In the mid 1950’s, Charles Broley, a retired banker from Winnipeg, Canada, began to suspect that pesticides (specifically DDT) were to blame for the decline of Bald Eagles. In 1942 DDT (dichlorodiphenyltrichloroethane) was considered a miracle - the answer to all the country’s insect problems. It killed every insect it came in contact with. It was sprayed extensively along the coast to control salt marsh mosquitoes. Farmers sprayed the pesticides on their crops, which eventually ended up in streams, rivers and lakes. It was not until the early 1960’s that Mr. Broley’s suspicions were found to be correct. Not only were Bald Eagles being harmed by the pesticide, but birds all over the country were dying. It was this dramatic decline in the bird populations that prompted Rachel Carson to write “Silent Spring.”

Toxins may not be dangerous in the water because they are diluted, but because some of these poisons are trapped in the bodies of fish and other animals (usually in fat tissue) they build up over time. When eagles eat these animals that have a large amount of toxins in them, the eagles then become poisoned. This concentrating of toxins through the food chain is known as biomagnification. Eagles like to eat bottom feeders (catfish, carp) which tend to pick up these toxic sediments from river and lake bottoms. Well, now you can guess the rest. Imagine, too, if you were an eagle, would you take a lot of little catfish over one big ol’ catfish that has washed up fresh on the shore? Unfortunately it is those older fish that have a lot more built-up toxins.