Where the Wild Mice Are

Tracy Burkhard, assistant professor of biology, was not always fascinated by mice. For many in the field of behavioral ecology, the focus is on birds, not mammals.

Tracy Burkhard, assistant professor of biology“Wild mice, and mammals in the wild generally, are understudied,” says Burkhard. “Birds are often out during the day in highly visible places like trees, bushes. Also, we can hear them quite clearly―as opposed to mice, whose vocalizations are often inaudible to human ears. Their songs and plumage are striking, too.”

Both birds and mice serve as significant links in the food chain. Their health can reveal essential information about the health of an entire ecosystem. And, while birds and lab mice are often the subjects of research, the same is not true for wild mice. Few researchers study mice behavior in the wild because they are a nocturnal species.

“It’s hard to just go out there with binoculars and watch mice behaving,” says Burkhard. “Even when wild mice species are out during the day, they are often not visible because of their small size. Importantly, their anti-predator behaviors make them far less likely to move around in places visible to human eyes.”

Since starting down the “mouse path,” Burkhard has studied a variety of rodent species, from meadow voles in a lab at the University of California at Berkeley to pygmy mice in Texas to singing mice in Costa Rica. The more she studied the muroid species of rodents―a category that includes mice, rats, voles, hamsters, lemmings, gerbils, and many others―the more interested she became.

“Muroid rodents are a cryptic species,” she says. “There is such a diversity of colors and shapes, sizes and tail lengths―and lifestyles, too.”

Myth-busting Mice “Lunar Phobia”

Burkhard, who joined Lewis & Clark in fall 2024, has been working with her students on a number of research projects, including studying a phenomenon known as “lunar phobia.” It refers to the behavioral adaptation of some animals to stay out of bright moonlight.

“When the moon is out, nocturnal prey species, like mice, won’t want to be out and about because they are more detectable by predators,” says Burkhard. “It’s an old wives’ tale that makes intuitive sense, but there’s been little rigorous testing to confirm it.”

Aversion to light is an integral part of many classic behavioral studies of laboratory rodents. It forms the basis for a lot of psychology, neuroscience, and physiology research, according to Burkhard. Recently, though, experts in these fields have recognized a lack of studies examining nocturnal rodent responses to moonlight in naturalistic conditions.

This summer, Angie Cabarle BA ’25 and Jonah Koenig BA ’25 worked with Burkhard to study the nocturnal behavior of Western deer mice as participants in the John S. Rogers Science Research Program. The Rogers students, along with research assistant Madison Johnson BA ’25, conducted field work in Tryon Creek State Natural Area, a 645-acre park adjacent to campus. Among their goals: quantifying both mouse activity and the risk of predator attacks under different lunar conditions.

Their data collection projects included placing as many as 70 trapping devices in different locations throughout the park every night. Each device was filled with peanut butter, oats, and some cotton for nesting to attract the mice. Early each morning, Burkhard and her students checked the devices to determine how many mice were active during the night. They also tracked mice behavior through strategically placed video cameras.

“Deer mice have huge eyes that they use to search for food at night,” says Burkhard. “There’s a trade-off. If there’s more light, a mouse might be able to find food easier, but it might also mean they are more detectable by predators.”

The hands-on research work Koenig has done under Burkhard’s guidance sparked his curiosity, and helped him find his purpose and a career path.

“I didn’t really know what I wanted to do. Then I went on study abroad to Australia led by Professor of Biology Tamily Weissman-Unni and discovered that I really like research,” says Koenig. “It’s been amazing to have the opportunity to start my research career here.”

Koenig will soon begin a graduate program at the University of Exeter in the United Kingdom, pursuing a master’s of science in biology evolution, behaviour, and ecology with an international field course.

Cabarle investigated predator behavior in Tryon Creek by placing lifelike deer mouse models in various places throughout the park. The models were made of plasticine clay, a material that allows for a detailed impression of teeth, claws, and talons. The models were meticulously painted to resemble Western deer mouse fur patterns. Burkhard and her students created the model mice using a silicone mold they developed through significant trial and error.

Searching for the “Charismatic” Pacific Jumping Mouse

Burkhard hopes to focus some of her research on the Pacific jumping mouse, a species native to Oregon and Washington. Only found in river areas and damp forests, this hibernating species spends up to 10 months of the year asleep. She has not yet seen one in the wild, so she is still investigating whether it will be a viable species to study.

“Hibernation is not only interesting from a physiological and metabolic perspective, but also from a behavioral perspective,” says Burkhard. “I’m interested in the trade-offs that emerge from this type of lifestyle.”

Other species, like the deer mice of Tryon Creek, are active the entire year, she says.

“Deer mice have a litter of pups every 28 days. They are constantly foraging, dispersing, guarding their home ranges, finding new mates, sticking with their old mates. They’re doing these ‘life history’ behaviors all the time. If you are a hibernating species and you’re active only one quarter of the year―just three months―you have to fit all of those important behaviors into one short period.”

Burkhard is interested in understanding how the shortened period of wakefulness might change the way the mice behave, such as how they allocate energy and resources.

“Will the shortened time period affect their mating system, for example, if they have only one chance?” she asks. “Is it more important that they immediately find a mate and have babies? Or does it matter more that they invest time into finding a good quality mate? I chose Pacific jumping mice because not a lot of people study them. They are saltatorial, meaning they’re adapted for jumping. They’ve got huge hind legs and long tails, which, for a jumping species, helps with balance. I think it’s a very charismatic species.”

Long term, Burkhard wants to find ways to modify classical behavioral tests and collect data in a noninvasive manner. This summer, she has been working with another student participating in the Rogers Science Program, Liam Stanley BA ’27. Stanley, under the guidance of Albert Bae and Ben Olsen, both assistant professors of physics, has worked on designing and building an enclosure prototype that wild mice could “opt into,” entering and exiting at their leisure.

“We’re calling it SQUEAK, which stands for the Station for the Quantification of Uncaged Ecological Activity of Kritters,” says Burkhard. “I want my students to get a chance to plan and conduct experiments since so many of them are going to go to graduate school. I want to be able to publish with them and to build a viable program at Lewis & Clark that is focused on undergraduate researchers.”

Biology Rogers Science Program