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Ecology

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Browsing Ecology by Author "Combrink, Leigh."

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    Assessing the success of red-billed oxpecker translocations as a conservation tool in KwaZulu-Natal, South Africa.
    (2016) Jordaan, Maryna.; Downs, Colleen Thelma.; Combrink, Leigh.
    There are numerous factors that contribute to a bird species becoming threatened and in need of increased conservation efforts in order to survive. Compared with fossil records, current extinction rates are much higher than expected, which emphasizes the need for conservation. Conservation translocations aim to increase the survival of threatened species by ameliorating their possibility of extinction, and contribute either to educational, scientific or supportive purposes in this. Reintroductions or translocations are a well-established method for increasing a species’ distribution and for restoring their historical range. Translocations are defined as human-mediated movements of organisms from one area and released in another. A translocation is only considered successful when a population is self-sustained through breeding of the released individuals and does not require intervention. Oxpeckers are African passerines from the starling lineage. Historically, red-billed oxpeckers (Buphagus erythrorhynchus) had a distributional range that extended from Eritrea to Somalia, through south-eastern Sudan to Zimbabwe and into the former Transvaal, Natal and Eastern Cape Provinces, South Africa. Oxpecker populations became threatened in South Africa in the early years of the 20th century. In southern Africa, red-billed oxpeckers became Near-Threatened as a result of cattle dips with substances toxic to the birds, and because of a significant decrease in their large game host species. Conservation efforts in the 1980s onwards have attempted to deal with the factors causing their demise. In 2002, The Endangered Wildlife Trust began translocating red-billed oxpeckers to areas where they had gone locally extinct, in an attempt to increase their current distribution and population in South Africa. Consequently, we documented and reviewed the various capture and quarantine methods, conducted since 1988 to the present, in the various translocations of red-billed oxpeckers. We also highlighted lessons learnt from these translocation events. To determine how successful these translocations were, we compared changes in the Southern African Bird Atlas Project (SABAP) reporting rate data and determined the presence or absence of red-billed oxpeckers at all the 24 translocation release sites in KwaZulu-Natal (KZN). In SABAP 1, data on species occurrences were collected at the Quarter Degree Grid Cell (QDGC) level. In SABAP 2, this was refined to pentads, where nine pentads are in one QDGC. Therefore, the reporting rate comparison was done at QDGC level. Prior to these translocations, red-billed oxpeckers were absent from all these sites. Specifically, we conducted transect surveys to determine red-billed oxpecker’s population estimates in Ithala Game Reserve (IGR) and Tembe Elephant Park (TEP). We also netted and ringed red-billed oxpeckers at these sites to obtain morphological and genetic data and to determine their breeding status. Furthermore, we distributed an online questionnaire to determine public perceptions on red-billed oxpecker’s range expansion in South Africa. We analysed the SABAP data using general linear modelling and the survey data using the Distance Programme in R Studio. There was a significant increase in reporting rates of red-billed oxpeckers in southern Africa since the end of SABAP1 in 1991 with several new areas where they had established. This was again confirmed from landowners reporting the first observation made of red-billed oxpeckers on their respective properties. Reporting rates at the specific translocated release sites had also increased. Twenty-four per cent of the QDGCs (n = 170) showed an increase in reporting rates in southern Africa, however, 36% of the QDGCs showed a decrease in reporting rates (n = 258). Fourteen per cent of the QDGCs (n = 100) showed new areas colonized by red-billed oxpeckers. In South Africa, red-billed oxpeckers had colonised several new areas, particularly near areas where reporting rates had increased. Twenty-six per cent of the QDGCs showed areas where red- billed oxpeckers were absent and had gone locally extinct (n = 187); however these areas were mostly in Botswana and Zimbabwe. We determined that habitat, host preference and host herd size were important factors when calculating population densities of red-billed oxpeckers. Detection probabilities for red-billed oxpeckers were highest in open bush habitat and where large herds were present. In IGR, red-billed oxpeckers were seen in 8% (n = 33) of the total of 391 observations made. In TEP, red-billed oxpeckers were observed in 6% (n = 24) of the total 378 observations made. In both IGR and TEP all red-billed oxpeckers we trapped and ringed had not been previously ringed and some had brood patches supporting their successful reproduction there. To date, a total of 24 reintroduction events and 13 population reinforcements have taken place, with a total of 1359 red-billed oxpeckers translocated in South Africa. The increase in reports of red-billed oxpecker sightings, especially at release sites and on nearby land, showed the importance of translocations for the conservation of oxpeckers. In addition, the placement of artificial nest boxes has increased the likelihood of red-billed oxpeckers breeding at their new translocated site. The recent down-grading of red-billed oxpeckers from Near Threatened to Least Concern, and the data collected in our study support the success of translocation as a conservation tool for this species. Translocations of red-billed oxpeckers in South Africa should be considered one of the more successful of such programmes as indicated by its success.
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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.