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Ecology and management of Himalayan thar and sympatric chamois in the Southern Alps, New Zealand

Forsyth, David M.
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This thesis investigated aspects of the ecology and management of Himalayan thar (Hemitragus jemlahicus) and sympatric chamois (Rupicapra rupicapra) in the eastern Southern Alps of New Zealand. The hypothesis that increasing densities of thar are associated with declining densities of chamois was investigated. Counts of thar and chamois at 53 sites within their sympatric range during 1978 revealed chamois densities to be significantly higher at sites without thar compared with those sites with thar. Although this result is consistent with the occurrence of interspecific competition, differential habitat selection could also explain the observed segregation of the species. Hence, 16 of 17 sites at which chamois and thar co-existed in 1978 were recounted during 1991-1996 to test predictions about the numerical response of chamois to increasing densities of thar. There was a six-fold increase in mean thar density between the two counts, whereas chamois density declined significantly. Chamois persisted at only three sites, two of which had the highest chamois densities in 1978. This is reliable evidence that increasing densities of thar exclude chamois from all but the most favoured habitats. Monthly observations of habitat selection by sympatric thar and chamois in Carneys Creek during 1993-1996 showed significant interspecific differences in selection of some habitat types. These differences were most pronounced in spring and summer, and least in autumn. It is concluded that chamois can co-exist with the low-density population of thar in Carneys Creek due to differential habitat selection. Thar selected a broader range of habitats than chamois in Carneys Creek in all seasons, suggesting that thar have a broader niche than chamois in the eastern Southern Alps. Nevertheless, there was strong overlap in the preference of thar and chamois for grassland and shrubland, suggesting a high potential for interspecific competition when thar densities increase. Observations of 24 interspecific interactions in the Two Thumb Range showed that chamois moved away from thar groups significantly more often than vice versa. I propose that as thar populations grow, increasing numbers of thar select habitats favoured by chamois; the resulting increase in the frequency of interspecific behavioural interactions is the proximate cause of chamois abandoning their home ranges. Behavioural avoidance of thar is an instantaneous and density-dependent mechanism that best explains the recent (1978-1996) decline of chamois in the eastern Southern Alps. Long-term trends in the summer adult male: female ratio of thar in the Two Thumb Range are described. Annual summer censuses were made in two catchments subject to different harvest strategies from 1984-1996. Densities in both catchments increased during the study. In Carneys Creek, subjected to unrestricted harvest, the summer population sex ratio was approximately equivalent to the estimated wider Southern Alps adult sex ratio during 1984-1991, but thereafter became increasingly male-biased. In North Branch, subjected to a small harvest of adult (trophy-size) males, the summer population was significantly female-biased in every year. A postal and telephone survey of recreational hunters who hunted in Carneys Creek during 1993 revealed the thar harvest to be strongly male-biased. Monthly counts of adult male (>4 years), sub-adult male (2-4 years) and female thar (>2 years) in Carneys Creek during 1993-1996 revealed an influx of sub-adult males during spring. Censuses of thar at six adjacent sites during summer 1996 indicated the likely source of these males to be an adjacent hunting reserve. High densities of females in the hunting reserve are postulated to have produced large numbers of sub-adult males that migrated to the northern Two Thumb Range because of a combination of preferred habitats and low overall density. Given the interspecific and intersexual differences in habitat selection, diet and mobility evident in sympatric thar and chamois, managers face a difficult task attempting to mitigate the deleterious impacts of these pests on conservation resources. This is compounded by the presence of hares (Lepus europaeus occidentalis), red deer (Cervus elaphus scoticus), and possums (Trichosurus vulpecula), all of which are likely to overlap in their habitat use and diet. Some ideas for the integrated management of the central Southern Alps herbivore pest community are presented. The need to understand competitive interactions between pests, as well as pest-resource dynamics, is highlighted.
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