Beginning of article  Arctic and American peregrine falcons
(Falco peregrinus tundrius and F. p. anatum, respectively) were
listed as endangered in 1970. At the time, some local
populations of American peregrine falcons in the eastern United
States had disappeared, and populations in western and northern
North America had been reduced by 80 percent or more.
Organochlorine pesticides such as DDT and its breakdown product
DDE were identified as the main cause of the decline. The
peregrines accumulated these chemicals in their tissues by
feeding on birds that had eaten DDT-contaminated insects or
seeds. These chemicals prevented normal calcium deposition
during eggshell formation, and caused females to lay thin-
shelled eggs that often broke before hatching. The use of DDT
was restricted in the United States and Canada in the early
1970's, and populations of peregrine falcons in North America
began to recover by the late 1970's.  After Arctic and American
peregrine falcons were listed, the Fish and Wildlife Servi