Indigo Bunting Photo courtesy of USGS

Every April, gorgeous blue birds arrive in Evanston yards and parks. Breeding male Indigo Buntings and Eastern Bluebirds are both decked out in brilliant blue feathers, and it is not unusual for casual observers to mistake one for the other. Read on to learn how to distinguish between these two beauties by appearance and behavior.

The Indigo Bunting (Passerina cyanea) is in the family Cardinalidae, along with the Northern Cardinal, Rose-breasted Grosbeak and the occasionally seen Blue Grosbeak. Members of the Cardinalidae family live only in the Western Hemisphere, many of them in Central and South America.

Indigo Buntings are stocky, sparrow-sized birds with short tails and silver-colored short, thick conical bills. Breeding males are entirely blue with a deeper blue head, and their wings may appear darker than the body. They breed from the Great Plains to the Atlantic coast and have lately been breeding in New Brunswick and Nova Scotia, possibly expanding their range north due to climate warming. Buntings can be found grubbing for insects, berries and seeds in weedy brush, at forest edges and along or on country roads.

In fall, before he migrates, the male molts most of his deep blue feathers and resembles the brown female. He may keep the blue feathers on his tail, wings and rump. At his winter home in Mexico, Central America, South Florida, Cuba or Jamaica, he will regain most of his exquisite blue. Buntings typically migrate north at night in small groups using star pattern as a guide, and “experienced” adults usually return to their old breeding sites.

A blue bird seen belting out a bright, cheerful song in spring is an Indigo Bunting. The male bunting will arrive in the Evanston area in mid-to-late April, about two weeks earlier than the dull-brown female. He may be in a coat of two colors, mostly blue but with some brown feathers that he will quickly lose. Upon arrival, he will start singing, often perched atop the tallest tree around. He will sing incessantly mornings and evening, moving down to a shrubby layer but still singing during the heat of the day. He will continue singing through spring and summer. Indigo Buntings learn their songs from older nearby males, which might account for neighborhood dialects. Indigo Buntings have been nicknamed “blue canaries.”

His mostly quiet all-brown mate constructs the nest alone, placing it in the crotch of a shrub. The open nest is positioned so that it is protected from the elements and hidden from view. Females are so elusive and their nests so well concealed that they have challenged attempts to study Indigo Bunting behavior. Indigo Buntings breed in Harms Woods.

The male Eastern Bluebird, in contrast to the spring male Indigo Bunting, is vivid blue only on its back and head. It is orange on its upper breast and flanks and white on its belly. The female is an elegant paler blue-grey with the same breast and flank pattern, plus a white eye-ring. Both sexes have small, thin, black bills and keep their plumage color during the year.

The Eastern Bluebird (Sialia sialis) is in the family Turdidae, (from the Latin for Thrush). Thrushes are found worldwide and are known for exquisite song, particularly the flute-like melodies of the Wood Thrush and the American Robin. The Eastern Bluebird’s song is softer and more subtle and rarely given from high treetops.

Eastern Bluebirds are found across eastern North America and as far south as Nicaragua. Some bluebirds are medium-distance migrants. Bluebirds breeding in Manitoba will fly 2,000 miles to Texas. Bluebirds breeding in the Chicago area may stay all winter or migrate short distances. Chicago-area Eastern Bluebirds have been counted on every recent Christmas bird count. During mild winters some can be found in the Indiana Dunes as well as in greater Chicago, sometimes in the vicinity of Illinois Beach State Park or Fort Sheridan.

Bluebirds are cavity nesters and willingly nest in man-made structures near buildings. When cavity-nesting Starlings and House Sparrows were introduced into the U.S., they competed for natural cavities sought after by other species, including bluebirds. The human response was to erect bluebird nest boxes, a successful venture that led to bluebirds breeding on golf courses, natural areas such as forest preserves, large farm fields, and bluebird “trails” along rural roadsides. Bluebirds eat insects and fruits. They often perch on a low branch, drop abruptly to the ground to capture an insect and then return to that same branch. They will also forage on grassy lawns, as will the Indigo Bunting. Because they are so accessible to people, unlike the Indigo Bunting, they are easily studied.

The usual picture of the exemplary behavior of the beloved bluebird is countered by Cornell’s Birds of North America Online, which says, “Despite their reputation as ‘sweet’ and ‘models of pacific family life,’ they are pugnacious in some situations, fighting most often with other species over access to nesting cavities. Not only males but females fight among themselves, and sometimes they kill each other over mates and nest sites.”

Ironically, neither the male Indigo Bunting nor the male Eastern Bluebird is actually “blue.” Blue feathers lack pigment, and their stunning color comes from the distribution and shape of air pockets, minute structures within the feather barbs that reflect, or scatter, only the short blue wavelengths of visible light, while absorbing the other wavelengths. Basically, this same light-scattering process makes the sky look blue. So even before modern science understood how blue feathers were produced, in his 1852 “Journal,” Henry David Thoreau could literally say, “The bluebird carries the sky on its back.”

Libby Hill is the author of "The Chicago River: a Natural and Unnatural History. She has been writing about birds and trees and Evanston's natural history for the Roundtable since 2004.