There are three sub-species of peregrine falcons found in Canada; only the anatum sub-species breeds in Alberta. Prior to the 1970s, peregrine falcons could be found throughout Alberta. They nested on cliffs along the major river systems of southern Alberta and, in northern Alberta, nested along the north shore of Lake Athabasca, the riverbanks of northeastern Alberta and on rock outcrops throughout the Canadian shield. This species was extirpated in southern Alberta in the early 1970s, mainly because of reproductive failure caused by organochlorine presticides.