Monkey see puzzle, monkey do, monkey eat

Rice engineering students develop enrichment device for Houston Zoo primates

The Allen’s swamp monkey, one of two at the Houston Zoo, was checking out a puzzle built by Rice University engineering students. The rewards were worth it all around: tasty peanuts for Naku and the satisfaction of a job well done for the students.

The Monkees, from left: Nathan Williams, Jack Kaplan, Alexandra Eifert, Emily Lisa and Julio Ledesma. Photo by Jeff Fitlow

The goal was to create an interactive enrichment device to engage the swamp monkeys. “They are very smart,” said Helen Boostrom, a senior primate keeper, of Naku, a male, and Oda, a female. “They like to take things apart and mess with things.”

The students delivered their final version of the project to the zoo in April and watched with glee as Naku went straight for the device and began to play.

“It’s awesome to see how much they love it,” said Emily Lisa, one of the inventors. “It took them a good amount of time to figure out how to use it and tilt the device in the correct way to get the food. So it’s great to see that they not only enjoy it but that it also challenges them.”

Naku, a swamp monkey at the Houston Zoo, checks out a puzzle feeder built by Rice University students. The feeder is one of a collection of enrichment devices that offer monkeys new challenges every day. Photo by Jeff Fitlow

Lisa and her teammates, Julio Ledesma, Jack Kaplan, Alexandra Eifert and Nathaniel Williams, designed three other prototypes before arriving at the final version. The simple puzzle has three shelves with staggered holes in a heavy-duty plastic box with a clear cover. Zookeepers put nuts or sunflower seeds on the top shelf so the monkeys have to work them down to the hole at the bottom.

The device built at Rice’s Oshman Engineering Design Kitchen will join a rotating set of challenges for the monkeys. “They get different enrichment devices every day,” Boostrom said. “Sometimes they’re puzzle feeders like this. Sometimes we make substrate forage piles, where we hide sunflower seeds and other things in wood shavings.

“We give them as much variation as we can, because in the wild they’d encounter all kinds of problems. Their habitat would be changing, so we want to be sure they’re exhibiting natural behaviors by challenging them. They have a lot to do here,” she said.

Rice engineering students have created an enrichment device for Allen's swamp monkeys at the Houston Zoo. The puzzle makes the monkeys think and work to get nuts and other food from the device. Photo by Jeff Fitlow

The box was designed primarily for Oda, “because if we design it for her, we design it for everyone else,” Kaplan said. “She can unscrew things, so we had to use lock nuts to make sure she couldn’t take our device apart. We also had to make sure there wasn’t a place where they could get a finger or hand stuck.”

Not unlike a baby’s rattle, the plastic box is built to be noisy. Corn in the rounded handles keeps Naku and Oda interested even if the food is gone. “If the handles pop off somehow, whatever comes out isn’t going to hurt them if they swallow it,” Eifert said.

An early prototype was only partially successful, puzzle-wise. “The problem was, it was completely mobile,” Williams said. “The male figured out that if he submerged it in the pond, which he liked to do, it would fill up with water. When he took it out all the food would rush out with the water.”

That’s why the students added a tether, a steel line inside sections of plastic pipe that protect the monkeys from harm. The monkeys can pick up and manipulate the box, but not move it too far. “Even though we knew they were smart, they were a lot cleverer than we gave them credit for,” Williams said.