Indigo Bunting (Passerina cyanea) is a familiar summer bird in the eastern United States and southern Canada, with males sporting an almost unnatural hue of bright blue that is richer on the face than on the breast and back. In the fall and winter males lose their blue plumage and resemble the brown females.
In the summer, Indigo Buntings breed in brushlands, open forests, powerline cuts, and woodland edges, and are often seen singing from conspicuous treetop perches or even roadside wires. Like many shrubland species, they are declining as shrublands regenerate to forest or are lost to suburbia or large-scale agriculture. Indigos avoid northern forest, so they don’t penetrate far into Maine or Canada, are largely absent from the Adirondack Mountains and ne. Minnesota, and only breed in southernmost Ontario and Quebec where more southerly forest types predominate. These areas of depressed abundance are clearly on the summer STEM maps. It is rare to see Indigo Buntings in urban or suburban areas, so the summer maps show conspicuous “holes” around large urban centers. Notice how the June and July maps (e.g., June 27) show conscious “holes” on the map at St. Louis, Atlanta, Washington D.C., Kansas City, Detroit, Shreveport, etc. At the western margin of the range you can see the species drop out as the prairies give way to the high plains, which are drier and have fewer trees. However, this species does turn up in small numbers in wetter river valleys through Arizona, Utah and other western states, and this is shown on the summer maps as very low predictions in areas where those habitats occur (e.g., the upper Rio Grande Valley in New Mexico). In this portion of the range, Indigo Buntings may hybridize with Lazuli Bunting, which is more a bird of brushy western mountain slopes.
In both spring and fall, Indigo Buntings show a fairly expected pattern of movement, gradually withdrawing from their summer range from September to November and gradually arriving from March to May. Not all species show such a gradual arrival and departure, as you will see in future STEM maps. During migration periods, watch for Indigo Buntings to “stack up” along the Gulf coast. This is obvious in the fall, when the Gulf coast starts lighting up in mid-October and remains bright even after most have left the country. These are birds presumably using coastal lowlands to fatten up prior to making their southward overwater flight, along with some migrants that may “fall out” on the coast. A similar effect is seen in spring, as new arrivals refuel after a Gulf coast crossing but before moving inland to breed: for example, notice the strong Gulf coast signal on the 21 March map. Indigos that winter the Yucatan and eastern Central America are trans-Gulf migrants, crossing the Gulf of Mexico on their spring and fall migrations.
In winter, Indigo Buntings are found in brushy areas and forest clearings on both slopes of Mexico. Indigos may mix with other Passerina buntings in mixed flocks where one can find Indigo, Painted, and Blue Grosbeak together in on the Caribbean slope of Mexico and Central America and can have those species plus Lazuli, Varied, and Orange-breasted Buntings together on the Pacific slope. A few Indigos winter in the southern United States, where they are often found at bird feeding stations, especially in Florida and south Texas. In spring, feederwatchers can hope to see the bright males farther north when they first arrive, but their diet usually shifts to insects by late spring and summer, which makes them always a treat to see at feeders.
To learn more about the life history of Indigo Bunting, please consider a subscription to Birds of North America (just $42/year), where experts in the species have written a full-length species account covering all aspects of the species biology, from migration to diet to conservation status.