Differences between Bornean and Sumatran orangutans.
I've listed them before but here they are again. It is quite a complicated area and not all animals, despite being purebred, show all or the same typical characteristics which is where DNA testing is sometimes needed.
Sumatrans; slimmer build, lighter ginger or 'butterscotch' coat colour, well deveoped yellow or white beard, tiny tufts of hairs cover naked parts of face and cheek pads of males. Males have flat, diamond-shaped pads. Coat texture more 'fleece-like' Both sexes much more agile and active than Bornean. Some males walk bipedally(upright) and both sexes freely brachiate/swing. Males more tolerant of group situations and rarely aggressive to young. Males reach full maturity(aquire pads etc) later than Bornean, often not till 18 years old.
Borneans; darker bluish skin, thinner, maroon-coloured coat, smoother not fuzzy hair. Orange beard, much less developed than S. Naked parts of face not wellhaired, adult male cheek pads covered in bare 'goosepimples' with no hair, pads rounded or oblong and often hang forward like blinkers. Both sexes heavier bodied and rather less active than S, and in captivity seem to acquire fat more easily, especially around head and gular/throat sac.. Males rarely able to walk bipedally. Adults generally less active climbers in captivity. Adult males more antisocial and may be aggressive to young.
I think there are differences in the arrangement/presence of the big toe/and nails, also the dimensions of the face/eyes/muzzle relative to each other. Bornean has more of an 'hour glass' shaped face.
Areas of confusion; occasional Bornean females may be almost as light- coloured as Sumatrans (e.g. Lola who was at Chester). Sumatrans also appear to have two different 'phases' a smaller dark one and a larger light one.(but both recognisably different from Bornean) while nowadays several different races/subspecies of Bornean are recognised.
Hybrids; may exhibit characteristics of both parents in any combination e.g. dark coat, light beard, or may resemble one purebred parent more closely. 'Rajang' at the Colchester Zoo is a good example of a 'typical' hybrid adult male with characteristics of both species.
Hybrids show no ill effects from being the product of the two different species. They are fertile and can, by breeding with a purebred individual, also produce other hybrids which have greater percentages of one or other species e.g. 3/4 or 7/8ths Sumatran or Bornean. There is a Moratorium on breeding from hybrid Orangutans in Zoos and they will gradually disappear from the captive population as they begin to die out..
