# Asymmetry in responsiveness to playback of geographic song variation after a recent range expansion in light-vented bulbuls

## TL;DR

Southern light-vented bulbuls respond only to their own dialects, while northern ones respond to a range of dialects, possibly due to recent range expansion.

## Contribution

The study reveals an asymmetric response pattern to geographic song variation in a recently expanded bird species.

## Key findings

- Southern populations show distinct dialects and respond only to their own songs.
- Northern populations exhibit gradual song divergence and respond to a wide range of dialects.
- Asymmetric responsiveness may influence future speciation in the species.

## Abstract

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 2 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 4 historical populations in the south and 6 newly established populations in the north. We tested responsiveness in 2 southern and 2 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, near-by, and far-away 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 nonlocal songs. In contrast, birds in the north showed a strong response to a wide-range of stimuli, just gradually fading from local, near-by, 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 responsiveness to the literature and review the current insights about the potential impact of song variation on avian speciation.

Songs of many songbirds vary geographically like human dialects and could play a role in reproductive separation of populations. We show that southern light-vented bulbuls have distinct dialects and responded nearly exclusively to anything else than their own dialect. Northern bulbuls are part of a recent range expansion, vary more gradually in song, and responded also to other dialects than their own. This asymmetric response may affect their chances of becoming separate species in future.