Invasive species are animals or plants that are nonnative to the region that were introduced by human intervention. Invasive species are animals and plants introduced by human activities as follows: (1) accidentally as "stowaways" on ships (rats and mice) and planes (brown tree snakes) or following escape from captivity (e.g., gray squirrels in the United Kingdom) or thoughtlessly released (e.g., pet Burmese pythons released into the Everglades in the USA); (2) deliberately introduced for esthetics (e.g., starlings), as game species (e.g., deer), for biological control, or for fur; and (3) as populations of feral domestic animals (e.g., camels, cats, dogs/dingos, donkeys, horses, and rabbits). Invasive mammals have a severe impact on the environment. Free-roaming, unowned, and feral cats impact the environment, killing, for instance, 12.3 billion mammals and 2.4 billion birds in the contiguous 48 States of the USA. Damage from dingos and other wild dogs in Australia is reported to be A$48.5 million per year while those from rabbits is estimated at A$206 million per year. Excluding the damage they create as pests, rodents have a dramatic effect on the environment with island habitats that are important breeding sites for seabirds being especially vulnerable to rats. Mitigation programs have been implemented in over 400 islands. It was assumed that the introduction of house mice had little significant effect on ecosystems and particularly birds breeding, but mice have been observed killing and eating chicks of Tristan albatrosses and Atlantic petrels. The gray squirrel is the second most damaging introduced species in the British Isles (after the Norway rat). Gray squirrels have also out-competed the native red squirrel in much of the United Kingdom leading to the decline and replacement of the latter. Wild pigs are responsible for $0.8 billion dollars per year in losses and damages in the USA. Feral donkeys (5 million) and horses (400,000) are another source of damage. Birds are also damaging invasive species. For example, about a hundred European starlings were introduced to the USA and today there are about 200 million starlings across the country. Losses and damages from feral pigeons in the USA are estimated at $1.1 billion dollars per year. Burmese pythons in the Everglades of Florida are decimating wildlife with bobcats, raccoons, and rabbit populations decreased by, respectively, 87.5, 99.3, and 100%. The brown tree snake grew from a female stowaway on a plane to a population of over 2 million in 1980. Electrical system damage alone is estimated at $1.7 billion per year. There are also amphibian (Cane toad), aquatic (e.g., sea lamprey, alewife, zebra mussel, and quagga mussel), and insect invasive species; the latter including Africanized or killer bees.