OCALA, Fla. (AP) -- Twenty endangered birds are learning how to migrate to Florida.

Operation Migration pilots in ultralight aircraft have been leading whooping crane chicks from Necedah, Wis., since Oct. 16. Half the chicks will end their flight at St. Marks National Wildlife Refuge in the Florida Panhandle. The other half will stop at the Chassahowitzka National Wildlife Refuge in central Florida.

In the spring, the birds will return north on their own.

The 12 male and eight female chicks are grounded in Franklin County, Ala., until at least Tuesday, waiting for crew members to return from a holiday break.

Officials say this year's birds will boost the total to 100 whooping cranes in the eastern migratory flock. The only existing wild migrating flock flies from Canada to the Texas Gulf Coast.