Blue of indigo bunting’s plumage is a trick of the light

Photo by Bryan Stevens • The male indigo bunting is a resplendent bird.

The indigo bunting is one of the reasons I love to pay attention to the clientele visiting my feeders. This small songbird likes to reside in the boundary region where forests and woodlands meet fields and pastures. Personally, the indigo bunting has always been a bird that is suggestive of the long, hot days of summer.

One of my earliest and still quite vivid birding memories is a recollection of a shockingly blue bird atop a blue spruce tree in my yard. Several decades later, the tree is no longer standing, but these beautiful birds — I now know these summer visitors were indigo buntings — still return each year to my yard and gardens.

Indigo buntings usually arrive in the region in late April, and I’ve seen them linger until late October, although most indigo buntings have left the region by late September.

Upon arrival, male indigo buntings become tenacious singers, repeating their jumbled notes even during the hottest hours of summer afternoons. The preference of this small songbird is to sing from the tops of tall trees, where they are often concealed by the green leaves. When I do get a glimpse of the obscured songster, often all I see is a dark shape silhouetted against the bright sky. Sometimes, if he plunges from the upper branches into the woodland understory, I get that telltale glimpse of blue feathers.

Photon by Bryan Stevens • Indigo Buntings will perch on wires and sing for hours even during hot summer days.

The male indigo bunting is the only solid blue bird in the eastern United States, but it’s all an illusion — literally a trick of the light. The indigo bunting’s feathers are not really blue; the male’s brilliant azure plumage is caused by the process of diffraction of light around the structure of the bird’s feathers. This process scatters all but the blue light, and the resulting color shifts from black to blue to turquoise as the angle of reflected light changes. In bright light, it can even look unnaturally vivid blue. In poor light, however, an indigo bunting male can appear black. Fortunately, indigo buntings have both a characteristic body shape and song, so even if the birds are not seen at their best, they can still be recognized.

Soon after returning to the eastern United States each spring, female buntings begin to gather materials to construct a well-crafted, cup-shaped nest. The male usually stays close to her, but he offers no assistance with nest building. She usually lays a clutch of three to four eggs, but she may nest another two times in a single season. She will incubate the eggs for almost two weeks, but the young remain in the nest another two weeks after being hatched as featherless, blind and helpless young completely dependent on the care of attentive parents. The task of raising so many broods in the space of only a few months requires the participation of both the female and her mate, who must work hard to bring enough insects to the nest to keep the young fed.

Like many species of songbirds, the male is by far the most colorful. In this instance, the male is also responsible for the species’ name. Indigo is a blue dye that was once an important crop in the South. The drab female may boast some blue highlights in her plumage. Juvenile birds just out of the nest also resemble the female. Pay close attention to any indigo buntings you observe as summer progresses. Juvenile birds will look mostly brown with just a hint of blue in the wings and the tail. These will be the young buntings that were hatched in spring and early summer. They will often accompany their parents to feeders.

Photo by Dan Sudia/USFWS • Female and young indigo bunting do not show the intense blue of adult males.

Indigo buntings are particularly fun birds to observe in late summer. Indigo bunting juveniles, like the young of many other birds, beg for tidbits from parents by “bowing,” spreading their wings and shivering. These actions usually prompt a parent to pop some morsel into an impatient youngster’s open bill. Indigo buntings are relatively easy to view. They frequent weedy fields and roadside brush. During the breeding season, males can also be seen singing from prominent perches. The song, a distinctive jumble of notes, can help observers find these dedicated singers.

The indigo bunting belongs to a genus of birds known as Passerina, which is included the family Cardinalidae, which includes birds like Northern cardinal and rose-breasted grosbeak. They are often lumped into a group known as North American buntings, although they are not closely related to such birds as snow bunting and lark bunting. The latter is even recognized as the official state bird for Colorado, a unique honor for this group of birds. The other members of the Passerina genus include lazuli bunting, varied bunting, painted bunting, rose-bellied bunting, orange-breasted bunting and blue grosbeak.

Worldwide, other birds known as buntings include such descriptively named species as slaty bunting, corn bunting, white-capped bunting, gray-necked bunting, cinereous bunting, lark-like bunting, cinnamon-breasted bunting, chestnut-eared bunting, little bunting, yellow-throated bunting, golden-breasted bunting, black-headed bunting, red-headed bunting and yellow bunting.

Photo by Bryan Stevens • Although bright blue, a male indigo bunting will often blend with its surroundings.

The male indigo bunting is one of the most colorful birds to visit feeders in the region. This species is also extremely fond of millet seed. I like to have some feeders stocked with millet when the buntings begin to return each spring. They will also feed on thistle and sunflower seeds. Away from our feeders, they also devour plenty of seeds from various noxious weeds. Because of the indigo bunting’s appetite for the seeds of destructive weeds, it is considered a beneficial bird.

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