A pair of dancing Sandhill Cranes
Most of the world’s fifteen crane species are threatened or endangered. One with an increasing population is the Sandhill Crane of North America.
■ Many people use the name crane for any large, tall, gray bird, but in most of North America these birds are Great Blue Herons (see this page). Cranes and herons are superficially similar but not related, and can be distinguished by many details of appearance, habits, and voice. Cranes are almost always in pairs or flocks (not solitary) and have pleasing bugling calls. They feed by picking gently at the ground (herons hunt fish with a sudden violent lunge), and cranes have a patch of red skin on their forehead and a “bustle” of curved feathers over their tail.
Great Blue Heron (left) and Sandhill Crane (right)
■ If you look carefully at a bird’s legs you’ll see that the “knee” joint seems to bend the wrong way—but that’s because it’s actually the ankle joint. The bones that are equivalent to most of our foot (shown in yellow) are fused together into a single long straight structure that is very leg-like, and what we call a bird’s foot is really just the toe bones. All of the leg muscles are close to the body, hidden and insulated by feathers, which is why the parts that we see are so spindly and skeletal, really just slender bones and tendons with a leathery covering.
A human leg (right) compared to a Sandhill Crane leg (left), with toes, foot, lower leg, and upper leg each color coded
■ During the breeding season, crane pairs are territorial and do not associate with other cranes as they raise their young—usually a single chick, sometimes two. At the end of the summer all cranes, including family groups and nonbreeders, gather in flocks to migrate south. Family groups generally remain together until about March, and often include one or more young from previous years along with the parents and their most recent offspring. Within these winter flocks social displays are common, including the spectacular and intricate “dancing” unique to cranes. A dance is initiated by the male, and involves bowing, calling, flapping, running, and leaping into the air. It is thought to be a courtship display, but it occurs throughout the winter, and dancing by one pair often stimulates other pairs nearby to begin dancing.
The dance of the Sandhill Crane