The air here this time of year usually is filled with the grunts and squawks of thousands of white pelicans and their chicks. The giant birds have made the refuge their home for at least 100 years.
Now their nesting grounds are quiet. The pelicans are gone - and no one knows why.
Everybody, from biologists to bartenders, has a theory.
"Those wildlife agents scared them away," said Jake Bohl, a blacksmith in Woodworth, a town of about 80 people 15 miles northeast of Chase Lake. "That's my explanation."
The 4,385-acre refuge in central North Dakota had been known as the home of the largest nesting colony of white pelicans in North America. The nearly 28,000 birds that showed up to nest here in early April took off in late May and early June, leaving their chicks and eggs behind.
Paul Guthmiller, an 85-year-old farmer, said he's seen pelicans in the area since he was a child. He figures heavy rains and cool temperatures in late May drove the birds away.
"I think there is too much water for them because of too much rain," Guthmiller said.
Normally, the pelicans stay at the refuge through September, raising their young and feasting on crawfish, small fish and salamanders from small ponds known as "prairie potholes." The area is filled with the stench of droppings from the thousands of birds and their chicks.
Now, sweet-smelling wildflowers have taken hold in the guano-rich soil.
Wildlife officials have considered diseases, food supply, water quality, weather, predators and other factors, but have found no satisfactory explanation for the exodus, said Mick Erickson, the Chase Lake refuge manager.
"Right now, everybody has an opinion," Erickson said. "But honestly, there isn't any explanation. This is the first time it's happened."
The white pelican is one of the largest birds in North America, measuring six feet from bill to tail. They weigh up to 20 pounds and have a wingspan of nearly 10 feet. While awkward on land, white pelicans are acrobats in the air.
Pelicans have been monitored at Chase Lake since 1905, when the birds numbered about 50. President Theodore Roosevelt designated the site as a bird refuge in 1908, when many of the birds were being killed for their feathers and for target practice.
Samples from about two dozen dead pelicans from the reserve and from other parts of the Upper Midwest are being tested at the National Wildlife Health Center in Madison, Wis.
"There has been no consistent finding as to cause of death," said Kathryn Converse, wildlife disease specialist with the center.
Researchers had found botulism in two of the dead pelicans from the reserve, Converse said. None of the pelicans had tested positive for West Nile or other viruses, she said.
Erickson said officials initially blamed a coyote that had a den about a mile from the nesting grounds, and killed it. But the exodus continued.
"It's weird," Erickson said. "We feel helpless because we don't know what else to look at."
Wildlife officials have been doing annual aerial surveys of the pelicans since 1972. The number of pelicans had tripled at the refuge in the past 30 years. A record 35,466 breeding pelicans and 17,733 nests were tallied in 2000 at Chase Lake, Erickson said.
This year, there have been reports of extraordinary pelican sightings in Illinois, Wisconsin, Montana, Nebraska and Michigan. But the numbers reported throughout the Upper Midwest do not add up to the nearly 28,000 recorded at the refuge in May, before the exodus, Erickson said.
A couple of hundred "loafers," or pelicans not yet of breeding age, remain at prairie potholes in the Chase Lake area, Erickson said.
Erickson is betting the big birds will return to Chase Lake next year.
"For whatever reason, they picked Chase Lake to nest for hundreds and maybe thousands of years," Erickson said. "I'm pretty confident they'll come back."
If the birds do return, Erickson said, access for birdwatchers would be limited during nesting.
The pelicans may be making some kind of a natural correction, said Ken Torkelson, a spokesman for the U.S. Fish and Wildlife Service in Bismarck.
"They've been relying on Chase Lake a long time, and maybe they felt it could no longer support the species so they picked up and moved some place that could," he said.
By James MacPherson