The Postal Service issued five 29-cent Hummingbirds commemorative stamps on June 15, 1992, during the National Audubon Society's convention at American University in Washington, DC. The stamps feature the broad-billed, calliope, costas, rubythroated, and rufous hummingbirds.
Hummingbirds, often called the helicopters of the avian world, have evolved a unique form of flight. While other birds can hover for a moment or two, the darting, start-stop, up-down, forward-backward flight of hummers belongs to them alone. Hummingbirds scull the air rather than stroke it, gaining constant lift from what is more of a forward-and backward movement than the more usual up-and-down flapping of other birds. When hovering, their bodies assume a nearly vertical position. To power such an extraordinary set of wings, which never have a rest when the bird is in flight, hummingbirds have the largest pectoral muscles for their size of any animal alive.
Designed by noted wildlife artist and veteran stamp designer Chuck Ripper, the stamps were printed on the photogravure press by the American Bank Note Company in booklets of twenty.
