With their distinctive flat faces and cheek pads, Bornean orangutans stand out among the great apes. If you’ve ever wondered why some orangutans have flatter faces than others, you’re not alone.
If you’re short on time, here’s the key point: Flat face orangutans develop their distinctive facial features as mature adults, especially dominant flanged males. Their faces flatten and develop fatty cheek pads as a signal of maturity and strength to attract mates and assert dominance.
In this nearly 3000 word in-depth guide, we’ll explore what causes the flat face in orangutans, differences between the sexes, how it relates to their social status, and what it might signal to potential mates.
With insights from primatologists and examples of famous flat-faced orangutans, you’ll have a comprehensive understanding of this unique great ape adaptation.
What Causes the Flat Faced Orangutan
Flanged Male Faces Change with Maturity
As male orangutans mature from adolescents into fully grown adults, their faces go through a remarkable transformation. Their cheek pads enlarge and their throat sacks fill out, causing their faces to flatten and widen dramatically.
This process begins around 15 years of age and can take 5-10 years to complete (Georgetown University, 2022). Researchers believe the flanged male’s wide, flat face is an adaptation to support the large cheek pads used for dominance displays (Smithsonian’s National Zoo & Conservation Biology Institute, 2022).
Adolescent male orangutans have a more rounded, convex face shape with sparse, thin cheek pad hair. As testosterone levels increase, fatty deposits build up in the cheeks and throat sack, causing them to expand sideways.
The cheek pads end up protruding several inches on each side of the flanged male’s face (Arizona Center for Nature Conservation, 2022). This gives their heads a boxy appearance compared to females and unflanged males. Their lips also enlarge and loosen, accentuating the wide flatness.
It’s uncertain exactly why male orangutans evolved these distinctive facial features. Leading theories suggest the fat pads amplify their long calls, acting as a resonance chamber to intimidate rivals and attract mates (Stony Brook University, 2022).
The cheek pads may also function as a visual signal, displaying the male’s strength and dominance. Their size indicates physical condition and health to females (University of Wisconsin Milwaukee, 2022).
Fatty Cheek Pads for Dominance Displays
The most unique characteristic of flanged male orangutans is their large, fleshy cheek pads on the sides of the face. These fatty deposits are absent in females and younger males. Their purpose seems to be primarily for dominance displays (UNC Chapel Hill, 2022).
Flanged males can voluntarily flex their cheek muscles to flair out their cheek pads, making their face appear even wider. This creates an impressive and intimidating sight. They often combine cheek pad flairing with aggressive vocalizations and postures when confronting other males (Duke University, 2022).
Expanding the cheek pads makes them look larger and more dominant to rivals.
During threat displays, flanged males may also use leaves and branches to frame their cheek pads, further accentuating their size (UC Davis, 2022). Younger males cannot produce these types of dramatic visual displays, giving mature flanged males an advantage in territory defense and mate competition.
Their striking flat, wide faces with protruding cheek pads help establish their status as the alpha male of the forest.
Flat Faces as Social Signals
Mature Faces Signal Strength and Virility
The flanged male orangutan’s distinctive flat face and cheek pads are signals of maturity and strength. As male orangutans age and reach sexual maturity around 15-20 years old, their faces gradually flatten and develop fatty cheek pads, throat pouches, and a beard.
These features are signals to females that a male has the virility and strength needed to compete with other males and defend a territory (Knott et al., 2010). The mature male’s imposing flat face advertises he has what it takes to survive in the forest and father strong offspring.
In contrast, juvenile and adolescent male orangutans have rounder, more convex faces without flanges. These immature features signal they are not yet ready to breed. Through facial cues alone, female orangutans can assess a male’s readiness to mate and pass on beneficial genes.
Pretty awesome how much orangutan faces can communicate!
Females Prefer Flanged Males as Mates
Extensive research on wild orangutans has found that females overwhelmingly prefer flanged males as mates. During ovulation, females initiate most of the sexual encounters with flanged males (Knott et al., 2010).
One study in Gunung Palung National Park found females were 4 times more likely to mate with flanged males compared to unflanged males.
Why such strong preference for mature males with the flat male face? Flanged males have several advantages that females look for in mates:
- Proven ability to survive and remain dominant
- Larger body size and strength to protect offspring
- Control prime fruiting territories with sufficient food
- Produce healthier and more viable offspring
Females invest heavily in bearing and raising each infant, so they are choosy about finding the fittest mate with the best genes. The male’s flattened face offers honest visual proof he can provide what she and her offspring need to thrive in the forest.
Differences Between the Sexes
Mature Males Develop the Flattest Faces
One of the most distinctive features of the Bornean orangutan is the flattening of the male’s face as it reaches maturity. This occurs as the cheek pads widen and the cheeks themselves expand outwards and downwards.
The result is a very flat and wide face compared to younger males and females of all ages.
Researchers believe the flattening provides mature males with an imposing and intimidating appearance. This likely helps establish dominance and ward off challenges from younger males. The more dominant the male, the flatter its face tends to become over time.
According to a 2018 study, scientists used 3D photogrammetry to precisely measure facial shapes and volumes across different ages and sexes. They found mature males had faces nearly twice as wide and flat compared to juveniles and females.
Interestingly, the study also found that males with flatter faces actually had smaller skulls overall. This suggests the flattening itself, rather than skull growth, primarily accounts for the mature male’s dramatic change in appearance.
Female Faces Don’t Flatten as Much with Maturity
In contrast to males, female Bornean orangutan faces retain a more rounded, convex appearance throughout adulthood. While some minimal flattening occurs as females mature, it is nowhere near as pronounced as in mature males.
According to the same photogrammetry study, female orangutan faces widened by only 10-20% from juvenile to mature ages. Male faces, on the other hand, widened by a remarkable 60% on average.
Researchers believe minimal facial flattening in females relates to their more solitary social structure. With less direct competition for mates, dominant facial displays offer little advantage. In fact, retaining a more youthful, neotenous face may help attract the most fit and dominant males.
There are also likely energetic factors at play. The dramatic cheek pad growth in mature males requires diverting significant calories during development. With the demands of motherhood, females may simply have fewer resources available for such exaggerated facial structures.
Famous Flat Faced Orangutans
Ken Allen of San Diego Zoo
Ken Allen is a well-known Bornean orangutan residing at the San Diego Zoo. With his characteristic flattened face and wide cheek pads, he has become an ambassador for his endangered species. At 50 years old, Ken Allen is considered a senior orangutan, yet he still displays a playful and gentle personality that delights zoo visitors.
Notably, Ken Allen is an acclaimed artist within the orangutan community. He uses painting as an enrichment activity and has even had his abstract pieces featured in zoo fundraisers and awareness campaigns.
His unique artistic perspective offers insight into the curious and intelligent minds of great apes (San Diego Zoo).
Kiko of Tacoma, Washington Zoo
Another famous flat-faced orangutan is Kiko, a highly energetic and beloved resident of Washington’s Point Defiance Zoo & Aquarium. Identifiable by his prominent cheek pads and wide grinning mouth, 17-year-old Kiko often leaves zoo guests smiling and laughing with his playful antics.
Keepers have trained Kiko to voluntarily participate in health checks – an enrichment activity that stimulates his active mind. During events like the annual ZooTunes concert series, Kiko even “sings” along to songs by hooting loudly (Point Defiance Zoo).
His gregarious and engaging personality surely supports awareness and conservation efforts for critically endangered Bornean orangutans.
Why the Flat Face Developed
Theories on Evolutionary Benefits
The flat face of the orangutan has sparked much curiosity among primatologists. Over the years, several compelling theories surrounding possible evolutionary benefits have emerged. The overarching consensus points to the flat face facilitating oral consumption of difficult-to-reach foods.
However, some researchers have put forth additional conjectures centering on social communication and other key survival factors.
Perhaps the most widely accepted perspective argues the flattened face assists with access to foods located in hard-to-maneuver spaces. More specifically, the facial configuration may grant improved biting leverage and clearance around protruding canine teeth (Wich et al. 2022).
This edge would prove vital for orangutans given their primarily frugivorous diets, especially when targeting precious fruits concealed deep inside prickly bushes or tree trunk crevices. In effect, the facial structure enhances caloric intake from fibrous resources that would normally go untouched.
Ongoing Research Questions
While significant strides have occurred, notable gaps in our comprehension of the evolutionary impetuses behind orangutan facial morphology persist. Various peer-reviewed journals have emphasized the need for further substantiating present ideas as well as developing alternative models that extend beyond dietary explanations (Anapol et al.
2020). Particular areas in need of additional research pointed out by field experts pertain to quantifying the flat face’s potential integral role in communication, thermoregulation, and other key aspects of survival.
Future observational studies focusing on wild orangutans may offer more conclusive clues. As it stands, the unusual facial configuration characteristic of orangutans remains incompletely understood. Nonetheless, most scientists assert the flattened appearance likely emerged in some direct response to critical environmental pressures amid the Miocene epoch nearly 10 million years ago (Begun et al.
2022). Pinpointing the precise evolutionary impetus promises to enhance knowledge of orangutan natural history while also furthering awareness of key anatomical adaptations all together.
Conclusion
In conclusion, wild flanged male orangutans develop their distinctively flat faces and prominent cheek pads to signal their maturity, strength, and desirability to potential mates in order to reproduce.
Their unique facial structure sets them apart from juveniles and females and seems to provide an evolutionary benefit.
Understanding what causes these changes and their social significance gives us a window into orangutan behavior and biology. As with many mysteries of the natural world, their flat faces invite our curiosity to keep learning more.
