Daybreak Dancers

Natural History, April, 1999 by Scott Weidensaul

The sun had set, and the cranes were becoming restive. Now the incoming flocks were gliding to a landing beyond the trees, out in the river itself, where they could sleep safe from coyotes and other predators. Security is paramount to sandhill cranes. Because they do not swim, they are unable to use deep water, as do ducks and geese, nor can they stay on land, where mammalian predators would be likely to find them. The Platte, with its shallow water and ever shifting sandbars, offers the perfect compromise. The cranes roost in places where the water is fast moving and only a foot or so deep, or on sandbars that have been cleaned of their vegetation by floods. Researchers (aided by Nebraska Air National Guard pilots in jets equipped with infrared detectors) have found that the cranes prefer areas where the channel is at least 150 yards wide, and they avoid places where the river is narrow, choked with trees, or near a bridge or road.

In the days when the Pawnee lived along the river, the Platte, then almost devoid of trees, was a much different watercourse. Snowmelt and runoff up in the headwaters, in the Colorado and Wyoming Rockies, once sent scouring floods down the Platte's channel every spring, ripping away cottonwoods and willows, rearranging the sandy channels almost from hour to hour and replenishing them with more sediment. The floodwater flowed into the spongelike marshes and wet meadows, then soaked down to recharge the subterranean aquifer, which kept the meadows moist even after the floods subsided.

But as early as the 1860s, irrigation ditches started bleeding the river, and between 1909 and 1940 a rash of dams plugged its two tributaries, the North and the South Platte. Today's river is a dim reflection of its old self; dammed and diverted, nearly three-quarters of the Platte's water now goes for irrigation or municipal use, siphoned off long before reaching the Big Bend. The amount of sand sweeping down the Platte, crucial to maintaining sandbars, has dropped by two-thirds in this century and now piles up behind reservoirs. Nor is the river able to cleanse itself--the braids of water and sand, which in the past spread over a mile-wide channel empty of trees, are now all but pinched off, like sclerotic arteries, their margins supporting thick stands of cottonwood.

Where once the sandhill cranes could spread out along more than two hundred miles of river, today almost the entire midcontinental population must shoehorn itself into relatively small staging areas along the streambeds of the Big Bend on the North Platte (see map, page 76). Even within these zones, good roosting sites are hard to find. The same locations are also crucial to many of the world's surviving whooping cranes, which are protected by the federal Endangered Species Act (ESA); they stop on the Big Bend while migrating from Texas to Manitoba. In part to avoid lengthy and costly ESA reviews of each new water project on the Platte, in 1994 the governors of Nebraska, Wyoming, and Colorado, along with the Department of the Interior, agreed to a multistage recovery program that for the first time tried to balance the needs of wildlife against the needs of humans. While not everyone believes the agreement goes far enough, proponents say it is the first step toward restoring habitat for cranes and other wildlife along the Platte.