Continent-wide vocal leapfrog pattern in Collared Scops Owls obfuscates species boundaries

Much confusion has surrounded the taxonomy of the Collared Scops Owl (Otus bakkamoena) complex, distributed widely across tropical and subtropical Asia. Often divided into three species, modern taxonomies disagree on its treatment, as a lack of deep mitochondrial DNA divergence is seemingly in contrast with patterns of vocal differentiation. Analysing a dataset of territorial calls of 122 individuals across Asia, we identified a vocal leapfrog pattern in which owl populations at the eastern and western ends of the distribution sound more similar to each other but are separated by different-sounding populations in between. The boundaries between vocal types are not congruent with traditional species boundaries. Our data allow for a re-drawing of species boundaries and reveal that Collared Scops Owls follow a biogeographic pattern rare in Southeast Asian birds. However, this pattern is shared with several other owl complexes in that peninsular Malaysian populations form part of a continental Asian species centred further north in Southeast Asia rather than forming part of a Sundaic species centred in the adjacent Indonesian Archipelago.