Endemic bird species are far more threatened than previously thought across the semiarid Caatinga dry forest domain

Biodiversity loss is a hallmark of human impacts on natural landscapes worldwide, particularly in dry tropical forest regions which have been historically neglected by ecological and conservation science, concealing the true history of local extinctions. Here, we (1) assess the magnitude and spatial extent of local extinctions of the endemic forest birds of the Caatinga dry forest domain of northeastern Brazil, one of the most biodiverse and densely populated semi-arid regions on Earth; and (2) explore the drivers of local extinctions of these species. We quantified differences between the contemporary and reconstructed historical distributions of these species using species distribution models to estimate the regional-scale spatial extent of local extinctions. We also assessed the importance of positive and negative environmental predictors of local extinctions using gradient boosting machine models, which are algorithms that combine multiple decision trees to improve predictive performance. Most of these species lost over 50 % of their historical range, which exacerbates regional scale extinction threat. Ten of the 13 endemic species considered are likely far more threatened than suggested in previous Red List assessments. Additionally, 88 % of the Caatinga domain has already recorded local extinctions of endemic forest birds. We show this is attributed to loss of aboveground phytomass, causing irreversible damage to dry forest habitats. Unexpectedly, local persistence of endemic forest birds was not positively affected by protected areas, likely because the historical regional-scale extinction filter predates their creation and establishment. Due to reduced ranges, these species have become more susceptible to global extinctions. Therefore, integrated conservation measures should be adopted, including natural resource management and forest restoration, to avert further historical losses of this unique biodiversity.