The American robin is active mostly during the day and assembles in large flocks at night. Its diet consists of invertebrates (such as beetlegrubs, earthworms, and caterpillars), fruits, and berries. It is one of the earliest bird species to lay its eggs, beginning to breed shortly after returning to its summer range from its winter range. The robin's nest consists of long coarse grass, twigs, paper, and feathers, and is smeared with mud and often cushioned with grass or other soft materials. It is among the earliest birds to sing at dawn, and its song consists of several discrete units that are repeated.
The adult robin's main predators are hawks, domestic cats, and snakes. When feeding in flocks, it can be vigilant, watching other birds for reactions to predators. Brown-headed cowbirds (Molothrus ater) lay eggs in robin nests (see brood parasite), but the robins usually reject the eggs.
This species was first described in 1766 by Carl Linnaeus in the twelfth edition of his Systema Naturae as Turdus migratorius. The binomial name derives from two Latin words: turdus, "thrush", and migratorius from migrare "to go". The term robin for this species has been recorded since at least 1703. There are about 65 species of medium to large thrushes in the genus Turdus, characterized by rounded heads, longish pointed wings, and usually melodious songs. A study of the mitochondrialcytochrome bgene indicates that the American robin is not part of the Central/South American clade of Turdus thrushes; instead it shows genetic similarities to the Kurrichane thrush, T. libonyanus, and the olive thrush, T. olivaceus, both African species. This conflicts with a 2007 DNA study of 60 of 65 Turdus species which places the American robin's closest relative as the rufous-collared thrush (T. rufitorques) of Central America. Though having distinct plumage, the two species are similar in vocalization and behavior. Beyond this, it lies in a small group of four species of otherwise Central American distribution, suggesting it recently spread northwards into North America.