The Indigo bunting is a small seed-eating bird in the cardinal family that is found in the Americas. During the breeding season, the adult male appears mostly a vibrant cerulean blue. Only the head is indigo. The wings and tail are black with cerulean blue edges. In fall and winter plumage, the male has brown edges to the blue body and head feathers, which overlap to make the bird appear mostly brown. The adult female is brown on the upper parts and lighter brown on the underparts. It has indistinct wing bars and is faintly streaked with darker markings underneath. The immature bird resembles the female in coloring, although a male may have hints of blue on the tail and shoulders and have darker streaks on the underside. In the adult female, the beak is light brown tinged with blue, and in the adult male, the upper half is brownish-black while the lower is light blue.
Indigo buntings breed from southern Canada to Maine, south to northern Florida and eastern Texas, and westward to southern Nevada. They are migratory and their winter range begins in southern Florida and central Mexico and stretches south through the West Indies and Central America to northern South America. Indigo buntings prefer to live in brushy forest edges, open deciduous woods, second-growth woodland, and farmland.
Indigo buntings are active during the day foraging for food on the ground or in trees or shrubs. In winter, they often feed in flocks with other Indigo buntings but are solitary feeders during the breeding season. These small birds communicate with each other through vocalizations and visual cues. A sharp 'chip!' call is used by both sexes and is used as an alarm call if a nest or chick is threatened. A high-pitched, buzzed 'zeeep' is used as a contact call when the Indigo bunting is in flight. The song of the male bird is a high-pitched buzzed 'sweet-sweet chew-chew sweet-sweet', lasting two to four seconds, sung to mark his territory to other males and to attract females. Each male has a single complex song, which he sings while perched on elevated objects, such as posts, wires, and bush-tops. In areas where the ranges of the Lazuli bunting and the Indigo bunting overlap, the males defend territories from each other. Migration usually takes place in April and May and then again in September and October. Indigo buntings often migrate during the night, using the stars to navigate. They do not rely on individual stars or the general brightness of groups of stars but instead use them as clues in navigation.
Indigo buntings are carnivores (insectivores) and herbivores (granivores). During the breeding season, they eat insects, seeds, and berries, including caterpillars, grasshoppers, spiders, beetles, and grass seeds. The seeds of grasses are the mainstay of their diet during the winter, although buds, and insects are eaten when available. The young are fed mainly insects at first, to provide them with protein. Indigo buntings do not drink frequently, generally obtaining sufficient water from their diet.
Indigo buntings are generally monogamous but not always faithful to their partner. Pairs usually nest in dense shrubs or low trees, 0.3-1 m (0.98-3.28 ft) above the ground, but rarely up to 9 m (30 ft). The nest itself is constructed of leaves, coarse grasses, stems, and strips of bark, lined with soft grass or deer hair, and is bound with spider web. It is constructed by the female, who cares for the eggs alone. The clutch consists of 1 to 4 eggs but usually contains 3 to 4. The eggs are white and usually unmarked, though some may be marked with brownish spots. The eggs are incubated for 12 to 13 days and the chicks are altricial at hatching; they are blind and helpless and fledge 10 to 12 days after hatching. Most pairs raise two broods per year, and the male may feed newly fledged young while the female incubates the next clutch of eggs.
Indigo buntings play an important role in their ecosystem. They help control the populations of the insects they eat and help distribute seeds of the plants and berries. In turn, these small birds also serve as food for other animals such as opossums, Red foxes, snakes, raccoons, and others.
According to All About Birds resource, the total breeding population of the Indigo bunting is 78,000,000 individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List but its numbers today are decreasing.