On the Relationship between Wing Disc Loading and Foraging Strategy in Hummingbirds

Nectivorous hummingbirds have two distinct foraging strategies. Territorial individuals exploit and defend high densities of flowers; nonterritorial ("traplining") individuals visit but do not defend dispersed flowers. Wing disc loading (ratio of body weight to area swept out by wings) and the cost of hovering flight were estimated for species in both groups. Trapliners have longer wings relative to body size, lower wing disc loading, and apparently lower energy requirements for hovering flight than territorial birds. This relationship of wing disc loading to foraging strategy also occurs within species that exhibit sexual dimorphism in foraging behavior. Therefore, we predict that the territorial species or sexes of hummingbirds within any given community will be found to have higher wing disc loading than the nonterritorial birds.