WEST ALTON • The sight of police, firetrucks and ambulances swarming below is nothing new for high-flying lineman Bryan Stewart. It usually just means another person has called 911 thinking his helicopter is in trouble.

"It's happened countless times," said Stewart, 38, of northern Alabama, whose job of about 10 years requires that he lean out of a swooping helicopter, "especially when you're working over a busy highway or in a big city."

It happened again this week in St. Charles County. As Stewart worked from a platform outside the chopper, wrapping power lines with 'swan diverters," a 911 caller reported a possible helicopter crash.

Stewart is teamed with a pilot and a flight mechanic, all specialists with Haverfield Aviation based in Gettysburg, Pa. They were hired by Ameren Missouri to attach more than 1,000 so-called diverters — which look like 2-foot-long yellow corkscrews made of a hard, flexible plastic — on power lines near the Riverlands Migratory Bird Sanctuary.

The devices are designed to keep trumpeter swans, one of North America's largest and once-endangered birds, from getting killed.

Ameren Missouri is spending about $50,000 on the three-day project scheduled to wrap up today, said company spokesman Tim Fox. The utility is working with the U.S. Fish and Wildlife Service and the Army Corps of Engineers to install the diverters every 15 feet along a 1.5-mile stretch of static power lines, which absorb lightning strikes and carry little to no electric current.

The diverters are meant to act as aerial buoys, alerting swans of potential danger.

Tim Santel, an investigator with the Fish and Wildlife Service, said about two dozen swans have been found dead or injured in the area from run-ins with power lines since spring, prompting officials to contact Ameren.

He said a trumpeter swan's average 30-pound weight and 7-foot wingspan make it slow to take off and unable to maneuver quickly in flight.

"It's like a B-52 trying to get off the ground," Santel said.

The project is timed a few weeks before several hundred of the swans begin swooping into the 3,700-acre sanctuary for winter, said Charlie Deutsch, a wildlife biologist for the corps. The birds migrate here from the north to feast on corn before returning to colder climates in February.

Thousands of birds die each year from striking power lines, research shows.

Diverters are an effective tool to repel swans from the deadly high wires, Deutsch said.

Though hunting ravaged the trumpeter swan population toward extinction around the turn of the 20th century, Deutsch said conservation efforts have helped the species rebound.

There are now an estimated 3,000 in the Midwest.

Stewart's helicopter will hover over Highway 67 from 9 to about noon today to install the remaining diverters. Drivers should expect delays as crews close some lanes throughout the morning to finish the work.

Though Stewart will be suspended from a body harness 100 feet above traffic, he won't be in distress.

"Some days, it's a little bit of an adrenaline rush," Stewart said. "Most of my friends back home think I'm nuts, but after awhile, it just becomes another job."