PLANET EARTH Caves

All these animals spend their entire lives within the cave. They're totally dependent on the digested remains of food that's brought here from outside. Each evening in just two hours three million bats leave the safety of the cave to hunt for insects in the forest outside. But not all will return. As they leave the cave the stream of bats form a **doughnut **（甜甜圈）-shaped ring.



The wheeling bats seem to confuse a rufus-bellied（大腹便便） eagle, but they must still survive the attacks of other, more specialized, birds of prey. Peregrine falcons（游隼） and bat hawks are the jetfighters（喷气式战斗机） of the bird world. Good hunting will end as the light fades so the bat hawks bolt their catches on the wing and fly straight back for more. Any bat separated from the group becomes a clear and obvious target and is asking for trouble.



Yet the nightly onslaught has little impact on bat numbers - by the morning the vast majority will be back in the safety of the cave. Bats are not the only commuters in these Bornean caves. There's a day shift as well. Returning from hunting in the sunlight these commuters rely on their loud clicks to find their way through the cave passages in total darkness.