Daybreak Dancers

Natural History, April, 1999 by Scott Weidensaul

Pairs of sandhill cranes were springing into the air---first one partner, then the other. The vast flock appeared to seethe.

Everywhere I turned, there were sandhill cranes. I was on the single dirt road that runs through Shoemaker Island, which sits in a wide, shallow stretch of the Platte River in central Nebraska. For hours I had watched ragged lines and skeins of cranes in the sky, and groups of dozens or hundreds scattered around the open fields, their calls filling the soft late-March air. But now, with sunset coming on, the cranes that had flown far off into the countryside to feed in harvested grain fields were pouring back by the thousands from every direction, preparing to spend the night at the river.

No stopover ground is more important for migrating cranes heading north in spring than the Platte. The fabled river--highway of the West, along which the Oregon Trail was blazed--is not a surging waterway but a series of shallow streams like loose cords braided across the land, each channel finding its own random path across the flat plains. From late February until early April, about a half million sandhill cranes--the world's largest assembly of cranes--along with small numbers of endangered whooping cranes in late March and April, gather on an eighty-mile stretch of the river known as the Big Bend, around the towns of Kearney and Grand Island, where the Platte sags down like a weighted belt.

Sandhill cranes are big birds with powerfully built bodies, long legs, muscular necks, and lance-shaped bills. Gray with red caps, they are about four feet tall but look bigger, an impression that is strengthened by their six-foot wingspans. Estimates for numbers of sandhill cranes in North America run up to 700,000, making this species the most abundant of an otherwise globally threatened family. Most nest in Canada and the Great Lakes states north to the Arctic islands and Alaska; some even cross into Siberia. Smaller numbers also breed in the Rockies, the Great Basin, the Cascades, and the Southeast. In winter, most migrate to a fairly small region along the western Gulf Coast, through Texas, southern New Mexico, and Arizona, and down into Mexico.

For about six weeks each spring, northbound cranes converge on the central Plains, where their flyway narrows like the pinched waist of an hourglass before fanning out again across Canada and Alaska. On the Platte and other traditional staging grounds, individual birds rest and feed for about a month, building fat reserves that will tide them over migration and the first hectic weeks of courtship on the still-frozen tundra and bogs of the North. By about the third week of March, the sandhill cranes on the Platte--many of them now sleek and refueled after feeding ravenously on waste grain left in the fields the previous fall--grow increasingly restless. When a period of strong southerly breezes sets in again, most of them race north, emptying the fields and sandbars almost overnight.

By luck, I'd hit the peak of the season. It was late March, and for weeks the numbers of cranes had been building. I followed Shoemaker Island's road around a right-angle turn, and on my left the fencerow fell away to reveal an old field maybe a half mile long. Into this single field were crowded tens of thousands of sandhill cranes, standing in gray ranks like weathered corn. I scanned the crowd for any whooping cranes--which stand a head taller than sandhills and have bright white plumage--but without success. The sandhills are extraordinarily skittish birds, and those within a hundred yards of the car rowed into flight as I came into view, then glided to a landing closer to the main flock. Hundreds more were landing every minute, planing down at a shallow angle, bugling and calling.

Sandhill cranes are among the loudest birds in the world: their secret is coiled like a snake inside their chests. Rather than simply connecting the lungs to the outside world, an adult crane's trachea, or windpipe, loops along the breastbone, forming a tube that, if stretched out, is almost as long as the bird itself. Like the voice of a human resounding through a metal pipe, the call of a sandhill crane is deepened and enriched as it passes through the coil, and the bony rings of the trachea, which are fused to the breastbone, make the whole apparatus vibrate during vocalization, amplifying the resonant calls and adding harmonics. The result, impossible to describe precisely, is pure magic, guaranteed to raise gooseflesh on someone hearing it for the first time.

When an especially large flock would begin its approach, the clamor was almost deafening, as the incoming birds sideslipped and tumbled like falling leaves, spilling air from their wings, then straightening out an instant before thumping down, one after another. Many of the cranes on the ground were dancing in couples, strengthening old pair-bonds in advance of the breeding season. One of the endearing things about cranes, besides their somewhat human size and lifetime monogamy, is their exuberant courtship display: a ritualized performance of leaps and bows, flapping wings and pumping heads. Dancing is especially common on the Platte in March, when their hormones are surging. Daybreak is the time of heaviest dancing, but as dusk approached, many pairs were springing into the air, first one partner, then the other, a movement multiplied hundreds of times so that the vast flock seethed.