Monkey Stories - Part 1

While I was at Arashiyama monkey park (on a mountain overlooking Kyoto) one morning I noticed several monkeys playing with rocks. They'd rub them around on the ground, several at a time, making a racket. Chimps run bipedally while dragging branches on the ground. That, too, makes a ton of noise and is done to intimidate other chimps. But this stone rubbing was definitely not like that. It happened while monkeys sat quietly and alone. They appeared to be completely absorbed in the stones, so much so that I thought the behavior was rather autistic-like.

Here's a video I found on You Tube of one monkey who is so focused on her stones that she completely ignores the infant who wants her attention.



This stone play has been observed at Arashiyama since 1979 when primatologist Michael Huffman first noticed it while researching the site. Huffman reports that by 1983, stone-play had become commonplace. Half of the monkeys in the community had been observed playing with the rocks and the vast majority of those monkeys were youngsters born in the 3 years after the behavior began. The youngest monkeys Huffman observed playing with rocks were just over one month old.

Playing with stones is a cultural tradition passed down from mother to daughter and from sister to sister. It then spreads out to playmates from other families. You might wonder why it spreads first among females. The answer is simple - Japanese macaques are a female-bonded species (in primatology terms they are matrilineal).

What I wondered was how this behavior got started in the first place. Surely some individual started it - but - that's not what intrigued me. To me, stone play looked an awful lot like gathering food. The monkeys appeared to be behaviorally prepared to collect round food, but what did they once gather?

As it turns out, monkeys who lived on Arashiyama used to have access to citrus trees that produced fruits about the size of the rocks the monkeys now play with. Whether they actually ate them or simply played with them is anyone's guess, but Huffman thinks this behavior has little to do with foraging behavior.

Instead, he sees it as play with another purpose - it aids motor development. The monkeys gain perceptual and motor skills that improve coordination.

Besides seeing monkeys rub rocks on the ground, I also observed one monkey with her arm full of stones. I mean FULL of stones.

She carried them a few feet and then dumped them all and walked away.

I also saw an older monkey sitting by a neat little pile of rocks he must have spent some time gathering. That was cute. I thought about asking if he wanted to play Go...