Territorial behaviour in the Tasmanian native hen: group and individual performance

We studied the territorial behaviour of the Tasmanian native hen, Gallinula mortierii, a cooperatively breeding gallinule, for three breeding seasons at Maria Island National Park, Tasmania, Australia. Our analyses of 2738 territorial contests among 54 groups revealed that 87% of interactions were won by the group that initiated the interaction, 7% yielded no clear result, and only 6% were won by the opposing group. Asymmetries in the resource-holding potential of competing groups were not involved in deciding the outcomes of territorial contests. Our results suggest that asymmetries in payoff were involved, as in each of the 3 years groups with better quality territories were more likely to start interactions, and as a result, were more likely to win them. Only 6% of territorial contests escalated to involve physical contact and changes in territory boundaries rarely resulted from individual contests. The quality of a group's territory either changed very little between breeding seasons, or markedly increased or decreased. We conclude that major changes in territory quality occurred only under relatively rare conditions where the risks associated with escalated contests were reduced, or where the payoffs from a favourable result were improved. Males put more effort into the defence of the group territory than did females. The extra effort of males was directed more towards extragroup males than towards extragroup females. Females, in contrast, were equally aggressive towards both sexes. This suggests that the agonistic behaviour of male Tasmanian native hens may contain a mate-guarding component as well as functioning in the defence of territory. (c) 1998 The Association for the Study of Animal Behaviour.