I love easy questions at almost 10 pm Pegger - thank you!!
The answer is that they didn't nest here, they nested where there were cliffs in the wild. Manitoba does have some cliffs in the northern part of the province but for whatever reason we don't know of any peregrines that nest there, though it seems unlikely that there isn't at least one pair!! But what we define as a cliff is not necessarily what they classify as a suitable cliff-face. By 1970, there was only one know pair of nesting peregines in Canada east of the Rocky Mountains and south of the Northwest Territories and that was on the banks of the Bow River in southern Alberta. In that case the banks were high enough that they were deemed suitable for nesting. And one of the first urban nesting peregrines was the "Sun Life Falcon" in Montreal in the in 37, before DDT was in use after the Second World War and decades before peregrine population crashed. She lived and raised 21 young on the 20th floor ledge for 16 years. She was very visible, very aggressive and very famous.