Demography and social organisation of the red-winged fairy-wren, Malurus elegans

The red-winged fairy-wren, Malurus elegans, is endemic to the high-rainfall region of south-western Australia. We studied it in Eucalyptus diversicolo r (karri) forest near Manjimup, Western Australia from 1980 to 1995. After a detailed study of breeding biology during 1980-86, we monitored dispersal and survival in known groups during 1987-95. M. elegans bred cooperatively , with 83% of groups (mean size 4.1) including one or more non-breeding mal es or females that helped to rear young and defend the territory. Survival of breeding adults (78%) and helper males (76%) was high. Territories and g roups persisted from year to year, even though one or other of the breeding pair was replaced. Most known dispersals were to a group only 1-2 territor ies distant. Dispersal was female-biased, mostly in their third or fourth y ear. A behaviour not recorded in other Malurus spp. was that some birds, ch iefly females, joined groups as helpers. The feeding rate of nestlings was not related to group size, but in larger groups the share of work done by t he breeding female decreased. Helpers did not enhance the survival of breed ing females, and had little overall effect on the production of fledglings. Females produced a mean of 2.4 fledglings, 1.8 independent young and 1.1 y earlings per year; survival of fledglings to the start of the following bre eding season was 44.2% (31-61%). We argue that the high levels of adult and juvenile survival influence many aspects of the social system in M. elegan s, such as large groups, the presence of female helpers, occurrence of immi grant helpers and delayed dispersal. We suggest that an important benefit o f delayed dispersal and group living is in promoting the survival of young birds, and increasing their chance of acquiring a territory.