An experimental test of the prolonged brood care model in the tufted titmouse (Baeolophus bicolor)

Abstract

The prolonged brood care model rests on the assumption that retaining an offspring through the winter months in the face of a limited food supply should have a cost for parents. We tested this idea with a New World permanent-resident bird, the tufted titmouse (Baeolophus bicolor). Using DNA fingerprinting, we assessed the degree of relatedness between adult and juvenile birds in 17 winter groups, finding that in 8 of the groups no young bird was the offspring of the territorial pair. We compared the nutritional condition of territorial adult birds in small forest fragments from which their own offspring and other young had been removed with the nutritional condition of control birds from unmanipulated fragments. Contrary to the model's assumption, the nutritional condition of adults in treatment groups (young removed) appeared to be worse, not better, than in groups where a related juvenile was present. These results suggest that the prolonged brood care model may not be universal in its application and that under some ecological conditions, retaining offspring through the winter can result in a net benefit for territorial adults despite the necessity of sharing resources.