Understanding the geographic origin of lineages is crucial for comprehending their biogeographical and evolutionary histories, as well as the historical connections among biomes. In northeastern Brazil, the Caatinga dry forest represents the largest and most biologically diverse patch of Seasonally Dry Tropical Forest in the Neotropics. Here, using the endemic avian taxa of the Caatinga, we aim to i) infer their biogeographical origins and timing of diversification, ii) investigate the relationships with taxa from other Neotropical domains, and iii) understand the processes driving the evolution and diversification of the Caatinga endemic avifauna.

We obtained previously published calibrated phylogenies of 40 bird species endemic to the Caatinga to reconstruct their ancestral geographic ranges through the R package BioGeoBEARS to infer and highlight the origins, mode, and tempo of evolution of the Caatinga avian endemics. Our results suggest that most avian endemics (21 taxa) are related to lineages from open habitats, including other dry forests or savannas; less than a quarter of the species (9 taxa) likely colonized the Caatinga from adjacent humid forests; we also highlight in situ origins (6 taxa), and cladogenetic events playing an important role in the colonization of the domain. Although most of the endemics seem to represent new arrivals from adjacent habitats, we also detected relatively old lineages that likely occupied these dry landscapes since the Miocene. We provide a much-needed framework for the evolution and biogeographic diversification of the Caatinga Dry Forest. The spatio-temporal patterns recovered here suggest an evolutionary history influenced not only by strict vicariance events but also by episodes of dispersal, which likely played a crucial role in the origin of its avifauna. These events were likely influenced by major climatic and geological events that formed ancient corridors, allowing connections between the Caatinga and both dry and humid forests in South America.