Social structure, habitat use and breeding biology of hedgerow Dunnocks Prunella modularis

Abstract

A population of Dunnocks Prunella modularis inhabiting hedgerows was studied over a period of four years in order to examine the habitat structure of breeding territories and to attempt to determine how the constraints imposed by the linear structure of hedgerows might influence the mating combinations and breeding success. Eleven monogamous and 14 polyandrous territories were observed. No examples of polygyny or polygynandry were recorded. Polyandrous territories were significantly larger than monogamous territories but contained significantly more grassland, which is of little value for Dunnock foraging. Overgrown hedgerows formed the largest component of territories, and young and overgrazed hedgerow types constituted only a small area. All territories supported large patches of Nettle Urtica dioica and Bramble Rubus fruticosus/Dog Rose Rosa canina, the latter supporting most Dunnock nests. Clutch sizes, nestling weights and numbers of young fledged did not differ significantly between monogamous and polyandrous systems, but sample sizes were small. It is suggested that the restricted availability of mature overgrown hedgerows, the relatively low breeding density and the linear shape of hedgerows contributed towards the less complex mating system. The preference for overgrown hedgerows with basal outgrowths of Nettle and Bramble/Rose is discussed in the light of the recent decline of the Dunnock on farmland.