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Transcript
 SW265 The effects of habitat, elephant damage and fire management on winter bird communities in Welgevonden, South Africa Tom Martin The mixed bushveldt habitats -­‐ open savannah interspersed with deciduous woodland stands -­‐ of the Welgevonden Game Reserve and its surroundings support an extremely rich bird community, this being a product of its transitional location between dry climatic zones to the west and wetter ecozones to the east. The Reserve has been surveyed intensively for the past five years, with a total of 350 species having been detected here to date. These include large and spectacular iconic South African species such as the Cape Vulture (Gyps coprotheres) and Gymnogene (Polyboroides typus), as well as stunningly beautiful smaller birds such as the Lilac-­‐breasted Roller (Coracias caudatus) and Southern Carmine Bee-­‐
eater (Merops nubicoides). Other characteristic bird families found in the Reserve include tiny, colourful Sunbirds, long-­‐tailed Whydahs and a large number of Kingfishers. The bird diversity in Welgevonden is at its highest during the South African summer, when many Northern hemisphere migrants arrive here to avoid the Eurasian winter. The South African winter months, when students choosing this dissertation option will be collecting their data, sees the Reserve hosting fewer species. This works to the advantage of researchers as the community is less complicated to survey at this time of year, and conclusions only need to be drawn on resident species, rather than resident-­‐migrant species complexes. As mentioned, one of the key reasons the Welgevonden Reserve supports such a high diversity of birds is the extensive range of habitats supported here. Geographical factors such as precipitation, soil type, and topography vary throughout the area, especially along the East-­‐West gradient, as these different variables support different vegetation categories. As such broad habitat structure, dominant tree families, and abundance of different feeding resources also varies spatially. Different birds are adapted to different habitat types, but having a broad mosaic of these habitats within a single protected area greatly contributes to its total biological richness. However, some habitats or broad geographical regions of the park may support a greater avian richness than others, or may be more suitable for specific feeding guilds or key species of high conservation concern, and being able to predict and map patterns of bird community diversity based on an understanding of habitat-­‐richness relationships would be a highly useful management tool to develop. Factors effecting habitat structure in Welgevonden are also temporal as well as spatial. The intense, swift-­‐moving brush fires, which break out sporadically in the Reserve, can drastically alter the habitat structure and feeding resources birds are reliant on, especially in lower habitat strata. Additionally, the Reserve’s large Elephant population can also have an enormous impact on bird habitats, with the passing of herds seeing trees being rooted over, branches being stripped, and undergrowth being trampled – damage that can take a long time to regenerate. Students taking this dissertation option will aim to determine how broad habitat types can determine bird diversity in the Welgevonden Game Reserve, which individual habitat structure variables are the strongest predictors of bird community composition, and how brushfire and elephant damage can impact upon community richness and structure. Students will conduct bird surveys across 40 established monitoring sites scattered across Welgevonden. These surveys will consist of a series of 10-­‐minute timed point-­‐counts, during which all birds seen and heard within a fixed radius will be recorded. These point-­‐counts will be conducted early in the morning, this being the period when most bird species are active and vocalizing, thus allowing researchers to record the highest number of contacts within a limited time period as possible. Birds will be identified by both sight and call; students will be assisted in bird identification by experienced ornithologists familiar with local South African species. Training will also be provided to allow students to recognize most of the areas common species within their first week of survey work. Once the morning bird counts are completed, students will then participate in completing extensive habitat structure surveys in the same location. Key variables measured will include undergrowth density, tree density, dominant tree species, dominant shrub species, and overall habitat heterogeneity. Students will also carefully record any fire and elephant damage observed in the study plots using raw counts of fire or elephant-­‐damaged trees and shrubs as well as a categorical scale of overall damage. The primary bird community and habitat structure data gathered in the field will provide powerful tools for students to examine relationships between bird community structure, habitat structure, and elephant and fire damage. These large datasets generated in the course of the Opwall season would be sufficient in themselves to explore this research topic, but should students desire to upscale their findings a number of other resources will be available for those undertaking this research topic. High-­‐
quality landscape-­‐scale vegetation and broad habitat maps of the reserve are available on-­‐site, as are high resolution aerial photographs and spatial datasets highlighting the areas of all management and natural burns over the last three years. In combination, these resources will allow students to determine which habitat categories in the Reserve are the most important resources for bird communities as a whole, as well as for different bird feeding guilds and key individual species of high conservation importance. Students will also be able to examine which specific habitat structure characteristics are the most important drivers of patterns in bird diversity, and the impact fire and elephant damage has on bird communities in different habitat categories. Operation Wallacea’s extensive spatial analysis resources could then be used to map the most valuable avian habitat areas across the Reserve, as well as mapping the areas most vulnerable to fire and elephant damage. Students would then be in a position to recommend priority conservation management areas which need to be protected and maintained in order to safeguard the future of the spectacular bird communities of the Welgevonden Game Reserve. Suggested Reading Baxter, P.W.J. & Getz, W.M. (2005). A model-­‐framed evaluation of elephant effects on tree and fire dynamics in African savannas. Ecological Applications 15, 1331-­‐1341. Ben-­‐Shahar, R. (1998). Changes in structure of savanna woodlands in northern Botswana following the impacts of elephants and fire. Plant Ecology 2, 189. Bibby CJ, Burgess ND, Hill DA, Mustoe, SH. (2002). Bird Census Techniques (Second edition). Academic press: London. Brace, R. (2007). Avifauna atlasing of the Mkuze Game Reserve. Operation Wallacea report. Available from: http://opwall.com/wp-­‐content/uploads/OPWALL-­‐BIRDS-­‐FINAL-­‐REPORT-­‐SOUTH-­‐AFRICA-­‐07.pdf Fisher, J.T., Witkowski, E.T.F., Erasmus, B.F.N., Van Aardt, J., Asner, G.P., Kwessels, K.J. & Mathieu, R. (2012). Human-­‐modified landscapes: patterns of fine-­‐scale woody vegetation structure in communal savannah rangelands. Environmental Conservation 39, 72-­‐82. Folse, L.J. (1982). An analysis of avifauna-­‐resource relationships on the serengeti plains. Ecological monographs 52: 111–127. Jansen, R., Little, R.M. & Crowe, T.M. (1999). Implications of grazing and burning of grasslands on the sustainable use of francolins (Francolinus spp.) and on overall bird conservation in the highlands of Mpumalanga province, South Africa. Biodiversity and Conservation 8, 587-­‐602. Kerley, G.H. & Landman, M. (2006). The impacts of elephants on biodiversity in the Eastern Cape Subtropical Thickets. South African Journal of Science 9, 395-­‐402. Long, P. & Higgins, F. (2012). Patterns of bird diversity in Welgevonden Game Reserve, South Africa: insights from distribution modelling using point count data in 2009. Operation Wallacea report. Available from http://opwall.com/wp-­‐content/uploads/Welgevonden-­‐report.pdf. Mentis, M.T. & Bailey, A.W. (1990) Changing perceptions of fire management in savanna parks. Journal of the Grassland Society of South Africa 7: 81–85. Sinclair, I., Hockey, P., Tarboton, W. & Ryan, P. (2012). Sassol bird of Southern Africa (Fourth edition). Struik Nature: Cape Town. Sutherland, W. J., Newton, I, & Green, R.E. (2004). Bird ecology and conservation: a handbook of techniques. Oxford University Press, Oxford, UK. Van Rensburg, B.J., Chown, S.L. & Gaston, K.J. (2002). Species richness, environmental correlates, and spatial scale: a test using South African birds. The American Naturalist 159, 566-­‐577. Williams, P.H., Burgess, N.D. & Rahbek, C. (2000). Flagship species, ecological complementarity and conserving the diversity of mammals and birds in sub-­‐Saharan Africa. Animal Conservation 3, 249-­‐260.