Fall migration takes place at a more leisurely pace than spring migration when birds race to get to their breeding grounds. 346 species of birds in the Western Hemisphere are Neotropical migrants. Tens of thousands of bird watchers come to the refuge complex each year to spot Neotropical songbirds, hawks, shorebirds, and waterfowl as well as the resident birds. Depending on the weather in any given year, some species will migrate down the coast of the Gulf of Mexico while others will take off over the Gulf. Because the refuge complex is right on the Mexican border, it is a crossroads of migration and hundreds of thousands of birds continuously fly back and forth between the United States and Mexico.
Some biologists worry that populations of some Neotropical migratory birds are declining.
The Neotropical migratory songbirds seem to be at greater risk than resident songbirds. Because Neotropical migratory songbirds travel over such long distances, they are vulnerable to loss of forest, grassland, wetland, and coastal habitats in their breeding grounds, wintering grounds, and a huge number of stop-over points along the way. It connects the two countries and is a wellspring of life for people, animals, and plants of Mexico and the United States. Four major climactic zones occur in the area and average rainfall ranges from nine inches near El Paso, Texas to 26 inches near the Gulf of Mexico. This makes for a great diversity habitats, providing many different types of homes for the large number of bird and other wildlife species that live in the area.