Rats- it's a pleasure to watch them. They're like tops'l men in Nelson's navy; scamper, scamper, up and under; overhangs no problem. They worked out the first bird table right away and now they've worked out the second. Birds, however, do deter them; a blue tit fluttering round their ears when they're trying to climb will drive them back- and even on the ground they'll retreat before an advancing robin. Balance of nature, see.