From a breeding range stretching nearly 5000 km east to west across the Boreal forest, the entire world population of Bay-breasted Warbler cram into a small area of humid tropical forests in Panama and north-west Colombia. Here densities are high and given their late departure (end of April), Bay-breasted Warblers probably store much of the energy they need for the first leg of their journey while still on their over-wintering grounds. It is also here that they molt into their dazzling chestnut, cream and black breeding plumage.