Disturbance of cliff nesting sites, shooting and egg collecting have
reduced peregrine falcon populations. However, the largest threat to
the peregrine of recent year is pesticides. Peregrines are predators at
the top of the food chain and accumulate high levels from their prey
since pesticide residue becomes more and more concentrated as it works
its way up the food chain. This phenomenon is known as bioaccumulation. (Fig 1.0)
DDT, an organochlorine compound used as a crop pesticide, was banned throughout North America in the 1970s. Organochlorines are not only toxic but highly persistent in living tissues, resisting breakdown and resulting in accumulation, particularly in long-lived predator species such as the peregrine falcon. DDE, the major breakdown compound of DDT, is still found in the tissues and eggs of peregrine falcons. These pesticide residues result in females laying very thin-shelled eggs, which cannot sustain the weight of incubation, thus causing reproductive failure.
While many South and Central American countries have banned the use of DDT, its use still persists in parts of Latin America, the wintering grounds of many peregrine populations. This use alone causes major problems for the peregrine. Blood samples taken from southern United States populations of peregrines during fall and spring migration showed that most of the pesticide burden was accumulated in wintering areas in Latin America. Young birds accumulated levels of DDE as high as those in adult birds just after one winter in the south.