When a Ficus dubia fig starting fruiting next to the Maliau Basin Study Centre in Sabah in May 2021 the first animals to arrive when the figs were still unripe was a Red Langur, Presbytis rubicunda.
Langurs have multiple stomachs for processing hard to digest leaves and they cannot eat sugary, sweet ripe fruits. Instead they eat the seeds of unripe fruits. Thus Red Langurs are seed predators of figs not seed dispersers like gibbons and hornbills.
All photos thanks to Alexander John and Roger Rajah
The sugar in ripe figs ferments inside langur stomachs causing the langur to die of bloat (gas). Therefore langurs often eat unripe figs and fig leaves but only rarely are seen eating ripe figs. Because langurs can eat unripe fruits and seeds they have first choice of any fruit crop which explains why langurs are the most common primate in virgin Bornean forests.
When the figs started to ripen this Black Hornbill arrived to feed on the ripe figs followed the next day by Rhinoceros and Helmeted Hornbills.