|A gorgeous male prothonotary warbler|
Photo: Dominic Sherony, Wikimedia Commons
Despite the very tough journey, they return in spring to take advantage of the seasonal bounty in seeds, vegetation, and insects.
But where they all go and what routes they take have eluded us - Cornell's Lab of Ornithology has pulled millions of locations of 118 species of migratory birds to create this amazing animated map of migration routes in the western hemisphere. Many of the data points were taken by "citizen scientists" -- regular people interested in birds who record what they see and hear to online databases, such as eBird.
In their published findings, the scientists concluded that "a combination of geographic features and broad-scale atmospheric conditions influence the choice of routes used during spring and fall migration."
If you plan your trip right, you might even see the same birds (or butterflies) in two different countries as they make their way north or south. Keep your eyes and ears open!