THEY call it the river that's ``a mile wide and a foot deep.'' Spring floods build up the sandy shoals of Nebraska's Platte River as it winds a shallow path through fields of corn and soybean stubble. Interstate 80 parallels the quiet waterway, and this stretch of central plain seems in every way a place that one passes through on the way to somewhere else. And so it is, even in the comings and goings of nature.
The Platte River Valley is the ``waistline'' in the remarkable, hourglass-shaped migration pattern of the sandhill crane. Each year about 500,000 of these colorful waterfowl converge on the 125-mile strip of the Platte that stretches from Lexington to Grand Island, Neb., creating a spring spectacle that is unforgettable - and endangered.
The sandhills, three-foot-tall gray and gray-brown birds with colorful red foreheads, spend their winters scattered from the Texas Gulf Coast westward to northern Mexico, New Mexico, and Arizona. In February they head north to the Platte, feasting on waste grains in the fertile pastures and roosting in the shallow waters at night.
``We look for the cranes every spring and it is one of the sure signs that spring is on the way,'' says Laverne Karr, a farmer from Doniphan, Neb., who has lived in the area for more than 80 years.
About mid-April, the birds fan out again, resuming their journey northward to their ancestral nesting grounds across the Arctic and into Siberia.
The arrival of the sandhills, which are first cousins of the whooping cranes, is a rite of spring here. On a warm day, the air is filled with the melodies of the cranes; in the sky, so high as to be nearly invisible, hundreds of sandhill cranes ``kettle,'' circling around and around as thermal currents take them higher and higher.
Several factors have made the Platte Valley an ideal stopover for these waterfowl as they move northward along the central flyway. There is ample food in the pastures and among the stubble of soybean and corn fields. Perhaps more important, the Platte offers ideal night roosting conditions for cranes, because the river is shallow and filled with sandbars. Sandhills prefer to spend the night standing in shallow water, a habit that provides protection from their natural predators.
After leaving the river sandbars at dawn to feed, the birds spend their days loafing in the fields and doing the strange dances that are a part of their courting ritual. Cranes do their courting and mating on their migration north.
These long-legged, ungainly-looking birds usually have another feeding period late in the afternoon and will again stage or gather in a field before flying to their roosting bars.
Ironically, the changing character of the Platte itself is putting the sandhills in jeopardy. The sandbars in the river were formed by spring flooding as the waters rose and receded. The scouring action of the water during the annual flooding kept the sandbars clean.
Through the years, the demand for irrigation water along the river, which has its headwaters in Wyoming and Colorado, has reduced the spring flows; the sandbars are no longer scoured clean and woody vegetation has taken over. Now there is barely enough water to maintain minimum flows.
The Audubon Society maintains the Lillian Annette Rowe Wildlife Sanctuary at Gibbon, Neb., where there is a crane-watching blind that people can make application to visit. Up to 30 people can visit at any one time.
Travelers who turn off the Interstate may find the sandhills coming close to the blacktop and gravel roads that crisscross the area, letting a car serve as a blind for observing them.
But sandhill cranes are quite easily ``spooked'' and will fly out of the fields if disturbed. Residents of the valley are quite protective of their migrating guests and do not want cars driving out into the sometimes wet fields to get closer to the cranes.
Audubon volunteers work throughout the year to keep many of the sandbars in the Platte cleaned for migrating cranes and other waterfowl such as ducks, geese that stop over here, or shore birds that nest here.
Other conservation groups have joined with Audubon in an effort to limit any further reductions in the flow of the Platte. At least a dozen future projects are being planned for the Platte and its tributaries.
Conservationists warn that further withdrawals of water from this river could affect the migration of the nation's only colony of whooping cranes, which also use this staging area.
The Rowe Sanctuary resident manager, Ken Strom, put it this way:
``With 70 percent of the flows of the Platte River already diverted for agricultural and other needs, and the fact that the Platte supports most of the world's populations of sandhill cranes and millions of mid-continent waterfowl and their migrations, here is an ecosystem that has been pushed to the breaking point.''