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

The prolonged brood care model rests on the assumption thatretaining an offspring through the winter months in the faceof a limited food supply should have a cost for parents. Wetested 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 juvenilebirds in 17 winter groups, finding that in 8 of the groups noyoung bird was the offspring of the territorial pair. We comparedthe nutritional condition of territorial adult birds in smallforest fragments from which their own offspring and other younghad been removed with the nutritional condition of controlbirds from unmanipulated fragments. Contrary to the model'sassumption, the nutritional condition of adults in treatmentgroups (young removed) appeared to be worse, not better, thanin groups where a related juvenile was present. These resultssuggest that the prolonged brood care model may not be universalin its application and that under some ecological conditions,retaining offspring through the winter can result in a netbenefit for territorial adults despite the necessity of sharingresources.