"Led" and not "lead"??? So they got adult cranes meanwhile to to the job alone or are there less cheery reasons?
Between 2001 – 2015, Operation Migration pilots used ultralight aircraft and played the role of surrogate parents to guide captive-hatched and imprinted Whooping cranes along a planned migration route, which began in Wisconsin and ended in Florida.
In early 2016, the U.S. Fish and Wildlife Service determined that the aircraft-guided method was too “artificial” and that cranes raised by costumed handlers, missed early learning opportunities. As a result, it was speculated that they did not properly nurture or protect their chicks when they had their own offspring. It was suggested that this inattentiveness was the cause of high pre-fledge mortality at the Necedah National Wildlife Refuge.
The U.S. Fish and Wildlife Service exercised its authority over the Endangered Species Act and ended the aircraft-guided reintroduction method.