How did DDT affect bald eagle reproduction?

The use of DDT had a devastating impact on bald eagle reproduction through the processes of bioaccumulation and biomagnification.

As the pesticide entered waterways, it was ingested by fish, which were then consumed by eagles. This caused the chemical to concentrate in the tissues of the birds. The primary reproductive consequence was the thinning of eggshells. Because the shells became so fragile, they would frequently crack under the weight of the parent birds during incubation, leading to reduced egg viability and fewer hatchlings.1234

This phenomenon, which also affected other birds of prey, resulted in severe population declines that pushed the bald eagle toward the brink of extinction. The subsequent ban of DDT in the 1970s, combined with protections under the Endangered Species Act, allowed the species to recover significantly.351