A feral cat is a domestic cat that was raised in the wild, without having experienced significant human contact. Feral cats differ from stray cats, in that strays were previously pets which became nomadic. Unlike strays, feral cats initially show hostility towards humans, particularly upon first contact. Feral cats may become invasive to ecosystems, particularly on insular islands, resulting in a decline in biodiversity. Non-indigenous feral cats often have few natural predators, and prey on local species unaccustomed to defending against cats. Ground nesting birds, small native mammals and even amphibian species are often impacted by invasive populations of feral cats, and have led to extinctions of these species in some cases.