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

The prolonged brood care model rests on the assumption that retaining an of fspring through the winter months in the face of a limited food supply shou ld have a cost for parents. We tested this idea with a New World permanent- resident bird, the tufted titmouse (Baeolophus bicolor). Using DNA fingerpr inting, we assessed the degree of relatedness between adult and juvenile bi rds 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 conditio n 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 assu mption, the nutritional condition of adults in treatment groups (young remo ved) appeared to be worse, not better, than in groups where a related juven ile was present. These results suggest that the prolonged brood care model may not be universal in its application and that under some ecological cond itions, retaining offspring through the winter can result in a net benefit for territorial adults despite the necessity of sharing resources.