Spanning 438 square kilometres, the lowland rainforest of Danum Valley, home to Borneo's ghost species, waits for a climatic cue to fruit in unison. Walk the trails with an expert guide to discover a forest that operates on a complex multi-year cycle.
Up to 80% of the emergent canopy in Danum Valley is made up of dipterocarp trees. The forest produces massive fruit crops at irregular intervals of 2 to 10 years, giving 3 to 5 months of warning once flowers appear.
"The forest fills with the hum of millions of giant honey bees arriving to pollinate the blooms."
Wildlife during a mast
When the seeds fall the forest floor turns into a feast. Animals that have scraped by on sparse diets suddenly have more calories than they can consume. Ground-feeding animals gather to eat the seeds and civets shift their hunting grounds.
In the canopy the boundaries break down. Macaques, hornbills and orangutans converge on the heavily fruiting branches. They feed side by side in a temporary truce driven by abundance, and sun bears use the sudden bounty to recover their body weight.
Orangutans in the canopy
When a mast happens, an event which also drove bearded pig migrations across Borneo, Bornean orangutans shift their diet completely. They abandon bark and leaves to gorge on the lipid-rich seeds. Because the fruiting trees are massive emergent structures they act as beacons, drawing them from surrounding areas.
Researchers have recorded local orangutan densities spiking during peak fruiting. A skilled guide who knows where a large tree is fruiting will often find multiple individuals in the same area. A mast year makes orangutans a realistic target.