Learning to Sing: Indigo Bunting

A male indigo bunting (Passerina cyanea) arrived on Owl Acres in early May after a long nocturnal trek from the Caribbean. He decided to stay and began singing his song to attract a mate. I’ve thought that a bird’s song was something hard-wired into his brain, and therefore all indigo buntings should sound the same. This assumption on my part is wrong. Birds, particularly songbirds like the indigo bunting, have regional dialects, and neighborhood accents. They learn their songs from their neighbors. A young male starting out in a neighborhood of buntings comes with his own unique song, one perhaps learned at his father’s knee. Rather than tout his individuality, though, he quickly changes his song to match the songs of other male indigo buntings in his new locale. Over his lifetime (on average two to three mating seasons) he may change his songs again to match new neighbors. As an older male, he may bring his own songs to the neighborhood to be copied by the youngsters. Like the folksongs we humans love and change and adapt, the indigo bunting songs morph over time as populations mix and change with the seasons. These changes are, of course, subtle. The generic song of the male indigo bunting is a series of couplets which birdwatchers call “sweet sweet, chew chew”. It’s more complex than that, though.

Another change for the male indigo bunting is more straightforward. When he molts to prepare for the breeding season, he puts on beautiful blue body feathers on his back and underside. The wings and tail feathers are black, and the feathers on his head are a darker blue.

Like most other blue birds, the gorgeous blue of the male indigo bunting is not created with pigments. Instead, it is a trick of the light. Structures in the feathers scatter the light, reflecting short blue wavelengths back to the observer. This is similar to the way that light scatters to create a blue sky even though there’s nothing really blue up there. After the breeding season, the male indigo buntings replace their magic blue feathers with plain brown ones that match the female’s garb.

The female indigo bunting selects the nest site. She builds her nest along railroad tracks, roads and field edges in low shrubs near the ground. Gathering leaves, stems, grasses and strips of bark, she spends up to eight days weaving her cup-shaped nest. When all is ready, she will lay three or four eggs. She’ll incubate and hatch her brood, feed them and clean up after them by removing their fecal sacs from the nest. She’ll send the nestlings out into the world when they’re less than two weeks old. At this point, she may mate with the same or another male and raise a second brood before it’s time for her Caribbean vacation.

During the breeding season, indigo buntings eat a lot of insects and spiders. They are fond of caterpillars, grasshoppers, bugs, beetles and small arachnids. They also enjoy grass seeds and berries. In the winter they flock together and eat some insects, but their primary food is grass seeds and seeds in rice fields.

Indigo bunting nests are vulnerable to predators including raccoons, snakes, foxes, and cats. When a nest is threatened, the adult may fake an injury and try to lead the predator away from the nest. She’ll call out as she goes, trying to keep the attention on herself instead of the nest. Hopefully she can fly away at the last minute.

The indigo buntings on Owl Acres will head south again in September.  If they survive the thousands of miles of travel and the hazards along the way, I’ll listen for their songs next spring. Perhaps there will be new cadences.

Photo from Wikimedia.org by lwolfartist. Alt text: Songbird sits on a sunflower bud.  Indigo Bunting has a solid, deep blue color