▁during ▁her ▁first ▁summer ▁there . ▁ ▁The ▁per egr ine ▁fal con ▁became ▁an ▁end anger ed ▁species ▁primarily ▁due ▁to ▁the ▁use ▁of ▁org ano ch lor ine ▁p estic ides , ▁especially ▁D DT , ▁the ▁break down ▁of ▁which ▁lower ed ▁est ro gen ▁levels ▁in ▁the ▁blood stream ▁of ▁female ▁per egr ine ▁fal cons ▁and ▁in hib ited ▁the ▁production ▁of ▁calci um , ▁causing ▁eggs ▁to ▁grow ▁th inner ▁by ▁up ▁to ▁ 2 0 ▁percent . ▁Since ▁per egr ine ▁fal cons ▁lay ▁their ▁eggs ▁on ▁rock y ▁led ges ▁rather ▁than ▁n ests , ▁the ▁th inned ▁shell s ▁would ▁break ▁under ▁the ▁stress ▁of ▁both ▁the ▁rock y ▁led ge ▁and ▁the ▁weight ▁of ▁the ▁parents ▁during ▁inc ub ation . ▁Following ▁ 1 9 7 0 , ▁recovery ▁efforts ▁for ▁the ▁per egr ine ▁fal con ▁population ▁have ▁been ▁successful . ▁The ▁agricult ural ▁use ▁of ▁D DT ▁was ▁b anned ▁in ▁the ▁United ▁States ▁in ▁ 1 9 7 2 , ▁and ▁recovery ▁teams ▁in ▁the ▁eastern ▁United ▁States ▁were ▁successful ▁in ▁bre eding ▁and ▁training ▁per egr ines ▁in ▁capt ivity ▁to ▁later ▁release ▁to ▁the ▁wild , ▁a ▁procedure ▁called ▁hack ing . ▁In ▁ 1 9 9 9 , ▁the ▁per egr ine ▁fal con ▁was ▁removed ▁from ▁the ▁U . S . ▁End anger ed ▁Species ▁list . ▁ ▁Content ▁summary ▁ ▁The ▁events ▁of ▁W ings ▁for ▁My ▁Fl ight ▁take ▁place ▁throughout ▁ 1 9