After DDT was banned nationwide in 1972, the effects of its use in this country were evident in bird populations. With many fewer insects to feed on, Eastern Bluebird and other songbird populations suffered significant declines, and bluebirds also died from eating insects contaminated by other pesticides used after the banning of DDT. Runoff carried DDT from fields to marshes, and it was also sprayed directly on marshes, where successive steps in the aquatic food chain concentrated it in the tissues of top predators such as ospreys. Affected ospreys laid eggs with thin shells likely to break during incubation.