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Arsenal Confirms Chimp's Ability to Plan, Study Says
Animal at Swedish Zoo Collects Stones to Hurl at Visitors

By David Brown
Washington Post Staff Writer
Tuesday, March 10, 2009

Santino evidently knows he's going to get upset, so he plans ahead.

The 30-year-old chimpanzee, who has lived in a Swedish zoo most of his life, sometimes gets agitated when zoo visitors begin to gather on the other side of the moat that surrounds his enclosure, where he is the dominant -- and only -- male in a group that includes half a dozen females.

He shows his displeasure by flinging stones or bits of concrete at the human intruders, but finding a suitable weapon on the spur of the moment perhaps isn't so easy. To prepare, Santino often begins his day by roaming the enclosure, finding stones and stacking them in handy piles.

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

The behavior, witnessed dozens of times, has made Santino something of a local celebrity.

It also made him the subject of a scientific paper, published yesterday, documenting one of the more elaborate examples of contingency planning in the animal world.

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

The animal's preparations include not only stockpiling the stones he finds but also, more recently, also fashioning projectiles from pieces of concrete he has broken off artificial rocks in his habitat.

Others have observed great apes planning, both in the wild and in captivity. Some birds in the corvid family, which 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.

Santino was born in a zoo in Munich in 1978 but has lived all but five years of his life at the 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 the group. 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 reopens 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, zookeepers 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, Santino began tapping stones against the concrete artificial rocks, evidently 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-size.

"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 that 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.

Osvath and others have tested chimpanzees' ability to plan. In one experiment, the animals were given a choice between eating grapes at the moment and getting and storing a rubber hose they could use sometime in the future to gain access to fruit soup, one of their favorite foods. Many chose the hose.

De Waal, who is also affiliated with the Yerkes National Primate Research Center in Atlanta, said he's observed a female chimp at a zoo in the Netherlands that in cold weather -- but not warm -- would bring an armful of straw from her enclosure when she went outside in order to have something to sit on.

Amy Fultz, a primatologist at Chimp Haven, a sanctuary in Louisiana for animals once used for entertainment or research, said she also has seen planning in some of the 132 chimpanzees living there.

As in the wild, some fashion tools from stalks of plants that they use to fish ants from anthills.

"One, named Karin, will gather up a particular species of verbena and save it in a place in her habitat. I have watched her go back and get them later in the day, or even later in the week," Fultz said.

One expert said planning by chimpanzees has been observed often enough in the wild that she questioned the novelty of Santino's behavior.

Sue Taylor Parker, a retired professor of biological anthropology at California's Sonoma State University who has compared the cognitive development of humans and primates, said wild chimpanzees sometimes carry rocks long distances to "anvil sites" for future use in cracking nuts. Cooperative hunting also implies a certain minimum of planning.

"Chimpanzee behavior that is at the edge of their highest abilities is always interesting to read about. I just question the uniqueness of this," she said. She added that the level of planning seen in Santino is roughly the same as that of 3-to-5-year-old children.

Unusual or not, Santino's rock-throwing may not be in evidence when spring comes to Sweden this year and he again sees visitors 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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