Bald Eagle Timeline: Chemical Cause Identified
As conservationists began noticing the thinness of the eagle eggs, a few scientists began to suspect a connection between sick eagles and a pesticide, called DDT, used by farmers to kill mosquitoes and other pests that bothered livestock. Our next timeline entry comes from Silent Spring, a book published in 1962, that summarized this research—and sparked a national conversation.
1962: Rachel Carson’s Silent Spring Published
“It was a spring without voices. On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices there was now no sound; only silence lay over the fields and woods and marsh.”
Rachel Carson, Silent Spring (New York: Houghton Mifflin, 1962), 1.
A widespread shift in America’s thinking happened when scientist and marine biologist Rachel Carson wrote Silent Spring. The book described DDT's effects on the eggs of the bald eagle and other raptors. The birds’ eggshells were thinned out, causing many of the chicks to die before they hatched. Carson also noted that because the birds are predators, bald eagles ingested the pesticide through their prey, making the chemical effects even stronger on those higher up the food chain. Lawmakers, and even the president of the United States, praised Carson for bringing this evidence to the public.
With more attention and research focused on this issue, evidence of the pesticide’s effects began to pile up. In 1969, the first controlled experiments showed a clear cause and effect relationship between DDT and reproductive problems in raptors such as eagles. In 1972, the federal government banned DDT use.
To learn more about Rachel Carson and the effect of Silent Spring, watch this video from American Experience.
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