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 as nuclear β-fibrinogen intron 7 sequence data shows that Swainson's thrush is the most ancient North American species of its genus; it is not closely related to other "Catharus" and the outward similarities with the other North American species are due to convergent evolution. 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