In some places, peregrines also have had to cope with habitat loss and human disturbance. However, pesticide contamination has by far been the main cause of peregrine declines. In an effort to produce birds for falconry, falconers began breeding peregrines in captivity. Using techniques developed by falconers, biologists also began to breed them, with the hope of eventually reintroducing birds to the wild. Breeding programs at Cornell University and other places have been successful and many chicks have been reintroduced to traditional peregrine habitat.
Reintroduction involves more than just turning birds loose at a site.
The hope is that the fledged birds will eventually return to the area and take up residence. Peregrine falcons are nesting again in many places east of the Mississippi. In 1976, University of Minnesota biologists brought five peregrine chicks from Cornell University to Wisconsin. The birds were hacked successfully at a traditional eyrie on the upper Mississippi River. None returned to breed in Wisconsin, however.