Every evening at dusk, one of the most extraordinary wildlife spectacles in Southeast Asia unfolds at the mouth of the Great Cave. Between 5 and 6 million wrinkle-lipped free-tailed bats (Chaerephon plicatus) pour from the cave in a continuous column — spiralling upward, fragmenting into ribbons, and streaming out across the forest to hunt insects above the forest canopy. The exodus, which takes 20–45 minutes, is audible from hundreds of metres away as a continuous rushing sound, like wind through a tunnel, overlaid with the echolocation clicks that are just at the threshold of human hearing.
The wrinkle-lipped bat is an insectivore that forages exclusively above the forest canopy. Its narrow, pointed wings give it the high-speed, direct flight needed to cover the enormous distances required to sustain a colony of this size. Females nurse a single pup per breeding season; the maternity colony inside the Great Cave sees thousands of births within a short window. Mothers locate their own pup among millions of others in the colony by a combination of individual vocalisations and olfactory cues — a navigational feat that remains incompletely understood.
The bat exodus and the edible-nest swiftlet return occur simultaneously and in opposite directions: as the bats pour out, the swiftlets stream in, creating a counter-rotating column of two species at the cave mouth. Bat hawks (Macheiramphus alcinus) and peregrine falcons station themselves at the cave mouth edges during the exodus, picking off individual bats in fast dives. This predator concentration is itself a spectacle — up to six or eight raptors working the column simultaneously have been recorded on peak evenings.
The best viewing point for the exodus is the platform at the base of the cave's West Mouth. Arrive at least 30 minutes before sunset — the bats begin emerging 15–20 minutes before the sun drops below the horizon. Bring binoculars but accept that much of the experience is about volume, sound, and movement rather than close-up detail. A red filter on a torch will let you see the bats without disrupting their echolocation. The boardwalk trail from the park office to the cave mouth takes about 45 minutes — plan your departure from the hostel accordingly.