Please, what animal is this?

I first saw it sprawled out on the wall of my back garden, sun-bathing. Well, that's what it looked like it was doing. It isn't a squirrel. It isn't a possum, or a raccoon. I don't think it's a Prairie Dog. It's too big to be a Pack Rat, isn't it? And it hasn't got a stripe, so it isn't (thank goodness!) a skunk.

Today it's on the window-sill of my study, eating birdseed.

It doesn't seem to be scared of people. Maybe it's somebody's escaped pet. A ferret, perhaps? No, it doesn't look much like a ferret.

But it really is cute, with its little ears and its little paws and its big, dark eyes.

So what is it?

Can anybody help?