Doctoral Degrees (Zoology and Entomology)
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Browsing Doctoral Degrees (Zoology and Entomology) by Subject "Animals -- South Africa -- Bloemfontein"
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Item Open Access Aspekte van die ekologie van avifauna op 'n binnelandse lughawe(University of the Free State, 1999-11) Kok, Alettta Catharina; Kok, O. B.; Van der Linde, T. C. de K.English: Owing to the world-wide increase in air traffic the number and intensity of collisions between birds and aircraft have increased accordingly. Bird strikes are not only responsible for considerable physical damage and fmancial losses, but also endanger human lives unnecessarily. Aspects of the ecology of avifauna at the Bloemfontein airport were, therefore, investigated in order to reduce hazards posed by birds at inland airports. Plant surveys conducted during 1994 and 1995 confirm the classification of the study area as a chy Cymbopogon-Themeda veld type. Based on botanical composition and basal cover the veld is in a relatively good condition. Regularly mowed experimental plots were characterised by a greater variety of plant species consisting of a lower percentage of climax grasses and a larger component of pioneer grasses, forbs and dwarf shrubs compared to undisturbed tall grass areas. A total of 270 pitfall traps were used over a continuous period of 15 months to determine the diversity, relative abundance and seasonal variation of terrestrial invertebrates in the study area. Members of seven classes, 23 orders and 57 families were identified of which insects comprised the most important component by far. As .opposed to this, flying and plantliving invertebrates which were monitored on a monthly basis by means of sweep-nets were represented by only two classes, comprising 13 orders and 70 families. Mouse trapping and incidental catches of smaller vertebrates in pitfall traps suggest a limited presence of amphibia, reptiles and small mammals. Broadly speaking significantly more invertebrates were collected during the wet than during the dry season. Evidently, the opposite trend applies with regard to the sampling of reptiles and small mammals. Although no direct relationship between catches and rainfall as environmental factor could be demonstrated, a significant correlation with temperature was indicated. Over a period of eleven years approximately 5 000 individuals representing 51 bird species which, potentially, posed a threat to aviation were collected at the Bloemfontein airport. More than half of the species concerned can be considered as I medium-sized terrestrial birds of which the crowned plover (Vane/Ius coronatus) is by far the most important. A similar species composition occurred at the Kimberley airport, in contrast to the greater percentage of water associated birds at the Johannesburg airport. Indirectly, food availability appears to be one of the main environmental factors involved in the presence of, amongst others, the five dominant bird species at the Bloemfontein airport. Analyses of the stomach contents of 3 544 bird carcasses from the Bloemfontein airport, supplemented by 906 stomach contents from the Johannesburg and Kimberley airports, indicate that insects can generally be considered the main food source of the birds concerned. Based on dry mass composition the Isoptera, followed by the Coleoptera and Orthoptera, constitute the most important component in the diet. The Isoptera, more specifically the harvester telmite (Hodotermes mossambicusi), is, moreover, the only important prey taxon showing a conspicuous utilisation peak during the relative food shortage of the dry season. Evidently, temporary superabundant food sources which periodically come about in grassland habitats are opportunistically utilised by the birds. Indications are that habitat manipulation at airports can serve as an effective long-term bird control strategy. Based on the superabundant availability of invertebrate prey species in short grass areas compared to that in tall grass, a socalled tall grass policy would not only lead to the reduction of available food sources, but would also hamper the prey searching abilities of the largely insectivorous avifauna. According to results obtained, chemical manipulation can also be successfully employed to limit the presence of harvester termites, the staple food of the majority of terrestrial bird species in grassland habitat, thereby bringing about a reduction in bird numbers. At the same time, a five layered model is discussed setting out the responsibilities of all the role players associated with the implementation of a successful bird control programme. Key words: Airport, avifauna, bird hazard, feeding ecology, harvester termites, pitfall trapping, grassland, habitat manipulation, management.