Sandhill Crane

The central Platte in Nebraska is a critical refuelling stop on the cranes' northward spring migration. Birds that wintered in Texas, New Mexico, and Mexico converge here in late February and March before continuing to breeding grounds in Canada, Alaska, and Siberia. The river offers exactly what they need — wide, shallow braided channels with bare sandbars where huge flocks can roost overnight safe from predators, surrounded by farmland where they spend the day eating waste corn to put on fat. For a few weeks the concentration reaches around half a million cranes — roughly 80 percent of the entire species — in a short stretch of valley, and the dawn and dusk flights between roost and fields are one of the most famous wildlife events on the continent.

Dancing is central to crane life. A dancing crane bows deeply, jumps into the air with wings partly spread, flaps, and often picks up a stick, clump of grass, or corn cob and throws it upward. Mated pairs dance as part of courtship and to reaffirm their bond each year, but unpaired birds and even young chicks dance too, and adults will break into it outside the breeding season. Researchers think it serves several purposes at once — synchronising a pair, advertising fitness to potential mates, and discharging nervous energy or aggression in a social flock. Because cranes pair for life, keeping the bond strong through ritual displays like dancing and unison calling matters to their breeding success.

The sandhill crane's windpipe is about 1.2 metres long — nearly as long as the bird is tall — and instead of running straight it coils in a loop inside the keel of the breastbone, much like the tubing of a trombone or French horn. This elongated, coiled trachea lets the bird produce very low frequencies and adds rich lower harmonics to its bugling call. Low-pitched sound travels through air and vegetation with less loss than high-pitched sound, so the rolling, rattling call carries for two to three kilometres or more across open country. Pairs also perform a "unison call," standing together and bugling in a precisely coordinated duet that helps defend their territory.

The species as a whole is not — it is listed as Least Concern, the large migratory populations number in the hundreds of thousands, and several have grown since the mid-20th century after earlier declines from hunting and wetland drainage. Regulated hunting seasons exist in some states. However, two small resident populations are in serious trouble — the Mississippi sandhill crane, down to a few hundred birds and dependent on an intensive captive-rearing and habitat programme in a single Gulf Coast refuge, and the Cuban sandhill crane, also numbering only in the hundreds. Both are threatened by loss of the open pine savanna and wet grassland they need.