Watch this endless river of bats emerging from this cave. This is Cueva de los Murciélagos in Mexico. Twilight approaches, bats begin spiralling out of caves in a counter-clockwise direction, possibly to elude predation, a cyclone emerging to feed. Bats have a magnetic substance called magnetite in their cells, an 'internal compass' helping them to navigate: https://www.sciencedaily.com/releases/2008/02/080226213443.htm