About a million bats fly out of the Mulu Cave in Sarawak, Malaysia, every evening to look for food. They fly out in batches and it sometimes takes two hours before they are all in the air. When they leave the cave they form a circle (see photo), before forming sinusoidal waves that stretch great distances. Why do they do this?
The sinusoidal wave still seems to be a matter of conjecture - Ed
• Mexican free-tailed bats emerging from caves in the southern US fly in the same circular pattern, and around the British Isles puffins approaching their burrows also fly in a "wheel flock". Fast-flying bats or birds adopt this as a protection against predators such as hawks, gulls or skuas.
I am unsure about the sinusoidal movement. Perhaps it arises because bats are safer from predators near the ground but have to seek their food higher in ...