Abstract

This, the first study of the breeding biology of the Mountain Swiftlet, Aerodramus hirundinaceus, was undertaken in the Twin Falls Cave at 2120 m near Tembagapura in Irian Jaya on the island of New Guinea. The cave was only 70 m long, but contained up to 32 nests, which were mostly built of foliose lichens and a little saliva, and rested on ledges on the walls of the cave. Two nests were touching but the others were up to 185 cm apart; this is a large distance for swiftlets and may be caused by lethal pressures from ticks. The nests averaged 65 × 64 × 10.9 mm internal dimensions with external heights of 58–210 mm. The breeding season was at its lowest in April–May when no nests (1994) and one nest (1993) was occupied and at its height between October and December when 21–24 nests were occupied. The clutch is one, weighing 2.00 g, which is ~20% of average adult weight, and is incubated by both parents. Replacement of lost eggs or young took a minimum of 6–43 days and a maximum of 13–64 days. Adults moulted while breeding. Fledging occurred in 67–74 days. Nestlings were fed 1–8 times a day, with parents never remaining at the nest for more than 5 minutes. Hatching success rate was 77% and the fledging success rate was 61%.