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Mary Hennen

Collections Assistant III

Collections Center
Evolutionary Biology

My primary work outside of the bird collection is with Peregrine Falcons (Falco peregrinus)living in and around Chicago. As recently as 1960's, peregrines had been extirpated east of the Rockies.

Many factors contributed to the decline of the peregrines, including habitat loss, hunting, and egg collecting, though the predominant cause was effects of organochlorines such as DDT. By comparing the egg shell thickness of the few remaining peregrines to historic oology collections including the Field Museum's, scientists discovered that DDT and it's byproducts interferred with calcium production in females causing them to lay thin eggs which subsequently were crushed during incubation.

During the 1970's, recovery efforts for the peregrines began with the banning of DDT in 1972 and in 1973 placing the species on the Endangered Species List. During the 1980's Chicago joined other programs in the Midwest to help reintroduce the peregrine back into the wild.

The Chicago Peregrine Program now directs it's focus towards monitoring & managing any peregrines in Illinois. The peregrine falcon was removed from the Federal Endangered Species List in 2000 though it remains listed as an Illinois State Threatened Species.