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Spring came without birdsong
Carson's finding
Rachel Carson collated the scientific research on those silent mornings in Silent Spring, published in 1962. She demonstrated that the missing dawn chorus came from the accumulation of DDT, a synthetic pesticide.
Eggshells and the ban
DDT thinned the eggshells of birds, and thinner shells meant reproductive failure. Carson publicised the alarm of a silent landscape, and the US eventually banned DDT. Without her book, many bird species may have been lost.
Silence as a signal
Her case shows what ecoacoustics later built on: a landscape with no animal sound is a sign of nature collapse. The dawn chorus is a measure of how a habitat is doing, and when it stops, something in the system underneath has failed.
How does DDT thin eggshells?
DDE, the main breakdown product of DDT, interferes with the shell gland's ability to deposit calcium, which leaves eggshells thinner. DDT also builds up as it passes up the food chain, so predators such as peregrine falcons, bald eagles, and brown pelicans carry the heaviest loads. Thin shells crack under the weight of the incubating parent.
How did Silent Spring lead to the DDT ban?
The book appeared first as a series in The New Yorker in 1962 and drew a huge public response. President John F. Kennedy asked his Science Advisory Committee to review the issue, and its 1963 report backed Carson's main findings. The US Environmental Protection Agency was created in 1970, and in 1972 its first administrator, William Ruckelshaus, banned most uses of DDT in the country.
How did bald eagles recover after DDT?
A 1963 count found only 417 nesting pairs of bald eagles in the lower 48 states, according to figures widely cited from the US Fish and Wildlife Service. After the DDT ban and protection under the Endangered Species Act, numbers climbed steadily. The eagle was removed from the endangered species list in 2007.
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