The wildlife refuge preserves habitat for the largest remaining population of the endangered Saint Croix ground lizard.

Much smaller populations of ground lizards live on nearby Protestant Cay (17°44′59″N 64°42′10″W / 17.74972°N 64.70278°W / 17.74972; -64.70278) and on Ruth Island.

Its extirpation from the mainland of Saint Croix is generally attributed to the introduction of the small Indian mongoose.

In 2008, the National Park Service reintroduced the lizard to Buck Island, translocating 57 individuals from Green Cay.

[1] Green Cay has, along with the nearby Southgate Coastal Reserve, been recognised as an Important Bird Area (IBA) by BirdLife International because they support populations of green-throated caribs, Antillean crested hummingbirds, American coots, brown pelicans, laughing gulls, least terns, royal terns, Caribbean elaenias and pearly-eyed thrashers.