Cooperative breeding and altruistic behaviour in the mexican jay, Aphelocoma ultramarina

Abstract

Summary The social organization of the Mexican jay is based on flocks typically of eight to twenty individuals which tend to be evenly dispersed through the appropriate habitat. Most flocks consist of two or more breeding pairs of adults plus a variable number of non-breeding yearlings and adults. The feeding of the young by all the members of the flock was studied in the field under natural conditions by colour banding the flock members. The feeding of the nestlings was shared by all flock members with 38 to 53 per cent of the feeding visits by the parents and the remainder by altruistic jays who were not parents of the nestlings they were feeding. Parents showed a significant preference for feeding their own nestlings as long as they remained in the nest. The feeding of young after they left the nest was also shared by all flock members, with about 26 per cent of the feeding visits by the parents and the remainder by altruistic jays who were not parents of the young they fed. Parents showed no preference for feeding their own fledglings as opposed to the fledglings of other parents.