If you’re a regular visitor to the Zoo, you may have noticed some changes recently in our 14-year-old male Bornean orangutan, Denda. He is experiencing the development of what are referred to as secondary sexual characteristics; male orangutans undergo this process as they mature.
These characteristics include larger body size, flanges, or cheek pads, on either side of his face, long hair, and development of a large throat sac which helps carry the adult male’s “long call” over great distances.
In nature, these fully-developed males are preferred by females for mating, but males that have not fully matured are still capable of producing offspring. In fact, there is rarely more than one flanged male within a certain range; the presence of one dominant male represses the development of this feature on other males, even if they are already sexually mature. Denda was able to successfully breed with Kumang when he was only 11, resulting in the birth of their offspring Bella.
Denda’s cheek pads began developing last fall and are quite noticeable. He’s also put on 50 pounds since early 2016! We’ve increased his diet to keep up with his growth, as he now weighs close to 200 pounds. A year ago, he was getting approximately the same amount of fruits and vegetables as his mate Kumang but we recently increased that amount by one third, and will most likely increase it again.
Denda’s size, strength, and hair will continue to grow into the coming summer months, until the hormones driving this growth spurt slowly level out and he becomes a fully-developed male. The entire process takes about one year.
The images below document Denda’s growth each week since mid-October. These photos give you a glimpse of Denda’s transformation and an understanding of why the word orangutan means “man of the forest” in Malaysian, the language spoken in this magnificent species’ native Borneo.
— Brian Sheets, Zoo Keeper