Jackie, the Austin bat colony of 1,500,000 that you saw is said to rise from their roost in the bridge counterclockwise. And so says this from the National Park Service...
"Hundreds of thousands of Mexican free-tailed bats, whirling counterclockwise, spill forth from a gigantic hole in the earth and are silhouetted against a colorful desert sky ... this is the bat flight experience at Carlsbad Caverns National Park."
And faldage, yes the coriolis effect is small on small sized structures but it tugs with unrelenting persistence. Animals that fly especially need every economy of energy that they can get.
By-the-way, in the morning after the night of feeding, the northern hemisphere bats fly back home, but they don't screw themselves (clockwise) back into the cave, instead they dive in a straight line to the mouth of the cave and on to their roost.
OP
