Habitat fragmentation affects culture transmission: patterns of song matching in Dupont's lark

1. Males of many bird species match song with neighbours during territorial interactions. Although bird vocal mimicry has received much attention, the relationships between song variation and ecological factors such as landscape geometry and habitat fragmentation are still poorly known, and most previous research has been limited to one or a few populations of a species. In this study we analysed the spatial patterns and ecological determinants of song matching in Dupont’s lark Chersophilus duponti, a rare and specialized steppe passerine. 2. By recording bird songs from 21 Spanish and Moroccan localities, we analysed the effect of habitat fragmentation and the availability of suitable steppe habitat on the patterns of song matching in Dupont’s lark, controlling for other potential determinants such as period in the breeding season, intensity of competition, geographical location and spatial distribution of individuals. 3. Both song-type sharing (match of song types in the repertoire) and spectrotemporal matching (convergence in the acoustic features of the same song type) were greater between counter-singing neighbours than between non-neighbours, and spatial autocorrelation (similarities between singing individuals) only occurred at short distances. The study localities differed in the amount of overall acoustic matching between individuals, seemingly as a consequence of local differences in the intensity of male competition and in the availability of suitable habitat. 4. The levels of song-type sharing between non-neighbours tended to increase and those among neighbours to decrease with the increase of steppeland availability. Moreover, the existing differences in sharing between neighbours and non-neighbours were significantly affected by the presence of elements of fragmentation in the steppe. In fragmented habitats, song sharing among neighbours was enhanced, possibly because of harsher competition for limited resources; conversely, sharing among non-neighbours dropped, probably because of the lack of interactions among individuals isolated by habitat barriers. 5. Synthesis and applications. Anthropogenic habitat barriers could alter bird perception of the spatial distribution of rivals over distance, leading to a contraction of the spatial range of the individual acoustic niche. We suggest that communication systems of habitat-sensitive species might be used as a behavioural indicator of anthropogenic environmental deterioration. Because of their rapidly evolving cultural nature, bird vocalizations might become an early warning system detecting the effects of fragmentation over relatively short times and before other indicators (such as genetic markers) show any change.