The bald eagle was protected by the Endangered Species Act for 40 years, but researchers are still finding toxic chemicals in the eagles' plasma. (Photo by William Bowerman)
The bald eagle came close to extinction
before strong measures were taken to help pull
it back. The eagle was protected by the Endangered
Species Act for 40 years. And the government banned
toxic compounds such as DDT that caused damage to the
eagles’ eggs. Bob Allen caught up with researchers
who are monitoring the health of the birds. They’re
finding the birds are still being exposed to toxic
chemicals:
Transcript
The bald eagle came close to extinction
before strong measures were taken to help pull
it back. The eagle was protected by the Endangered
Species Act for 40 years. And the government banned
toxic compounds such as DDT that caused damage to the
eagles’ eggs. Bob Allen caught up with researchers
who are monitoring the health of the birds. They’re
finding the birds are still being exposed to toxic
chemicals:
We’re on a steep, heavily wooded hillside about a mile above a
barrier dam on the Muskegon River in Michigan. The land is part of a private
church camp. So, human intrusion on the site is low. And the
pond behind the dam provides plenty of food for eagles rearing
their young.
Once every five years researchers are permitted to come here and
take young birds from the nest.
“Usually we try to keep people about a quarter mile away from the
nest. And that way we don’t have human disturbance that
would cause them to fail.”
Bill Bowerman is a wildlife toxicologist from Clemson
University. He first became part of this eagle survey as a grad
student at Michigan State more than 20 years ago, about the time
researchers began taking blood and feather samples.
Wildlife veterinarian Jim Sikarskie says eagles sit atop
the aquatic food chain, so any contaminants in the ecosystem
eventually show up in them:
“The contaminants that are in the plasma from the blood and
from the feathers then help us evaluate the quality of the water in
the area around the nest. So we do birds from different watersheds
every 5 years as part of the water quality surveillance plan.”
The nest is a tangled mass of twigs in an aspen tree swaying in a
strong breeze about 60 feet off the ground. As the research team
approaches, the female lifts off and begins to circle and squawk
just above the tree-tops.
They lay out syringes and test tubes on the ground. Walter
Nessen gets ready to climb the tree. He’s worked with
Bowerman monitoring sea eagles in his native South Africa.
Walter buckles into his harness and straps a pair of climbing
spikes to his boots. He has the kind of wiry strength and agility
that makes for a good climber. He prefers not to use gloves to
handle the eaglets because he relies on a sense of feel between
his hands and their legs:
“Immature birds, nestlings, are quite delicate because their
feathers are not hard-pinned. In other words, there’s still
blood circulating inside the feathers as it’s growing. One has
to be careful not to bend them or break them because they
will not develop further. That’s the most important thing.
The other thing is you need to take care the birds have big
claws. It’s one of the first things developing on the birds so
they can attack you and claw you and scratch you and that
kind of thing.”
Walter wraps his climbing rope, really a polyester-covered steel
cable, around the trunk of the tree, locks it into his harness and up
he goes.
First he checks nestlings to be sure they’re old enough and in
good condition before lowering them down in a special padded
“eagle bag.”
With young eagles on the ground, everyone becomes hushed and
businesslike. Bowerman writes down the eaglet’s weight and
other measurements. They’re four to five pounds with some
down-like feathers still clinging to them. Most prominent are
their dark beaks and yellow-orange claws.
Sikarskie carefully drops a cloth hat over an eaglet’s head to keep
the bird calm. Then, he talks a young grad student through
taking her first blood sample from the underside of a delicate
wing.
The two nestlings are examined for parasites. Then, they’re leg
banded, tucked gently back in the bags and hoisted aloft. They’re
out of the nest for maybe fifteen minutes.
Places like this, far upriver from the Great Lakes, were refuges
for eagles back in the DDT era. Eagles survived here because
fish couldn’t pass above barrier dams on the rivers and carry their
toxic burden with them, and Bowerman says the difference is still
noticeable today:
“If you live along the Great Lakes you still have higher levels
of PCBs. You still find DDE, which is the egg shell thinning
compound that caused the eagle’s decline in the first place. If
you’re in an area like this which is upstream of the Great
Lakes, there’s much less level in these inland birds.”
Eagle research in Michigan extends back 47 years.
Bowerman calls it the oldest continuous wildlife survey in the
world. It’s a record that documents the recovery of a species in
trouble, but sometimes the information has a more immediate
impact.
Bowerman says some years ago, tests on baby eagle’s blood
from Michigan showed a spike of an unknown chemical. Lab
tests found it to be from a product called Scotch Guard, a stain
repellent for fabric produced by the 3M Company.
When told about it, 3M hired Bowerman’s professor, John Geise,
to find out how widespread the compound was:
“John’s lab went all across the world collecting tissues of
different wildlife species. And they found it world-wide. And
that’s why 3M took scotch guard off the market.”
Bowerman worries that monitoring efforts will slack off when
bald eagles are off the Endangered Species list, and that new
contaminants will be missed. But he can’t help being inspired
by the birds’ recovery:
“Does it make you any more alive to watch that beautiful
eagle soaring around? And it’s really neat to see how many
there are now. So this is just spectacular.”
For the Environment Report, I’m Bob Allen.
