An elevational shift facilitated the Mesoamerican diversification of Azure-hooded Jays () during the Great American Biotic Interchange.

The Great American Biotic Interchange (GABI) was a key biogeographic event in the history of the Americas. The rising of the Panamanian land bridge ended the isolation of South America and ushered in a period of dispersal, mass extinction, and new community assemblages, which sparked competition, adaptation, and speciation. Diversification across many bird groups, and the elevational zonation of others, ties back to events triggered by the GABI. But the exact timing of these events is still being revealed, with recent studies suggesting a much earlier time window for faunal exchange, perhaps as early as 20 million years ago (Mya). Using a time-calibrated phylogenetic tree, we show that the jay genus is emblematic of bird dispersal trends, with an early, pre-land bridge dispersal from Mesoamerica to South America 6.3-7.3 Mya, followed by a back-colonization of to Mesoamerica 2.3-4.8 Mya, likely after the land bridge was complete. As species came into contact in Mesoamerica, they avoided competition due to a prior shift to lower elevation in the ancestor of . This shift allowed to integrate itself into the Mesoamerican highland avifauna, which our time-calibrated phylogeny suggests was already populated by higher-elevation, congeneric dwarf-jays (, , , and ). The outcome of these events and fortuitous elevational zonation was that could continue colonizing new highland areas farther north during the Pleistocene. Resultingly, four lineages became isolated in allopatric, highland regions from Panama to Mexico, diverging in genetics, morphology, plumage, and vocalizations. At least two of these lineages are best described as species ( and ). Continued study will further document the influence of the GABI and help clarify how dispersal and vicariance shaped modern-day species assemblages in the Americas.