The refuge's habitats — bottomland hardwood forest, freshwater and brackish marsh, lagoons, canals, and bayous — provide for the needs of 340 species of birds. Thousands of waterfowl use the refuge in late winter and spring. Wading birds are seen year-round. For many neotropical migrant birds, the refuge is the last stop-over on the Mississippi Flyway before they cross the Gulf of Mexico. The marshes along Lakes Pontchartrain and Borgne serve as estuarine nurseries for fish and crabs. Freshwater lagoons, bayous and lakes produce largemouth bass, crappie, bluegill, catfish, and crawfish. American alligators are frequently seen.