The sensitivity of echolocation by the Grey Swiftlet Aerodramus spodiopygius

Experiments were carried out to study the sensitivity of the echolocation system of the Grey Swiftlet Aerodramus spodiopygius to cylindrical aluminium rods of 1, 5, 10 and 20 mm diameters. Using a method of statistical analysis which enabled the data to be compared with the chance performance of a randomly moving (non-echolocating) missile, the results indicated that this species could echolocate the 20 mm diameter rods but those of smaller diameter were hit in an approximately random fashion. It is concluded that the sensitivity threshold of A. spodiopygius lies between 10 and 20 mm diameter for cylindrical metal rods under the prevailing experimental conditions. Comparisons with other data on the sensitivity of this and other swiftlet species are discussed.