Caribbean Islands facilitated the colonization of Western Hemisphere barn owls, yet experienced rampant extinction.

Island biodiversity reflects multiple evolutionary roles, encompassing lineages derived from nearby continents, relict taxa and, in limited cases, sources of continental diversity. Reconstructing the biogeographic history and island-mainland diversification dynamics requires an integrated understanding of speciation, extinction and dispersal processes to and from islands. Extensive Holocene extinctions may obscure patterns of diversity and connectivity. Tytonidae (barn and bay owls) is a bird group with a worldwide distribution and numerous Quaternary extinctions. Here, we use ultraconserved elements and mitogenomes extracted from tissues, historical museum specimens and fossils to reconstruct phylogenetic relationships and colonization pathways, with a focus on Western Hemisphere taxa. We also summarize extinct Tyto diversity to evaluate Quaternary diversity trends. Our results align with previous studies in supporting an Eastern origin for Western Hemisphere Tyto. We found that the Caribbean was, and still is, the centre of Tyto diversity in the Western Hemisphere, although nearly all Caribbean Tyto (and their mammalian prey) are now extinct. Unexpectedly, we identified two independent Tyto colonization events of the Galápagos. Our study provides strong evidence that islands can serve as sources of diversity for some continental lineages, as well as museums of diversity that harbour unique lineages prone to disturbance-driven extinction.