Density and distribution of passerines in a managed coniferous forest : the influence of landscape structure
This study utilises breeding bird data collected by Patterson et al. 1995 (1991 and 1992) and C.A.McSorley (1998 and 1999), in Kielder Forest, collected using the point count survey methodology. Survey sites in 1998 and 1999 were selected utilising a stratified random technique. Repeated counts of birds generate seasonally and annually correlated bird densities, however there are some significant differences in density from early to late spring. Thus, it is justifiable to use the maximum density over early and late spring for further analyses. Annual correlations are discussed in terms of resource availability. Small-scale density patterns are affected by the interactions between patch tree age, edge comparison and the distance from the patch boundary. Patch boundary avoidance or preference is observed for many species. Low densities are generally found in hard edges. These results are discussed in the context of the trade-off between higher food availability and higher predation risk at patch edges. The occurrence and density of passerines in 1999 are modelled using patch variables generated using a geographical information system (GIS) and a spatial quantification program, FRAGSTATS. The power of associations are mediocre to good (r(^2)evalues are generally approx. 0.2). The performances of the models using 1998 data for validation are mixed. However, some of these models could be used as tools for predicting the effects of forest restructuring on the passerines of Kielder. The factors determining why some species are widespread and locally common, and vice versa are investigated. The results show that resource availability affects the interspecific abundance-distribution relationship. Willow warblers aggregate more readily than residents do, perhaps as a result of utilisation of heterospecific and conspecific cues to quantify habitat 'quality’. The results from all chapters are put into a national ornithological context and discussed in terms of forest management. Further work is also proposed in the final chapter.