Although many of the terms used to denote color in birds may be unknown to apprentice observers of avifauna, most learn the meaning of the word cerulean rather quickly. The ready recognition of this word in the Americas stems specifically from one winning wood warbler, the Cerulean Warbler. This species’ exceptional coloration, blue where so many of its peers are olive, yellow, black, and brown, and rarity place it high atop most North American birders’ lists of favorites. Cerulean is a fitting characterization for Dendroica cerulea as the male is adorned in a deep sky blue while the female presents peppy blue-green plumage. Cerulean the color describes a variety of shades from dark aquamarine to light cobalt.
In the New World, the warbler from the north shares cerulean with a manakin in the south. For other birds named for this color, one would have to travel all the way to Indonesia. That vast archipelago accommodates Cerulean Kingfishers, Paradise-Kingfishers, and Cuckooshrikes.
Cerulean derives from the Latin caeruleus, meaning dark blue or azure. Thus, we can consider the term synonymous with azure, though the different shades of each are optically distinct from the other. Azure avians abound across the world. Central and South America host most of them, with various tanagers, jays, gallinules, hummingbirds, parrots, and pittas exhibiting azure anatomy. Yet certain Australian kingfishers and Eurasian tits and magpies ensure that azure is part of the international lexicon.
B.B. King posed the plaintive question, “How Blue Can You Get?” For some members of Class Aves, the answer is, “Very,” though not quite in the way the Beale Street Blues Boy meant. A bevy of birds bear the pure, unadorned descriptor of blue. But while hundreds of different blue birds, along with a handful of bluebirds, can be found, not many are named for specific shades of the color for sorrow and Southern twelve-bar brilliance. Indigo, as I’ve mentioned before, usually alludes to blue plumage in birds, even though the color is technically violet. Ultramarine also serves to describe an extremely intense hue in this wavelength; a glance is all it takes to spot the ultra in the Ultramarine Lorikeet, Flycatchers, Grosbeak, or (of course) Kingfisher.