Avian community composition and patterns of bird distribution within birch-heath mosaics in north-east Scotland

Abstract

Territory mapping and transect counts were made in upland birch scrub (46 ha) in north-east Scotland to document the bird community and assess responses of birds to habitat variation. The bird community was species poor, supporting approximately 20 species. Richness and diversity were low compared with other British scrub habitats . The two dominant species were Willow Warbler (52% of territory mapping registrations) and Chaffinch (18% of registrations) . Densities derived from territory mapping and transect counts (Distance sampling) were similar. Willow Warbler densities were high and comparable with preferred habitats in lowland England and Fennoscandia. Contour mapping, correlation and canonical correspondence analysis demonstrated that successional stage, represented by birch cover, was the single most important factor determining community composition and individual species' distributions. Meadow Pipits persisted at low densities in sparse birch; Tree Pipits occurred throughout the range of birch densities. Willow Warblers preferred areas of medium height birch at intermediate canopy cover. Wren, Great Tit and Long-tailed Tit occurred in older birch scrub. The relatively simple bird-habitat relationships reported are contrasted with more complex patterns elsewhere. These findings are discussed in the context of scrub and woodland regeneration in upland Britain with particular reference to mosaics and maintenance of avian diversity.