We have crows primarily in this city (Edmonton too I suspect) because our urban forest is old enough (and tall enough) to provide nesting habitat for them. Not to mention that we have lots of food here - human-derived (garbage, road kill, planted gardens) and naturally-derived (berries, bugs, eggs, chicks, small mammals). They like to nest primarily in tall (over 50') spruce trees here, though I've seen them in large elms as well. Not a bad thing since merlins need crows to make nests for them. So if you have crows, you can have merlins. Both are noisy but if you have merlins, you won't have crows. As for the songbirds, the number of songbirds hasn't decreased (and yes, folks have actually done research on this) but rather they are being more secretive. They aren't as vocal, they will sit in more dense cover (juniper, cedar) and they won't stick to a regular schedule at feeders or the like. Crows (and squirrels, blue jays, grackles, raccoons) will predate nests (pretty much all nests) for eggs and chicks. Merlins on the other hand, do wait until they are on the wing but they are much more enthusiastic and exhibitionistic diners - they like to eat on telephone poles or garage roofs.
So enjoy your adult, mature trees and if you would prefer merlins to crows, be glad the crows are there now. Since the merlins don't repair the nests they use, they need to find new nests fairly frequently. So if you have crows again this year, maybe next year for merlins ....
Help any?