| Popis: |
A study was conducted on the feeding behaviour of giraffe within the Bloemfontein vicinity, central Free State. Full-day field surveys were done on a monthly basis over a period of 12 months (March 2003 â February 2004) on four different study areas. Night observations were only conducted on a seasonal basis during full moon periods, to make use of maximum vision. Utilisation frequencies and âdurations for each plant species, as utilised by the giraffe, were carefully documented. The daily activity patterns of giraffe were determined by means of the momentary-scanning method. Plant surveys were conducted through circle, quadrants distributed in transects over each of the four study areas to determine the woody composition for each area. Approximately 100 g of leaf material of the most important food plants of giraffe were gathered on a monthly basis for subsequent chemical analyses (calcium and cru-protein). Prehistoric signs of giraffe by means of fossils and rock art have been noted by several writers since the nineteen thirties and forties. The first signs of the presence of giraffe in South Africa by whites were detected in rock art. The Limpopo Province lies in the savannah biome and therefore contains the best habitat for giraffe. It is thus self-evident that most conservation areas with giraffe can be found in the Limpopo Province. There is no earlier physical evidence of giraffe in the Free State. This province is also not part of the current range of giraffe. The biggest concentration of established giraffe presently occurs in the Boshof-district in the western Free State. This can be attributed to the vegetation which correlates with the savannah biome, namely the occurrence of Acacia trees. The extent of the adaptation of giraffe in the central Free State is mainly unknown. As a whole the active browsing of giraffe in this study was responsible for more than half (53 %) of the daily activities. Giraffe only spend 4 % of the total daily time in the lying position, usually when environmental temperatures are high. In contrast with the day-activities, browsing was responsible for less than a third (31 %) of their activity during night time. Peaks in the lying position where all individuals were involved, occurred long before and shortly after midnight alternating with browsing. During this study period giraffe in the central Free State browsed a total of 28 plant species. According to the utilization frequency and -time, the sweet-thorn, asparagus and buffalo-thorn are the most important components in the diet of giraffe. Collectively these three plant species constitute approximately 74 % of all observations and were consumed through out the year. Leaves of deciduous trees and shrubs are the staple food during the wet season but, as the plants shed their leaves and the food stock decrease, there is a change in the food preference. In this connection an increase in the utilisation of evergreen trees, woody- and offshoot fodder during the dry season, is significant. Unidentified grasses constitute nearly 2 % of the total diet of giraffe. Grasses were utilised mainly in August and September, the most critical time of the year which can possibly suggest an imbalance in the diet, which relates to calcium deficiencies. Osteophagia was detected in especially cows and younger individuals during the dry season, probably due to the fact that either cows in calf, nursing cows or growing individuals are more susceptible to mineral deficiencies in their diet. Although the availability of leaves in the dry season is limited, the asparagus leaves are available for utilization until late in this season. Sweet-thorn legumes and buffalo-thorn fruit are also available during the dry season and are utilised together with the sprigs. An increase occurred in the cru-protein contents for some of the leaves, including the sweet-thorn, during the dry season. There is a noticeable increase in the calcium content of the three dominant preferable plant species during the dry season. It seems as if the chemical composition and availability of the three dominant plant species per se play a less important role in the giraffeâs diet compared to the preference these animals show towards certain plant species. Giraffe are mainly browsers of thorny, deciduous trees, especially the Acacia species. Exotic plant species such as eucalyptus-, pine-, poplar- and willow trees as well as conyza weeds, cotoneaster and prickly pear are seasonally utilised in the central Free State. This phenomenon is more significant during the dry season when leaf materials of deciduous plants of the preference plants are absent and thus show a shortage. Critical periods for giraffe feeding in the central Free State are during the late dry- and early wet season (August â October), and not the dry season as a whole. The topography and composition of vegetation in the central Free State have to allow for seasonal habitat selection. Thus there is a correlation between the occurrence of the giraffe in the Free State and the occurrence of their preference food, namely Acacia-tree species. |
