Food Patchiness, Territory Overlap and Social Systems: An Experiment with Dunnocks Prunella modularis

Abstract

1. Dunnocks Prunella modularis inhabit dense scrub where females defend small, exclusive territories. Individuals have one to two mates depending on how the territories of males overlap the female territories, resulting in monogamy, polygyny, polyandry or polygynandry. 2. The congeneric alpine accentor Prunella collaris inhabits high mountains where food is more patchily distributed. Two to five females have large, overlapping ranges defended by two to five males in a polygynandrous group. 3. We tested whether dunnocks would adopt the alpine accentor's social system when provided with an artificial patchy food supply. 4. At regular feeding sites, where food was provided each day, dunnocks defended small, exclusive territories. At variable feeders, where food was allocated at random each day to one of several adjacent sites, dunnocks adopted larger, overlapping ranges typical of alpine accentors, with two to five males overlapping two to four females. 5. Unlike alpine accentors, however, the dunnocks with variable feeders did not have a consistent dominance hierarchy over the whole of the shared range and females did not gain mating access to more males. 6. We suggest that whereas ecological conditions influence the spacing system, social relationships are affected by individual conflicts of interest.