By night, spectral bats leave their roost and swoop through the tree canopy of Costa Rica, wings outstretched as far as three feet wide, in search of prey: unsuspecting mice and rats, birds called motmots, even other bats. Sometimes, after they snag something good, they will fly back home with the doomed victim in their stalactite teeth and willingly give up a meal to another bat inside the roost. At the end of the day, the world's largest carnivorous bat is a rather cooperative creature.