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Original pencil on paper drawing not available for purchase.

"Contour feather Contour feathers form the bulk of a bird's visible plumage. Their vanes are symmetrically arranged around the rachis, and the barbules interlock to form a smooth, waterproof whole. They often have an afterfeather, a plumy appendage at the base of the vane that adds additional insulation. Contour feathers vary greatly in size and appearance, from the iridescent head feathers of a hummingbird to a duck's long belly feathers to the broad back and flank feathers on an eagle. Colors, breeding adaptations, and other variations abound -- a peacock's display, the ear tufts of an owl, and the spongelike belly plumes of a sandgrouse are all modified contour feathers."

Text from "Feathers: the evolution of a natural miracle," by Thor Hanson. Copyright © 2011 by Thor Hanson. Used by permission of the author.