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Chicago Blues in Nature: Indigo Bunting and Eastern Bluebird

Indigo bunting in bright sunlight. Note iridescent plumage and dark wings, and no wing bars. The finch-like beak is also a key feature of the indigo bunting.
Indigo bunting in bright sunlight. Note iridescent plumage and dark wings, and no wing bars. The finch-like beak is also a key feature of the indigo bunting.
Christopher Cudworth

The city of Chicago, known for its urban Blues music, has competition out there in nature.

There is a singer in the suburbs that belts out music all day long, even through the heat of the afternoon and through the dog days of August. Many birders would not be surprised to hear the Indigo Bunting singing all through the night, it is that determined a singer.

You can recognize the song of the Indigo Bunting by its unique and consistent pattern, which if put in words sounds like this: "Seebit seebit-teew-teew--tsseet tseet-whe'wt-whe'wt."

Catching sight of an Indigo Bunting is a definite reward, but while the bird is often content to belt out its song from the middle of the woods, it is also frequently found in wood margins, near walking paths and along biking or prairie paths.

Male Indigo buntings often perch on open sunny branches where their iridescent plumage can dazzle the eye even against the bright blue background of a summer sky. The bird appears deep shimmery blue all over in bright light. Only its wings are darker plumage and can often appear blackish even in bright light. The Indigo bunting has no wing bars and sports a finchlike beak that it uses to eat both plant and insect food.

Female Indigo buntings are brown above, tan or streaked below. Even expert birders do not find as many females as male buntings in the wild. They are there, but their more secretive ways and brownish coloration are the product of evolutionary traits found in many species of birds, whose abilities in raising young are dependent on cryptic coloration and less demonstrative overall behavior.

Male Indigo buntings busy themselves singing to establish and protect their territories. Their arrival in May signals the beginning of breeding season in Illinois as surely as the song of robins. Indigo buntings are slightly more rural in their habitat tastes, typically breeding not in backyards but in local forest preserves where their song is one of the hallmarks of wooded, brushy habitat. In Illinois Indigo buntings keep summer company with other woodland bird species such as wood thrush, rose-breasted grosbeak, Eastern wood pewee, red-eyed vireo, white-breasted nuthatch, black-capped chickadee, blue-gray gnatcatcher, Eastern phoebe, and rufous-sided towhee.

Because Indigo buntings like a variety of wooded and brushy habitats, they often cross territory with another bluesy Illinois species of bird, the Eastern bluebird, which is where some people less familiar with birds can become confused. If the Indigo bunting is all blue, why isn't it called the "bluebird?"

It isn't that Eastern bluebirds got their first, or anything like that. Eastern bluebirds are most definitely blue, but not blue all over. When seen in bright sunlight, the blue on a male Eastern bluebird is equally remarkable to the human eye. In fact the blue back of an Eastern bluebird can look unreal at times. The pure cobalt blue on the back of a male Eastern bluebird contrasts strongly with its orangey-red breast and white underparts.

Truly there are few more beautiful birds in North America than the Eastern bluebird, whose character and temperament are as attractive as its coloration. Bluebirds are a generally non-aggressive species that loves the company of fellow bluebirds out of breeding season, but prefers to be left alone to mate and raise young during the summer months. As a result of their laid-back, leave-me-be approach, the Eastern bluebird struggled in population numbers thanks to the invasion of highly aggressive species such as European starlings, which kicked bluebirds out of the nest holes they preferred in trees.

To rescue bluebirds from extermination across much of North America, bluebird nesting box programs were begun, with houses designed especially to accommodate the size and needs of Eastern bluebirds. Still there were problems, as tree swallows, a species native to North America, also liked the bluebird boxes. But it was discovered through experimentation that placing dual boxes in habitat suitable for both species reduced competition between these two species. Tree swallows fought off other tree swallows, but did not object if bluebirds moved into the box next door. In the world of wild bird real estate, this might be known as bluelining. But that is a topic for a different day.

Wherever nesting bluebirds can be found, the females in their muted version of male plumage can be found. Female Eastern bluebirds have a pale orange breast, grayish back and largely blue wings and tail. In bright light female bluebirds can be just as striking as males, with a distinguishing feature of a clear white eye-ring a great field mark for the female.

Young Eastern bluebirds are charming representatives of the youthful bird world. They have a bright eye ring like the female, but their evolutionary roots in the thrush world are revealed in their juvenile plumage. The young exhibit a cascade of rich brown and white eyelets in rows down the front of the breast. They are often seen in the company of adults who wean them by feeding them insects through the summer months until the young are capable of fending for themselves.

The song of bluebirds is an almost subliminal uttering that has a muffled sound, yet is beautiful in its tone and scale. The "churhl churhlee chrurhlee" noise can almost escape the ear if you are not paying attention. Yet once heard, one almost always longs to hear it again, especially in spring when the long winter months have subsided. A singing Eastern bluebird in pale morning sunlight is its own reward, 100 times over.

There are only a few species in Illinois for which either the Eastern bluebird or Indigo bunting can be mistaken.

Another species of finchlike bird, the Blue grosbeak, reaches the northern tip of its range here in Illinois. A few pairs breed every year in the Chicago area, but the overall presence of Blue grosbeak may yet be poorly documented. Not for lack of trying by birders, but by the relative ease by which the Blue grosbeak can be mistaken for an Indigo bunting at first glance. The Blue grosbeak is a generally more robust species than the smaller Indigo bunting which is much like a sparrow in length and size. Blue grosbeaks are a full inch larger and have a much stouter beak. The male Blue grosbeak has a similar indigo coloration in breeding plumage, yet it sports rich chocolate brown wing bars. Females are pale brown with deeper brown wings and a pale blue rump. The song of the Blue grosbeak is an emphatic series of rising and falling notes, and its call is a loud "chink" that eager birders would easily recognize again, once heard.

The problem for many birders is that Indigo buntings can present a mixed plumage in young birds or in transitional plumage. Many a birder has exulted at the sight of a possible Blue grosbeak in early June only to realize their bird is simply an Indigo bunting with a few brown patches left over.

On rare occasions in early spring or late fall, Illinois will see the arrival of western species such as Mountain bluebird or Western bluebird. These are normally only found by expert birders who spend quite a bit of time in the field and know the markings of these species from previous experience.

One interesting note about the color blue in the birds: It is the result not of blue pigment but of a refractive mechanism in the structure of the feathers. What you are witnessing when you see a bluebird, indigo bunting, blue jay or other blue birds is light bouncing out of box cells in the bird's plumage. In other words, it works like a very limited rainbow.

But we don't need the exotic to thrill us here in the Illinois when the Indigo bunting and Eastern bluebird provide plenty of "blues" for us to enjoy. You can find both species throughout August and into early September when songbird migration begins. That's when Indigo buntings depart for the south while Eastern bluebirds flock up and hang out through the winter if the mild weather allows. Eastern bluebirds will even stuff themselves together in a nesting box during cold spells to share heat and survive, giving new meaning to the meaning of the "winter blues."

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