A DIMINISHING HABITAT
As the Platte River declines, trees on sandbars besiege and limit important nesting areas.
MAX POST VAN DER BURG
"There are some who can do without wild things, and some who cannot."
-Aldo Leopold, from "A Sand County Almanac"
In 1973, Congress decided U.S. citizens could not do without wildlife and enacted the Endangered Species Act.
Along the Platte River in Nebraska, the Act protects three imperiled species of birds - the whooping crane, piping plover and interior least tern - and one species of fish, the pallid sturgeon. These species share a reliance on the habitat endowed by the Platte.
Historical accounts of the Platte paint a picture of a "braided" waterway, which is a wide, shallow, muddy river laced with sandbars. Pioneers described the Platte as "a mile wide, an inch deep, too thin to plow, too thick to drink."
Every year, spring floods created new sandbars by moving sediment, mainly sandy soil. Combined with breaking ice jams, these floods would also remove vegetation, including trees, from existing sandbars. It was against this ever-changing backdrop that the four threatened and endangered species came to depend on the central Platte, from Lexington to Columbus, and on the lower Platte, from Columbus to the confluence with the Missouri River.
Fast forward to today.
These sections of the Platte are narrower and deeper, and the sandbars are besieged with trees. Still, the tall and graceful whooping crane - one of the rarest birds in North America - depends on the central Platte and nearby habitat.
In 1978, using its authority under the Endangered Species Act, the U.S. Fish and Wildlife Service designated 56 miles of the Platte between Lexington and Denman as critical habitat for the endangered crane. This designation also covers three miles of land on both sides of the Platte, including wetlands such as those of the Rainwater Basin of south-central Nebraska. The Platte remains an oasis for migrating whooping cranes because it stays wet in the spring.
"During migration, cranes spend every night in a wetland of some sort," said Felipe Chavez-Ramirez, executive director of the Platte River Whooping Crane Trust in Wood River. "Today, the Platte provides the most reliable roosting sites because it maintains water during the spring migration."
Other regions, like the Rainwater Basin, have basically been dry the past few years, he said.
The central Platte and Rainwater Basin are in the central flyway, a long, narrow route connecting migrating birds from the South with breeding grounds in the North. Whooping cranes, with a wild population of about 216, fly this route each year. About 7 percent of the wild population rests for a few days on the central Platte.
But trees and other vegetation have encroached on roosting sites.
"Lots of large trees limit visibility, and cranes like to see what's around them because it helps them avoid predators," Chavez-Ramirez said.
Red foxes and bobcats have been known to kill cranes. Predators also seem to affect the behavior of two small shorebirds, the threatened piping plover and endangered interior least tern.
They normally build their nests - shallow depressions in the sand - on sandbars in the river, out of reach of predators such as domestic dogs and cats. To this end, critical habitat for plovers in Nebraska includes stretches of the Loup and Niobrara as well as the Platte.
But the arboreal invasion of sandbars in the Platte limits nesting areas.
Today, terns and plovers unable to find good nesting sites on sandbars in the Platte will nest on gravel-mine sandpiles, where they are exposed to predators.
As of 2001, fewer than 100 piping plovers and just more than 400 terns were counted on the central and lower stretches of the Platte, yet neither species seemed to be nesting in the central portion of the river.
"We haven't recorded either of the birds nesting in the central Platte recently, except a few cases on mechanically cleared islands," said Renae Held, program coordinator of the Tern and Plover Conservation Partnership. "All of the tern and plover nesting in the central Platte region occurs in gravel mines now. However, both birds do still nest on the lower Platte even though the habitat is declining."
Rising water also signals to fish species, such as the dinosaur-like pallid sturgeon, that it's time to mate and lay eggs. The endangered pallid sturgeon, with its long, flat snout and bony plates, spawns in warm, muddy waters. Spawning used to occur throughout much of the Missouri and Mississippi rivers, but dams, water diversions and channel dredging have limited the fish to a few areas on both rivers.
"For the stretch of the Missouri downstream from Gavins Point Dam, the Platte is virtually the only tributary that retains any of the spawning habitat that pallid sturgeon use or seem to be looking for," said Ed Peters, emeritus professor in fisheries biology at the University of Nebraska-Lincoln. "But if the Missouri was the way it used to be, the Platte probably wouldn't be as important."
Despite the limited habitat now provided by the Platte, it is hard for scientists to find pallid sturgeon, especially young ones.
"Even in areas with prime habitat, it's been impossible to find young individuals," Peters said. "We're only finding 5- to 20-year-old individuals in the Platte, whereas in other portions of its range we're finding some evidence of reproduction."
Peters estimates roughly 100 to 300 pallid sturgeon use the Platte, but without signs of reproduction, the future of the fish remains uncertain. What is known is that the loss of a species like the pallid sturgeon could signify trouble for the ecosystem of the Great Plains.
"The Platte has always been an important part of that system," Peters said. "A species like the pallid sturgeon is probably a pretty good indicator of the quality of the river since it can't just leave and go someplace else."
The Endangered Species Act was designed to deal with species that rely on disappearing habitat and have no other place to go. Ultimately, this law is the driving force behind projects such as the Platte River Cooperative Agreement, which can be viewed as a regional declaration of the need for wild things.
