Bald Eagle

by Mollie Mondoux

The bald eagle (Haliaeetus leucocephalus) is a large and magnificent bird, about 30 to 43 inches from beak to tail with a wingspan of 6-1/2 to 8 feet. Ironically, the bald eagle's weak, thin chittering voice does not match its magnificent stature or its national symbol status.

Bald eagles live mostly near seacoasts, lakes, or rivers where they build large nests of sticks placed in tall trees. A small concentration of bald eagles frequently winters in Oregon's Willamette Valley, roosting in the Coburg hills and hunting in the nearby fields.

Although it is impossible to know whether these wintering eagles are local or migrants, the local breeding population seems to be expanding. The Oregon Department of Fish and Wildlife finds new nests each year, usually along the Willamette River.

Bald eagles generally eat a lot of fish, and their fish-eating habits have partially contributed to their population decline. Pesticide run-off from farmlands can concentrate in fish tissues, which then get passed to bald eagles eating the fish. In 1978, the bald eagle was listed as endangered throughout most of the contiguous United States (given a threatened status in Oregon and four other states) under the Endangered Species Act.

Due to the banning of the organochlorine pesticide DDT and the success of captive breeding programs, the bald eagle population has made a recovery in the last 20 years and its status was upgraded to threatened in 1995.

Poisoned Bald Eagle Rehabilitated and Released

By Louise Shimmel and Mollie Mondoux

Jim Monroe, a sheep rancher in Lebanon, Oregon likes watching the bald eagles fly over his fields as they come and go from their winter roosts in the hills behind his place. On February 7th, 1998 he saw an adult bald eagle with white head and tail feathers, but it wasn’t flying overhead. It was lying spread eagle in his neighbor’s grass field and he knew something was wrong. Monroe called the Benton County Sheriff’s office and was put in touch with the Cascades Raptor Center in Eugene.

When found, the eagle could move only its head and wings. Its pupils were in spasm and its legs were locked in the rigid paralysis characteristic of organophosphate poisoning. The eagle’s feet were so tightly clenched that its talons were piercing its toes.

There are dozens of organophospates found in thousands of products on the market, with uses ranging from nematicides to external parasiticides. These products come in spray, powder, and granular forms, with granular forms being readily eaten by songbirds or other birds and mammals foraging in treated fields.

These affected animals are then consumed by raptors. It is possible that spraying a field before a rain will cause pooling and run-off that could affect birds bathing, swimming, or drinking that water. There have even been incidences of illegal use of these pesticides to lace carcasses with the specific goal of poisoning scavengers.

Organophosphate insecticides are harmful to nerve cells. They deactivate the enzyme that breaks down a chemical substance (neurotransmitter) at certain nerve endings and junctions. If this neurotransmitter is not broken down, it builds up at nerve endings, and the poisoned animal is continually stimulated, eventually dying of respiratory failure.

Sub-lethal doses can cause weakness, uncoordinated movements, inability to stand, rigid paralysis, clenched talons, rapid respiration, muscle twitching, rapid alternating contraction and dilation of the pupil and other eye spasms, and even the absence of the pupillary light reflex.

Although it’s not known how this bald eagle was poisoned, Cascade Raptor Center (CRC) based the treatment on the clinical signs. Blood tests later confirmed organophosphate poisoning. Within four days the eagle regained some use of its legs and within eight days, it could stand. It continued to improve, and after 16 days, it was transferred to the Chintimini Wildlife Center in Corvallis, Oregon.

At Chintimini, the eagle could exercise and regain flight conditioning in the 30-foot x 60- foot flight cage. Cascade Raptor Center does not have a large flight cage, so sharing Chintimini’s conditioning facilities helped to get the bald eagle recuperated sooner.

The two rehabilitation centers had planned a bald eagle release party on March 7th, 1998 at the E. E. Wilson Wildlife Sanctuary, but the eagle had its own ideas of when to leave.

Several days before the planned release, Jeff Picton, CWC’s Executive Director, noticed that the eagle was becoming increasingly stressed, flying about the flight cage crashing into the cage’s mesh, hanging from it, and tearing holes.

Picton worried that the bird might break some of its feathers, which would delay its release. It was imperative to release the eagle immediately. “After all,” Picton said, “our number one concern here is this bird’s welfare.”

And so, on March 5th, after the eagle had been at CWC for 10 days, Picton opened the flight cage door and without ceremony shooed the bald eagle off. With just a few strokes, the bird’s huge, powerful wings carried it low over CWC’s fields at first, but soon it soared, circled, and took off over the trees.