The Bat Exodus in Mulu Caves
Part of the Mulu Caves travel guide — see every topic in All Mulu Caves Guides.
Every evening, weather permitting, the colony of wrinkle-lipped bats living in Deer Cave — estimated in the millions — leaves the cave mouth to feed, and it does so in a way that is genuinely unlike anything else. Rather than pouring out in a cloud, the bats emerge in discrete spiralling ribbons that twist and coil across the sky, corkscrewing outward one after another for anything from twenty minutes to well over an hour. There is a purpose-built observatory below the cave mouth, and it is the single most reliable spectacle in Mulu.
What happens
From around five or six in the evening, depending on the season and the light, bats begin to emerge from Deer Cave's mouth. They do not fly straight out: they gather and leave in coiling ribbons that wind across the sky in shapes that look almost deliberate, which is thought to be an anti-predation behaviour — bat hawks and peregrines wait at the cave mouth, and a dense twisting column is harder to pick from than a diffuse cloud. Successive ribbons emerge one after another, and on a good evening it continues for over an hour.
The observatory
A covered viewing area with benches sits on the boardwalk below Deer Cave's mouth, about a forty-five-minute walk from park headquarters, and the standard afternoon cave tour ends there. Guides explain what is happening and point out the raptors. Arrive by around five and be prepared to wait; the timing varies and the bats do not read the schedule. Bring insect repellent, water and something to sit on. It is free if you have already done the cave tour and reachable independently along the boardwalk.
When it does not happen
The exodus does not occur every evening. Heavy rain suppresses it, and on wet evenings the bats stay in — which in a rainforest with very high annual rainfall is a real proportion of nights. It is also less impressive when it happens in stages rather than in a sustained run. This is a genuine argument for staying in Mulu three or four nights rather than two, since it gives you multiple attempts at the one thing everybody comes to see.
Photographing it
Difficult. The light is failing, the subjects are small, fast and far away, and the ribbons only read as ribbons at a distance. A long lens and a fast shutter freeze individual bats and lose the shape; a slower shutter gives you a smear. The frame that works is usually wide enough to include the cliff face and the sky, exposed for the sky, with the ribbon as a dark twisting line against it. A tripod helps and the observatory is crowded. Video, honestly, captures it better than a still does.
The Bat Exodus at a glance
| Species | Wrinkle-lipped bats, estimated in the millions |
|---|---|
| When | Around 5–6pm, weather permitting |
| The behaviour | Spiralling ribbons, thought to defeat bat hawks |
| Duration | Twenty minutes to over an hour |
| Where | A covered observatory below Deer Cave's mouth |
| Does not happen | In heavy rain — a real proportion of nights |