15 Other observers also documented that the great peregrine decline in the eastern United States occurred long before any DDT was present in the environment. And in Great Britain, in 1969, a three-year government study noted that the decline of peregrine falcons in Britain had ended in 1966 even though DDT levels were as abundant as ever. In addition, later research refuted the original studies that had pointed to DDT as a cause for eggshell thinning. After reassessing their findings using more modern methodology, Drs. Hickey and Anderson admitted that the egg extracts they had studied contained little or no DDT and said they were now pursuing PCBs, chemicals used as capacitor insulators, as the culprit.
Calcium deficiency is a known cause of thin eggshells.
After much criticism, Bitman repeated the test, this time with sufficient calcium levels. The birds produced eggs without thinned shells. The uses of DDT under the regulations involved here do not have a deleterious effect on freshwater fish, estuarine organisms, wild birds, or other wildlife. . . . The effect of the ban in other nations was less salutary, however. After spraying was stopped in 1964, malaria cases began to rise again and reached 2.5 million in 1969.