The social organization of the Scarlet Robin Petroica multicolor and Flame Robin P. phoenicea in southeastern Australia: a comparison between sedentary and migratory flycatchers

Abstract

Scarlet Robins Petroica multicolor and Flame Robins P. phoenicea occurred sympatrically during the breeding season in southeastern Australia. Scarlet Robins that occur territories in forest habitat remained there throughout the year, while those, mostly first‐year birds, that occupied territories in grassland habitat were present only during the non‐breeding season. Flame Robins were present for 9 months of the year and were territorial for 6 of those months. The migratory Flame Robin did not show more intense or prolonged territorial or courtship behaviour than the sedentary Scarlet Robin, despite having to obtain territories and mates when it returned each year. It is suggested that the similarities between the two species' social organizations arise partly from high adult survivorship (70–75%) and lengthy breeding seasons (4–5 months). High adult survivorship and scarcity of suitable breeding habitat also caused intense competition for territories and mates, and appears to have led to the evolution of bright, signalling plumages among female and young male Scarlet Robins. Scarcity of females and breeding habitat may have caused delayed maturation of plumage among male Flame Robins.