The polygynandrous mating system of the alpine accentor, Prunella collaris. I. Ecological causes and reproductive conflicts

Davies, N. B. and Hartley, I. R. and Hatchwell, B. J. and Desrochers, A. and Skeer, J. and Nebel, D. (1995) The polygynandrous mating system of the alpine accentor, Prunella collaris. I. Ecological causes and reproductive conflicts. Animal Behaviour, 49 (3). pp. 769-788. ISSN 0003-3472

Abstract

On the mountain tops of the French Pyrenees (1950-2410 m), alpine accentors bred in polygynandrous groups in which an alpha male, and from one to three unrelated and usually younger subordinate males, shared a large undefended range (mean 18 ha) within which from two to four unrelated females had overlapping ranges (mean 11 ha per female). Group size was not related to range size of males or females but was influenced by the temporal availability of fertile females; alpha males monopolized more mates when females were more asynchronous in their onset of breeding, which was related to age and habitat (snow melt). The diet, determined from prey remains in faeces, was mainly small invertebrates, particularly taxa that dominate the fallout fauna, swept up by the wind from the valleys below. The birds' unusually large ranges were necessary to exploit these prey, which sweep netting showed to be scarcer on the mountain tops than down by the tree line, and also more patchily distributed in space and time. Nestlings were fed either by the female alone or with the help of from one to three males. Male help varied depending on which males mated and on the activities of other females in the group (males preferred to compete for matings than to feed chicks). Chick mass increased with male help, but females could fledge all their young successfully with little or no help, even in severe weather. Sexual conflict is similar to that in dunnocks, Prunella modularis; females gain through increased male help by giving shared paternity to several males while alpha males do best by monopolizing all the matings. Differences in dunnock and alpine accentor mating systems are related to ecology, and it is suggested that the dunnock's variable mating system reflects its derivation from a mountain-living ancestor.