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Wild chimpanzees' crab consumption revealed by Kyoto University assisted research

An infant male chimpanzee is filmed at a swamp eating a crab, in these images provided by Kathelijne Koops, an international collaborative researcher with the Leading Graduate Primatology and Wildlife Science Kyoto University.

KYOTO -- An international research group, including members of Kyoto University, has confirmed for the first time that chimpanzees in the wild regularly eat freshwater crabs, based on the observation and study of groups of the apes in Guinea, West Africa.

The research group included participation from Kyoto University Institute for Advanced Study's deputy director-general and distinguished professor Tetsuro Matsuzawa. Until now it wasn't known that hominid species, which includes chimpanzees, eat crabs. Their findings, published on May 29 in the electronic science publication "Journal of Human Evolution," are expected to be useful in tracing when early humans first began consuming aquatic creatures.

The chimpanzee diet primarily consists of fruit, and they are also known to feed on insects including bee larvae and ants. The kinds of bugs they eat also vary depending on the specific characteristics of their habitat and the group they are living in.

Observations of two groups of wild chimpanzees were carried out over 25 square kilometers in tropical forests in the Nimba Range, a world heritage site. Four cameras with sensors were installed in a 1 kilometer area of a swamp visited by small groups of the apes. In data collected between 2012 and 2014, the chimpanzees were recorded eating crabs 181 times.

The legs and shells left over from crabs whose insides have been consumed by Chimpanzees are shown in this photo provided by Kathelijne Koops, an international collaborative researcher with the Leading Graduate Primatology and Wildlife Science Kyoto University.

Compared to males, females with infants were more regularly observed dining on the crustaceans, with each instance lasting over an hour. Chimpanzees in the Nimba Range are known to consume safari ants, but analysis of their feces showed that in periods when they aren't eating the insects they often opt for the nutritionally similar crabs. The research group says they didn't find a connection to crab consumption from amounts of fruit and rain or whether it was a rainy or dry period.

Up to now, researchers thought that early humans began eating aquatic creatures like fish and crabs after they left the forest for the savanna. This latest discovery suggests the possibility that such creatures were consumed by our ancestors when they still lived in forested areas.

Distinguished professor Tetsuro Matsuzawa said, "Male chimpanzees hunt animals like squirrels as prey. But for the non-hunting females and infants, crabs appear to be a source of essential nutrition like fatty acids and minerals. The chimpanzee diet is shaped as the culture of their habitats and groups. There's a high chance their consumption of crabs is part of their culture."

(Japanese original by Mai Suganuma, Kyoto Bureau)

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