When reports came out of Africa in recent weeks that researchers for the first time in history were seeing wild gorillas using sticks and rocks as tools, keepers at Lincoln Park Zoo weren’t exactly surprised.
Earlier this year, zoo researchers watched two female gorillas figure out how to use sticks to retrieve two of their favorite snack foods–ketchup and mustard–from holes in a fake termite mound. It took weeks, but the apes finally learned that if they inserted a stick of the right length into the holes, the stick would come out coated with a slurpable treat.
Already they had watched as zoo gorillas tackled “food puzzles,” or lengths of PVC pipe sealed at each end, pierced with holes and stuffed with raisins or peanut butter. Sometimes the apes shook treats out of the holes, but other times they seemed to use sticks to dig at the food, a behavior that could be construed as tool use.
“We had seen our gorillas do this, as had keepers at other zoos, but because gorillas aren’t known to be tool users in the wild, it was thought this knowledge of captive gorillas using them was not applicable,” said Elizabeth Lonsdorf, the zoo’s director of conservation resources.
But in late September, field researchers in the Republic of Congo reported they had seen a female lowland gorilla use long sticks to gauge water depth while walking through a swamp pond. A different female selected and laid down a dead tree trunk to cross a deep swamp patch.
Other researchers at a lowland gorilla sanctuary in Congo reported earlier this month on an orphaned, 2 1/2-year-old female gorilla who smashes palm nuts between rocks to extract oil–an even more complex behavior known as the “hammer and anvil” technique.
This proof that tool use is a natural behavior for gorillas represents a surprisingly profound discovery. Previously it was thought humans and chimpanzees were the only primates that have the cognitive powers needed to fashion and use tools to accomplish certain tasks. Seeing gorillas use tools indicates that cognitive power probably occurred far earlier in history than previously thought, when all the great apes had a common ancestor.
It also points up the irony, said Lonsdorf that only in the recent past has science begun to study man’s closest genetic relatives–gorillas, chimps and orangutans–just when human activity has wild apes on a fast path to extinction.
“Before we really get to know and understand their lives in the wilderness, they could be gone,” Lonsdorf said.
Lonsdorf said it doesn’t surprise her that scientists are only now observing tool use by gorillas in the wild.
“Most of what we know about wild gorillas is from a very small population of mountain gorillas, who live in an atypical environment for their species,” Lonsdorf said. “Mountain gorillas live in a salad bowl, feeding on a relatively narrow selection of easily obtainable fruits and leaves that they have no trouble finding or eating.”
For that reason, they have little incentive to develop tools.
With fewer than 700 mountain gorillas left, zoos keep and breed only lowland gorillas. Though more numerous than their mountain cousins, far less is known about lowland gorillas in the wild because they live in heavily forested, swampy terrain where it is difficult to find them and even harder to follow them for observation.
As big logging companies have begun clear-cutting their forests in recent years, however, scientists have increased efforts to get in the swamps and learn about them in hopes of slowing the wholesale destruction of their world. The discovery of the two females using tools in the swamp in the Republic of Congo grew out of those efforts.
Soon after Lincoln Park moved its resident troops of lowland gorillas and chimpanzees into the zoo’s new apehouse in July 2004, Lonsdorf and her colleagues started a comparative study of tool use between gorillas and chimps.
One of the ape habitats in the building is equipped with a fake termite mound. Because it is built flush to a viewing window, the public can see into the mound’s hollow interior.
That is where keepers can attach tubes filled with mustard or ketchup to small holes that are open to the apes and allow them to smell the treats.
Keepers leave sticks and straw of varying lengths near the mound, but it is up to the apes to decide to pick up a stick or stem and try to insert it into a hole. If the stick is long enough, it will come out coated with the condiment.
Quick learners
The experiment started with a troop of chimps known as Hank’s group after one of its male leaders. In the wild, chimps learn from their mothers to “fish” for termites to eat by carefully poking sticks and straw into termite mound holes.
“The chimps caught on the very first day,” said Lonsdorf, “at least the female chimps did. From then on … they would get so excited when they heard keepers inside the termite mound, they were sticking their sticks through the hole before the mustard tubes were attached. It got so I worried they’d poke a keeper’s eye out.”
The male chimps weren’t so quick to pick up on the technique, she said, which also is the case in the wild.
“One little male in Hank’s group tried it unsuccessfully,” she said, and other young males didn’t try at all. “It took Hank four weeks to catch on.”
Last January, keepers moved Hank’s group out and brought in a gorilla group headed by JoJo, a silverback. Unlike the chimps, JoJo’s family had frequently played with the PVC pipe food puzzles in the past.
More Top Picks Executive Function Skills How To Build Them In Kids
“We baited our termite holes at random times between 11 a.m. and 2 p.m., sometimes two days a week, sometimes three,” said Lonsdorf. “We don’t want them to become accustomed to it through routine.”
The gorillas, especially the adult females, quickly noticed something was happening when they heard the keepers inside the mound after two weeks of no treats. Ignoring the sticks under their feet, they’d spend 15 or 20 minutes trying fruitlessly to stick their fingers into the holes before losing interest.
“It took almost two months before any of the gorillas figured it out,” Lonsdorf said. The two adult females, Makari, 18, and Bahati, 15, were the ones who succeeded.
No other gorillas ever learned to use the sticks.
Early in September, keepers switched Hank’s group back in. As the research continues, JoJo’s family likely will be returned to the habitat at some point next year to see if more gorillas learn how to use the sticks.
“It’s a good situation for comparative studies in which the chimps and gorillas are given the opportunity to do the same tasks in the same environment,” Lonsdorf said.
New experiment
She and the zoo’s chief animal behaviorist, Steve Ross, already are trying to devise a second tool experiment, providing hard-shelled nuts to the apes and a hammer-like object to break them open.
The trick for the scientists is to figure out how they can add a big rock to the exhibit that is anchored with an unbreakable chain or cable so it can’t be carried away by the animals.
“Obviously we can’t leave a big boulder in there,” said Lonsdorf, “because JoJo or Hank might try tossing it through a window.”
———-