A majestic and raucous gathering of sandhill cranes

By Jeff Mitton

I look upriver, to a fading sunset, for the din is loudest there. I can see at least a dozen strands of cranes, returning to a watery roost on a sand bar in the North Platte River.

The flocks descend through the sunset and cruise over the marshes, wary of foxes, coyotes, eagles, owls and humans. Then up and away to make another pass as other flocks wheel and descend.

These are big birds, almost four feet tall, with wingspans of six feet. They fly with their necks and legs straight out and long primary feathers at the wingtips deftly working the wind. Large cranes can be seen far away, but they are heard before they are seen -- flying cranes bugle and rattle constantly.

Their return to the roost is both a majestic and raucous spectacle.

The sandhill crane,Grus canadensis, has a grey body, red forehead, white cheeks and a long, pointed black bill. The legs are long and black; the feet have three toes pointing forward and one back. Males and female are similar, though males are a little larger. Immature birds, called colts, are reddish brown above and grey on the undersides.

The sandhill crane is an ancient species, though its age is a matter of debate. The oldest fossil that is unequivocally a sandhill is 2.5 million years old, considerably older than the fossils of most birds. Several crane fossils are 10 million years old, though these may be sandhills, or may be their ancestors.

Six subspecies of cranes are recognized, based partially on size and partially on geography, but I suspect that this will change, for some subspecies seem to be merely portions of a continuum in size.

Non-migratory or year-round populations are on Cuba and in Florida, Georgia and Alabama. Winter havens for migratory cranes are in Florida, Louisiana, Texas, Mexico, New Mexico and California.

Two migration routes are local. Cranes overwintering in the Bosque del Apache National Wildlife Refuge, 100 miles south of Albuquerque rest for several weeks in the San Luis Valley on their migration to nesting areas in Colorado, Wyoming, Idaho and Montana. The largest migration begins in Texas and Mexico and pauses at the Platte and North Platte Rivers in Nebraska. The migration continues to nesting areas around the Great Lakes, in Canada west and north of Hudson's Bay and Alaska. From Alaska, about 60,000 cranes continue across the Bering Strait to nest in Siberia.

Cranes pause along the Platte River for about a month, fattening up as they forage in the marshes and cornfields. At this time, family units of two adults and one colt are discernible. The adults dance and jump high into the air, and the colt dances with its parents. Adults pair for life, but the colt leaves its parents before they arrive at the nesting sites.

Cranes do not mate until they are 3 to 7 years old, and some cranes live for 25 years.

The wildlife areas along the Platte River insulate the spectator from contemporary life, for the whine of tires on the interstate and the lights of tiny towns cannot penetrate the depths of the marsh. The bedlam and spectacle of migrating cranes is enthralling, a scene of prehistoric wilderness.

Jeff Mitton (mitton@colorado.edu) is chair of the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.

April 16, 2010