Wednesday, June 12, 2024

Young male indigo buntings have brownish patches mixed in with their blue feathers. (Photo: Karl Niemi)

In “A Report on the Birds of Massachusetts Made to the Legislature in the Session of 1838-9,” W. B. O. Peabody reports:

The Indigo Bird … is a spirited and beautiful summer resident, where, from the tops of trees, from roofs, and chimneys and lightning rods, we hear his sweet lisping song, which at first is exceedingly pleasant, but at length wearies the ear by its perpetual repetition throughout the summer day.

Known for both their ceaseless singing and their color, most indigo buntings begin arriving in Massachusetts in mid-May. Some males may arrive as much as a month earlier, though. Indigo buntings migrate at night, using the stars’ rotation to help them find their way. In 1967, a Cornell scientist placed three groups of indigo buntings inside a large cage inside a planetarium. One group was placed in the planetarium under stars that performed a normal rotation around the North Star. These birds oriented themselves away from the North Star, in the appropriate southern direction for migration. Birds that were exposed to stars with no rotation or rotation around a different star migrated in different patterns. This experiment showed that migratory birds rely on the rotational pattern of the stars to find their way north or south.

Indigo bunting females, winter males and young are tawny brown. (Photo: Tom Murray)

Indigo buntings, like other birds that migrate at night, begin their flights at sunset or slightly later. These birds appear to use polarized light patterns to provide information about their initial flight direction as they begin their nightly journey.

In May, these brightly blue-colored and conspicuous male migrants set up territories, where, to attract females, they sing for hours and hours from high branches. Young males modify their song to sound like the songs of older males, so eventually all the males in an area sing songs that sound similar. The brown female migrants arrive almost unnoticed because they spend their days hidden quietly in dense vegetation.

An indigo bunting at Horn Pond on May 24. (Photo: Karl Niemi)

These 5-inch birds prefer edges of woodlands next to bushy fields, overgrown pastures or power lines to set up breeding territories. Females build nests in low shrubs or berry bushes. You can tell you are nearing a nest because the male and female make a chip call when you get about 40 feet away.

When the female lays eggs (about three or four), the male stays close by; once she starts incubating the eggs, he travels farther to feed and to sing. The female incubates the eggs for about 10 days. Then she cares for the youngsters by herself, while the male guards the nest area from predators.

An indigo bunting in Groton in September 2022. (Photo: Tom Murray)

The young are altricial, which means they do not have down when they are born and require significant care. After four or five days, the young open their eyes. After six days, they sport feathers. The young leave the nest after about 10 days. The male and the female feed these fledglings for a few weeks. The youngsters stay hidden in the brush, calling so the parents can find them.

At this point, the female might lay a second set of eggs and the male becomes the sole provider for the fledglings. The youngsters remain near the parents until the family is ready to migrate south. From August to October, these birds migrate due south about 1,200 miles to southern Florida, the Caribbean or northern South America.

An indigo bunting surveys the scene in Cambridge. (Photo: Brian Rusnica)

At the end of the breeding season, the adult male and female molt; the male loses his bright blue breeding feathers for tawny brown winter feathers which makes the name indigo bunting a bit misleading. Even during breeding season, only parts of the head are the deep purplish blue of true indigo, and the rest of his body is a lighter cerulean blue.

Like all blue birds, there is actually no blue pigment in the feathers of the indigo bunting. These birds appear blue because of the way light is reflected and refracted from complex microscopic structures in the feathers.

In North Cambridge, an indigo bunting is well hidden in the leaves on Sept. 29, 2022. (Photo: Richard George)

Indigo buntings are easier to spot than many other birds because the blue male stands out against the trees and because the male likes to find the highest perch from which to sing – and then remains in this spot for long periods. Other birds might dart about in the shadows, but once you hear an indigo singing, just look up high.

As ornithologist Edward Howe Forbush observed:

The male seems to delight in singing during the hottest part of the summer days, when other birds are resting in the shade. He will sing his way from the bottom of a tree to the top, going up branch by branch until he has reached the topmost spire, and there, fully exposed to the blazing sun, he will sing and sing and sing.

A singing indigo bunting in Pepperell on May 17, 2021. (Photo: Tom Murray)

whitespace

Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.


Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.