 These granite cliffs are important for peregrines. In fact, each year, popular climbing routes in the area close temporarily to give nesting falcons their space. Historically, peregrines bred throughout New Hampshire's White Mountains, but widespread use of the pesticide DDT caused them to disappear from the state and throughout eastern North America by the 1960s. Biologists released captive-raised peregrines, hoping to reestablish the species in the wild.