Foraging segregation in a breeding bird guild declines following nesting

Abstract

Ecological communities appear to have structure, and exploitation of food resources have commonly been implicated in contributing to that apparent structure. Avian communities are frequently used in foraging research, but such studies do not usually document within-landscape patterns of change over seasonal time. I studied a guild of twelve small, foliage-gleaning, insectivorous songbirds in their breeding landscape in central Ontario, Canada. By focussing on foraging preferences indicated by tree species, foraging height, and foraging maneuvers, I compared patterns among the breeding period (June), midsummer (late July and early August), and early autumn (late August to mid September) within the one landscape. Correspondence analysis indicates that each species foraged in a distinct manner, yet there was substantial foraging overlap at all times in preferred (i) foraging tree species, (ii) foraging height, and (iii) foraging maneuvers. As the season progressed, patterns related to preferred foraging height and foraging maneuvers did not change dramatically. However, patterns of preferred foraging tree species did change progressively from breeding to autumn. During the breeding period, the guild tended to exploit different tree species in a manner correlated with the relative availabilities of those species, but this was not the case in midsummer or autumn. By autumn, foraging tree preferences among species were much more homogeneous, especially among wood-warblers of the genus Dendroica Gray, 1842. Consequently, based on preferred foraging tree species, whatever segregation existed during breeding was largely disassembled by autumn.