Consistent feeding positions of great tit parents

Abstract

When parent birds arrive at the nest to provision their young, their position on the nest rim may influence which chick or chicks are fed. As a result, the consistency of feeding positions of the individual parents, and the difference in position between the parents, may affect how equitably food is divided among the chicks. We studied the positions of parent great tits, Parus major, landing on the nest to feed their chicks. Individual parents were consistent in their position within observation periods, on different days within the same breeding attempt, and at breeding attempts in different years. Within each sex, there were individual differences in position within single observation bouts, in average position across days within a breeding attempt, and in average position across years. At the majority of nests, the two parents differed in positions. The distribution of angular distances between the parents differed from that expected if the parents' positions were independent, with the observed median being less than that expected. The angular distance between the parents was not related to 22 different characteristics of the brood and parents. We conclude that consistency (i.e. a departure from a random uniform distribution) in position is explained by habit formation, and to a lesser extent by an overall preference for particular locations, and by nest configuration. We also conclude that there is little scope and no evidence for the parents strategically adjusting their angular separation.