The signaling function of plumage characteristics in female tree swallows and implications for reproductive success and life-history decisions.

The existence of elaborate plumages in birds has traditionally been explained as a result of mate choice by females for these traits in males. Ornate plumage traits are thought to be costly to produce and maintain, allowing females to gain accurate information about potential mates based on the expression of these traits. Female plumage traits, on the other hand, are less understood and have been rarely studied as having signaling potential. In an attempt to reduce this gap in knowledge, I investigated the potential signaling function of specific plumage characteristics in female tree swallows (Tachycineta bicolor). Tree swallows are one of only two species of North American passerines where females, rather than males, have delayed plumage maturation (DPM). Females in their second year of life (SY) display mainly brown subadult-coloured' feathers on their dorsal surface, while older (after-second year of life: ASY) females primarily have iridescent blue-green adult-coloured' feathers. There is, however, much variation in the number of adult-coloured feathers in the dorsal plumage of SY females. To date, only one study has experimentally examined the potential signaling function of DPM in female tree swallows, and no study has yet examined variation in the amount of DPM exhibited among SY females. Although plumage colour of ASY female tree swallows is less variable compared to SY females, such variation in ASY females is related to reproductive success, making both SY and ASY female plumage characteristics potentially indicative of quality. In this thesis, I investigated 1) if conspecifics behave differently towards SY and ASY females based solely on plumage colouration, indicating that DPM could signal subordinate status and inexperience during the breeding season, 2) if variability in the amount of DPM in SY female tree swallows is a condition-dependent trait and therefore possibly a target of sexual selection, and 3) whether variation in plumage traits of ASY female tree swallows is