Managers of the eastern migratory flock of Whooping Cranes may attempt to alter the birds’ breeding season next spring at Necedah National Wildlife Refuge in central Wisconsin. The goal: to produce more successful nests.
Most nests at the refuge have failed due to the black fly. Adult flies emerge in great numbers in spring, torment the birds, then die off. For the few weeks that the insects are around, the big white cranes are easy targets as they sit on nests, incubating eggs.
For a couple of years, in an experiment, a biological control agent known as Bti was applied to areas near the refuge where the flies hatch, causing their number to fall. Last spring, Bti was not applied, and the flies again forced the birds to abandon their nests en masse.
Whooping Cranes that have been introduced into an environment are newcomers, biologists say; the environment should not be altered simply for their benefit. Trout, swallows, and other refuge residents feed on the black fly. Removing it would certainly have an effect on them.
If a new proposal is approved in the coming months, biologists will remove the birds’ eggs next spring and hatch them in captivity.
The hope is that at least 30 percent of the wild crane pairs will re-nest within a few weeks, after the flies have died off for the year. By forcing the cranes to double-clutch, managers may boost the Whoopers’ breeding success significantly.
A version of this article appeared in the December 2013 issue of BirdWatching magazine.