Data from: Asymmetry in responsiveness to playback of geographic song variation after a recent range expansion

Birdsong variation among populations within species has been regarded as a
possible precursor for variation between species and may play a role in
speciation. However, acoustic variation between two populations of the
same or different species can have a variable impact on mutual
responsiveness, and we currently lack sufficient insight into the
underlying reasons. We report here on geographic song variation and
responsiveness to playback for the light-vented bulbul (Pycnonotus
sinensis), a species with recent range expansion in China. We recorded
songs in four historical populations in the south and six newly
established populations in the north. We tested responsiveness in two
southern and two northern locations to songs from southern and northern
birds. Besides songs from the other distribution range (south to north and
north to south), we used recordings for playback from local, nearby, and
faraway dialects from within their own distribution range. We confirmed
distinct dialectal differentiation in the south and a more gradual pattern
of geographic song divergence in the north. Birds in the south showed very
little response to almost all non-local songs. In contrast, birds in the
north showed a strong response to a wide range of stimuli, just gradually
fading from local, nearby, to far-away northern dialects, which may be
related to song type sharing or individual mobility and aggression
associated with the recent range expansion. We hereby add an asymmetric
response pattern in response to the literature and review the current
insights about the potential impact of song variation on avian speciation.