Where squirrels collide: Are Minnesota’s southern flying squirrels overtaking their northern cousins?

Forest researchers in north-central Minnesota are bringing the little-analyzed world of an elusive night creature into the light.

There is a dearth of state research about flying squirrels, a diminutive, rarely seen critter with outsized skills. Minnesota has two species of the little aerialists, a southern and a northern, and where they meet has caught the attention of the Natural Resources Research Institute at the University of Minnesota.

About the size of a chipmunk, the smaller, southern critter prefers a landscape of deciduous hardwoods, such as maple and oak. Its northern counterpart nests and lives among conifers like spruce, pine and fir.

Both species overlap in habitat, such as in the mixed woodland west of Duluth, extending toward Bemidji. Researchers suspect the southern species is increasingly moving north into that zone, attracted by warmer winters, and the scientists want to learn what it means for the squirrels. The southern variety’s presence could be putting pressure on their northern cousins. In Wisconsin, northerns are a protected species of concern.

The multi-pronged study is designed to know the squirrel in new ways. Researchers have set up acoustic devices to capture squirrels chirping and chattering to get a baseline of where flying squirrels live in Minnesota. To date, the team also has fanned out primarily in forests in the Duluth and Cloquet areas where the squirrels are known to overlap. There, they have trapped and collared both species to track how far the squirrels travel and where they anchor down. More trapping is possible next spring in the Remer area, where acoustic detectors are set up, project leader and ecologist Anna Mangan said.

Wildlife ecologist Michael Joyce said the role of climate is unmistakable.

“Where we are seeing this change … that is an indication that things are changing in our forests,” he said.

Additionally, the animals are possibly contributing to changes in the habitat with their eating habits. Acorns and maple seeds are a prime food source for southern flying squirrels.

“As they’re coming north, they are spreading those seeds further,” Mangan said.

What could be lost where they coexist is the northerns’ contributions to forest health. They eat truffle mushrooms, whose fungal spores then spread through the critters' droppings and help trees and plants grow, she said.

Flying squirrels own the night. They dial into their surroundings with large eyes and ears. When they travel between treetops, they leap and catch air, kite-like, in the stretchy flaps of skin connecting their front and hind legs. They don’t fly so much as glide, most times between 20 to 30 feet and sometimes as far as 150. Their long, flat tails act like a rudder, controlling their flight and landing.

How the northern and southern flying squirrels coexist isn’t well-known, Joyce said, but the smaller southerns are more aggressive and could begin outcompeting northerns. In one unrelated study, southern flying squirrels forced northerns out of dwellings in deciduous tree cavities. Conversely, the NRRI team has seen Minnesota’s species occupying the same trees.

To date, 122 flying squirrels have been trapped, 22 of each species collared.

“It’s not as simple as they overlap or they don’t. There are a lot of different scales,” Joyce said.

Southern flying squirrels also could have an upper hand in health. They can host a parasite called Strongyloides robustus that can be lethal if transmitted to northerns. The parasite is present in Minnesota but at a low level, Joyce said.

Proceeds from the state lottery in the Environment and Natural Resources Trust Fund funded the study.

Joyce said it’s difficult to estimate the number of flying squirrels in Minnesota but “there are millions and millions.”

“If you live in an area that has some mature woods around you, you probably have one to a dozen flying squirrels around you,” Joyce said.

Flying squirrels are part of the state’s natural history and worth studying, he said.

Joyce and Mangan hope their findings can help state wildlife managers better understand flying squirrels and make decisions that help protect them if needed.

“If this is a case where there is not some big functional change as you lose northerns for southerns, that would be good to know because we don’t have enough funding to help every species,” Joyce said. “It hurts me a little to say that but you have to be practical. We can’t manage for everything.”