The first white settlers, who arrived early in the 19th century, found a type of dog and a black rat, both of which had been brought by the Maori about 500 years earlier. The only wild mammals at present are descended from deer, rabbits, goats, pigs, weasels, ferrets, and opossums—all of which were imported. No snakes and few species of insects inhabit New Zealand. The tuatara, a lizardlike reptile that emerged more than 200 million years ago, survives exclusively on a few islands off the coast of New Zealand.It has a large population of wild birds, including 23 native species. Among the native species are songbirds, including the bellbird and tui, and flightless species, including the kiwi, kakapo, takahe, and weka. The survival of the flightless birds is attributed to the absence of predatory animals. The sparrow, blackbird, thrush, skylark, magpie, and myna are well-acclimated imported species. New Zealand abounds in a great mixture of seabirds and numerous migratory birds.