If you ever go to Austin Texas a thing you must do is see the bat bridge. It is a bride with grooves in it to allow it to expand and contract that also house millions of bats. In the summer at night, the bats will rise out in handfuls and fill the air. It is possible to take a 1.5 mile kayak tour to see it at the shop 'Live, Love, Paddle' which is an awesome kayak/canoe/paddle-board shop. It is an amazing phenomenon. Peace!