Blue
Grosbeaks
(Guiraca caerulea)
Barbara Ballentine
Blue Grosbeaks
Blue grosbeaks exhibit intra-specific variation in plumage coloration. Because variation in plumage coloration in blue grosbeaks is related to territory quality and body size, plumage color may function as a signal. Using captive experiments, I tested if female-choice was functioning in the evolution of bright plumage coloration in blue grosbeaks. I found that females chose male irrespective of plumage color manipulation. Thus, I concluded that female-choice was not a selective pressure driving the evolution of bright plumage coloration but may function in male-male competition. Additionally, I investigated the function of song in blue grosbeaks in terms of female-choice by examining changes in song patterns as it related to female fertile periods. I found that males sang more complex songs during female fertile periods than during non-fertile periods. I concluded that song complexity in blue grosbeaks might function in female choice. Thus, multiple sexual ornaments in blue grosbeaks may serve different functions with plumage color functioning as a signal in male-male competition and song complexity functioning in female choice.