The magnitude of loss for Peregrines worldwide reached its peak by the 1960's. Breeding populations in North America were 10% of historic levels and in the UK numbers were reduced by an estimated 80%. While various factors such as habitat destruction, egg collecting & illegal hunting of the species contributed to the decline, the predominant cause was the buildup of organo-chlorines—DDT and its byproducts—in the birds. These accumulated chemicals caused addling of eggs, abnormal reproductive behavior in adults, and thinning of shells, which led to egg breakage.
By the 1970's, governments banned the use of DDT and the Peregrine Falcon was given protective status. Aided by the reintroduction of Peregrines through a process called hacking, wild populations recovered.
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