It was not until 1962, with the publication of a book called Silent Spring, that people began to look at the long term effects of the use of chemicals. In the book Silent Spring, marine biologist and author Rachel Carson documented the effects of chemical pesticides on the environment.
In particular Carson noted that the chemical Dichlorodiphenyltrichloroethane, better known as DDT, seemed to cause birds to produce thinner egg shells which resulted in decreases in the population of several bird species. DDT would travel up the food chain as insects with the poison in their system would be eaten by fish or small birds. The poison would be transferred to the fish or bird which would then get eaten by a larger bird. DDT would build up on birds that were higher up in the food chain each time they would eat some infected prey. Eventually the DDT would alter the birds calcium metabolism resulting in the production of thin shelled eggs that would usually break during incubation.
DDT effected many species of birds but some of the birds that were hit the worst were pelicans, brown pelicans worse then white, peregrine falcons, golden eagles and bald eagles. Silent Spring helped to launch the environmental movement and caused an uproar that eventually led to the ban of DDT in the US in 1972. Since DDT was banned all of the species mentioned above have made significant recoveries and all of those that were listed on the Endangered Species List have since been delisted.
The last to be removed from the Endangered Species List was the bald eagle which was removed in 2007. Bald eagles sightings are now quite common here in Minnesota. There are more eagles in Minnesota then any other state in the continental US. In 2007 they had counted 1312 nesting pair in Minnesota, in comparison their were only around 400 nesting pair in the entire continental US back in 1963, which was the year that I was born. In the winter eagles from all over Minnesota, Wisconsin, Michigan and south central Canada congregate in several locations in southern Minnesota where they can find open water in which to fish. Reeds Landing is a small town on the Mississippi that sits across from where the Chippewa River empties into the Mississippi. The water typically stays open all year which is why you can great views of eagles like the ones above if you are willing to brave the intense January weather in Minnesota.