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

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.

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 diversicolor (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 males or females that helped to rear young and defend the territory. Survival of breeding adults (78%) and helper males (76%) was high. Territories and groups 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 territories distant. Dispersal was female-biased, mostly in their third or fourth year. A behaviour not recorded in other Malurus spp. was that some birds, chiefly 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 the breeding female decreased. Helpers did not enhance the survival of breeding 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 yearlings per year; survival of fledglings to the start of the following breeding season was44.2% (31–61%). We argue that the high levels of adult and juvenile survival influence many aspects of the social system in M. elegans, such as large groups, the presence of female helpers, occurrence of immigrant helpers and delayed dispersal. We suggest that an important benefit of delayed dispersal and group living is in promoting the survival of young birds, and increasing their chance of acquiring a territory.

The effects of fire on a population of Red-winged Fairy-wrens Malurus elegans in Karri forest in southwestern Australia

In April 1994, an intense fire burnt part of Smith's Brook Nature Reserve near Manjimup, Western Australia where we had studied an individually marked population of the Red-winged Fairy-wren Malurus elegans in Karri Eucalyptus diversicolor forest since 1980. We estimated the population size in a 25 ha area at the start of the breeding season each year 1980?95, including two years post-fire. In the 32 territories present in 1993, the entire area of 26 was almost completely burnt to a height of 10 m, with few remaining unburnt patches. The mean population size for the 13 years 1981?93 was 119 birds in a mean of 29 groups. In November 1993, 126 birds were present in 32 groups. In November 1994, following the April fire, there were 114 birds in 31 groups, but nesting substrate was very scarce, breeding was delayed, and only 0.18 yearling males per group were produced, compared with 0.52 for the years 1981?93. By November 1995, the population had fallen to 73 birds in 23 groups with nine territories vacant. The time necessary for the population to recover to its prefire level was estimated from long-term demographic data to be at least 10 years, longer than the present cycle of 7?9 years for prescribed burns in the southern (Karri) State Forests of Western Australia.