It begins before it begins. Somewhere around half past four, while the river is still a sound rather than a sight, the forest holds one long breath — and then a gibbon lets it out for everyone. The call starts low, gathers itself, and rises into that swooping whoop that carries for a kilometre through 130 million years of canopy. If you are on a balcony at Borneo Rainforest Lodge or standing in the cold at Bukit Atur, this is your overture.

By five, the great argus has joined in from the ridge — a hard, two-note announcement that sounds less like a bird and more like someone testing the forest's public-address system. Listen carefully between calls and you can pick out the first pittas rehearsing on the forest floor, still invisible, always closer than they sound.

"The dawn chorus is the one appointment in Danum Valley that keeps perfect time — the wildlife sets the schedule, and you are merely permitted to attend."

Half past five: the changeover

This is the hour the night shift clocks off. Frogs thin out along the streams, the last civets slide home, and the light — when it finally comes — arrives as a grey suggestion rather than a sunrise. On the canopy walkway you feel it before you see it: the mist starts to move, the temperature ticks upward, and the leaf litter below begins to crackle with things that were silent all night.

Then the hornbills commute. Rhinoceros hornbills first, usually in pairs, their wingbeats loud enough to make first-time visitors duck; the smaller species follow in loose processions along the river. Between six and seven you may hear — and if you are fortunate, see — representatives of all eight Bornean species without moving your feet.

What to bring, where to stand

Bring less than you think: a head torch with a red mode, binoculars, and patience. The walkway rewards stillness at its mid-span platforms; Bukit Atur rewards the 4.45 am alarm with a sea of cloud that breaks up exactly as the chorus peaks. Guides at all three lodges know the current soloists — fruiting trees move the concert around the forest week by week, which is the best possible reason to come back.

However you hear it, the chorus ends the same way: not with silence but with saturation, as the day's full cast comes in at once and the individual voices dissolve into the general green noise of the world's oldest rainforest. By then breakfast is on, and the forest has already forgotten it performed at all.