Hoppers‘ beaver expert shares the wild facts of these dam builders
How do scientists actually study beavers? How do beavers build dams? And what is “beaver butt juice”?
Dr. Sam and Nisha in Pixar’s Hoppers.
Field researchers will go to considerable lengths to study animals in the wild. In Hoppers (2026), scientists have reached perhaps the pinnacle of just how far they’re willing to go in the name of science: they hop into a robot beaver body and join a beaver colony.
But what do real beaver experts actually do to study these industrious creatures? To help distinguish the fact from fiction, Scientific American spoke to Emily Fairfax, who studies ecohydrology at the University of Minnesota and worked with the Hoppers team to make sure the beaver depictions were dam right. (Her university web brags, “When Fairfax says she can talk about beavers all day, she’s not kidding.”)
[An edited transcript of the interview follows.]
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In Hoppers, scientists observe from afar, dress up as animals and even send in robots. Is that really how we’re studying beavers in the wild?
We do study animals in the wild that way. If you’re rehabbing a baby animal, you might want to dress up as an adult version of it so that it doesn’t learn that humans are its parents. We do use robots, although I don’t shape mine like beavers. I fly drones pretty often in the field. We also use game cameras, which are cameras that we can tie to trees and study beavers that way. I think it would be amazing if we could hop into an actual animal’s body and go in there and communicate with them, because you can only learn so much from the aerial view from 10,000 feet.
In the film, beavers are referred to as a keystone species—what does that mean? Are there animals that could replace the beaver in a wetland?
A keystone species is an animal that, for whatever reason, a lot of other animals and plants depend on. Oftentimes our keystone species are ecosystem engineers that are capable of transforming the physical earth and making unique environmental conditions. In the case of the beaver, what they’re doing is: they’re making wetlands, and there’s no other animal other than beavers and people that can go out and make wetlands. Also, we try to mimic beavers pretty often for restoration; we do things called beaver dam analogues, which are fake beaver dams, to try to get some of those benefits of the beaver dam itself.
Do you think you could build a dam nearly as good as the beavers do?
Not a chance. Even having worked as an engineer myself, I have said many times that the first time I went to a beaver pond, I realized I couldn’t make that with the same materials. Then I realized I also couldn’t make this if you gave me a backhoe and you even gave me the blueprint for it.
Do beavers work together to build these wetlands, or is it just one beaver on a mission?
No, the family units are really important to beavers. Disrupting a beaver family is actually one of the most damaging things you can do to beavers because their environment is designed so that every single beaver is busy.
One of my favorite running jokes in the movie is about the beaver oils. At one point, someone says they smell like vanilla, and our king beaver keeps trying to share his oils, but the recipient isn’t particularly interested in them. How accurate was this depiction, and why do they have these oils at all?
It was disturbingly accurate. Beavers have oils that they excrete from [their rear end] and will scoop those oils up into their paws while they groom themselves. Beaver oils are called castoreum, and they come from the castor sacks, which are inside the beaver. In the 1970s and 1980s, if you ate something or drank something that had “natural vanilla flavoring” or “natural raspberry flavoring,” that was actually beaver’s castoreum. So you have, in essence, tasted beaver butt juice.
The movie also starts with a really funny depiction of a class pet, but do you think beavers would actually make a good class pet?
Beavers would be the worst class pet! You would come back from recess, and all your desks would be chewed up and pushed into a dam. They’re so stubborn. They’re also big. Adult beavers weigh between 40 and 110 pounds.
The film overall deals with climate change and humans affecting natural habitats. How are beavers being affected by these changes in the real world?
Beavers are one of the most resilient species to climate change, thankfully. If they’re in a prairie, if they’re in a forest, if they’re in the mountains or the deserts, it doesn’t matter: they can create a good wetland habitat. Something that has been challenging for people and beavers is that as the Arctic is thawing, the permafrost is becoming no more. Beavers have been in the Arctic many times in their evolutionary history, but every time they’ve been up there, the Arctic has been a jungle. So when we see them moving north now, we are very worried that they’re going to create more wetlands, which might accelerate that permafrost thaw.
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