RUSSELLVILLE -- An assisted migration of juvenile whooping cranes has been put on hold in Russellville as organizers of the trip and government regulators try to work out a compromise that would send the rare birds on their way to Florida.

The Federal Aviation Administration prohibits pilots of ultralight aircraft from being paid to fly. Operation Migration, the group that leads young whooping cranes from Wisconsin to Florida each year compensates its pilots.

The flock of nine whooping cranes being led by the ultralight pilots arrived in Russellville on Dec. 11 for what was expected to be an brief rest stop. Bad weather initially kept the birds grounded in Franklin County before Operation Migration officials agreed to temporarily suspend the 1,285-mile journey while attempting to resolve the problem with using paid pilots.

An attorney for Operation Migration has asked the FAA for a waiver from the no pay rule for ultralight pilots to allow the trip to continue.

If the problem cannot be resolved, U.S. Fish and Wildlife Service officials might move the whooping cranes to a nearby wildlife refuge, or Operation Migration officials could transport them in cages to wildlife refuges in Florida.

Whooping cranes are one of the rarest birds in North America, with 436 remaining in the wild.

The assisted migrations are part of the an effort to restore the whooping crane population. Once whooping cranes that were raised in captivity are led from their summer homes in Wisconsin to winter homes in Florida, they can make the journey on their own.

While the migration is halted in Franklin County, the whooping cranes are being kept in a protected enclosure near Russellville Airport.