The Adaptive Significance of Colour Patterns in the Old World Leaf Warblers, Genus Phylloscopus

The great diversity of colour patterns in birds remains largely unexplained (Burtt 1986, Butcher and Rohwer 1989). Experimental and comparative studies have been used to identify some adaptive correlates, including intra-specific communication (Hill 1990, 1994, Slagsvold and Saetre 1991, Saetre and Slagsvold 1992, Marchetti 1993), camouflage (Gaston 1974, Burtt 1986), abrasion resistance (Burtt 1986), inter-specific signalling (Baker and Parker 1979, Goetmark 1993, 1995, Saetre et al. 1993) and flushing out prey (Jablonski 1996). While we might expect plumage patterns to represent a compromise between all these and other selection pressures, two hypotheses have been recently proposed to explain the diversity of colour patterns within the genus Phylloscopus (Old World leaf warblers). Marchetti (1993) ascribes a role for intra-specific communication (i.e., signalling to potential mates or competitors) in the evolution of colour patterns, whereas Jablonski (1996) suggests that conspicuous coloration might be important for flushing prey. In this note we assess the role of prey-flushing in the Phylloscopus warblers using quantitative data on foraging and colour patterns.