Orangutans of Borneo: An Encounter with a Flanged Male

On our first morning in the rainforest at Danau Girang Field Centre, nestled on the Lower Kinabatangan river in Borneo, we were woken by the people of the forest. We watched a female orangutan and her baby move through the trees in the morning light. You can read our post about this experience here. In the distance, we also had a brief glimpse of something bigger and louder, but dismissed it as either noisy proboscis monkeys or a young male orangutan.

A few days later while attempting to get some rest in our accommodation, something large moved through the trees just outside our window again. There is no electricity during the three hours between 2pm-5pm at the field centre. Being the hottest part of the day, many people retire to their rooms after a cold shower to wait out the thirty-something degrees Celsius heat, 100% humidity, and jungle stillness.

In my sleepy, yet uncomfortable state, I dismissed the movement as a group of pesky macaques. Emma, however, decided to investigate the noise and peered through the mosquito screen. She was greeted by Hantu (Malay for ‘ghost’), the Centre’s huge, mature, flanged male orangutan. Once again, I was up like a shot, frantically chucking on my clothes and cramming my feet into boots.

He quickly moved high into the canopy and watched us for quite some time. By this point Emma had gathered all the students and researchers. Their excitement matched ours.

After a while of eating fruit, he began his decent. The strength in his arms was equally impressive and intimidating.

We moved as a group to a better vantage point, but had no luck. There was no movement. He was gone. As we collectively scratched our heads, someone called to us, to let us know he had moved silently 200m to rear of the field centre.

Hantu gave us one more pose. Perhaps the best we could wish for, sitting in the loop of a low hanging vine before disappearing into a curtain of green.

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Flanged Male Orangutan Facts

• The large cheek pads seen in the images above are called flanges

• Not all mature male orangutans develop these strange cheek pads

• Orangutans exhibit what’s called bimaturism, by which adult males take on one of two distinct face shapes

• For flanged males, in addition to cheek pads, they have a large, pendulous throat sac used to resonate their deep calls. These calls can be heard 1.2 miles (2 kilometers) away. This is especially impressive, as the forest is noisy, and because of its dense make up, sounds tend to die out quickly.

• Flanged males are seen to be more dominant and are more successful at fathering offspring

• Un-flanged males have relatively low levels of testosterone, but those developing cheek pads have a dramatic increase testosterone levels. This may indicate the need for high testosterone levels to develop secondary sexual characteristics. Once flanges are developed the testosterone level appears to level out.

•  The trigger that initiates this change from un-flanged to flanged is still unknown

• Males have territories that are around 15 square miles (39 square km) and are very territorial and aggressive towards other males

• Males tend to be more nomadic, visiting female ranges as needed

• According to National Geographic, the arm-span of a male can reach 7 feet (2 meters) from fingertip to fingertip

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Want to read more?

Check out our previous Borneo blog posts:

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References and Further Reading

Animal Fact Guide Website  – http://www.animalfactguide.com/animal-facts/bornean-orangutan/
(Retrieved 18 October, 2017)

BBC Website – http://www.bbc.com/earth/story/20151027-new-insights-into-strange-faced-orangutans
(Retrieved 19 October, 2017)

Cardiff University Website, Danau Girang Field Centre – http://www.cardiff.ac.uk/danau-girang-field-centre
(Retrieved 19 October, 2017)

Iflscience Website – http://www.iflscience.com/plants-and-animals/male-orangutans-cheek-pads-father-more-offspring/
(Retrieved 19 October, 2017)

IUCN Red List Website, Bornean Orangutan – http://www.iucnredlist.org/details/17975/0
(Retrieved 18 October, 2017)

National Geographic Website – https://www.nationalgeographic.com/animals/mammals/group/orangutans/
(Retrieved 19 October, 2017)

Orangutan Foundation International Website – https://orangutan.org/orangutan-facts/quick-orangutan-facts-figures/
(Retrieved 18 October, 2017)

San Diego Zoo Website – http://animals.sandiegozoo.org/animals/orangutan
(Retrieved 19 October, 2017)

World Wildlife Foundation Website – https://www.worldwildlife.org/species/bornean-orangutan
(Retrieved 18 October, 2017)

 

 

 

 

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