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 egg.