I have noticed blackbirds doing this before on hot days, they sit out in the full sun with their wings out and a very strange look in their eyes. I guess that somehow they are trying to rid themselves of fleas and ticks and lice. Perhaps by heating the feathers so much all the extra wildlife leaps off the host and off to the cooler ground below. Here are a couple of shots from yesterday
They sit there for 10 minutes or so, the cat sits and watches them but doesn't bother to have a go at catching them at all.