An Experimental Test of Competition for Space between Blackcaps Sylvia atricapilla and Garden Warblers Sylvia borin in the Breeding Season

Abstract

Blackcaps and garden warblers show a high degree of interspecific territoriality in the breeding season. Many blackcaps arrive in the breeding habitat before the 1st garden warblers do so. Removal of these established blackcaps has shown that some of the area which they settle is acceptable to garden warblers and is occupied by the latter only in the absence of blackcaps. Some portions of available habitat are not settled by garden warblers when blackcaps previously established there are removed, and so are apparently suitable for blackcaps only. The 2 spp. are partially segregated by habitat but otherwise compete strongly for space, with the earlier-arriving blackcaps being able to exclude the later-arriving garden warblers from areas acceptable to both species.