The distribution and breeding performance of the buzzard Buteo buteo in relation to habitat : an application using remote sensing and Geographical Information Systems
The British uplands support a rich assemblage of a number of predatory and scavenging birds, including golden eagle, merlin, red kite, hen harrier, raven and buzzard, with nationally and internationally important populations of some of these species. A feature all these species have in common is the requirement for large foraging ranges by individuals which means that large tracts of suitable habitat are necessary to support viable populations. Current changes in upland land use such as afforestation and changing agricultural practices give cause for concern. The conservation of these species and others like them requires a greater understanding of how these birds interact with the landscape and how their distribution and breeding performance reflects their habitat. Ecologists are becoming increasingly aware of the potential of Geographical Information Systems (GIS) for exploring these relationships between animal species and their habitat. In this thesis, the buzzard was chosen as a model species to explore ways of predicting bird distributions and breeding performance from readily available data using GIS. This study was carried out in mid-Argyll, Scotland. The distribution and breeding performance of buzzards was determined for a number of study areas, chosen to represent the full spectrum of habitats to be encountered in mid-Argyll, during 1989 and 1990. Parameters of breeding performance used were laying date, clutch size, initial brood size and fledging success. Brood quality was also assessed, based on nestling growth. The breeding performance of buzzards in mid-Argyll was included in a comparison of published data from studies elsewhere in Britain. Laying dates were found to be consistent throughout the country while clutch size, initial brood size and fledging success were seen to differ between studies. No patterns which might relate to latitudinal or climatic trends were apparent and differences were considered to be due to overall habitat differences between the regions considered. While buzzards in mid-Argyll tended to produce low clutch sizes the population as a whole showed high fledging success. While buzzards nestlings in mid-Argyll had good survival rates the high fledging success is probably best explained by absence of human interference, malicious or otherwise in this area. An important consideration when looking at the distribution of a bird size such as the buzzard is whether this might be influenced by nest site availability. Buzzards in mid-Argyll used a number of distinct nest site habitats. While the majority of buzzards nested in trees, a substantial proportion were found nesting on steep banks and crags. Considering the adaptability of buzzards in their choice of nest site and the abundance of acceptable sites it was considered that the availability of potential nest sites was unlikely to influence buzzard distribution in mid-Argyll.