Very Cold Small Mammals
My car shuddered and groaned before turning over reluctantly and revving to life. The thermometer had displayed negative 32 degrees as I headed out the door, and my weather app countered with negative 37. Looking back through my kitchen window, I could see Ally Moser Scott filling up thermoses with hot water, and organizing her hand warmers, balaclava, and boots. I was headed to a comfortably heated office. She was preparing to be outside all morning in this potentially dangerous cold.
Ally is a master’s student in Professor Jon Pauli’s lab down at the University of Wisconsin Madison. Her thesis is “assessing the population ecology of small mammals in northern Wisconsin to evaluate prey availability for the American marten.” The field part of her research entailed setting up several 25-trap grids in different forest types, and then checking the live traps for nine days straight in order to estimate the numbers of small mammals in each habitat.
With 75 traps to check per day, it’s a good thing that Ally has help. Sarah Nagel, who earned a degree in Ecology and Evolutionary Biology from Minnesota State University Moorhead, is gaining field experience by being Ally’s research technician. Ally and Sarah are staying at the Cable Natural History Museum’s Jackson Burke House, which is convenient to their research sites near Clam Lake and Mellen in the Chequamegon-Nicolet National Forest.
Although Ally and Sarah are willing to brave our recent polar vortex in the name of science, I looked at the weather forecast closely and picked a slightly warmer day to join them on their trap lines. It was barely below zero with a light drizzle of snowflakes when we loaded up in the work truck at 7:00 a.m.
I wasn’t sure what to expect as we walked single file into the woods at the first study site in a spruce swamp. Because the small mammals that Ally is trying to catch spend most of the winter hiding out and staying warm beneath the snow, it’s important to her research that humans don’t tramp all over the trap grids and mess with mouse habitat. We stepped as exactly as possible into the boot prints that were established the first time someone walked among the traps.
Sprigs of Labrador tea, a common bog plant, poked out of snow, which drifted among the scaly trunks of spruce trees. Also scattered among the trees in a 5 x 5 grid, were 25 wide, black, corrugated tubes, each about two feet in diameter and 30 inches tall. Each tube was covered by a square board and a rounded cap of snow. This research takes a village. Last fall, a crew of staff and volunteers from The Great Lakes Indian Fish & Wildlife Commission (GLIFWC) pitched in to help place these tubes. Then, volunteers from GLIFWC returned regularly to put bait in the tubes, just to make sure that the small mammals were comfortable using these odd habitats.
Finally, when Ally came up to start her 9-day trapping session here, she and Sarah baited and set a metal live trap inside each tube. The bait packets are an ingenious system of a thin plastic bag filled with a little stuffing and sunflower seeds. The small mammals can easily chew into the bag, eat the seeds, and make a warm nest with the stuffing. Although the plastic may seem dangerous, it can add a layer of warmth, and doesn’t cause suffocation. With the bitter cold, the researchers also strap a big air-activated heat packet to each trap. It must be a fairly comfortable set-up for the critters, because some get “trap happy” and come back day after day for a free lunch.
For example, when Ally pulled a little deer mouse out of one trap, it was already sporting tiny metal ear tags. It had already been weighed, its hind foot measured, and its ears pierced, on a previous day. Sarah recorded the ear tag numbers on her data sheet, and the wide-eyed mouse was free to scurry away.
You may be wondering why scientists would go to so much trouble, and brave the recent bitter cold, just to count the little critters in an area. The answer lies in a slightly bigger critter: American martens. These beautiful animals have been reintroduced to Wisconsin, but aren’t thriving as hoped. Resource managers want to know why. A few years ago, Phil Manlick, now a PhD student in Professor Pauli’s lab, stayed at the Museum’s staff house to study American martens in the area through DNA samples from hair and scat. His results showed that the local martens are eating mostly shrews and road-killed deer instead of their preferred food of red-backed voles.
Ally’s research is following up on those findings. Maybe martens are eating shrews because voles aren’t available? During my single day on the trap line, we certainly caught more shrews than mice, and Ally has only caught a few red-backed voles so far.
My toes were chilled by the end of that morning afield, but the temperatures I endured were nothing compared to the deep freeze that Ally and Sarah navigated safely three days in a row. Her research will eventually earn her a master’s degree. In the meantime, she and Sarah have earned some bragging rights for toughing out the bitter cold.
Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at http://cablemuseum.org/natural-connections-book/. Listen to the podcast at www.cablemusum.org!
For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: "Bee Amazed" is now open!