GIBBON, Neb. — Power lines — not eagles, raccoons or coyotes — are the whopping danger facing migrating sandhill cranes on the Platte River.
“They're the biggest predator on the river,” said Bill Taddicken, director of Rowe Sanctuary near Gibbon.
Power line collisions kill dozens of sandhill cranes at the sanctuary annually. Power lines once killed hundreds of birds at Rowe Sanctuary, but evidence indicates that a new style of reflective device strung along transmission lines at the major roosting area has reduced the death toll, according to wildlife biologists.
Despite the success in reducing sandhill crane deaths, biologists worry that someday a power line collision will kill an endangered whooping crane, the tallest bird in North America and a species once on the brink of extinction. No whooping crane death has been recorded at the Rowe Sanctuary lines, but power line collisions along the birds' Texas-to-Canada migration route are the greatest source of mortality for whoopers of flying age.
Fewer than 300 white-feathered whoopers remain in the wild, and like their gray-feathered sandhill crane cousins, most migrate through Nebraska every spring. The National Audubon Society's Rowe Sanctuary is located in a stretch along the Platte in south-central Nebraska that has had the highest incidences of whooping crane sightings on the river over the past 25 years.
Greg Wright, a wildlife biologist at the Crane Trust about 20 miles downriver, said the reflective devices seem to make two Dawson Public Power District transmission lines strung across a braided river channel easier for sandhill cranes to see. Wright has been involved in two scientific studies of the power lines.
The device is an acrylic tag called a FireFly. It is the latest in a series of various whirligigs, flashers and other pieces of metal strung along power lines to help make them more visible to birds.
The new-style bird diverters measure 3˝ by 6 inches and are covered with yellow and orange reflective tape and a coating that glows in the dark. The devices were installed at 40-foot intervals, but alternating attachment points on adjoining lines put a tag every 20 feet from the perspective of an airborne bird.
More than 460 swiveling diverters were installed five years ago. They were replaced the next year with a revised design to withstand Nebraska wind.
After the diverters were in place, a third to half as many sandhill cranes were killed. An estimated 50 to 93 cranes were killed in power line collisions at Rowe in 2008, and 37 to 70 were killed in 2009.
“They've been fairly effective in reducing the losses the power lines are causing,” Wright said of the plastic paddles.
Gwen Kautz, general manager of Lexington, Neb.-based Dawson Public Power, called the success of the diverters gratifying.
“If they've documented a 50 percent reduction in carcasses, that's awesome,” she said.
Rowe Sanctuary is near the midpoint of a stretch of the Platte where more than 500,000 sandhill cranes and millions of waterfowl descend to rest and feed for several weeks while migrating to northern nesting grounds every spring. Bird numbers peak now, as cranes pour into the state.
At the sanctuary, an estimated 80,000 cranes pack onto sandbars, sparsely vegetated islands and in the river shallows south of Interstate 80 every night. Cranes typically leave night roosts on the river during the first two hours after sunrise to feed in surrounding wet meadows and farmland. They return to the river during the last hour of daylight. It's not uncommon to see an average of 500 cranes per minute pass over the Platte as flocks seek roosting sites.
But there's danger in the cranes' flight paths.
Dawson Public Power's 69-kilovolt power line arrays bisect the sanctuary and cross a river channel that is up to 500 yards wide. One array crosses the river about 100 yards west of the sanctuary's visitor center. The other array is about a mile east. Electrified lines and other cables are strung 10 to 15 yards above the ground between H-shaped wooden poles.
Collisions mainly occur when large, resting flocks flush out of the river, Wright said. Sandhill cranes are particularly vulnerable to collisions because of their large size and poor maneuverability, biologists say.
The most dramatic collisions that biologists witnessed occurred in April 2008. Two large flocks of more than 1,000 cranes suddenly erupted into flight — perhaps spooked by a coyote — in separate episodes after sunset. Fifty-three cranes hit power lines. Researchers watched the carnage through night-vision goggles.
“It was incredible,” Wright said. “I hated to see it, but at least we learned why it was happening. Their roosts were in close proximity to the power line.”
In most cases, however, cranes have reacted more often and earlier to power lines marked with FireFlys. Biologists have watched the birds gradually fly higher as they approach Rowe's eastern power lines.
Moonlight or cloud cover doesn't seem to influence the ability of cranes to detect and avoid power lines marked with the devices, Wright said. There is no obvious relationship between the number of collisions and strong winds or bad weather. Cranes also better avoided lines with FireFlys than power lines marked with aviation balls as diverters, other studies show.
Biologists count crane carcasses found in the river and on adjacent land to estimate the number of birds killed in power line collisions. The total is adjusted upward to reflect carcasses removed by scavengers, losses to downstream flow and missed observations.
Hundreds of cranes are thought to die in similar high-wire encounters across Nebraska.
Cranes not killed outright in the collisions with a broken neck or other injury usually suffer broken wings or legs that prevent them from continuing the migration, said Carl Wolfe of Republican City. Wolfe is a retired Nebraska Game and Parks Commission wildlife biologist who works as a volunteer guide at Rowe Sanctuary.
“The outcome is that they tumble to the ground,” Wolfe said. “But what tugs at the heartstrings is to see a crane on a sandbar with a broken wing or leg. So often, the mate returns two, three, four times and stands there, apparently to urge it to move on — and you know it can't.”
Visitors sometimes insist that something be done to help wounded cranes.
“What do they want us to do?” Wolfe said. “It's nature at work. It can be cruel, but it's a fact of life. It's survival of the fittest.”
A 2008 study suggested that nearly 90 percent of crane deaths due to power lines at Rowe could be eliminated if the eastern power line was somehow rerouted or reconfigured, such as housing the cables in a pipeline beneath or just over the river channel.
Kautz, the power district executive, said the cost of bringing down the lines would have to be borne by others, not electricity customers. She estimated the expense at hundreds of thousands of dollars.
“We don't think customers in Brady and Overton should have to pay for something that doesn't benefit their specific area,” she said. “I'm a bird-lover myself, but power districts are frugal.”
The reflective tags were the result of a cooperative project by the sanctuary, power district and state and federal wildlife agencies and organizations to find ways to reduce power line casualties. The National Fish and Wildlife Foundation paid $23,000 for the first round of devices. It cost Dawson Public Power $25,000 to $30,000 to install the initial tags. Their replacements went in via helicopter for $10,000.
Taddicken said that more needs to be done, that he wants to see the power lines gone.
“We're still losing birds every year to those power lines,” he said. “This area is the sandhill crane capital of the world. The cranes attract people from around the world and bring tens of millions of dollars into the economy. I think we should be able to find better solutions.”
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