Every evening from March to September, just before sunset, as many as 12 million Mexican free-tailed bats erupt from Frio Cave in search of dinner. The bat colony is the second largest in the world. Tour guides lead a caravan of visitors driving their own cars two miles from the ranch gates to Frio Cave, then guests are taken to the top of a hill to witness the winged spectacle. With the sun low in the sky and the bat signal shining, the cloud of bats bursts forth alongside cave swallows and rock wrens, seeking insects to eat while evading birds of prey such as kestrels and peregrine falcons. After spending the spring and summer mating in Frio Cave, the bats resume their migration to Mexico and the college students return to their dorms.