On page 15 of the BHW a great article by Keith Turnbull (Barnsley Tyke) about a survey done by fellow fancier Darren Cantrill,about the feeding habits of the peregrine and how their numbers fluctuate depending on the routes taken by us when flying our birds,when switching our routes every few years,we cut of their feed supply,and so reduce the number of chicks reared,plenty of food for thought here.