Orangutan loris capture and meat-eating

2 minute read

Madeleine Hardus and colleagues Hardus:2012 describe long-term observations of hunting by Sumatran orangutans.

The paper is straightforward in its description of the hunting observations: They hunt slow lorises, the practice is rare, it occurs at times when their other preferred foods are scarce, some individuals hunt but most don’t, and food sharing among individuals other than mother-infant pairs wasn’t observed. This isn’t the first time hunting has been reported by wild orangutans, what it does is report a longer-term observation of one hunting female, tying this case to earlier observations.

I’m pointing to the paper because it includes some discussion about the requirements of meat eating for early hominins. These orangutans take a long time to chew up a slow lorus.

Orangutans used more than twice the amount of time (160.9 g/h) to eat the same amount of meat than chimpanzees (348 g/h) (Wrangham 2009; Wrangham and Conklin-Brittain 2003). Other chimpanzee data shows that this species is able to consume meat at much higher rates, i.e., 1.91.2 kg/h (Gilby 2006). This difference between orangutans and chimpanzees may suggest that higher sociality in chimpan- zees influences intake rates, where individuals are surrounded by conspecifics when eating meat, and where meat is a highly preferred food item and stealing occurs (Boesch and Boesch 1989; Goodall 1986; Stanford 1999).

I’ll point out that orangutans may make a better model for early hominin jaw mechanics than chimpanzees do, because the sizes of jaw musculature and teeth are more comparable. Neither orangutans nor australopithecines have teeth that look well-made for reducing fibrous, tough meat into smaller pieces. Recent humans have been able to cook meat, which reduces its mechanical resistance to chewing. Early hominins didn’t cook, so getting some high fraction of their caloric requirements from meat (even if only seasonally) might have taken a lot of time.

According to orangutan data (ingestion rate of 185 kcal/h), Australopithecus africanus would have had to chew for ca. 2 h to achieve 25% of these caloric requirements purely from meat (Table III, orangutansA. africanus), while achieving the remaining 75% of its caloric requirements from food sources with faster chewing/intake rates, e.g., leaves or insects. This constitutes a considerable period of the day for orangutans, which spend ca. 6 h/d feeding (Morrogh-Bernard et al. 2009), and does not include the time necessary for the collection of vertebrate prey.

That sounds like a lot of chewing time, but it’s not an insuperable barrier. The isotopic values for A. africanus and A. robustus suggest the possibility of up to 25% meat consumption, although they may have gotten C4 plant input by several different food sources (e.g., corms, edible stems, aquatic animals) as well as meat. Altogether, the chewing time analysis shuts off one line of argument that early hominins would have faced extreme constraints preventing them from moving to a more meat-intensive diet before the control and routine use of fire.