Resource distribution, aggressive asymmetries and variable access to resources in the nectar feeding bellbird

Summary

A continuum concept of spatial organization linking territoriality and social hierarchy suggests that individuals will alter their degree of exclusiveness and priority of access to resources in accord with the net benefits of aggression. Thus changes in resource distribution will produce changes in the control of resource space for any one individual. Similarly when comparing among individuals, responses will change in accord with their aggressive abilities when compared to those of possible opponents. The existence of such a continuum model of spacing was investigated in a nectar feeder, the New Zealand bellbird (Anthornis melanura: Meliphagidae). A natural change in spatial distribution of resources from highly concentrated to dispersed provided an opportunity to follow changes in access for known individuals. Comparison of individuals of different hierarchical status, sex and residential status was also possible within each system as was an estimate of comparative rewards. At the concentrated resource, individuals could be ranked in a dominance hierarchy although spatial separation between more dominant individuals did occur. At the more spatially dispersed resource, most individuals obtained a level of exclusive use. Access to both resources varied for different individuals but the asymmetries that related to greater access in one system also produced greater access in the other resource.