Throwing rocks

Chimpanzee Santino throws rocks at visitors when he thinks it gets to crowded at the monkey house. With this behaviour the chimpanzee male from a Swedish zoo gave researchers enough material for a scientific publication.
Long before the zoo opened Santino collected the stones in the monkey house and put them ready. Once he got annoyed by the crowdedness at the monkey house he would start pelting the visitors. When the stones were all out at the residence, he started to rip off pieces from the fake concrete rocks and used these as projectiles. Nobody got seriously injured at these attacks. Usually visitors were not hit or merely grazed by the stones.

The fact that Santino throws rocks at visitors is in itself not very remarkable. He is the alpha male of the group and he likes to manipulate his surroundings. According to the researchers, all these visitors he has no control over are highly frustrating to him. The reason for the extra research and the publication was the planning of the attacks. The researchers say that this behaviour shows that chimpanzees are able to plan ahead. Santino predicts that he might get angry and prepares himself for that. Such complex behaviour has now been observed for the first time. It had previously been shown only in laboratory experiments that chimpanzees could plan ahead, but this had not been observed yet outside the lab.

The research results have been published in the scientific journal Current Biology.