Long-term genetic and demographic surveys reveal the impact of population history, habitat change, and conservation efforts on the globally endangered Turdus helleri (Taita Thrush)

Predicting the fate of threatened populations remains a challenge in conservation biology. The study of genetic and demographic time series is crucial to unravel the role of population history, anthropogenic disturbance and conservation actions on current demographic and genetic patterns. However, such studies are still rare in threatened species. In this study, we integrate a quarter century of population demographic (capture–mark–recapture) and genetic (microsatellites) data for the globally endangered Turdus helleri (Taita Thrush), a songbird endemic to the fragmented cloud forest of the Taita Hills, southeast Kenya. We found that the two largest remaining populations are prone to high demographic and genetic stochasticity. Furthermore, despite relatively high genetic diversity, the increase in inbreeding in recent years suggests vulnerability to extinction. Moreover, while the smallest population was close to extinction, assisted gene flow midway through the study led to a demographic rescue. We conclude that habitat protection, continued monitoring and conservation efforts are required for long-term survival of the endangered T. helleri, as the species may be prone to an extinction debt.