Birds and the urban ecology of Potchefstroom
Smith, Nicoleen Celeste
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Human activities cause drastic changes in the environment, such as the fragmentation of habitats, which is the greatest threat to the world's biodiversity and biogeography. By using birds to study habitat changes, it is possible that the type of habitat qualities that may still be possible near and in cities could be determined. It is possible that by improving the quality or conditions of habitats for birds, habitat qualities for other fauna would also improve. Birds are also considered to be good indicators as they are collectively sensitive to changes in their environments; however, they are also easy and relatively inexpensive to survey. There is no single definition for an urban area, however, these are the places where environmental problems greatly affect the quality of life. Urbanisation is a continuous complex process and in order to understand the ecology of urban areas, the reasons and factors behind this process need to be understood. Cities themselves represent the extremes of human-modified environments and usually only contain a few remnants of the original habitat. On the other hand, many cities in South Africa are characterised by secondary woodland, as trees and other plants are planted in gardens and parks. This creates habitat that could be advantageous to birds. Biotopes have been used to map this aspect of cities, and it has generally been assumed that birds will distribute accordingly. The hypothesis for this study was as follows: Due to the mobility of birds, coupled with their ability to use multiple biotopes (e.g. nesting and feeding), urban bird communities or bird demography will show patterns different from vegetation and structure based biotopes alone, and could therefore be considered as avitopes. The primary aim of this study was to determine the distribution patterns of avian diversity in Potchefstroom. Secondary aims/objectives for this study included: Determining the bird species distribution in Potchefstroom using point counts Determining the distribution of feeding and nesting guilds in Potchefstroom Determining whether it is possible to identify urban avian indicators with this type of research To investigate, develop and define the concept of "active-habitat selectors" (AHS) To introduce, develop and define the concept of "avitopes" The research area included the city of Potchefstroom, with its associated suburban areas, lkageng, Promosa, Mohadin, the rural areas and the surrounding natural areas. Point counts were used to identify bird species at 56 different sites. The data was analysed using to two different programmes, GS+ and Primer 5. The data was analysed according to species richness, species abundance and numbers of birds. I found that species were most abundant in the agricultural areas, the eastern residential areas and the military areas. The socio-economic factors affecting the abundance and distribution of all the species, still needs to be further researched. When looking at the total avian biomass for this study, biomass was highest in the industrial area, which is probably the most highly urbanised site in the study area, due to the high numbers of doves and pigeons. The results for species richness indicated that the greatest species richness occurred in the less highly urbanised areas, and was lowest in the more highly urbanised (industrial) areas. The lower half of the western part of lkageng also had a low species richness, even though this is not a highly urbanised area. However, it is possible that conditions in this area are highly unsuitable for bird species due to various reasons such nesting availability, resource availability, density of people etc. When looking at the results for granivores, the majority of the species, and more so their numbers, were found primarily in the urbanised areas, with some present in the agricultural areas. However, this could possibly be put down to the fact that the agricultural areas are primarily a foraging area. In the case of omnivores, the highest numbers were found in the military areas and included only a small part of the very top section of the residential areas. The military areas are not highly urbanised areas. However, it is possible the reason for their low occurrence in the more urbanised areas was due to the insufficient observation time, since omnivores were observed in many of the more urban areas whilst not sampling in those areas. Omnivores and granivores are superior competitors when compared to other species, as they are better able to exploit urban food resources. In the case of the insectivores, the majority of them were located outside of the more urbanised areas; however, a focal point did occur in the very southern tip of the eastern residential areas. It is possible that they nest in this part of the residential areas but forage in the nearby agricultural areas. Birds were therefore not restricted to a single area or biotope, as they are able to utilise various suitable areas for different purposes e.g. foraging, nesting etc. Because of their mobility and ability to choose a suitable habitat, I have introduced the concept of active-habitat-selectors (AHS) in this study. Various elements support this idea, such as birds being able to choose a suitable habitat through choice, rather than as an automatic response, and that birds are able to continuously select habitats to support their needs etc. A preliminary definition for AHS could be the following: Active habitat selectors are those species of which the adult individuals within their lifetime are almost continuously able to select multiple, suitable habitats for different purposes, through choice, due to their mobility and comparative knowledge of different available habitats that are in range. The concept of avitopes has also been introduced and various elements have been taken into account with its definition. Some of these elements include, birds are good indicators of environmental change, they are not restricted to any single areas, etc. Various elements should be considered when defining avitopes. A preliminary definition could be: Avitopes are geographically delineated areas, defined by diversity indices, and do not take into account non-naturally occurring, nonvagrant, and otherwise generalist bird species. There are still arguable aspects of these definitions, which will require more development, refinement and research. All the objectives for this study have been achieved and new issues identified, that will require further investigation.