The indigo bunting (Passerina cyanea) is a small seed-eating bird in the cardinal family, Cardinalidae.

This timing, which is consistent with fossil evidence, coincides with a late-Miocene cooling, which caused the evolution of a variety of western grassland habitats.

Evolving to reduce size may have allowed buntings to exploit grass seeds as a food source.

[11] 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.

First year birds also tend to have a fleshy, yellow gape in the corner of the mouth, apparent in all months except October and November.

[14] As indicated by data collected from Charles H. Blake from his banding experiments in Hillsborough, NC, the Indigo Bunting has a weighted annual survival rate of 0.585.

[16] The habitat of the indigo bunting is brushy forest edges, open deciduous woods, second growth woodland, and farmland.

[17] Increases in population size have been seen in the event of forest clearings and development of land into farms.

Each male has a single complex song,[13] which he sings while perched on elevated objects, such as posts, wires, and bush-tops.

Only a small percentage of buntings remain as summer residents instead of migrating (7.2% of banded birds in Burke's observation).

Research indicates that indigo buntings placed in funnel cages outside on cloudless autumn nights or in artificial planetariums made more southern directional choices.

When introduced to increasingly overcast nights, many bunting's abilities to distinctively make southern directional changes decreased, possibly indicating a negative correlation between Zugunruhe and cloud coverage.

Prior experiments removing certain constellations and stars (Big Dipper, Cassiopeia or Polaris) from the sky had minimal effect on Zugunruhe.

[18] Quantitative methods of estimating flight range instead look at metabolic rates of the bunting and how much fat it has to use as fuel.

With an average speed of 20 mph, 5 extra grams of fat (47.5 kcal of energy) extends a bunting's range to six hundred and eighty-eight miles (1,107 km).

Most pairs raise two broods per year, and the male may feed newly fledged young while the females incubate the next clutch of eggs.

[22] In winter, it often feeds in flocks with other indigo buntings, but is a solitary feeder during the breeding season.

[13] During the breeding season, the species eats seeds of grasses and herbs, berries, spiders and insects, including caterpillars, grasshoppers, true bugs, and beetles.

[22] The indigo bunting does not drink frequently, generally obtaining sufficient water from its diet.

[13] Indigo bunting nests are vulnerable to a variety of climbing and flying predators, including Virginia opossum (Didelphis virginiana), red fox (Vulpes vulpes), domestic cat (Felis catus), blue jay (Cyanocitta cristata), eastern racer (Coluber constrictor) and raccoon (Procyon lotor).

[19] The species is classified as being of least concern according to the International Union for Conservation of Nature, with an estimated range of 5,900,000 km2 (2,300,000 sq mi) and a population of 28 million individuals.