Fur thieves on the loose in Maine forest, study finds

The Penobscot Experimental Forest is home to true treasures for its residents, each containing riches beyond belief. These caches contain no gold or jewels: they are filled with white pine seeds and were placed by a team of researchers from the University of Maine with one goal: to catch fur thieves in the act.

Brigit Humphreys, a UMaine graduate student studying ecology and environmental sciences, has worked for two years in the forest, located about 10 miles north of Bangor, in an effort to determine which animal personalities are predisposed to theft.

Humphreys studies the behavior of small mammals in the wild. His research adds to a growing body of knowledge showing that the unique personalities of each small mammal play a critical role in forest regeneration by impacting seed dispersal. It also completes a larger project that took eight years to complete and is nearing completion.

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

“Seed dispersal is an extremely important aspect to Maine’s economy, recreation, and aesthetics. Much research focuses on species or communities, but many individual aspects have been ignored by science. idea is to pay more attention to the individual and how variation and personality at the individual level is actually very important for ecosystems, tree growth and forest regeneration.

Humphreys worked under the supervision of Professor Alessio Mortelliti of the Department of Wildlife, Fisheries and Conservation Biology. From June to October 2022, Humphreys and a team of researchers 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 the next. After catching the animals, the team collected data on their personality traits and marked each one.

Once the grid was cleared of traps, Humphreys and his team planted artificial seed caches throughout the area, equipping each with a circular antenna buried around the cache. The caches contained seeds of white pine, which are an economically important species in Maine and a perennially preferred seed species among the small mammals involved in the study. Game cameras have also been installed to observe thieves in the act.

“The idea is that when an individual that we have tagged passes through the antenna, the antenna picks up their unique tag, so we know what that individual’s personality was,” Humphreys said.

His findings indicate that the personality of small mammals determines flight efficiency in mice and voles, with some individuals being more successful than others at stealing seeds. The most accomplished thieves: deer mice.

“We found that more exploratory deer mice were more likely to find caches to pilfer, which makes perfect sense because they probably move around more and don’t consider the risk of predation as much, so they are able to find them .caches and stealing them were our main personality findings,” Humphreys said.

“We found that individuals with lower body condition, so leaner animals, were more likely to pilfer because they were desperately hungry. We also saw a sex effect. Female voles were more likely to pilfer, this which is consistent with previous research on the same species.”

Humphreys and his team also observed many other curious and hungry species during the study.

“More than 10 different species came and raided the caches,” Humphreys said. “Some of them were unexpected, like raccoons came and took some of the seeds, which was interesting. Other common thieves were American red squirrels, eastern chipmunks, Sorex shrews and jumping mice. For jumping mice, there were only a few individuals that we caught, but the ones that were present in our areas were very effective. They captured about 10 caches in one night.

Humphreys’ findings were recently published in the Journal of Animal Ecology as part of the special report: “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 take-home message from all the research we do is that individuals matter,” Humphreys said. “The scientific community strives to conserve biodiversity, but beyond biodiversity, we must conserve behavioral diversity within a species if we truly want to have fully functioning ecosystems.”