The U.S. Fish and Wildlife Service is planning a gathering of pelican experts to try to solve the mystery of why the big birds abandoned the Chase Lake National Wildlife Refuge in central North Dakota.

No date has been set, but the meeting would include biologists and officials from refuges throughout the Upper Midwest, said Ken Torkelson, a Fish and Wildlife spokesman in Bismarck.

Last year, nearly 30,000 pelicans left the refuge near Medina, leaving their chicks and eggs behind. This year, the refuge saw a massive die-off of pelican chicks, followed by an exodus of their parents.

"Next year may bring a whole new mystery," Torkelson said.

Wildlife officials plan to discuss the pelicans' exodus and develop a plan for funding to further study the big birds.

"There have not been the answers we've been looking for yet," Torkelson said.

Samples of dozens of dead pelicans from the refuge and from other parts of the Upper Midwest are being tested at the National Wildlife Health Center in Madison, Wis. Torkelson said results are still pending.

About 200 pelicans remain in central North Dakota, but none are at Chase Lake, Torkelson said.

The white pelican colony at the 4,385-acre Chase Lake refuge has been the largest in North America, peaking at 35,466 birds in 2000.

Many of the big birds that left Chase Lake earlier this year probably headed to Canada, where extraordinary sightings were recorded, Torkelson said.

Pelicans typically leave Chase Lake in late September to their wintering grounds along the Gulf Coast.

"Most, if not nearly all, have migrated," Torkelson said. "They're headed toward hurricane country. Come next April, we'll know if they came back to nest."