Echolocation and the systematics of swiftlets

Abstract

During his period of interest in swifts, David Lack drew attention to the importance of nesting behaviour and nest type as guides to the systematics of the Apodidae (Lack, 1956). This approach has been particularly fruitful among the Indo-Pacific assemblage known colloquially as ‘swiftlets’, recognised as a tribe Collocaliini by Brooke (1970) and as a subfamily Collocaliinae by Condon (1975). Among these swifts, in several instances, the type of nest built has proved to be critical in specific determination. Another characteristic exhibited only by the living bird that has claimed attention is the capacity of some (but not all) swiftlets to orientate in darkness by echolocation. Because the component frequencies of the click-like orientation sound fall largely within the range audible to man, it is detectable without instruments in field conditions. As a consequence, the distribution of this capacity among the swiftlets is now reasonably well known. Together with those included in this chapter, sound spectrograms have been published of the orientation clicks of six taxa, representing four species. Tests of the ability to detect and avoid obstacles in darkness have been made on three of these taxa. Data are thus available for evaluating the importance of echolocation in the ecology of these birds, and for considering its significance as a taxonomic character.

After graduating from Cambridge, Lord Medway joined the Sarawak Museum (1956–58); archaeological duties (especially at Niah cave) provided the initial opportunity to study the cave-dwelling swiftlets. Subsequent research was encouraged under the supervision of Lord Zuckerman at Birmingham, and later by a fellowship from the Yayasan Siswa Lokantara, Indonesia (1960–61). Service with the University of Malaya (1961–70) provided further opportunities. Now settled in Britain, he has still been able to keep field contact with this fascinating group of birds on sporadic expeditions to the Indo-Pacific region. Since 1973 he has also been editor of Ibis.

David Pye studied Zoology at Aberystwyth and Bedford College, London. He is especially interested in the acoustic mechanisms of echolocation and in ultrasonic communication by animals. In his current research he uses low power microwave radar to measure the motions of flying bats while recording them in the field. He and Lord Medway first met as students on a field course. He is now Professor of Zoology at Queen Mary College, London.