This entry is part 5 of 6 in the series RAINBOW

Indigo Buntings

One of the most distinctive birds of the Americas is the indigo bunting.

Named for its resemblance to an ancient dye, the bird can be brilliantly colored.

Indigo is the black sheep of the ROYGBIV colors. Is it closer to blue or purple? Is it even a distinct color? In the development of the visible color spectrum, Isaac Newton introduced indigo and orange to the five established hues, allowing the colors to mimic the seven musical notes, as thinkers of the time intensely associated sound and light. So, we could view indigo as a completely fabricated building block.

The bunting looks closer to blue, as does the eponymous dye. Confusingly, though, some “indigo” designations for computer representation are violet, while others are blue. Crayola’s “indigo” is purplish, too.

Despite resembling the dye, the indigo bunting actually contains no blue in its feathers.

Like many other blue things in nature, its appearance arises because of the way light scatters from its body. The bunting’s feathers absorb everything but indigo and blue, so that’s what we see.

A passerine member of the family Cardinalidae, buntings are related to cardinals, grosbeaks, tanagers, and sparrows. A small-ish songbird, usually between four and six inches long, the indigo bunting produces a call that sounds like “sweet-sweet chew-chew sweet-sweet.”

The species displays sexual dimorphism, as only the males exhibit bright colors, but they only do so during the breeding season. During the winter, the males turn brown, appearing the same color as females.

The birds spend their summers across much of the southern and eastern United States, as well as southern Canada.

They head south for the winter, spending the colder months in Mexico, Central America, and the Caribbean.

In the 1960s, indigo buntings were part of a revolutionary experiment about avian migration.

Buntings migrate during the night. Experiments had shown that they used stars to orient themselves in the proper direction. They could find south when the night sky was the only thing they could see; likewise, on cloudy nights, they had trouble pointing in the proper direction.

Ecologist Stephen Emlen devised an ingenious test to see what the birds utilized in the firmament to provide guidance. Using a funnel-shaped contraption that could show the birds exactly what Emlen wanted, he placed an inkpad at the bottom to follow the bunting’s tracks. Through a series of trials and guesses, Emlen discovered that the buntings don’t use specific constellations or stars, but rather the way that all the constellations and stars rotate around Polaris. And it wasn’t dependent on Polaris, either. Using juvenile birds that had never migrated, he devised a way to make Betelgeuse the North Star. The birds, once again, watched how the rest of the sky rotated around this point and were able to fly south.

Somehow, buntings and other night migrants are hard-coded to look for rotation, which allows them to fly to the right spots even when the Sun isn’t shining!