Abstract
M.Sc. (Biodiversity and Conservation)
Of the ~9,920 extant bird species, 1,253 of them are threatened. The decline of birds, particularly the House Sparrow and the starlings, over about the last three decades have been well-documented. In Great Britain, the numbers of House Sparrows have declined by as much as 60%, the starlings by 41% and the Turtle Doves by 71 %. In South Africa, the numbers of Cape Turtle Dove and the Laughing Dove have declined by 10%. A difference also exists between the numbers decline in the urban and the rural areas in other parts of the world, with the overall declines being greater in the rural areas.
Bird counts were performed for two weeks in the winter and two weeks in the summer of two consecutive years (2012 and 2013). These counts (using a point count method) were performed in an urban area (Auckland Park) and a rural area (Vaalwater). These two areas fell in two provinces namely Gauteng and Limpopo. In this study, the density indices of four bird species were determined in Gauteng (urban-) and Limpopo (rural) Provinces. Data obtained from the Avian Demographic Unit (ADU) of the University of Cape Town (UCT) for two national counts, SABAP1 (1987-1992) and SABAP2 (2007-2012), were statistically analysed. The numbers were compared for each species between the two provinces and an assessment of whether the overall indices of density had declined in the last 26 years made. After determining the declines, three reasons were investigated. These are: interspecific competition through a behavioural study, climate changes variations by weather service data analysis, and air pollutions by macrophage enumeration. The behavioural studies were performed in the same areas where the counts were done and the survey observed the relationship between the birds of interest and other invasive species like the Indian Mynas. These observations were done for 30 minutes daily at various sites, on the Auckland Park Campus of the University of Johannesburg and on the farms in the Vaalwater area. Temperature, rainfall and humidity data were obtained from South African Weather Service for the time that corresponds to the two bird counting (atlas) projects. By performing descriptive statistics on the climate data for the two provinces, a deduction could be drawn as to whether or not the weather patterns influenced the indices of density of the birds. The macrophage enumeration was conducted after the birds were captured with the aid of mist nets, lavage on the lung-air sac system performed and the cells stained.
The numbers of macrophages in the urban birds were compared to the numbers in the rural ones. Comparison was made between the different species to determine which species were most affected by high levels of air pollution.
Bird counts showed that higher numbers of Laughing Doves, Cape Turtle Doves and Cape Glossy Starlings occurred in the Vaalwater area compared to Auckland Park, while the House Sparrows were the only species that occurred in higher numbers in the urban area. The long term data analysis indicated that the House Sparrows and Laughing Doves declined between the two atlas projects (SABAP1 and SABAP2) in both provinces while the Cape Glossy Starlings increased in both areas. The Cape Turtle Doves increased in Gauteng and decreased in Limpopo between the two bird counting projects. The behavioural study showed that competition between native and invasive species like the Indian Myna, Hadida and Egyptian Goose over food resources possibly contributed to the declines in the numbers of birds. Even though the House Sparrows are also an invasive species, no aggressive behavior was noticed from them towards the other species. Weather might be an influential factor as the temperatures in Gauteng increase with 0.1°C and in Limpopo it increased by 0.45°C when the conditions were compared for the atlas project timeframes; 1987-1992 and 2007-2012. The rainfall decreased in these timeframes in both provinces, (Gauteng from 497.3mm to 441.7mm and Limpopo from 799.9mm to 451.3mm) while the humidity was higher during the second timeframe (69.1kg/mᵌ) than the first (67.5 kg/mᵌ) in the Gauteng Province and the opposite was true for the humidity levels in Limpopo (73.8 kg/mᵌ against 71.4kg/mᵌ). Under such circumstances plant growth and ultimately the food source of the birds should have decreased. The macrophage study indicated that air pollution might not be a major factor in the declines as the numbers of macrophages normalized with body mass for all the species in the urban areas were significantly higher than the rural birds’ macrophage numbers. However, as higher number of birds were present in the urban area (according to the atlas data analysis), air pollution cannot be the foremost reason for the bird number declines. It can, however, be a contributing factor along for example with parasites. The specific cause of the bird number declines is still uncertain. A combination of factors appears to be involved.