Vegetarian orang-utans eat world's cutest animal

by Michael Marshall
from the New Scientist
Thanks to Tracy K for the link!




When fruit is scarce, try chomping on a slow loris. That seems to be the strategy adopted by the normally vegetarian orang-utans, which have been spotted knocking the small primates out of trees and killing them with a bite to the head.

Sumatran orang-utans (Pongo abelii) get almost all their nutrients from fruit and other plant products, but there are a few isolated reports of them eating meat (American Journal of Primatology, vol 43, p 159). Madeleine Hardus of the University of Amsterdam in the Netherlands and colleagues have now observed three more cases, bringing the total to nine.

In 2007 Hardus was tracking two orangs in the canopy above her – a female called Yet and her infant Yeni – when Yet abruptly changed direction and approached a slow loris (Nycticebus coucang). She knocked it out of the tree, crashed down to the ground, bit the stunned loris's head, then carried the body back into the tree to eat it. When Yeni begged, she was allowed to share the meat. The great apes each chomped on opposite ends of the dead primate, sharing it between them like lovers might a strand of spaghetti.

Searching through the scientific literature, Hardus found detailed studies of six orang-utan hunts. All stunned their prey before eating it, which Hardus thinks may be to avoid being bitten. Slow lorises are unique among primates in that their saliva is toxic.

All the documented hunts took place when there was little fruit available, which may push the apes to meat-eating, says Hardus.

By contrast, chimpanzees hunt more when fruit is abundant, perhaps because it doesn't matter if they waste energy on a failed hunt.

The sample is unavoidably small, but the data have been thoughtfully analysed, says Richard Wrangham of Harvard University.

Only five individual orang-utans have been observed hunting. Yet has so far been caught in the act four times – three times by Hardus, and once by another researcher – making her the best documented hunter.

In other accounts, the apes stumbled upon their prey, but Yet systematically changed direction and headed straight for the loris, which Hardus says may be because she has learned to smell them. Because a few cases have been documented within a 40-kilometre range, all using the same killing method, she thinks it may be a cultural behaviour, passed from orang-utan to orang-utan.

Madeleine E. Hardus, Adriano R. Lameira, Astri Zulfa, S. Suci Utami Atmoko Han de Vries, Serge A Wich (2012) Behavioral, Ecological, and Evolutionary Aspects of Meat-Eating by Sumatran Orangutans (Pongo abelii). International Journal of Primatology, DOI: 10.1007/s10764-011-9574-z

Abstract
Meat-eating is an important aspect of human evolution, but how meat became a substantial component of the human diet is still poorly understood. Meat-eating in our closest relatives, the great apes, may provide insight into the emergence of this trait, but most existing data are for chimpanzees. We report 3 rare cases of meat-eating of slow lorises, Nycticebus coucang, by 1 Sumatran orangutan mother–infant dyad in Ketambe, Indonesia, to examine how orangutans find slow lorises and share meat. We combine these 3 cases with 2 previous ones to test the hypothesis that slow loris captures by orangutans are seasonal and dependent on fruit availability. We also provide the first (to our knowledge) quantitative data and high-definition video recordings of meat chewing rates by great apes, which we use to estimate the minimum time necessary for a female Australopithecus africanus to reach its daily energy requirements when feeding partially on raw meat. Captures seemed to be opportunistic but orangutans may have used olfactory cues to detect the prey. The mother often rejected meat sharing requests and only the infant initiated meat sharing. Slow loris captures occurred only during low ripe fruit availability, suggesting that meat may represent a filler fallback food for orangutans. Orangutans ate meat more than twice as slowly as chimpanzees (Pan troglodytes), suggesting that group living may function as a meat intake accelerator in hominoids. Using orangutan data as a model, time spent chewing per day would not require an excessive amount of time for our social ancestors (australopithecines and hominids), as long as meat represented no more than a quarter of their diet.