Song thrush thrush recognizes the cuckoo's non-mimetic eggs. However, the song thrush does not demonstrate the same aggression toward the adult cuckoo that is shown by the blackbird. The introduced birds in New Zealand, where the cuckoo does not occur, have, over the past 130 years, retained the ability to recognise and reject non-mimetic eggs. Adult birds may be killed by cats, little owls and sparrowhawks, and eggs and nestlings are taken by magpies, jays, and, where present, grey squirrels. As with other passerine birds, parasites are common, and include endoparasites, such as the nematode "Splendidofilaria (Avifilaria) mavis" whose specific name "mavis"
Swainson's thrush Swainson's thrush Swainson's thrush ("Catharus ustulatus"), also called olive-backed thrush, is a medium-sized thrush. It is a member of genus "Catharus" and is typical of it in terms of its subdued coloration and beautiful voice. Swainson's thrush was named after William Swainson, an English ornithologist. The genus name "Catharus" comes from the Ancient Greek "katharos", "pure or clean" and refers to the plumage of the orange-billed nightingale-thrush "C. aurantiirostris". The specific "ustuatus" is Latin for "burnt", from "urere", "to burn". The breeding habitat of Swainson's thrush is coniferous woods with dense undergrowth across Canada, Alaska, and the northern United States;