Agonistic behaviors between Chestnut-sided (Setophaga pensylvanica) and Golden-winged (Vermivora chrysoptera) warblers are unlikely a result of plumage misidentification

Abstract

Plumage coloration within species is often a signal of competitive ability and can influence territorial aggression between males. Agonistic interactions among males of different co-occurring species could result from misidentification (misdirected conspecific aggression). Reflectance spectrometry of plumage coupled with models of avian vision can be used to infer whether plumage color differences can be distinguished by birds. Here we investigate crown coloration similarity as a potential explanation for aggression between the imperiled Golden-winged Warbler (Vermivora chrysoptera) and the comparatively abundant Chestnut-sided Warbler (Setophaga pensylvanica). Because the yellow crown coloration of the two species appears identical to humans, we hypothesized that misidentification of heterospecifics as conspecifics could escalate agonistic interactions. Using museum study skins, we tested whether the yellow crown coloration of the two species should be distinguishable to the birds. Spectral reflectance data demonstrate that plumage color differs between the two species and avian vision models suggest these color differences should be easily discriminated. Thus, we conclude that plumage coloration similarity between these wood warblers is unlikely to cause misidentification of heterospecifics as conspecifics and may just be a result of phylogenic constraint. As populations of Golden-winged Warblers are experiencing accelerating declines, research focusing on the role interspecific competition plays on reduced productivity and survival is warranted.