Influence of Winter Ranging Behaviour on the Social Organization of a Cooperatively Breeding Bird Species, The Apostlebird

Abstract

Most cooperative breeding bird species live in family groups that are formed through the prolonged association of offspring with their parents. Research into cooperative families has in particular investigated the balance between cooperation and conflict over reproductive decisions. As a consequence of this research focus, social interactions among group members outside the breeding season are rarely studied, despite the fact that they are likely to be crucial for social decisions. We investigated the social dynamics and ranging behaviour of the family group living cooperatively breeding apostlebird (Struthidea cinerea) outside the breeding season. Group size changed between, but not within, the seasons, being smaller during the breeding season than in the winter season. This change in group size was a consequence of breeding groups merging after breeding, then splitting again before the next breeding season. While breeding groups used small, non‐overlapping home ranges ( = 113 ha) around the nesting site, during winter groups moved up to 1200 ha ( = 598 ha), and interacted frequently with up to four other winter groups. In particular large groups often joined together during winter and spent up to 50% of their time associating with other large winter groups. This apparent fission‐fusion system facilitated the exchange of group members, offering the possibility to form new breeding coalitions and new groups. The results of this study suggest that behaviour outside the breeding season can be of considerable importance to the social dynamics of both families and cooperative breeding in such systems.

The importance of fission–fusion social group dynamics in birds

“…Seasonality of social behaviour also occurs in passerines, although typically these species are more social during the non‐breeding season (Morse , Griesser et al . , Aplin et al . ).…”

“…For example, in co‐operatively breeding Apostlebirds Struthidea cinerea and Chestnut‐crowned Babblers Pomatostomus ruficeps , non‐breeding flocks are larger and formed of several co‐operatively breeding units (Griesser et al . , Browning et al . ), resulting in fission–fusion social dynamics across an annual cycle.…”

Looking for unity in diversity: human cooperative childcare in comparative perspective

“…For instance, in callitrichid monkeys [97,106] [107] (M.G. 2017, unpublished data) and acorn woodpeckers [108].…”

Isolation and characterization of 12 polymorphic tetranucleotide microsatellite loci in the apostlebird (Struthidea cinerea)

“…The species readily habituates to human presence and the mud nests in which they breed are built in very open sites making them particular suitable for intensive behavioural study (e.g. Griesser et al 2009). As such the apostlebird provides an excellent model system for the detailed study of questions that are of critical importance to our understanding of the evolution of sociality in vertebrates.…”