“Danger–Mad Marmot” warned the sign on the laboratory door. Inside stuffed woodchucks and other woodchuck memorabilia cover Stam Zervanos’s desk and study area.
Zervanos, a biology professor at Penn State University’s Berks-Lehigh Valley College near Reading, has been studying woodchucks, the least social of the marmot genus, for eight years. As a physiological ecologist, he is particularly interested in woodchuck hibernation.
Using radiotelemetry to continuously monitor the body temperature of hibernating woodchucks, Zervanos discovered that even though they go into deep torpor, they awaken every week or ten days throughout the winter, but unlike chipmunks, which also awaken from deep torpor, they don’t eat stored food. Instead, Zervanos speculates that such arousals in woodchucks may be necessary “to maintain muscle integrity, especially in males, which must be in top form coming out of the den.”
They arouse fairly quickly and are awake from a few hours to half a day. Then their body temperature, which reached its normal 96 degrees Fahrenheit, goes back down to its hibernating 47 degrees or so more slowly than it went up.
Males, though, are awake for longer periods than females, especially near the end of hibernation, and their body temperature, when hibernating, is higher, so they use 38% more energy during hibernation than females. Males also enter hibernation five days later than females and arouse for the last time three days earlier.
Most importantly, for those who might scoff at Groundhog Day and Punxsutawney Phil’s annual weather predictions, “In spring, most woodchucks [also known as groundhogs] emerged above ground two to four weeks before their last torpor bout with a mean date of emergence [being] the fourth of February,” Zervanos writes in a recent paper. That’s mighty close to Groundhog Day on February 2. And woodchucks may indeed be “sampling the external environment,” adds Zervanos.
But they are also sampling each other. The males visit female burrows, and the females remain at home to receive them. No hanky-panky is involved however, only “bonding activity in preparation for mating,” Zervanos says. These normally solitary animals need to reacquaint themselves with their neighbors because woodchucks do move around depending on their age, sex, or even inclination. And females far outnumber the males in part because in late winter and early spring, when cover is scarce and predators are hungry, the more active male woodchucks are easier for predators to catch.
In early February males also survey their territories while females assess the availability of food. Then both sexes settle into a final bout of deep torpor that lasts until early March. Only then do they mate. Their two to eight young are born a month later.
All this and more Zervanos and his research assistant June Brown have learned at their 60-acre study site–the Pieffer Farm on the campus–where approximately 30 woodchucks live. This mixture of woods and fields provides ideal habitat for them. So does the rest of the campus. During our visit in mid-March, Brown showed my husband Bruce, our son Dave, and me woodchuck holes in front of the campus bookstore, under the sundial near the library, and, most appropriately, in front of Luerssen Building where Zervanos has his office.
From there we followed June through the large trees that encompass the Nature Area of the Berks-Lehigh Valley College to the busy, two-lane Broadcasting Road, which we crossed to reach the Pieffer Farm. That road, as well as foxes, hawks, and the occasional coyote, accounts for the deaths of some of Zervanos’s subjects. Brown said that all of the previous year’s young were still in the study area because they had taken over a big male’s separate burrows after a fox killed him. Usually most juvenile woodchucks disperse in their first year in Pennsylvania.
But Christine Maher, a biology professor at the University of Southern Maine in Portland who is also studying woodchucks in the field, has discovered that in her study population as many as half of the juveniles, both male and female, delay dispersal until their second summer and a few even delay until their third summer. Her females are two years old when they mate, but most of Zervanos’s are yearlings.
Maher has also found that woodchucks are more sociable than previous studies have shown. Her male and female adults, she says, often interact outside their breeding season, and her female adults build burrows near their mothers, while males move away.
The date of Groundhog Day doesn’t make as much sense at Maher’s latitude. She first sees adult male woodchucks above ground around March 3 and the first adult females on March 25. Most of her woodchucks also go into hibernation in late September, a month or more before Zervanos’s woodchucks.
All of Maher’s woodchucks hibernate; 10% of Zervanos’s don’t, and farther south, a colleague at Clemson University in South Carolina has found that few of his woodchucks hibernate. Is there a genetic basis for hibernation, Zervanos asks. If Maine and South Carolina woodchucks were brought to Pennsylvania, would their hibernation patterns change? Zervanos calls this a “common garden experiment to see what effect environment has on genetics,” and he hopes to find out. The study of hibernation may also yield some medical insights or applications, Zervanos says, since deep torpor seems to interrupt the activities of viruses, and possibly of internal parasites also.
Woodchucks can even enter deep torpor in the middle of summer to conserve water and energy, as Zervanos found out during the drought and heat wave of 1999. Five of eight of his radio-telemetried woodchucks did this. The three that didn’t lived close to water.
No matter what discoveries he makes about woodchuck behavior, Zervanos, like Maher, has found exceptions to the rule. For instance, one female traveled 360 feet over snow to enter a male’s burrow and stayed several days before returning to her burrow. (Maybe she thought it was leap year.)
Another female, more aggressive and antisocial than most, moved off into the woods and didn’t hibernate for two years. She also didn’t bear any young. Only when she hibernated, in her third year, did she give birth.
Brown, a dedicated observer who spends many hours watching individual woodchucks through binoculars, told us that some woodchucks have placid dispositions and others are unremittingly hostile. Last year two juvenile males shared a burrow even though most woodchucks are solitary creatures. She watched another woodchuck chase a hawk even though hawks usually chase (and eat) woodchucks.
As a casual observer of woodchuck behavior, I have watched a woodchuck chase a cottontail rabbit and have twice watched woodchucks fight. But probably my closest encounter with woodchucks occurred late last September when I was writing this column in my study.
I heard bumping noises down in the kitchen, but I thought it was our son Dave getting himself an early lunch. When I went downstairs to the kitchen to put the soup on, a small woodchuck dashed past me.
I slammed the door between the dining room and kitchen and yelled to Bruce, “There’s a woodchuck in the kitchen.”
Bruce propped open the back kitchen door and then hunted around our small kitchen for the creature. Finally, with the help of a flashlight, he found it hiding under the refrigerator.
He pried off the refrigerator’s bottom front panel and the woodchuck didn’t move. After considerable gentle prodding with the broom handle, the woodchuck suddenly ran out from beneath the refrigerator and on out the back kitchen door.
That woodchuck had been unusually curious all season, knocking over our walking sticks on the veranda, poking about on the back steps, and eating directly beneath our bow window. It lives, as far as we can tell, beneath our front porch where woodchucks have maintained a burrow system for decades and never before bothered us.
But how did it get into our kitchen? At first, we thought it had found an entrance through the foundation and into our basement, climbed up the basement stairs through the open door into our dining room and on into the kitchen the same way Carolina wrens did during the bitter January of 1993, but that hole, Dave reminded us, had been blocked off. And even though we searched the basement, we couldn’t find any other holes.
That evening, as Bruce was settling down to read in the living room, he called to me.
“Come here and see this.”
I could tell by the tone of his voice that he had something important to show me. He pointed to the screened window behind the piano. There was a hole in it. The piano itself had several fresh scratches and some dirt on it. Our hardwood living room floor also had a couple long fresh scratches.
Not content to explore our veranda and back porch, the woodchuck had climbed up the table we have sitting on the veranda next to the window. It had then torn a hole in the screen and clambered through, landing on the piano. The loud thump I had heard was probably the creature tumbling off the piano and on to the floor. After casing the living room, it had wandered through the dining room and into the kitchen. Luckily, it had not climbed up any of our chairs or left any odiferous packages.
But why had it broken into our home? Surely not to give me a conclusion to my woodchuck column.
Maybe it was curious. Maybe it was looking for a place to hibernate. Maybe it was a Mad Marmot–crazy or angry or both.
But I have to agree with Zervanos who told us during our visit, “They’re interesting animals and the more I study them, the more I’m amazed at their behavior.”
We are too.
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