During the winter months, the refuge supports peak populations of over 300,000 ducks and geese. Large wintering concentrations of white-fronted and snow geese can be found here. Pintail, blue-winged and green-winged teal, mallards, ring-necked ducks, gadwalls, and American wigeon are common on the refuge during the winter months. Breeding populations of black-bellied whistling-ducks, wood ducks, and blue-winged teal are found on the refuge during the summer months.
A variety of wading birds are common on the refuge, particularly during the breeding season. The first American nesting colony of cattle egrets outside of Florida was found here. One of the only roseate spoonbill nesting rookeries in Louisiana is located in Lacassine Pool, a 16,000 acre freshwater impoundment found on the refuge. Other common marsh and water birds include neotropic cormorants; anhingas; great blue, tricolored, and little blue herons; great and snowy egrets; black-crowned and yellow-crowned night herons; white and white-faced ibises; king rails; American coots; common moorhens; purple gallinules; and black-necked stilts. A complete refuge bird list is available online or in brochure format.
The refuge also provides suitable habitat for armadillos, swamp rabbits, fox squirrel, nutria, mink, otters, raccoons, coyotes, white-tailed deer, and a large population of American alligators. Numerous fish, frog, turtle, and snake species can also be found on the refuge.
Lacassine NWR offers numerous wildlife observation/photography opportunities. A wildlife Drive and two obervation platforms are open year-round. A calendar of wildlife events is available online to provide refuge visitors with a general guide to seasonal events on the refuge.