Browsing by Author "Thabethe, Vuyisile."

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Aspects of avian thermal physiology and frugivory of indigenous and invasive fruits in South Africa.
(2014) Thabethe, Vuyisile.; Downs, Colleen Thelma.
Indigenous and invasive plants have long been recognised as an important food source for avian frugivores worldwide. It has been suggested that seed germination success can vary amongst avian and plant species and that ingestion by avian frugivores can enhance, reduce or have no effect on seed germination. Few studies have looked at the role of both invasive and indigenous avian species on the germination success of invasive and indigenous plants in South Africa. Therefore the first aim of this study was to determine the effects of invasive rose-ringed parakeets (Psittacula krameri) and indigenous Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos on seed germination of invasive alien plant species (Solanum mauritianum, Cinnamomum camphora, Psidium guajava, and Morus alba). The second aim was to determine the effect of invasive rose-ringed parakeets on seed viability and germination of indigenous Ficus species (i.e. F. lutea, F. burkei, F. sur and F. natalensis). Previous studies have shown that many avian frugivores prefer invasive alien fruits suggesting that they may be able to efficiently assimilate energy from these fruits. However few studies have focused on the consumption and digestive efficiency of invasive fleshly fruits by indigenous and invasive birds simultaneously in one study. Consequently this study also investigated the digestive efficiency of invasive and indigenous avian frugivores feeding on invasive fleshy fruits. Finally, this study assessed the seasonal effects on the thermoregulation of invasive rose-ringed parakeets. As invasive bird species are spreading in South Africa, understanding the physiological responses that equip them to tolerate a wide range of climatic conditions would be useful for modelling potential distributions and effectively managing them. Seed ingestion by Knysna and purple-crested turacos resulted in significantly higher germination success than those from whole fruits for all invasive alien plant species in this study. Germination success of manually pulp-removed seeds did not differ from that of turacos ingested seeds, suggesting that seed coat abrasion was not important for germination of these invasive alien plants. Seed passage through the digestive tract of rose-ringed parakeets resulted in significantly reduced germination success and viability of all ingested plant species, suggestion that seed ingestion by this species is disadvantageous to these plant species. These results suggest that Knysna and purple-crested turacos are legitimate seed dispersers of the four fleshy-fruited invasive plants, while rose-ringed parakeets are mainly seed predators. Results obtained from this study also suggest that rose-ringed parakeets are mainly seed predators of Ficus fruit, as none of the ingested seeds managed to germinate. In addition, all three avian species investigated managed to meet their energetic demands by feeding on invasive alien fruit only, suggesting that these plant species may sustain avian frugivores especially during periods of food scarcity. Furthermore, the results obtained also suggest that rose-ringed parakeets show seasonal thermoregulatory responses representing energy conservation, as expected. This suggests that rose-ringed parakeets are physiologically equipped to cope with a range of environmental conditions and this partly explains their global success as an invasive species.
Aspects of the ecology of African woolly-necked storks (Ciconia microscelis) in an anthropogenic changing landscape in KwaZulu-Natal, South Africa.
(2018) Thabethe, Vuyisile.; Downs, Colleen Thelma.
Urbanisation is the fastest-growing forms of anthropogenic land use change and a major threat to biodiversity worldwide. However, despite the negative impacts of urbanisation on native species, some species persist in urbanised environments and this thesis aimed to examine one such species, the African woolly-necked stork (Ciconia microscelis). African woolly-necked storks have recently colonised urbanised environments in KwaZulu-Natal, South Africa, and are now common in suburban areas in particular. Despite its proximity to human settlements and recent high abundance in suburban areas, knowledge of the African woolly-necked stork remains poorly documented in South Africa. Therefore, this thesis aimed to investigate the aspects of ecology of African woolly-necked storks within the suburban landscape to determine what factors facilitate their ability to persist in these environments. Firstly, I assessed the long-term trends in occupancy, colonisation and extinction of African woolly-necked storks as a function of change in land cover across KwaZulu-Natal Province, South Africa. This was accomplished by applying dynamic occupancy models to Counts in South Africa. African woolly-necked stork wetland occupancy was relatively stable (ψ = 0.37-0.39) across years. However, they rapidly extended their distribution range to urbanised environments, becoming common in man-made wetlands. Overall, this study found that the increased area of anthropogenic areas led to an increase in the probability of wetland colonisation by African woolly-necked storks. Secondly, I investigated the foraging opportunities that might be responsible for the recent colonisation of urbanised environment by African woolly-necked storks. I found that a significant number of householders (71%) deliberately fed African woolly-necked storks daily throughout the year and the majority provided meat while others fed inappropriate food such as bread. Furthermore, I found that, African woolly-necked storks were relatively habituated in urban areas of KwaZulu-Natal, with some even feeding from hand and others going inside homes to find the supplemental food. These results showed that the African woolly-necked stork is successfully utilising and exploiting anthropogenic food – a novel behaviour for this species. Thirdly, given that the selection of appropriate nest sites has major implications on reproduction success and survival of urban bird species, I was interested to determine if African woolly-necked storks bred in urbanised areas and, if so, which features of the nest site and surrounding habitat influenced their occupancy. I found 30 African woolly-necked stork nests in suburban areas of KwaZulu-Natal. African woolly-necked storks have successfully established breeding sites in suburban areas (mostly in domestic gardens), especially near swimming pools, while exotic pine (Pinus elliottii) and eucalyptus (Eucalyptus spp.) trees were the most preferred trees. Anthropogenic structures were also used as nesting sites suggesting a nesting behaviour shift. Lastly, after acquiring evidence that African woolly-necked storks successfully utilise anthropogenic food and have established a breeding population in urban areas, I was interested to know what food they provisioned to their nestlings. Furthermore, I investigated the breeding behaviour of African woolly-necked storks using direct observations and infrared camera traps during three breeding seasons (2015-2017). Although anthropogenic food was provided to nestlings, African woolly-necked storks provisioned their nestlings predominantly with natural food, primarily amphibians, particularly guttural toads (Amietophrynus gutturalis). African woolly-necked storks consistently reoccupied most nest sites across study years since initial discovery, suggesting that this population was at least stable. For the first time, I documented evidence of cooperative breeding where more than two adults provided care to a single nest. (Amietophrynus gutturalis). African woolly-necked storks consistently reoccupied most nest sites across study years since initial discovery, suggesting that this population was at least stable. For the first time, I documented evidence of cooperative breeding where more than two adults provided care to a single nest.