Breeding biology of the Rainbow Pitta, Pitta iris, a species endemic to Australian monsoon-tropical rainforests

Abstract

The Rainbow Pitta, Pitta iris, is endemic to the monsoon rainforests of the wet–dry tropics of north-western Australia. In the Darwin region, Northern Territory, the breeding season lasted 3–4 months, eggs being laid from mid October to late February over three years (1992–95). This period coincided with the wet season, and the start and length of the breeding season varied annually with rainfall. The number of nests was correlated with both rainfall and the abundance of earthworms, the major food item of the species during the wet season. During one season two out of four intensively studied pairs attempted second broods, building new nests only 3–5 days after the first brood fledged. The large domed nests were built in a variety of plant species and sites, but half were built on the tops of stumps or in tree-trunk forks. Heights of the 111 nests varied from ground level (9% only) to 20 m, averaging 5.4 m. Both sexes built the nest, incubated eggs and fed the young. Clutches consisted of 3–5 eggs, the average being 3.9 eggs (n = 21). The incubation and nestling periods each averaged only 14 days. Nests were rarely left unattended, and six incubation bouts averaged 87 min (s.d. = 27 min). Fledglings remained in their natal territory for 15–20 days before dispersing to other forest patches. Fledglings had significantly shorter primary and tail feathers than adults, but tarsus length was similar. The relatively large clutch, and short breeding season, nest cycle and period of dependency of this species are atypical for Australian and tropical passerines in general, but may be typical for this predominantly south-east Asian family. In the Rainbow Pitta, these life-history traits may be facilitated by the super-abundance of earthworms during the wet season.