WI DNR news
February 7, 2001

MADISON – A female bald eagle that was found injured along a northern Wisconsin roadside last fall, then rehabilitated and released near Devil's Lake last December, is now leading a group of biologists back to her Crandon home thanks to a radio transmitter she is carrying in a small backpack.

The eagle was first reported to Department of Natural Resources officials in October when a concerned citizen noticed a bald eagle being cradled under the protective wing of what appeared to be its mate. When the pair was approached, one eagle flew away, but the other couldn't fly and was taken into captivity.

The injured eagle was brought to Marge Gibson, a raptor rehabilitator, and who determined that an unknown pesticide had poisoned the eagle's nerves, impairing her sight as well as weakening her wings and legs. The eagle was given an antidote for the toxin, in addition to fluids and rest. In December, the eagle was released in the Sauk City area.

Even though DDT, the pesticide responsible for the near extinction of bald eagles, was banned in Wisconsin, eagles are still in danger from other pesticides.

"This type of injury is being seen more and more," Gibson said.

After she was released, biologists tracked the eagle with a transmitter sewed into a carrying pouch with cotton thread, which will allow it to fall off in about a year. This "backpack" weighs only 54 grams, about the size of a small apple.

On Feb. 1, over a month after her release, the eagle was found missing in the Sauk City area. After searching the area with a plane and attempting to find her transmitter signal, a DNR pilot finally spotted her flying toward her former territory. Biologists don't know whether she was returning early to her nesting site or if she is going back to the area where she previously spent her winters.

It is questions like these that a cooperative study conducted by the DNR, Raptor Education Group Inc., and the Ferry Bluff Eagle Council are hoping to answer. By using transmitters to track these eagles, biologists will have a better understanding of how eagles use different habitats in the winter.

"Knowing what resources eagles use is important because it will allow biologists to protect these resources, preventing the bald eagle from rejoining the endangered species list from which it was recently removed," said Pat Manthey, an avian ecologist with the DNR Bureau of Endangered Resources.

The study will also answer questions concerning the average distance eagles can travel in a day, the routes they take to their destinations and where they prefer gather at night, called roosting.

Another objective of the study is to gather information on how eagles adapt to their environment after rehabilitation. Because the pesticides that injure many of these birds also cause permanent nerve damage, tracking the eagles allows biologists to gauge the success of an eagle's recovery.