By Judy Ferris, Master Naturalist & Guest Blogger
Who would think that this dazzling blue bird would go largely unnoticed? Meet the Indigo Bunting! They are one of the most common birds in the eastern United States. Though they are abundant in Calvert County, we seldom stop to admire these charming blue gems. Members of the Cardinal family, Indigo Buntings are small birds. They are just five inches long, and weigh about the same as a pencil. Indigo Buntings are only solid blue bird in the eastern United States.
Female Indigo Buntings are drab brown in color as befits a Mom who raises several broods of chicks in the underbrush just a few feet above the ground. Male Indigo Buntings are brilliant blue both above and below. In reality, however, that bright blue is merely an illusion. There is no blue pigment in bird feathers. All blue color is created by unique structures within each individual feather (Sibley 2020). A male Indigo Bunting’s feathers are actually black! Those structures within the feather, however, diffract the light, scattering all but the blue. Thus we see the bird’s color shifting from black to turquoise to brilliant blue depending on the light and our viewing angle (Prum et al 1998). Magic feathers! If you catch it right, the blue color is stunning.
Indigo Buntings are migratory songbirds. They arrive in Maryland in early May. As soon as they arrive, they set right to work establishing territories, finding a mate, creating a nest, and starting that first brood of eggs. Sounds exhausting doesn’t it? Like many human couples, buntings establish a division of labor. With their scintillating color and an irrepressible urge to sing, males take charge of establishing and defending territory. Indigo Buntings prefer edge habitats where woodlands meet grasslands. There, the males perch in an elevated location to show-off their gorgeous color as their song rings out across a field. They sing seemingly non-stop from sun up to sunset to proclaim that this territory is MINE MINE MINE! Meanwhile, the female keeps a low profile. She builds the nest alone and incubates the eggs. The nest is an elaborate cup-like structure of leaves and coarse grasses built in shrubbery about 3 feet above the ground. It may be lined with soft grass or deer hair and is tidily bound with spider webs.
Most bunting pairs raise two broods of 3 to 4 chicks per summer. The male may feed newly fledged chicks while the female incubates the second brood (Kaufman 2001). When it comes to feeding the chicks, insects – packed with protein and fat – are by far the best baby food for young birds. Eventually, berries and seeds are introduced into their diet as well.
As the days grow shorter in autumn and the second or third brood of chicks is fledged, those hormones kick in again. Mom and Dad Indigo Bunting feel the urge to fatten up and move south to their wintering grounds. In late September, they leave for destinations in south Florida, the Caribbean, Central America, or northern South America to spend the winter.
Indigo Buntings have been the subject of considerable study with regard to migration. Early studies in the 1960’s performed in planetariums indicate that Indigo Buntings use stars to navigate (Emlen 1967). Though going around the Gulf of Mexico is always an option, the majority of Indigo Buntings choose to make the risky Gulf of Mexico crossing. After breeding season, adult Indigo Buntings tend to be lean, weighing in at about 13 grams. Adding an additional 5 grams of fat will allow them to fly at an average speed of 20 miles per hour for 688 miles. The average length of a Gulf crossing is about 600 miles. Thus if all goes well, the birds can make a non-stop flight (Johnston 1965).
Arriving at their winter destinations, Indigo Buntings, especially the males, toss their summertime personas in the dumpster. They adopt an entirely different life-style for the winter! The male is no longer the party boy in the bright blue suit doing karaoke at the top of a bush. In autumn his brilliant plumage becomes brown, almost indistinguishable from the female. Perhaps this is the bird equivalent of wearing shorts, T-shirts, and flip flops. Instead of living as a solitary pair or family, buntings often hang out with other buntings in a group during the winter. Even their diet changes dramatically. Instead of eating insects, both males and females hunt for grass seeds. In short, they live a quiet, low-profile life at or near ground level.
As spring approaches, however, hormones once again kick in. The compulsion to move north increases urgently with each passing day. A late winter molt bursts open that long-hidden summer wardrobe and the male Indigo Bunting is once again cloaked in magic feathers of dazzling blue. It’s time to head north!
How to Find Indigo Buntings
Take time in the next few weeks to admire one of these blue beauties before they fall silent and prepare for migration. We’re looking for a brilliant blue bird that sings from sun up to sun set. How do we go about finding it?
- First find suitable habitat; locations where grassy meadows meet woodlands are ideal. At ACLT, try the North entrance and park near the ACLT office. Walk toward the barn and you will see a fence surrounding a garden. Both Indigo Buntings and Bluebirds are often seen atop this fence.
- Next, use your ears! Indigo Buntings have a distinctive song. It sounds like an enthusiastic Fire! Fire! Where? Where? Here! Here! Click on the link from Cornell’s excellent “All About Birds” website. The second song from the top, recorded in Maine, is the one that I hear most often here in Maryland. At this time of year, however, you may hear all kinds of variations as young birds begin to practice singing.
Try using Cornell’s free Merlin Bird ID app on your phone. It enables you to ID birds by sound.
- Once you hear the bird, you’ll have an idea of where to look for it. Male Indigo Buntings are show-offs. Look for them atop a bush, a fence post, a power line, or a low tree. You may even hear a rival Indigo Bunting singing from its territory on the opposite side of the field! If you have a pair of binoculars, you will be treated to a symphony in blue!