Context-dependent colonization of terrestrial habitat 'islands' by a long-distance migrant bird

Abstract

Landscape context can affect how individuals perceive patch quality during colonization. However, although context-dependent colonization has been observed in aquatic environments, it has rarely been studied in terrestrial environments or at large spatial scales. In this paper, we assessed how landscape context influenced colonization rates in a large-scale (ca 7000 km2) terrestrial system where colonizers (Willow Warbler Phylloscopus trochilus) are capable of rapid, long-distance movements. Bioacoustic recorders were used to detect first song dates (an indicator of colonization or re-colonization) and settlement in 23 naturally replicated habitat patches. We compared support for three competing hypotheses describing colonization patterns that depend on landscape context ('redirection', 'landscape-selection' and 'relative patch size') with two patch-level hypotheses (patch 'quality' and 'heterospecific attraction'). First songwas earlierwhen habitat availability in the landscape was low, supporting the 'redirection' hypothesis. Settlement probability was best predicted by patch 'quality' and was lower in woodlands with a dense understorey. Results suggest that colonization of habitat patches by male P. trochilus after spring migration is spatially hierarchical. First, initial colonization depends on landscape context, and settlement is then determined by fine-scale vegetation characteristics. More broadly, we suggest that patterns observed in fragmented aquatic environments (e.g. 'redirection') can, in some circumstances, be extended to large-scale terrestrial environments.