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Various mechanisms and ways populations can be isolated from each other can eventually result in cultural and genetic differentiation. In songbirds, culturally transmitted sexual signals such as breeding song can be used as a measure of differentiation since songs can also be impacted by geographic isolation resulting in population-level differences in song structure. Studies in different parts of the world have found differences in song structure across ancient geographic barriers and also across contemporary habitat barriers owing to deforestation. However, very few studies have examined the effect of both ancient barriers and recent deforestation in the same system. Shola Sky Islands provide a unique landscape where some mountain-top islands are isolated by ancient valleys, while others are separated by recent deforestation. Our research includes examining landscape connectivity with remote sensing imageries to understand landscape isolation. We then collect bird song data across the landscape using a combination of automated recorders and hand-held recordings of species species. For the automated recorders, we examined variation across different levels of deforestation. For the species-specific study on the Sholicola species complex, threatened and endemic songbirds, we examined the geographical variation in song structure across six populations on isolated mountaintops or ‘sky islands’ of the Western Ghats. We examined several frequency- and temporal spectral, traits and two syntax traits from 835 songs of 38 individuals across the six populations. Our studies revealed three major song clusters based on a discriminant model of spectral traits, degree of similarity of syntax features, as well as responses of birds to opportunistic playback. However some traits like Complex Vocal Mechanisms (CVM), relating to the use of syrinxes, clearly differentiated both ancient and recently fragmented populations. We suggest that CVMs may have a cultural basis and can be used to identify culturally isolated populations that cannot be differentiated using genetic markers or commonly used frequency-based song traits. We also present preliminary results from the automated recorder data. Our results demonstrate bird songs can be used to reconstruct phylogenetic groups and impacts of habitat fragmentation even when scenarios of isolation are complex.
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