The Indigo Bunting — Passerina cyanea — is a species of small bird that is included in the family Cardinalidae. It lives a migratory lifestyle, with a range extending from northern Florida up to southern Canada during the breeding season, and from southern Florida to northern South America during the offseason/winter. The species travels primarily by night, using the constellations/stars of the night for navigation. The bird lives primarily within farmlands, open woodlands, and brush areas. The species is relatively closely related to the Lazuli Bunting, and the two species readily interbreed in the areas where their ranges overlap, such as in the Great Plains.
The Indigo Bunting is classified as a small bird, typically being less than a half foot in body length, with a wingspan of between 7-9 inches. And an average weight of between 0.40–0.75 ounces. The species displays significant sexual dimorphism with regards to its coloration — the males turn a strong blue color during the summer and are brown the rest of the year, while the females are brown year-round. The reasons for the color change during the summer are very likely related to sexual selection. Another notable fact is that the nest-building and incubation are done entirely by the females in this species, the males don’t participate. The birds are known to be generally monogamous, “but not always faithful to their partner. Most pairings raise two broods per year, and the male may feed newly fledged young while the females incubate the next clutch of eggs.” The diet of the Indigo Bunting is mostly based around insects during the summer, and seeds during the winter.
While the Indigo Bunting appears (on the surface) to be very similar to the aforementioned Lazuli Bunting, the two species actually diverged from one another quite awhile back — an estimated 4.1 and 7.3 million years ago.
The species has been known as a vagrant in “Antigua and Barbuda, Barbados, Denmark, Ecuador, Germany, Iceland, Ireland, Netherlands, the Netherlands Antilles, Saint Pierre and Miquelon, Serbia and the United Kingdom.”
The species appears to rely primarily on vocalizations and visual cues for communication. “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 another. Migration takes place in April and May and then again in September and October. The Indigo Bunting often migrates during the night, using the stars to direct itself. In captivity, since it cannot migrate, it experiences disorientation in April and May and in September and October if it cannot see the stars from its enclosure.”
“The Brown-headed Cowbird may parasitize this species. Indigo Buntings abandon their nest if a cowbird egg appears before they lay any of their own eggs, but accept the egg after that point. Pairs with parasitized nests have less reproductive success. The bunting chicks hatch, but have lower survival rates as they must compete with the cowbird chick for food.”