If you’ve visited Regenstein Center for African Apes over the past year, you may have noticed Hank’s group of chimpanzees carrying small lengths of PVC pipes. These weren’t signs of a do-it-yourself home-improvement project. Instead, the tubes functioned as currency in a new study by zoo scientists.
How did it work? A researcher from the Lester E. Fisher Center for the Study and Conservation of Apes stood at a mesh barrier next to a container holding 150 of the plastic tubes. The chimpanzees could collect a tube and immediately push it back through the mesh to claim a carrot reward. Or they could carry them to another mesh barrier roughly 10 feet away to receive a grape instead—a tastier treat from the chimpanzees’ perspective.
By offering different rewards for different levels of effort, the researchers established a basic economic framework for the chimpanzees. In doing so, they also set up a system to explore how these complex social primates respond to rewards and motivations.
Amazingly, none of the exchange behaviors were taught to the apes. The team, led by Research Scientist Lydia Hopper, Ph.D., and Adjunct Scientist Kristin Bonnie, Ph.D., distributed the tokens and simply waited for the first chimpanzee to push a tube back through the mesh. Male Optimus made that breakthrough, receiving the first carrot reward. Female Chuckie figured out the grape-exchange site soon after.
Hopper and Fisher Center Research Assistant Laura Kurtycz later increased the effort required for the exchanges, moving the carrot site over to the initial grape site and establishing a new grape site all the way across the exhibit. In doing so, they saw some interesting patterns in the apes’ preferences. In the first phase, when the chimpanzees could trade the token right back at the spot they received it for a carrot, they preferred doing that to traveling to get a grape. But in phase two, when they had to travel for either treat, they walked further to get their preferred grape.
That wasn’t the only wrinkle observed. Some dominant chimpanzees opted to steal grapes at the exchange site instead of doing the work of carrying the tokens themselves. In response, subordinate chimpanzees, like Chuckie, tried to hoard their tokens, waiting to exchange them when none of the other groupmates were looking.
In another eureka moment, most of the chimpanzees figured out it was easier to carry multiple tokens in a single trip instead of going back and forth with single tokens. Even after that shortcut, though, the apes were more active when taking part in the voluntary research, a positive outcome for their well-being.
This token-exchange study was carried out over more than a year in a great partnership with the zoo’s animal care experts. The luxury of time enabled researchers to track ebbs and flows in participation, including dominant male Hank, who took a year to make his first trade—and then became an enthusiastic participant.
The token exchange sessions will come to an end in the next couple weeks as this portion of the research wraps up. But the chimpanzees won’t lack for brain teasers. Beyond the enrichment provided by care staff, the apes will also soon take part in another project. This one will have them use two tools to accomplish a single task: extracting a treat from a tricky “termite mound,” much as some peers do in the wild.
It’s another fascinating look into their minds—and ours as well. I look forward to sharing more updates as we have them.
Great Ape Economics