Competition and the Structure of an Avian Foraging Guild

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Abstract
Using data on microhabitat overlap the intensities of interspecific competition experienced by 7 spp. [Dendroica graciae, D. coronata, Cardellina rubrifrons, Peucedromus taeniatus, Vireo solitarius, Sitta pygmaea and Parus gambeli] of foliage gleaning birds in a southeastern Arizona [USA] pine forest were estimated. Pairwise interaction coefficients were determined from resource weighted niche overlaps. The effects of indirect competition were included by inverting a matrix of interaction coefficients. These data were used to examine 3 predictions about this foliage gleaning guild. The 1st species to drop out of the guild to the north should be the one experiencing the most intense competition in southeastern Arizona [USA]; those species experiencing the least competition should be the most variable in morphological structures associated with foraging; and those species experiencing the most intense competition should be most sensitive to changes in resource levels. These predictions were supported by the data. The species experiencing the most intense competition, the olive warbler (P. taeniatus), is a specialist in microhabitat use and foraging behavior. Olive warblers forage by gleaning and probing pine fascicles more efficiently than most other species in the guild and consequently may alleviate very intense diffuse competition by harvesting a portion of the resource spectrum unavailable to other species.