Natal dispersal, philopatry and cooperative breeding in Eastern Yellow Robin Eopsaltria australis

Abstract

ABSTRACT Delayed natal dispersal is thought to have evolved in response to survival benefits of philopatry and group formation under environmental and/or demographic constraints, with kin selection subsequently promoting the emergence of cooperative breeding behaviours. We studied sociality and natal and breeding dispersal of a colour-banded population of Eastern Yellow Robin Eopsaltria australis over 10 years to better understand the evolution of facultative cooperative breeding in this long-lived, territorial songbird. Breeding group size averaged 3.08 (range 2–6) adults and 82% of helpers were males. All male young delayed dispersal to help one or both parents (82.1%), another first order relative (12.5%) or other relatives (5.4%) for between one and four years before establishing as a dominant breeder. The social relationships of female helpers was confirmed in only two instances, with the helper being the daughter of the breeding pair. Helpers significantly increased annual productivity, which averaged 1.44 (95% confidence intervals: 1.07–1.81) with no helpers and 2.04 (95% confidence intervals: 1.74–2.34) with helpers present. Male young were highly philopatric; most either inherited the natal territory or budded off a portion of the natal territory, and none dispersed more than one territory away. Most females appeared to disperse further after reaching independence to become floaters. Breeding dispersal was limited to females, who dispersed after either divorce or to avoid incest once a son inherited the territory. These results confirm that Eastern Yellow Robin helpers likely gain indirect fitness benefits from helping.