Many studies have related assemblage richness, or the incidence and abundance of individual bird species, to landscape structure. But without understanding the ecological mechanisms and processes underlying observed effects, this remains a description of pattern. Where such patterns are inconsistent among species, landscapes or regions, conceptual advance is limited. Despite this, few studies have tested hypotheses underlying these effects (Thompson et al., 2000). This chapter summarises patterns of avian response to landscape structure and critically examines the evidence for different mechanisms that have been proposed to cause such effects. I focus on avian studies from semi-arid, temperate and boreal regions.

Much landscape-scale research has been driven by urgent concerns over the recent fragmentation of contiguous or extensive natural ecosystems (Andrén, 1994; Thompson et al., 2000; Schmiegelow and Mönkkönen, 2002; Fahrig, 2003). However, faunal composition and responses to patch size, isolation, edges and context may differ between recently fragmented landscapes and ancient mosaics created by millennia of human land use (see also Chapters 3 and 19). Where possible, therefore, I try to contrast evidence from temperate and boreal regions of North and South America, Finland and Scandinavia, with research from southern and western Europe.