The Breeding Biology of the Splendid Fairy-wren Malurus splendens: the Significance of Multiple Broods

Abstract

A colour-banded population of Malurus splendens was studied from 1973-1988 in up to 34 cooperativebreeding territorial groups in woodland-heath near Perth. The study is considered in three parts: 1973-77, with regular minor patchy fires; 1978-84, with no fires; and 1985-1988, after a major fire in January 1985. Eggs were laid from late August to January, mostly in September-November. Rain in mid- to late August may delay the start of laying. Groups without dependent young may continue breeding into January but most such late attempts fail during periods o;f extreme heat. Before November, most nests were within 1 m of the ground; later nests were higher. Most clutches were of three eggs (mean = 2.90) and clutch size did not vary during the breeding season or from year to year. Incubation lasted 14-15 days (13-14 d in December), nestlings hatched synchronously and fledged 10-12 days later. Parasitism by cuckoos varied between years, affecting from 0 to 52% of nests (mean = 21%); the most common nest predators were reptiles and cats. Fertility was 93% and over all years 49% of eggs produced fledglings (1973-77: 56%; 1978-84: 58%; 1985-88: 33%); 52% of nests produced at least one fledgling. Replacement clutches were laid soon after a nest failed, often within seven days. M. splendens is multi-brooded; variation in reproductive effort occurs through the number of clutches, not clutch size. Overall, 36% of females renested after successfully rearing a brood; 22% of females reared two broods, with considerable variation between years (63.6% in 1978; 2.8% in 1985). Groups produced a mean of 3.2 fledglings and 2.2 independent young per year; even in years with a high rate of nest failure, 75% of groups produced at least one fledgling. Breeding success did not differ between early and late nests, and fledglings survived equally well. The production of multiple broods is an important feature in the life history of M. splendens and other resident Australian passerines.