Commissioned by President Theodore Roosevelt in 1909, Refugio Nacional de Vida Silvestre de Culebra is one of the nation's oldest wildlife refuges. Some 1,500 acres of the island make up a protected area. It's a lure for hikers and bird-watchers: Culebra teems with seabirds, from laughing gulls and roseate terns to red-billed tropic birds and sooty terns. Maps of trails in the refuge are hard to come by, but you can stop by the U.S. Fish & Wildlife Service office east of the airport to find out about trail conditions and determine whether you're headed to an area that requires a permit. The office also can tell you whether the leatherback turtles are nesting. From mid-April to mid-July, volunteers help monitor and tag these creatures, which nest on nearby beaches, especially Playa Resaca and Playa Brava. If you'd like to volunteer, you must agree to help out for at least three nights.