An Unusual Sort of Home

We have a cowbell hanging up at the back of our house, a clichéd memento from a trip to the Alps. For the most part, I forget it's there, normally receiving an abrupt reminder when I clonk my head on it en-route to the garage. But recently we've been having some strange experiences in its vicinity. For instance, the other day when I blundered out there to unlock the garage door, I was shocked to hear a frantic fluttering of wings, mere millimetres from my ear as I walked by the bell. Now, admittedly it was getting dark, but I was pretty sure I would have seen any bird perched on it. I mentioned it to he who fixes the computer and he confirmed that he'd had similar experiences. Our suspicions rose as further incidents occurred.
So today when I went out to unlock the door I kept a careful watch on the bell. I'll confess right now, I did jump, and I may even have gasped, but as I passed by, a bird (we've since discovered it's a bluetit) flew out from inside the bell. Dry, impossible for predators to get inside, the enterprising bluetit has obviously decided it makes the perfect shelter.
I've yet to work out how he perches inside it. I have visions of him tying himself to the clapper so he can nod off without falling out. However he does it, he's definitely claimed our Alpine memento as his home.
Now, I must remember not to accidentally walk into it when going to the garage.