Two years ago, when the farmer chopped down all the evergreen trees on the slope above our garden, he inadvertently removed nearly all the suitable locations for birds to nest. I never thought of it until this week, when I saw that at a height of about ten feet (3m.) above the ground someone’s been nailing bijou avian mud huts to the remaining birch trunks.

I started to notice them one afternoon while I was going for a walk with the dogs and goats. At first I thought they must be someone’s art project (there’s a lot of that sort of thing around here), but bird houses make more sense. I must have seen at least fifty of them, maybe there are lots more.
Mounted on almost every remaining tree there are four different shapes that comprise what I assume to be four different housing types to accommodate the habits of different species. This one below is kind of interesting because, unless they are expecting the birds to unscrew the hooks on either side with their beaks, there’s no visible entry. To scare away small children (or perhaps to attract their interest, it’s all guesswork) the front panel has a Hallowe’en-type imprint, the owl as predator, and there are some slats from a bamboo blind hanging underneath, probably to sharpen claws and beaks. None of the owls I’ve seen around here would fit in this box; it’s not much bigger than a jumbo box of cornflakes.
This one below has a tiny slit, like a letterbox, that my wife says is the entry. She says they make it that small so that squirrels can’t get in – I don’t know how she knows this kind of thing – so maybe someone ought to be making houses for the squirrels too. Empty says that red squirrels can’t remember where they’ve left their hoards of nuts, so maybe they also forget where they live, lose their keys etc., “forget” to pay the rent.
I think the houses are made out of potters’ clay that has been rolled out flat like pastry and then shaped and fired. That means they won’t rot, but they might get a bit cold without some straw inside; I suppose it’s up to the birds to provide that sort of thing. The houses all have a yellow number on the side as if someone’s expecting the post office to deliver the mail.

Good luck with that, the postman won’t come up to our house.
Update: These are homes for bats not birds. See rr’s comment & link, below.