Not A Nice Birdy.

In northern England, where these cursed corvidae are wreaking unprecedented havoc on the songbird population (at the same time as every other factor under the sun is granted full blame by the wet and weak) - they are pretty much getting 'a free pass'.
If you have a decent airgun - put a chicken carcass down in your garden to tempt them - then show some guts - kill 'em! And as many as you can until they realise that your garden is not for them. (They aren't stoopid.)