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Abstract
Many bird species display elaborate plumage characteristics. The evolution of these traits, and their associated functions, is a central area of study in avian biology. Conspicuous plumage characteristics can be important in many different contexts and may have multiple functions, both between and within bird species. Additionally, these traits often incur various costs to their bearer. To better understand such conspicuous plumage traits, I studied a prominently displayed plumage characteristic of male Black-throated Blue Warblers (Setophaga caerulescens), the wing spot. I examined this trait in the contexts of social communication, reproduction, and survival. With regard to communication, I found that the male Black-throated Blue Warbler wing spot was important in intraspecific male-male communication even in situations where males were familiar with one another. However, regarding the wing spots potential importance in a reproductive context, I did not find a relationship between male wing spot length and extra-pair paternity in this species. Instead, I found that extra-pair paternity increased with male age and size. Thus, any function of the male wing spot in communication with conspecific females remains unclear. Female warblers may still use the male wing spot as a cue or signal, but not in the context of extra-pair paternity. Moreover, I found that male wing spot length was not important in explaining annual survival, thus it is unlikely that displaying a wing spot carries an obvious survival cost. Other associated costs with displaying a long wing spot are possible and should be investigated. Taken together, the Black-throated Blue Warbler male wing spot appears to function, during the breeding period, primarily as a signal in male-male communication.