Bachman's warbler population genomics
Habitat loss is one of the main drivers of extinction worldwide. Naturally rare species with large breeding ranges and specialized habitat restrictions are expected to be more susceptible to habitat loss and its follow-on effects such as population isolation, genetic drift, loss of genetic diversity, and increased inbreeding. The Bachman's warbler (Vermivora bachmanii), last seen in 1988, is theorized to have gone extinct due to extensive loss of its specialized habitat in the 19th and 20th centuries. However, little research was conducted on Bachman's warblers prior to their extinction; thus, little is known about their pre-extinction population size or range wide connectivity. Using both mitochondrial DNA and single-nucleotide polymorphisms, we looked for evidence of population structuring in Bachman's warbler using museum samples obtained from both breeding and migration sites across the species' entire range prior to major population declines. We found weak genetic structuring between sampling regions, with differentiation driven by isolation-by-distance. Coupled with estimates of historically large and stable Ne, this suggests that neither natural rarity nor intrinsic population isolation are likely contributors to the Bachman's warbler extinction, which instead was likely driven by the rapid destruction of their specialist habitat.