceived. These latter records are, therefore, more likely to be representative of what may be expected from this population in the future.
Introduced Addo NP. The records of 28 conceptions at Addo are shown diagramatically relative to long term rainfall (Figure 3). There appears to be a clear spring to mid-summer peak in conception time.
