You might think orangutans are vegetarian and for the most part you’d be correct, but they have been known to occasionally enjoy the odd piece of meat. A new paper demonstrates this (with photos and a video for your viewing pleasure) as it reports on a Borneo orangutan (Pongo pygmaeus) that was spotted catching, killing, and eating one of the world’s cutest animals: the slow loris.
Published in the journal Primates, the study authors describe their observation made in 2017 at the Tuanan Orangutan Research Station in the Kapuas region of Central Kalimantan, Borneo.
The researchers were familiar with the diets of these animals, having been tracking their behavior intermittently from 2003 to 2017. During that study period, it seemed the animals' most common foods were fruit (61 percent), young leaves (14 percent), flowers (8 percent), and insects (5 percent).
You can imagine the researchers’ surprise, then, when they spotted a male orangutan named Molong go ham sammich on a fellow primate. They actually hadn’t been intending to observe Molong but instead a female named Kerry and her 3-year-old infant Ketambe, but as he was hanging around in what’s referred to as “a party” they included his behavior in their record keeping.
A good thing, too, as what they saw on that fateful day proved to be a significant data point. It began when Molong leaped out of the trees and started running along the ground. They’d assumed he was moving away from an approaching male as they heard long vocalizations coming from elsewhere, but soon saw that he was in fact chasing a slow loris (Nycticebus borneanus).
This was strange as slow lorises are strictly arboreal animals that stick to the treetops, so how did it get on the ground? Molong carried on chasing the loris by hopping onto branches and back onto the ground again until the animal was just a meter away and he swatted it off of a branch. It's possible Molong knocked this animal out of the tree to begin with, a technique that's been used by Sumatran orangutans to stun the same prey as seen in the video from Hardus et al., 2012 below.
As the loris fell, Molong snapped off the branch it landed on and held it out away from his body as he scaled the tree. The loris's ordeal finally came to a grisly end as Molong, holding his victim by its feet, bit its nape and killed it. Once it was dead, he grabbed it with both hands and tucked in.
The sounds of Molong cronching on the unfortunate loris's head attracted the attention of Kerry who, infant in tow, approached him and appeared to beg for scraps. Cruelly, he appeared to occasionally offer up shreds of the decapitated slow loris only to keep them to himself. Nobody likes a greedy gobble gannet, Molong.
Killing a loris is risky business, even for a massive orangutan, as these big-eyed tree babies pack a powerful venom. It’s secreted from glands on their elbows which they rub on their teeth before biting would-be predators. It’s powerful enough to send humans into anaphylactic shock so could certainly be unpleasant for one of our close relatives.
This could perhaps explain why Molong handled the animal so gingerly until it was dead. And why such resourceful methods were used to pursue it in leaping into the trees repeatedly and carrying the slow loris on a snapped-off branch rather than with his hands.
Molong’s meal was one of just two observations of orangutans eating vertebrates made during the research period, the other of which was a hungry orangutan who decided to raid a nest of mice like a bowl of so many crunchy snacks.
Given the time needed to make just two observations, it would appear that Bornean orangutans eating vertebrates is quite rare but it’s very possible that more frequent meat consumption is being missed for lack of researchers on the ground.
“In conclusion, we describe the first predation and consumption event of a wild Bornean orangutan on a slow loris,” wrote the study authors, who maintain that while such predation events are “rare and most likely opportunistic”, long-term field research is needed if we’re to witness the grisly hunts as they unfold.