Research shows that hairy thieves are on the loose in a Maine forest

Scattered throughout the Penobscot Experimental Forest are veritable treasure troves for its residents, each containing unimaginable wealth. These caches do not contain gold or jewelry; they are filled with eastern white pine seeds and were placed by a team of researchers from the University of Maine with one goal: to catch furry thieves in the act.

Brigit Humphreys, a graduate student at the University of Maine studying ecology and environmental sciences, has spent the past two years working in the forest about 10 miles north of Bangor in an effort to determine which animal personalities are susceptible to theft.

Humphreys has studied the behavior of small mammals in the wild. Her research adds to a growing body of knowledge showing that the unique personalities of individual small mammals play a crucial role in forest recovery by influencing seed dispersal. It also complements a larger project that has been in the works for eight years and is nearing completion.

“The goal of the project was to find out how the personalities of small mammals and animals in general influence different ecological processes,” Humphreys said. “We’re focusing on small mammals because they’re a great study system. They’re plentiful, we get a really good sample size and we can actually do experiments with them in the forest.

“Seed dispersal is a super important aspect to Maine’s economy, recreation and aesthetics. A lot of research focuses on the species or community level, but many of the individual aspects have been ignored in science. The idea is to focus more on the individual and how variation and personality at the individual level are actually very important for ecosystems, tree growth and forest regeneration.”

Humphreys has worked under the direction of Professor Alessio Mortelliti of the Department of Wildlife, Fisheries, and Conservation Biology. From June to October 2022, Humphreys and a team of researchers will set traps for small mammals, including squirrels, chipmunks, mice, voles and shrews. They worked in a six-grid system, slowly moving about 150 traps from one grid to another. Upon capturing the animals, the team collected data on their personality traits and tagged each of them.

After clearing a grid of traps, Humphreys and her team planted artificial seed repositories in the area, equipping each with a circular antenna buried around the repository. The caches contain seeds of eastern white pine, an economically important species in Maine and a seed species consistently preferred among the small mammals involved in the study. Game cameras were also set up to observe thieves in the act.

“The idea is that when a person we’ve tagged passes over the antenna, the antenna picks up their unique tag, so we know what that person’s personality was,” Humphreys said.

Her findings indicate that small mammal personality determines the effectiveness of theft in mice and voles, with some individuals being more successful at stealing seeds than others. The most talented thieves: deer mice.

“We found that more exploratory deer mice were more likely to find caches to steal, which makes a lot of sense because they’re probably moving around more and they’re less likely to consider predation risk, so they’re able to find these caches and steal that were our key personality outcomes,” Humphreys said.

“We found that individuals with lower body condition, i.e. lean animals, were more likely to steal because they were desperately hungry. We also found a sex effect. Female voles were more likely to steal, which ties in with previous research on the same species of voles.”

Humphreys and her team also observed many other curious and hungry species over the course of the study.

“We had over 10 different species come and raid the caches,” Humphreys said. “Some of them were unexpected, like raccoons coming to take some of the seeds, which was interesting. The other common thieves were American red squirrels, eastern squirrels, Sorex shrews and jumping mice. For the jumping mice, there were only one few individuals we caught them, but the ones that were in our areas were very effective. They were getting about 10 caches a night.”

Humphreys’ findings were recently published in the Journal of Animal Ecology as part of the special feature: “Intraspecific variation in ecology and evolution.” She is currently working on the final part of the overall project, which focuses on comparing behavioral diversity in areas with different forest management styles.

“The message from all the research we do is that individuals matter,” Humphreys said. “There is a big push in the scientific community to conserve biodiversity, but beyond biodiversity, we also need to conserve behavioral diversity within a species if we really want to have fully functional ecosystems.”