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Doctoral Degrees (Ecology)

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Browsing Doctoral Degrees (Ecology) by Author "Combrink, Leigh."

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    The habitat, nesting and foraging requirements of southern ground-hornbills in the Kruger National Park.
    (2016) Combrink, Leigh.; Downs, Colleen Thelma.
    Southern ground-hornbills Bucorvus leadbeateri are large, terrestrial, carnivorous birds that inhabit the savanna and bushveld habitats of much of Africa, south of the equator. They were once prevalent in north-eastern South Africa, but as a result of extensive habitat loss and persecution, their population has suffered a significant decline. They are currently listed nationally as Endangered and globally as Vulnerable. In an effort to curtail this decline in South Africa, a National Species Recovery Plan was developed, with reintroductions of the birds into suitable habitat outside of protected areas listed as a viable conservation intervention for the species. This plan also highlighted a number of knowledge gaps which need to be addressed and which are essential to the long-term conservation of the species. The exact habitat requirements (including specifics of nest cavities) and the foraging ecology of southern ground-hornbills were both listed as areas where data are lacking. Consequently the main aim of this study was to determine the habitat, nesting and foraging requirements of the southern ground-hornbills with the intention of developing management guidelines for areas planned as reintroduction sites for the species. Our study focused on the population of southern ground-hornbills located within the Kruger National Park. We found that the particular characteristics of the southern ground-hornbill nest (cavity dimensions, tree species, height of cavity etc.) did not affect nesting success of the birds. The proximity of roads was important, with more successful nests being situated closer to roads. Habitat structure and diversity of vegetation around the nest also influenced the success of the particular group, with nests with more open habitats and a wider variety of vegetation types being more successful. Nest cavity temperatures were significantly different to ambient for selected nests studied across the 2013-2014 and 2014-2015 breeding seasons. We also found that nest temperature did not affect their nesting success. Interestingly, the artificial nest within our study area showed extremes in temperature (significantly higher and lower than ambient maximum and minimum temperatures, respectively) despite this being one of the most successful nests studied. As southern ground-hornbills are carnivorous, they are known to take a variety of prey items and have been considered generalists. One of the important current questions in foraging ecology is whether generalist populations consist of individuals (or in our case, groups) that are all generalists, or if the generalist population comprises a number of dietary specialists. We tested this theory for southern ground-hornbills using stable isotope analyses of feather and bill samples. Our results show that they are obligate generalists at the group level, suggesting that they access and consume prey species in accordance with their availability in the landscape. At the individual level, based on the two bill samples obtained, there could be some form of specialization occurring. With our relatively small sample size we were unable to determine whether this was in fact specialization or whether these results were reflecting local environmental changes, affecting the isotopic signatures of the vegetation and thereby, prey species of southern ground-hornbills. We used satellite tracking technology to investigate home range sizes and habitat use of southern ground-hornbills within the Kruger National Park and surrounding conservation areas. We then used first-passage time analysis to determine whether certain movement behaviours were influenced by habitat type. We found that there were marked seasonal differences in home range size and that all groups showed a range restriction during the wetter months (coinciding with the breeding season), where activities are concentrated around the nest site. Grassland, open woodland and dense thicket habitats were found to be important habitats for foraging and grassland and open woodland areas were used in accordance with their availability within the groups’ respective territories year-round. The results from this study have been consolidated into recommendations for areas being considered as potential release sites for captive-reared southern ground-hornbills. This research investigated what the habitat, nesting and foraging requirements of southern ground-hornbills are with the aim of adding to the current data on the species as well as addressing these knowledge gaps as highlighted in the National Species Recovery Plan. Each aspect of this PhD study provided results that can be used in current and future conservation interventions, and in particular, reintroductions in areas outside of protected areas. These results are applicable to populations within South Africa, but can also be applied to the species across its range.