An experimental study of mating competition in monogamous and polyandrous dunnocks, Prunella modularis: II. Influence of removal and replacement experiments on mating systems

Abstract

‘Remove and release’ experiments were performed on 72 male dunnocks to investigate defence of mating opportunities, defence of territories, and factors influencing male status. Males were removed for 2–9 days, at various stages of the mating and incubation periods; all settled back on their territories when released. Territory size of males and females was unaffected by removals. When alpha (dominant) males were removed from trios, beta (subordinate) males successfully defended the territory alone and obtained significantly more mating access to fertile females, with no increase in the access of neighbouring males. By contrast, removal of monogamous males resulted in a significant increase in the mating access of neighbouring males and also led to changes in the mating system in 38% of cases. It is concluded that (1) polyandry does not arise because two males are necessary for successful defence of the territory against neighbours, and (2) mate guarding by alpha and monogamous males is necessary for maintaining exclusive mating access to females. In trios, removed alpha males were more likely to lose status when released if they had not previously obtained exclusive access to females during egg-laying days. Mating access (and hence brood value) was therefore an important asymmetry determining male dominance, supporting the ‘value asymmetry’ hypothesis for dominance. In monogamous pairs, removed males were again more likely to lose status and sole control of a territory if they had not previously obtained exclusive access to females on egg-laying days, but there was also strong support for the ‘resource-holding potential’ hypothesis because young newcomers were more casily usurped than were old newcomers.