MILWAUKEE — Experts
say swarms of black flies appear to be the best explanation for why
endangered whooping cranes are abandoning their nests at a Wisconsin
But the Milwaukee
Journal Sentinel reported Sunday (http://bit.ly/11Psf93
) that the pesky insects at the 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
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 watchers.
There have been
successes. Five chicks have hatched and joined the wild population.
Ultralight aircraft have successfully guided young birds south for the
fall migration while other young whooping cranes have followed older
cranes in successful migrations south and north.
But the work has yet
to produce a self-sustaining flock.
The whooping crane
population in the eastern U.S. stands at 106 migrating birds, numbers
that have been built up by the release each spring of chicks born in
Most of the 600 or so
whooping cranes in existence are part of the only other migrating
population, which winters along the Texas Gulf Coast and summers in
Alberta, Canada. That population is faring relatively well.
In the east, however,
"we would have hoped that we would have a trajectory by now where
they were well on their way to a sustainable population," said
Jeb Barzen, director of field ecology for the Baraboo-based
International Crane Foundation, part of the Whooping Crane Eastern
Partnership, formed in 1999 to lead recovery efforts.
cranes, the tallest birds in North America, were once frequent targets
of unregulated hunting. The world's migrating population was down to
15 in 1941.
A few years ago,
crane watchers noticed that the reintroduced birds would pair off at
Necedah, build nests and lay eggs. But then they would abruptly
abandon their nests. The leading hypothesis pointed at the hordes of
biting black flies at the marshy area. As an experiment in 2011 and
2012, biologists treated two rivers near the refuge with a soil
bacterium known as Bti, which is used an alternative to chemical
pesticides. Black fly numbers fell significantly.
Four chicks hatched
in 2011, but all eventually died. Several more chicks hatched in 2012,
and two survived.
Bti treatments were
not used this spring, and the black flies returned. So far, 18 nests
have been abandoned amid dense clouds of black flies. No chicks have
hatched this year.
While the flies
appear to be the problem, Barzen said, researchers still need to learn
more about the role of predators, habitat quality and food supply,
whether adults have sufficient energy stores to mate and raise chicks
after migrating back to Wisconsin, whether they've gained enough
experience at nesting and parenting, and whether cranes raised in the
wild make better parents than those raised in captivity.
Given the struggles
at Necedah, starting in 2011 the partnership released whooping cranes
in the Horicon Marsh near Waupun and the White River Marsh State
Wildlife Area near Berlin, where Barzen said conditions might be
better. There are no black flies. There are no wolves and there are
fewer other predators such as otters and bobcats. The soil is also
richer which might mean more food.
"Our hope is
that in another five to 10 years, we will know what it takes to make
it work," Barzen said.