The islands are covered with a dense scrub. The northern and southern islands are more fertile than those in the central group, and the eastern islands generally are more fertile than the western. Coconut, breadfruit, plantain, papaya, mango, and banyan trees flourish. Shrubs and flowers are widespread. Rats, rabbits, and flying foxes are the only indigenous mammals. Birds include ducks, bitterns, crows, curlews, snipes, and various sea birds. Small scorpions, beetles, and land crabs are common. Inland lagoons and coastal reefs contain tropical ocean fish, crustaceans, and turtles; the surrounding waters contain sharks, swordfish, and porpoises.