Helmeted Hornbill  Buceros vigil feeding on ripe Ficus dubia figs next to the Belalong Canopy Walkway in Brunei. Photo by Hans Hazebroek

Ficus dubia produces the largest fig fruit of any strangling fig in Borneo. This is an evolutionary strategy by the fig tree  (1) To ensure that the fig is swallowed only by the largest frugivorous birds i.e. hornbills and (2) To avoid seed predation of the fig seeds by green pigeons.

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Female Large Green Pigeon photographed from the Belalong Canopy Walkway in Brunei. The Large Green Pigeon is a fig seed predator. Photo: Hanyrol H. Ahmad Sah

Because they have no teeth, green pigeons have to swallow figs whole when they are ripe but still firm. Like chickens and pheasants, green pigeons have small stones (grit) in their gizzards which are used to grind up fig seeds.

Ficus dubia figs are so large that only the Large Green Pigeon  (only one out of five species in Borneo) can swallow Ficus dubia figs whole.



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Ripe Ficus dubia figs  photographed at Belalong Canopy Walkway by Hanyrol H. Ahmd Sah
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Mountain Imperial Pigeons  are nomadic and fly long distances looking for ripe fig crops both in the mountains and lowland forests of Borneo.

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A Mountain Imperial Pigeon checking out a fruiting fig tree below at the Belalong Canopy Walkway in Brunei. Imperial Pigeons are not fig seed predators. They swallow and defecate fig seeds thus dispersing strangling figs long distances. Thus  the evolutionary strategy adopted by Ficus dubia is to grow figs too large for green pigeons to swallow but not so large so that they cannot be swallowed by hornbills and imperial pigeons.