Migratory birds are some of nature’s most magnificent creatures, playing significant ecological, economic, and cultural roles in the U.S. and internationally. Neotropical migratory birds, sometimes called nearctic-neotropical migrants, are those species that nest in the United States and Canada ("nearctic" region) and migrate south to the tropical regions of Mexico, Central America, South America, and the Caribbean ("neotropics") for the winter. Migration is predicated primarily upon food resources. Since most insects become unavailable during our harsh winters, insect-eating birds find abundant food resources in the tropics. Many raptor species also follow this migrating food chain. Over half of all bird species nesting in the US are classified as neotropical migratory birds. Some or all of the populations of 338 species—which include many of our songbirds, waterfowl, birds of prey, waterbirds and shorebirds—migrate each fall to the tropics.
The legislative definition of Migratory Birds are species that in the course of their annual migration traverse certain parts of the United States, Canada, Mexico, Russia, or Japan. This includes not only neotropical (long-distance) migrants, but also temperate (short-distance) migrants and resident species. Migratory birds may be at risk due to lack of adequate protection during the nesting season or while on their way to and from their breeding grounds.