Life history of the white-breasted robin, Eopsaltria georgiana (Petroicidae), in south-western Australia

Abstract

The white-breasted robin, Eopsaltria georgiana, is endemic to south-western Australia. We studied breeding, dispersal and survival in known groups from 1978 until 1987, with some groups followed until 1992, in Eucalyptus diversicolor (karri) forest near Manjimup, Western Australia. E. georgiana bred cooperatively, with 66% of groups including one or more birds in addition to the breeding pair (mean group size 3.1); these helpers were predominantly males and assisted the senior male in feeding the female on the nest and the young and defending the territory. The survival of adults was high (males 86%; females 79%). Breeding territories and groups persisted from year to year, although in the non-breeding season, males ranged more widely. Dispersal was female-biased; most females and some males dispersed in their first year. Divorce was rare; breeding males that disappeared were replaced by a helper from within the group if one was present, and females were replaced from outside the group. Eggs were laid between July and December. Clutch size was almost always 2, incubation lasted 16–17 days and nestlings fledged 13–14 days later. Juveniles were dependent on adult provisioning for 6–8 weeks. We found no parasitism by cuckoos. Of 429 nests found, 74% fledged at least one young, and overall nesting success calculated by the Mayfield method was 63%. The median time between initiation of two successive clutches was 54 days, and 52% of females renested after fledging one brood; at least two broods per year were fledged by 44% of females. Groups produced a mean of 2.8 fledglings, 1.3 independent young and 0.7 yearlings per year. The most productive groups were those with two or more helpers on high-quality territories, but we could not separate the effects of helpers and territory quality. E. georgiana has the 'slow' life history typical of many Australian passerines – cooperative breeding, sedentary, resident all year round in an equable habitat that promotes high survival of breeding adults. Their low reproductive rate produces a small crop of yearlings, some of which may stay in the parental home range.