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Rock-stashing chimpanzee shows humanlike planning

Agitated ape hurls stash at zoo visitors

WASHINGTON – It’s a little disappointing, but perhaps not surprising, that a newly documented example of planning ahead by our closest nonhuman relative involves laying up weapons.

In a scientific paper published Monday, a primatologist describes an adult male chimpanzee in a Swedish zoo often collects stones before opening time so he can have them ready later when visitors arrive and he becomes agitated.

On some days, he’s barraged visitors with up to 20 projectiles thrown in rapid succession, always thrown underhand. Several times he has hit spectators standing about 30 feet across a water-filled moat.

The animal’s preparations include not only stockpiling stones he finds, but more recently also fashioning projectiles from pieces of cement that have broken off artificial rocks in his habitat.

“Many animals plan. But this is planning for a future psychological state. That is what is so advanced,” said Mathias Osvath, the director of the primate research station at Lund University and author of the paper in the journal Current Biology.

Others have also observed great apes planning, both in the wild and in captivity. Some birds in the corvid family that includes jays and ravens also plan for future contingencies. In general, though, planning by animals is thought to occur only when the payoff is immediate and more or less certain.

“People always assume that animals live in the present. This seems to indicate that they don’t live entirely in the present,” said Frans de Waal, a primatologist at Emory University in Atlanta, who was not involved in the research.

The chimpanzee, named Santino, was born in a zoo in Munich in 1978 but has lived all but five years of his life at Furuvik Zoo, about 60 miles north of Stockholm.

He began throwing stones at age 16 when he became the sole – and therefore dominant – male in a group that included about a half-dozen females. None of the other chimpanzees, including a male that was in the group briefly, stored or threw stones.

The troop’s habitat is an island surrounded by a moat. The stone-throwing is more frequent early in the season when the zoo re-opens after the winter and Santino sees crowds of people across the water for the first time in months. Sometimes particular individuals seem to bother him, Osvath said.

On some days, zoo keepers have found as many as five caches, containing three to eight stones each, along the shore facing the viewing area. Once, a hidden observer saw him gather stones five mornings in a row before the zoo opened.

Most of the stones are taken from the shallows at the edge of the moat. About a year after his storing and throwing began, however, the animal began tapping stones against the concrete artificial rocks, listening for a hollow sound that indicates a fissure. He would then hit the concrete harder until a piece chipped off, occasionally then hitting it again to make it fist-sized.

“I have seen him going around doing this. It is very impressive,” Osvath said.

The throwing behavior is part of a normal display of dominance and territorial protection by male chimpanzees, and occasionally involves throwing feces. Osvath doesn’t think this animal is particularly smart or aggressive.

“I don’t think he is unusual in any way. If anything, chimpanzees in the wild would plan more, I suspect,” he said.

Unusual or not, Santino’s rock-throwing may not be in evidence when spring comes to Sweden this year and he emerges to see visitors again across the water.

In order to decrease his agitation, which was fueled in part by high testosterone levels characteristic of dominant males, the animal was castrated last fall.


 

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