Sex, melanic coloration, and sibling competition during the postfledging dependence period

Success in sibling competition is one of the main factors determining individual body condition in the early stages of life and consequently offspring survival and fitness. In birds, most studies on this topic have been focused on the nesting period, but sibling competition still continues during the postfledging period. We studied sibling competition over 3 years during the postfledgling dependence period in the Eurasian kestrel Falco tinnunculus, a reversed sexually size dimorphic species. Contrary to that in the nesting stage, male fledglings showed a higher competitive capacity than females resulting from their greater success in capturing larger prey items delivered by parents. Furthermore, male fledglings showing grayer coloration in the rump captured greater number of larger prey than browner males. Our results suggest that patterns of sibling competition in nestlings can differ from those found during postfledging, revealing the importance of studying this period in order to achieve a more complete view of sibling competition. In addition, kestrel fledglings with grayer rumps were more likely to have larger prey items, suggesting that this character can be interpreted as a phenotypic indicator of quality. Copyright 2008, Oxford University Press.