The distribution of life on earth has been profoundly shaped by its climate history. Explaining global biodiversity patterns is impossible without understanding how climate shifts affect populations. Acquiring new information about how populations react to climate change is a matter of urgent practical importance in light of the climate and biodiversity crisis. New analytical methods that draw upon genomic data help eliminate our reliance on a patchy fossil record, and allow us to utilize museum specimens to reconstruct millions of years of species’ demographic histories. Implementing this approach on a large scale provides the opportunity to move beyond the study of individual species’ responses to climate change and makes it possible to determine how climatic shifts have affected complete regional floras and faunas. In this project I will utilize a unique and unprecedented genomic dataset to reconstruct the demographic histories of the entire avifauna of the world’s largest tropical island through the Pleistocene, an epoch of massive climatic change 2.6-.01 mya that shaped the distribution of life on earth. I will test a fundamental yet largely unproven hypothesis: that warming and cooling events in earth’s recent history led to corresponding increases and decreases in the cold-adapted montane species and the warm-adapted lowland species of the tropics. By revealing how tropical faunas reacted to past climate change, I will provide historical context for predicting populations’ response to global warming, and launch a new direction in climate and biodiversity research.