I have been privileged to see the famous bat colony of Austin, Texas, emerge--once. I was too awed by the sheer numbers (up to a million and a half) to actually notice whether they wheeled clockwise or not, but as I cast my mind back, the image seems to be clockwise.
Here's a link that explains about drag, lift, and thrust. Possibly these are subject to the Coriolis effect.
http://www.ucmp.berkeley.edu/vertebrates/flight/physics.html
Here is a link to the first of 5 or 6 pictures of them emerging. But if anyone can tell which way, you're a better observer than I am.
http://www.pbase.com/image/264541