Asymmetrical occurrence of altruistic behaviour within and between pair-bonds of large-billed crows

Abstract

Altruistic behaviour, such as allogrooming and allofeeding, has been suggested to be crucial for maintenance of cooperative relationship especially between non-kin individuals. Monogamous pair-bond, which is widespread in birds, is a form of cooperation for breeding between a male and a female. Many previous studies reported that altruistic behaviour within pair-bonds occurred primarily from males to females. However, most of those findings were obtained from the observations during the breeding season, and therefore it remains unknown what sex-different patterns of altruistic behaviour occur outside the breeding season for life long monogamous birds. The present observation study investigated sex differences of altruistic behaviour within pair-bonds outside the breeding context in a life-long monogamy, large-billed crows (Corvus macrorhynchous). Specifically, frequency of allopreening and allofeeding were compared between sexes and also between pair-bonds. We found that frequency of both behaviour was different between sexes, and inconsistent within and between pair-bonds. Our findings suggest that altruistic behaviour within pair-bonds may occur asymmetrically between sexes but vary between pair-bonds in large-billed crows.