Experts say a swarm of black flies appears to be the best explanation for why endangered whooping cranes are abandoning their nests at a Wisconsin wildlife refuge.
But the Milwaukee Journal Sentinel reports the pesky insects at Necedah National Wildlife Refuge near Tomah aren't the only reason the birds are struggling.
Whooping cranes were reintroduced at the refuge in 2001 in the hope they would once again inhabit, and potentially flourish in, the eastern United States.
The effort has included a multimillion-dollar investment of public and private funds, a collaboration of government and citizen groups, and bands of dedicated crane devotees who track the whoopers' every movement.
While there have been successes along the way, the work has yet to produce a self-sustaining flock.