Observations on the behavioural ecology of the Atiu Swiftlet Aerodramus sawtelli

The Atiu Swiftlet Aerodramus sawtelli is endemic to the Cook Island of Atiu and has an estimated total population of less than 400, rendering it one of the world’s most globally endangered bird species. Over a series of five visits to Atiu, we collected data on the distribution of foraging swiftlets on the island, and their foraging and echolocation behaviour. The bird favours forests, agriculturally developed areas such as croplands, and populated sections of the island (e.g. gardens) but avoids the dry, upraised coral ring (makatea) of Atiu. It appears able to readily exploit new insects after they have immigrated to Atiu and may act as a natural control agent on pest species (e.g. Xyleborus perforans and Atrichopogon jacobsoni). We reanalysed the swiftlets’ echolocation calls within one of their roost caves in conjunction with new recordings. The calls do not contain ultrasonic components and are uniquely single clicks compared to the echolocation vocalisations of other swiftlet species. The minimal impact of human disturbance on the remote nesting caves of this bird suggests that its numbers, although small, represent a stable population