I love this thread!
So my parents in Lancashire have a few owl boxes in their garden, and we always have a tawny owl nesting. When the babies get big enough, they crawl out of the boxes and drop to the floor, then they're meant to climb up a nearby tree while they get their proper feathers. Unfortunately though, we've had years where they fall and it's raining and they get completely waterlogged before they can climb again and they get cold and die - so my Dad has saved numerous babies by making a "baby owl" box part-way up a tree where he'll put them if he finds them on the ground so their mum can keep feeding them while they grow. I have a photo of him somewhere sitting with a very wet baby tawny owl wrapped in a teatowel trying to warm it up. He said it stank!
One year, a wild wood duck decided to nest in the owl box instead.
He's also heard a cuckoo - he and his friend both heard it while they were out walking separately and both thought it was the other playing a joke, hiding in the tree shouting 'cuckoo'!
They also have a pair of great spotted woodpeckers and a peregrine falcon. Bullfinches, starlings (so many starlings!), chaffinches, robins, wrens, pigeons, etc are all very common.
I'm in the Lake District and we just have the typical "city" birds - pigeons, magpies, crows, etc...and hundreds of starlings currently living in the roof of the house opposite.