Durians targeted at Hornbill dispersal

ABOVE: A male Wreathed Hornbill  Ryticeros undulatus  swallowing the red aril covered seed of Durio acutifolius a specialist hornbill dispersed durian growing near the summit of Bukit Lambir in Lambir National Park in Sarawak.

Borneo’s forests  are the world center of durian distribution hosting 21 out of  a world total of some 30 durian species. Of these 21 Borneo species at least 6 species are obviously targeted at dispersal by hornbills and large imperial pigeons.

DIFFERENCES BETWEEN WILD BIRD AND MAMMAL DISPERSED DURIAN FRUITS

1. Bird dispersed durians split open (dehisce) on the tree exposing the  red or orange aril covered seed to passing birds. Mammal dispersed durians fall to the ground when ripe normally in the middle of the night, and split on the ground.
2. Bird dispersed durians do not smell. Mammal dispersed durians emit a powerful smell which can be detected from several kilometers away.
3. Either or both the fruit and or the aril are orange or red  in bird dispersed durians. The arils of mammal dispersed durian seeds are cream or white.
4. On average bird dispersed durian fruit are smaller than mammal dispersed durian fruit, but the seeds of bird durians are larger than the seeds of mammal durians.
5. The cultivated durian Durio zibethinus  was originally a mammal dispersed durian but wild hybrids between bird and mammal durians occur and may be occasionally cultivated.