tool use – even more widespread than you thought

Yesterday my ‘Facebook science feed’ (ie daily browsing) brought me this stunning image (click the picture for the hyperlink). It’s from the book Thinkers of the Jungle: the Orangutan Report (Shuster, Smits & Ullal, 2008) & shows a young orangutan apparently using a long stick in lieu of a spear, copying local fishermen as they hunted with spears. (It’s been blogged about here by Kambiz Kamrani.)

Which is pretty darned amazing. Tool use, & various tool cultures, are now quite well-documented in our nearest living relatives, the chimpanzees, but this is the first time I’d heard about it in a wild orangutan. Also novel: the concept that another great ape might also sometimes eat vertebrates (again, well-documented in the members of some chimpanzee troops). So I decided to dig a little deeper.

It turns out that orangutans do on occasion eat meat, although reports of this are rare. Back in 1997 Sri Suci Utami & Jan van Hooff reported on a total of seven incidents of carnivory by three different female orangutans in Sumatra. More recently Madelaine Hardus & her colleagues (2012) looked at a few additional instances of this behaviour – which in all recorded cases has female orangutans doing the eating and slow lorises as the prey – and considered whether it might be seasonal and related to the availability of other food sources (they felt that it was). Both research teams characterised the behaviour as opportunistic as there was no evidence of any organised hunting activity: it was more a case of a foraging orangutan happening across a slow loris. And they noted that the data are too few to allow any firm conclusions about either the frequency of this behaviour or whether it might be skewed towards one gender or the other.

Nor was this the first documented example of tool use by these Asian great apes. While it’s apparently well-known in captive animals, Carel van Schaik first documented this behaviour among wild-living orangutans back in 1994, in Sumatra (apparently it’s not been observed in populations from Borneo). The animals he was watching were in relatively high densities and surprisingly tolerant of each other – plenty of opportunity to watch and learn from the activities of others, which may be why tool use hasn’t been seen in the wild in Borneo, where the animals are much more widely dispersed).

van Schaik documented the use of sticks to prise open extremely prickly fruit in order to get at the soft flesh within, but more recently he and a group of co-workers provided evidence that, like their cousins the chimps, orangutans in different areas have developed different cultures (around behaviours broader than simply using tools). Which demonstrates (again) that culture is not something that is solely ‘ours’, and suggests that such behaviour may have been around for a very long time indeed, given the antiquity of the split between the lineages leading to modern orangutans and (eventually) Homo sapiens. As van Schaik and his team concluded:

Hence, great-ape cultures exist, and may have done so for at least 14 million years.

M.E.Hardus, A.R.Lameira, A.Zulfa, S.S.Utami Atmoko, H.de Vries & S.A.Wich (2012) Behavioural, Ecological, and Evolutionary Aspects of Meat-Eating by Sumatran Orangutans (Pongo abelli). International Journal of Primatology 33: 287-304. DOI: 10.1007/s10764-011-9574-z

S.S.Utami & J.A.R.A.M.van Hooff (1997) Meat-Eating by Adult Female Sumatran Orangutans (Pongo pygmaeus abelli). American Journal of Primatology 43: 159-165

C.P.van Schaik, M.Ancrenaz, G.Borgen, B.Galdikas, C.D.Knott, I.Singleton, A.Suzuki, S.S.Utami & M.Merrill (2003) Orangutan Cultures and the Evolution of Material Culture. Science 299 (5603): 102-105. DOI: 10.1126/science.1078004