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Human beings have introduced other species around the world both accidentally and intentionally. Accidental introductions resulted from escape from captivity (monk parakeets [Myiopsitta monachus] in Florida), stowaways (rats [Ranus spp.] and house mice [Mus musculus] worldwide; brown tree snakes [Boiga irregularis] in Guam), or expansion of species' ranges. Intentional introductions occurred for various reasons including: 1) aesthetics (songbirds into Hawaii, grey squirrel [Sciurus carolinensis] into Europe, and European songbirds imported by British colonists into North America, Australia, and New Zealand); 2) economics (nutria [Myocastor coypus] introduced in the eastern US., and Arctic fox [Alopex lagopus] onto Aleutian Islands for development of fur industries); 3) recreation (pheasants [Phasianus colchicus] and cbukar [Afectoris chukar] introduced as game species from Asia to North America, and red deer [Cervus elaphus] introduced into New Zealand); 4) food (domestic livestock worldwide, rabbits [Oryetolagus cunniculus] into Australia, pigs [Sus scrofa] into Hawaii); 5) for biological control (mongooses [Herpestes auropunctatus] to control rats in Hawaii, fox [Vulpes vulpes] to control rabbits in Australia, and giant toad [Bufo marinus] to control cane beetles in Australia); or 6) releases from captive populations (bulbuls [Pycnonotus jocosus] in Florida and domestic ferrets [Mustela putorius] in California, mink [Mustela vison] and muskrat [Ondntra zibethicus in Europe, and horse [Equus caballus], donkey [Equus minus], and other ungulates into Australia and western North America). The majority of biological introductions fail. Of those that succeed, only a small fraction become serious pests. Many introductions, like livestock or pheasants into the US., have been generally beneficial; however, some introduced species become invasive, defined as nonnative species which cause substantial economic or ecological h m . The U.S. has at least 221 nonnative terrestrial vertebrate species and New Zealand has 35 introduced birds and 33 mammals, where previously the only mammals consisted of 3 bats.  About 44 mammals have been introduced into Australia, of which 27 have become established, 13' along with 3 species of amphibians and reptiles and numerous birds. Ten species of terrestrial mammals on the Galapagos are aliens.