ABSTRACT
Songbird Model, the Zebra Finch .......................................................................................490 23.4 The Antioxidant Role of Carotenoids in a Colorful Raptor ............................................... 492 23.5 Developmental Predictors of Coloration in Altricial Birds: Studies of
Blue Tits and Great Tits ...................................................................................................... 494 23.6 Developmental Predictors of Adult Coloration in Precocial Captive Bird Models ............ 497 23.7 Carotenoid Signaling of Social Status in Widowbirds ....................................................... 499 23.8 Female Coloration and Mutual Sexual Signaling in Northern Cardinals .......................... 501 23.9 Carotenoid Coloration and Environmental Contamination: Great Tits as
Bioindicators ....................................................................................................................... 503 Acknowledgments ..........................................................................................................................505 References ......................................................................................................................................505
Many animals deposit carotenoids into external body tissues, such as skin, feathers, or other keratinized structures like the beak, where they impart rich red, orange, or yellow colors (e.g., in amingos and guppies) or even purple and green hues when in combination with other colorgenerating mechanisms (e.g., melanin pigments, structural coloration) (McGraw 2006). The carotenoid basis for such colors has been known for 75 years (Volker 1938), and with that has come widespread interest in the biological causes and consequences of carotenoid-based color displays. Special interest has been shown in species where the sexes differ in coloration (e.g., Badyaev and Hill 2000, Gray 1996); in most cases, males display larger areas of or more intense carotenoid coloration and use such colors as a means of signaling their worth as a mate to females of their species or of signaling their competitive advantages to rival males. Sexual selection is recognized as a powerful and important evolutionary force, which has shaped variation in behavior, physiology, and morphology, not least variation in carotenoid coloration within and among species (Andersson 1994). However, sometimes adult females or even young animals can display this form of coloration, and investigations into the nature and role of carotenoids in these instances have proven to be excellent tests of the limits and generalities of theories on animal signal use (e.g., Jawor et al. (2004) and Tschirren et al. (2005)).
