Habitat selection, numbers and demographics of large mammalian herbivores in Ithala Game Reserve, KwaZulu-Natal.
O'Kane, C. A. J.
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With the purpose of improving the conservation management of Ithala Game Reserve and other similar reserves, the aims of this study were to determine the reserve's large mammalian herbivores' habitat occupancy, numbers and demographics, to investigate the feasibility of road strip counts as a census method for the same herbivores and to establish what environmental factors influence their habitat occupancy, numbers and demographics. Four years of demographic data were collected by vehicle transects on giraffe, kudu, wildebeest and impala. During the final two years additional positional data, using GPS, were collected on these and the reserve's other large herbivores. Sightings were recorded on the basis of habitat type occupied, a GIS was then used to define area sampled and hence derive habitat occupancy densities. GIS was further used to determine both absolute population sizes and, by over-laying other available GIS data, the relevance of distance to surface water, soil type and degree of slope to species' habitat preferences. Species showed non-random, significant habitat selections broadly in line with established preferences. Deterioration in habitat quality in winter generally lead to changes in habitat selection and the extent and nature of these changes related to the severity of resource pressure for individual species. This in turn was influenced by the species digestive strategy i.e. ruminant versus non-ruminant, grazer versus browser. Generally species showed a dry season move down the slope, moving, in some cases, onto heavier soils. Hartebeest, warthog, wildebeest and impala were strongly attracted to winter grass flushes. Lack of predation may be influencing the habitat selection decisions of impala and giraffe and kudu females, as well as allowing giraffe, wildebeest and impala to attain comparatively high densities. Giraffe density (effectively 1.8 km - 2) was abnormally high and their habitat quality poor, leading to a decline in numbers and low fecundity-related demographics. Wildebeest density (6 km -2) was also abnormally high and this may be instrumental in the poor performance of the rare tsessebe population, which is in decline and shows low fecundity-related demo graphics, increased dry season pressure on other grazers in general and impala 111 unexpectedly preferring browse habitats, rather than grasslands, in the wet season. Wildebeest fecundity declined in response to lower rainfall over the early period of lactation. Herbivores with an open social structure generally showed a dry season decrease in group size, although wildebeest and hartebeest showed, atypically, an Increase. Giraffe, zebra and impala adult sex ratios were comparatively less female biased, probably due to minimal predation. Territorial behaviour, virtually year round by wildebeest bulls and over the rut by impala bulls, imposed spatial sexual segregation between breeding and bachelor herds in these species. Outside of these periods, and generally in species not exhibiting territoriality, social sexual segregation was maintained and appeared to relate to differing activity budgets. Areas of concern for management are highlighted. Numbers results were generally acceptable and the method is proposed as a cost effective alternative in reserves with diverse topography. Underlying environmental determinants of habitat occupancy, numbers and demographics, together with associated annual or seasonal changes, were habitat quality, competition and predation.