The bald eagle is an American wildlife success story. Almost extinct due to hunting, habitat loss and the effects of pesticides like DDT,* the bald eagle has made a stunning recovery.

In 1782, the Continental Congress made the bald eagle our national bird. Bald eagle populations dropped from more than 100,000 nesting eagles at that time to only about 400 breeding pairs in 1963. Today, there are more than 7,500 breeding pairs in the lower 48 states - including an increasing number of nests found in Illinois.

Bald eagles nest in the northern United States and Canada, migrating south during the winter when rivers and lakes freeze. They are often seen at locks and dams where water remains open year all winter for fishing.

Today, bald eagles are important tourist draws for river communities. Many river towns host eagle watching festivals in winter.

Their nests are giant collections of sticks called eyries. They add to the nests each year until they are several feet across. Additional source: U.S. Fish and Wildlife Service

 *DDT was originally created in 1873. Only when its use as an insecticide was discovered in 1939, however, did it come into widespread use. The scientist who made this discovery was awarded the Nobel Prize in 1948.

After World War II, it became especially popular due to its effectiveness against mosquitoes that spread malaria and lice that carried typhus. The World Health Organization estimated that 25 million lives were saved because of its use. Problems soon surfaced, however, as many insects began to develop resistance to the insecticide. It was also discovered to be highly toxic to fish.

Because it does not break down easily, DDT builds up in the fatty tissues. Animals that ingest it, carry it for some time. It takes an animal eight years to metabolize one half of the DDT it consumes. Birds, like the bald eagle, ingested DDT after eating contaminated fish. The DDT caused the bird's egg shells to be brittle and thin and to break easily. Eggs often were broken in the nest when the parents sat on them during incubation. This was one of the reasons populations declined to dangerous levels.

DDT was banned in the United States in 1973, although it is still used in other parts of the world. Birds that migrate to other continents are still at risk. primary source: University of Oxford, Department of Chemistry