Bat Exodus / Swarm
Bat watching is one of the highlights of Mulu National Park. At dusk, usually about 5pm to 7pm, millions of bats would swarm out of the Deer Cave in order to hunt for insects. On some occasions they have been known to fly out at 4pm, usually on darker, cloudy days.
The bats will come out and circle at the cave entrance for a few minutes to 'collect' everyone before proceeding out in a single wavy file. This circling cannot be seen from the bat observatory, however, as you only see them flying out by the millions in a wavy formation. Only those who come out from exploring the caves at the right time will get a chance to see this amazing sight.
In order to watch the phenomenon, a one hour trek through nature from the park entrance is required to reach the Bat Observatory of the park. A park guide is required. A fee of MYR10.00 is required per head per entry to the Mulu national park.
Bats are also known to swarm out at Niah Caves. Swiftlets also fly in swarms back to the Niah Caves in the evenings.