Breeding Biology of the White-rumped Swiftlet at Chillagoe

Abstract

The White-rumped Swiftlet Aerodramus spodiopygius chillagoensis was studied during a good and a poor season at Chillagoe, Queensland. Most of the nests were in totally dark sections of caves where a single nest and colonies containing 4-264 nests were visited. The clutch of one was incubated for an average of 26.6 days during the better season when 64% of eggs hatched successfully. Lost clutches or young broods were usually replaced within 14 days. Fledging success in the good season was 69% giving a breeding success of 44% or 0.9 young fledged from the two broods of a breeding pair. In the poor season incubation took 27.8 days, hatching success was 60%, fledging success was 50% and the nestling period had increased from 46.1 days in the better year to 51.0 days in the poor year. While the fledging rate for the single-egg clutch of chillagoensis is well below that of the two-egg clutch of A. s. assimilis, the unique practice of laying a second single-egg clutch for the first chick to incubate, increases the breeding rate in good seasons to almost that of arsimih. There is no sexual dimorphism and both sexes share in incubation and feeding nestlings. Chicks were fed an average of 5.2 times a day. Most chick mortality resulted from the chicks falling from their nests, while the major ectoparasites (louse-flies) are thought to be unimportant to survival. Even though immediate energy demands were increased by synchronising moult and breeding, the length of time to complete the moult of primaries was as short as any apodid studied so far and is shorter than some that moult independently of breeding.