Santino knew the humans were coming. So each morning, he trolled for stones and fashioned concrete disks to be stashed in strategic locations until it was time to hurl them at his pesky visitors.
As a chimpanzee, Santino wasn't thought to be capable of anticipating events in a way that so closely resembled human behavior. But cognitive psychologist Mathias Osvath became convinced after watching the 30-year-old primate repeat his routine for a decade at a Swedish zoo, according to a report published this week in the journal Current Biology.
"Such planning implies advanced consciousness and cognition traditionally not associated with animals," wrote Osvath, research director at the Lund University primate research station in Gavle, Sweden. In human evolution, "similar forms of stone manipulation constitute the most ancient signs of culture."
Santino began throwing stones at zoo visitors in 1994, soon after he became the dominant male chimp at Furuvik Zoo in Gavle. For three years, the episodes were infrequent. Then he began bombarding his guests on a regular basis, prompting his keepers to investigate.
They conducted stakeouts and observed Santino scooping rocks from the moat in his island enclosure and organizing them into neat piles. Sometimes he would break off pieces of concrete from the center of the island and fashion them into "manufactured missiles," according to the study.
Hours later, he would aim them at zoo visitors in a burst of activity described by one of his keepers as "a hailstorm."
While assembling his caches, Santino was invariably calm. While unleashing them, he was agitated.
"This is what makes this special," Osvath said in an interview. "He is planning for a future psychological state."
Psychology professor Roger Fouts, co-director of the Chimpanzee and Human Communication Institute at Central Washington University in Ellensburg, Wash., said Santino's behavior was notable but not altogether different from that of wild chimps observed in Tanzania and the Ivory Coast. Those animals are known to gather tools for future use, such as heavy rocks that are handy for cracking nuts.
At his own institute, he said, a 33-year-old chimp named Tatu uses American Sign Language to ask about "bird meat" in anticipation of Thanksgiving and "candy tree" before Christmas.
Craig Stanford, co-director of the Jane Goodall Research Center at USC, said he had watched Tanzanian chimps collect sticks to fish for termites even when they were far from a termite mound. In his view, Santino's behavior may be as much a sign of boredom as intelligence.
"His whole life is spent in a small enclosure with very few outlets for his creativity," Stanford said.