So similar and yet so different: taxonomic status of Pallid Swift Apus pallidus and Common Swift Apus apus

Capsule: Common Swift Apus apus and Pallid Swift Apus Pallidus are morphologically very similar but are genetically distinct and diverged 1.9–2.1 million years ago (mya). Aims: To examine genetic differentiation and to estimate separation time between Common and Pallid Swifts. Methods: Estimation of differences in three different mitochondrial DNA markers (COI, ND2 and control region), and a fourth marker, the cytb, that did not differ between taxa. Fossils were used to calibrate the estimate of separation date between the two taxa. Results: The genetic between-species distances were 0.010, 0.006 and 0.033 for the three markers, respectively. These values were from three to ten times higher than within-species distances. Results show that the separation dates back to 1.9–2.1 mya, at the Plio-Pleistocene transition, when global climate underwent a period of significant cooling and Northern latitudes were probably more favourable to the Common than to the Pallid Swift. Conclusion: Differences in breeding biology, migration, moult and vocalizations between the two species are mirrored by a clear genetic separation.