In addition to their feeding on the ground, thrushes usually remain close to the ground most of the time, staying under the cover of forest or scrub. In order to find invertebrates, animals without a backbone, to eat, they scratch with their feet and turn over dead leaves and other debris with their bills. Thrushes and chats tend to be territorial birds during breeding, using their song to attract mates and to warn off any males that might be intending to interfere in their territory. In winter and for migration, some species form into large flocks. Thrushes prefer the shelter of warm and dry spots at night. Non-breeding birds might roost alone; many roost in communes; and still others are known to roost in groups of hundreds. The fieldfare has been observed roosting in flocks of 20,000—a mixed-thrush group found roosting in France one winter held 200,000 birds. Such roosts for all of these birds tend to be in dense thickets with temperatures even both inside and out, with minimum exposure to wind or other elements. The rock thrushes do roost alone in rock crevices or in high tree branches, and sometimes even inside the roofs of old, secluded buildings. Ring ouzels also roost alone, but among rocks and boulders.
Breeding begins when the birds are one year old, and these birds tend to remain monogamous (muh-NAH-guh-mus; having only one mate) for the mating season. On occasion, both male and female might mate with others. The males sing during the breeding season, usually perched in a visible spot or in the tree canopy.
The typical nest is shaped as an open cup that has been lined with grassy material and sticks. Sometimes mud is used to hold it together better. Some nests are placed in trees or other objects—American robins are known to place nests in the rafters of old buildings, or even into the secure roofs of porches and doorways, including such unusual places as traffic lights, or in boats or cars that are in regular use so they can access the nest freely. Some species build their nest on the ground or in tree cavities. The female is almost entirely responsible for building the nest, and it is usually preserved for a second brood of birds. The clutch can number from two to ten eggs, though it is usually four to five. One female incubates (warms enough for hatching) the birds for ten to seventeen days. Many species have two broods per year, and some have three or more. Survival of the chicks can often be at risk. All but one or two of a large brood might survive, with the others dying through disease, predators, starvation, or accident.
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