How is this guy feeling?

How is this guy feeling? (Photo: BY-SA 3.0)

The Philadelphia Zoo is pretty small. Over the past couple of years, to help some of its residents stretch out a bit, the zoo has started installing what they call an “animal exploration trail system“—a network of corridors and tubes that critters can use to crawl, swing, and stroll between enclosures. Visitors, naturally, love it—they can watch monkeys strut and skitter above their heads. Zookeepers like it, too: it hits all the sweet spots of textbook animal enrichment, offering their charges room to roam, environmental variety, and personal choice.

But after all these rave human reviews, one question remains: What do the animals think?

Marieke Gartner is the Philadelphia Zoo’s in-house animal well-being researcher. A trained psychologist, she has spent the last 11 years becoming, essentially, a quantitative animal whisperer. “What the zoo wanted me to do is figure out how the animals view the trail,” she explains. “Do they value it at all? Is it increasing their well-being? Do they like it?”

Tigers exploring the Philadelphia Zoo's new animal trails.

Tigers exploring the Philadelphia Zoo’s new animal trails. (Photo: Philadelphia Zoo)

It’s tricky to get an answer out of an animal. You can’t ask a lemur to fill out a questionnaire, or put a lion on a therapist’s couch. Over the past couple of decades, though, scientists like Gartner have put their human heads together to try and better understand what’s going in animal ones.

One experimental method focuses on how hard animals will work to attain a particular type of reward, which helps researchers figure out how much they like certain things. Mink, for example, will go all out to reach a swimming hole, choosing it over toys, tunnels, or a cozy nest, and even muscling down weighted doors in order to splash around. Gartner hasn’t tried this method yet—“there are a lot of logistical considerations in a zoo,” she says—but she’s thinking about it.

Another involves measuring what’s called “anticipatory behavior.” Lab rats have been demonstrating this for ages, wincing before shocks and getting excited for food pellets, and recently, experts have begun paying attention to similar behaviors in zoo animals.

Anticipation is a powerful emotion in itself—just looking forward to something releases neurochemicals associated with pleasure, in both people and nonhuman animals. Although constant anticipation might indicate that the animal doesn’t have enough to look forward to, small bursts of it are a promising sign. If tigers anticipate entering the trail, pacing back and forth and looking at it frequently, it means they’re feeling good before they even go in. 

There is another way, which is both roundabout and more direct, to assess animal well-being: ask those humans who are closest to them. For a recent study, published this month in the Journal of Applied Animal Welfare Science, Gartner had keepers from various zoos fill out questionnaires on behalf of the big cats they know best.

“Just like with a human, you get a really good picture of who the animal is by interacting with them in different contexts, different times, and different situations,” says Gartner.

Keepers were asked to judge how well the snow leopards close to them were doing.

Keepers were asked to judge how well the snow leopards close to them were doing. (Photo: Pixel-mixer/Pixabay)

Asked to think back on their whole relationship, the keepers made assessments: how good was each cat at achieving their goals? Did they enjoy socializing with other cats? How often did they seem content? For the last question, they put themselves in the cats’ (metaphorical) shoes: “Imagine how happy you would be if you were this cat for a week,” the survey requested. “You would be exactly like this cat. You would behave the same way as this cat, would perceive the world the same way as this cat, and would feel things the same way as this cat.”

Zookeepers returned with detailed reports, which Gartner is excited to unpack. Understanding what makes each creature tick can help zoos tailor environments to their specific needs.”You can really use it to target individual animals, and their health,” says Gartner. A neurotic leopard, for example, might want more places to hide, while a curious one might enjoy a batch of new toys instead. 

Such surveys, which have been used for years, are philosophically interesting, too. They’re statistically well-validated: the associations they tend to produce—between, say, personality traits and perceived happiness—are common across keepers, time periods, and even cultures. Alex Weiss, a subjective well-being expert at the University of Edinburgh and a coauthor of Gartner’s big cat study, gave a similar questionnaire to chimpanzee experts, and has thought a lot about why the method seems to work so well. “At a scientific level, I expect that there are all kinds of cues that chimps are giving off,” he says. “Something just gives them the impression that the animal’s happy.”

A white-cheeked spider monkey takes advantage of the "treetop trail."

A white-cheeked spider monkey takes advantage of the ”treetop trail.” (Photo: Philadelphia Zoo)

As Weiss points out, we’re only four to six million years removed from chimps ourselves. “The most parsimonious explanation is that there are a lot of things that are common between us,” he says. While it may feel less than rigorous to say that a chimp “looks sad,” indulging that instinct to analyze facial expressions and behavior patterns has proved revealing after all. “Something about those individuals is sending off a signal that gives a possible window into their internal states,” says Weiss. 

Gartner is still in the introductory phase of her studies at the Philadelphia Zoo. She has a long way to go before she can answer, on behalf of the tigers and lemurs, yay or nay to the zoo’s new trails. But so far, signs seem promising—even the intuitive ones. “The lemurs had to be chased back in sometimes,” said Gartner. They had little interest in leaving the tunnels. “To me, that’s a pretty good indicator.”

Naturecultures is a weekly column that explores the changing relationships between humanity and wilder things. Have something you want covered (or uncovered)? Send tips to