Testing species limits of non-echolocating Philippine swiftlets (Collocalia spp.) using molecular genetic data

Swiftlets are small, insectivorous birds that are distributed from the Indian Ocean, through southeast Asia and north Australia, to the Pacific. About 22 species of swiflets nest in caves or other dark places, where they navigate using a crude form of echolocation (Chantler and Driessens 1995). Three additional species, which are incapable of echolocation, do not nest in the dark. The 25 species of swiftlets are considered by many authors to represent the most difficult problem in the taxonomy of birds (e.g., Mayr 1937). This is because swiftlets show extreme morphological similarity, making species limits extremely difficult to decipher. Lee et a/. (1996) used DNA sequence data to show that morphologically-based species concepts are seriously flawed for swiftlets. They also showed that the echolocating species (Aerodramus spp.) are not closely related to the non-echolocating species (Collocalia spp.).