EXTRA-PAIR MATING, MALE PLUMAGE COLORATION AND SEXUAL SELECTION IN YELLOW WARBLERS (DENDROICA-PETECHIA)

Extra-pair mating has been proposed as a source of sexual selection re sponsible for secondary sexual traits that are common among socially m onogamous birds, although supporting evidence is scant. In the sociall y monogamous yellow warbler, males are larger than females, and unlike females, have extensive reddish streaking on their breasts. Using DNA fingerprinting we show that within-pair parentage was positively rela ted to male size, and that extra-pair mating success was positively re lated to the amount of streaking on the breast. To our knowledge, this is the first intraspecific evidence of an association between a male plumage ornament and gains of extra-pair paternity that is apparently independent of age. This study confirms that extra-pair mating can be an important mechanism of sexual selection even when the most successf ul sires are commonly cuckolded, and refutes a previous hypothesis tha t the variation in plumage and behaviour among male yellow warblers is an example of alternative, equally successful, evolutionarily stable strategies (ESS). More generally, the demonstrated independence of wit hin-pair and extra-pair success and their associated traits indicates that where animals have multiple secondary sexual traits, different tr aits may be selected by different mechanisms that contribute to total reproductive success.