Bermuda's wildlife is limited to those species which were able to fly to the island or were carried by winds and currents. This has resulted in some groups such as mammals being poorly represented. Once on the island, organisms had to adapt to local conditions such as the climate, lack of fresh water, frequent storms and salt spray. The islands shrank as water levels rose at the end of the Pleistocene epoch and fewer species were able to survive in the reduced land-area.
Today the variety of species on Bermuda has been greatly increased by introductions, both deliberate and accidental. Many of these introduced species now pose a threat to the native flora and fauna.
At the time of the first human settlement, Bermuda was dominated by forests of Bermuda cedar (Juniperus bermudiana). By the 1830s, the shipbuilding industry had denuded the landscape, but the forest was able to recover. In the 1940s the cedar forests were devastated by introduced scale insects which killed roughly 8 million trees. Replanting using resistant trees has taken place since then but the area covered by cedar is still only 10% of what it formerly was. Another important component of the original forest was Bermuda palmetto (Sabal bermudana), a small palm tree which now only grows in a few small patches, notably at Paget Marsh. Other trees and shrubs include Bermuda olivewood (Cassine laneana) and Bermuda snowberry (Chiococca bermudiana). There are remnant patches of mangrove swamp around the coast and at some inland sites where black mangrove (Avicennia nitida) and red mangrove (Rhizophora mangle) grow.
Bermuda has four endemic ferns: Bermuda maidenhair fern (Adiantum bellum), Bermuda shield fern (Goniopteris bermudiana), Bermuda cave fern (Ctenitis sloanei) and Governor Laffan's fern (Diplazium laffanianum). The latter is extinct in the wild but is grown at Bermuda Botanical Gardens. The endemic flora of the island also includes two mosses, ten lichens and forty fungi.
There are no native amphibians but two species of whistling frog (Eleutherodactylus) and the Cane Toad have been introduced. All three are declining and one species, Eleutherodactylus gossei, has probably already disappeared.
There is one endemic species, the Bermuda Petrel or Cahow (Pterodroma cahow). There is also an endemic subspecies, the Bermuda White-eyed Vireo or Chick-of-the-village (Vireo griseus bermudianus). The national bird of Bermuda is the White-tailed Tropicbird or Longtail which is a summer migrant to Bermuda, its most northerly breeding site in the world. Other native birds include the Eastern Bluebird, Grey Catbird and perhaps the Common Ground-Dove. The Common Moorhen is the commonest native waterbird with very small numbers of American Coot and Pied-billed Grebe breeding. Small numbers of Common Tern nest around the coast. The Barn Owl and Mourning Dove colonized the island during the 20th century and the Green Heron has recently begun to breed.
Of the introduced birds, the European Starling, House Sparrow, Great Kiskadee, Rock Dove and American Crow are all very numerous and considered to be pests. Other introduced species include the Mallard, Northern Cardinal, European Goldfinch and small numbers of Orange-cheeked and Common Waxbills. The Yellow-crowned Night Heron was introduced in the 1970s to replace the extinct native heron.
Fossil remains of a variety of species have been found on the island including a crane, an owl and the Short-tailed Albatross. Some of these became extinct as the islands' land-mass shrunk while others were exterminated by early settlers. The Bermuda Petrel was thought to be extinct until its rediscovery in 1951.
Among the many non-breeding migrants are a variety of shorebirds, herons and ducks. In spring many shearwaters can be seen of the South Shore. Over 30 species of New World warbler are seen each year with the Yellow-rumped Warbler being the most abundant. The arrival of many species is dependent on weather conditions with low-pressure systems moving across from North America bringing many birds. Among the rare visitors to have occurred are the Siberian Flycatcher from Asia and the Fork-tailed Flycatcher and Tropical Kingbird from South America.
More than 1100 kinds of insect and spider are found on Bermuda including 41 endemic insects and a possibly endemic spider. 18 species of butterfly have been seen, about six of these breed including the large Monarch butterfly and the very common Bermuda buckeye (Junonia coenia bergi). More than 200 moths have been recorded, one of the most conspicuous is Pseudosphinx tetrio which can reach 9cm in length.
Bermuda has lost a number of its endemic invertebrates including the Bermuda cicada (Tibicen bermudiana) which became extinct when the cedar forests disappeared. Some species feared extinct have been rediscovered including the Bermuda land snail (Poecilozonties circumfirmatus) and the Bermuda ant (Odontomachus insularis).
Bermuda lies on the western edge of the Sargasso Sea, an area with high salinity and temperature and few currents. Large quantities of seaweed of the genus Sargassum are present and there are high concentrations of plankton but the area is less attractive to commercial fish species and seabirds.
Greater diversity is present in the coral reefs which surround the island.
A variety of whales, dolphins and porpoises have been recorded in the waters around Bermuda. The commonest of these is the Humpback Whale which passes the islands in April and May during its northward migration.