One of the most familiar songbirds throughout much of North America is the Indigo Bunting. Its spirited song can be heard anytime from sunrise to sunset in the spring and summer, with only an occasional glimpse of the brilliant blue male songster. Birders in North Carolina learn to look and listen in brushy and weedy places for this common summer resident throughout the state. Parts of both the common and scientific names refer to the bright blue color of the older males. Interestingly enough, the blue and iridescent colors in birds are never produced by pigments and are actually structural colors. The blues are produced by minute particles in the feather that are smaller in diameter than the wavelength of red light. These particles are able to influence only shorter wavelengths, which appear blue and scattered (reflected) in all directions. This blue color remains stable at all angles in reflected light, unless the bird gets between the light and observer. With all that said it is also interesting to note that many inexperienced birders mistake it for the Eastern Bluebird. Closer examination will detail it is very different indeed.
This small bunting is common throughout the state, but since it is a neotropical migrant, it is rarely present during our winter. Neotropical (New World) migratory birds breed during summer in temperate North America, migrating north each spring from wintering areas, then fly back south to spend the bulk of the year in Mexico, Central or South America, or the Caribbean. Thus unlike the Eastern Bluebird, which can be seen commonly in winter in North Carolina, the Indigo Bunting heads to warmer climes.
Since this bird is a denizen of open landscapes and partial to abandoned fields with thickly grown grasses, weeds, brambles and shrubs bordered by trees, it has plenty of suitable habitat in our state. It is no doubt more common now than before European settlement. In other words it is a bird that seems to do well in disturbed sites, occupying the transient, scrubby vegetation that covers areas after farms are abandoned, clearcutting occurs or woodlands are impacted by more natural disturbances like fire or storms.According to Breeding Bird Survey data prior to 1986, this native migratory bird seems to be increasing in range and densities on a continental basis, though local decreases and extinctions are occurring in areas of increasing forest growth (like the northeast). They decrease with intensive agriculture, frequent mowing of herbs along roadsides and farms, reversion of old fields to forests, and increasing urbanization. However recent trends (last ten years) do seem to indicate a slight decrease in Indigo Buntings on a continental scale, although they seem to be an abundant bird for now in our state.
The Indigo Bunting is sexually dimorphic (males and females look different). Adult males areblue and have no wing bars. The female is mostly unstreaked and light brown, although some females may be tinged with blue. Young resemble the female with faint light colored wing bars. First-year males during the breeding season are variable in color, blue or mixed blue and brown. After the breeding season males molt and resemble females temporarily. They are equipped with stout conical bills for crushing seeds, which helps distinguish them from the more insectivorous birds, like warblers. The similarly colored male Blue Grosbeak is a bigger bird with a larger bill, as well as brown (or tan) wing bars. Eastern Bluebirds are all blue, bigger and have longer, thinner bills.
A small bird that is as obvious as the male Indigo Bunting, would do well to keep a low profile. Accordingly, he spends much time concealed in dense foliage but will perch exposed to sing. This species build nests in a variety of low weeds, brambles and shrubs. The female chooses a site within her mate’s territory and does all the nest construction herself. The nest is cup-like and well hidden, often within a few feet of the ground. Males may have more than one mate and females may be fertilized by males other than their social mate. Females do all the incubating and feed the young, making up to 50 food delivery trips to the nest per day.
Males spend quite a bit of time singing during the spring to establish and defend a territory, and often do it all day long. Especially early in the year they are exposed and easy to see. The male bunting’s song consists of a rapid series of high-pitched buzzy notes that are delivered in pairs, like--"sweet-sweet, zweet-zweet, sayt-sayt, zeet-zeet--with every other pair of notes harsher and more strident than the preceding couplet. The male broadcasts from favorite perches in his territory, often visiting them in predictable order throughout the day. While the song sounds rambling and monotonous to the untrained human ear, detailed analysis has shown it to be a complex and highly organized performance. More than 100 distinct song notes have been catalogued for the species, and a single male may incorporate up to eight of these in his own song. The songs males learn and sing depend on social interactions with other males in their first breeding season and not on songs they hear as nestlings or fledglings. Males holding adjacent territories often sing the same song, which can be noticeably different from the chorus from another field not far away. Dominant males hold the best quality territory, and this is what females really chooses--the best territory.
Males arrive on breeding grounds a few weeks before females in April, and most Indigo Buntings are gone from our state by mid October. Indigo Buntings winter in weedy fields, citrus orchards, savanna, weedy cropland and low second growth areas mainly in Mexico (especially eastern coastal regions), Central America, throughout the Caribbean and into the top part of South America. Some winter in southern Florida, and winter strays linger in the Carolinas occasionally.
Indigo Buntings breed throughout all of eastern North America, and occur over most of our state. On average, the species has a low survival rate, although some individuals may live at least 9 years.
Numbers of Indigo Buntings increase with growth of shrubs and herbs, and disturbance tends to cause these conditions. They are valuable dispersers of seeds, and also feed the young insects. People sometimes attract them to feeders in migration or during summer. On tropical wintering grounds, these birds are commonly killed for food and sport. They appear to be a popular cage bird in towns in Yucatan, Mexico.
Suggested ReadingBirds of the Carolinas by Potter,
Parnell and Teulings, 1980, UNC Press
The Birder’s Handbook by Ehrlich, Dobkin, and Wheye, 1988, Fireside Books
A Guide to the Birds of Costa Rica, by Stiles and Skutch, 1989, Cornell U. Press