The indigo bunting averages ﬁve and one-half inches in length (tail tip to bill tip in preserved specimen). The female has brown feathers. The male has brilliant blue feathers in breeding season and a mixture of brown and blue feathers the rest of the year.
The indigo bunting is a common migrant and summer resident statewide and a rare winter resident in the southern one-third of Illinois. A bird of open areas, it can be found in cultivated ﬁelds but is more common near bottomland forests. Its song can be heard throughout the day in the spring and summer. The song includes different pitches usually with paired notes, like “sweet-sweet” or “chew-chew.” The indigo bunting migrates at night, with spring migrants beginning to arrive in April. The males arrive before the females. The breeding season occurs from May through mid-August. The nest is built by the female in dense vegetation close to the ground and composed of dried grasses, bark strips, twigs and other plant materials. It is lined with grasses, rootlets, hair and feathers. The female may use a snake skin in the nest base. Three or four, pale-blue eggs are deposited by the female, and she alone incubates them over the 12- to 13-day incubation period. Two broods may be raised in one year. The nest is often parasitized by the brown-headed cowbird that deposits an egg that the indigo bunting will hatch and raise, taking food and care away from its own young. Fall migrants begin arriving in Illinois in mid-August. Most indigo buntings winter from Central America to Colombia in South America, although a few have been seen in the winter in the southern one-third of Illinois. This bird eats insects, fruits and seeds.