Marmota monax

Image Hosted by

This enigmatic megalith measures about seven feet tall and sits all by itself in the middle of a lawn behind the old sheep barns on the Penn State Berks campus, near Reading, Pennsylvania.

Earlier, travelling east on U.S. Route 22 between Huntingdon and Lewistown, we had passed a barn with huge letters painted on the side: “At the End of the Road, I Will Meet God.” An hour later, on an off-ramp of I-81, we got rear-ended, but far from meeting our maker, the car sustained no damage whatsoever, thanks to the trusty tire-carrier. (The other car did get its hood crunched a little.)

We had come to the Berks campus not to meet God, but to interview the foremost groundhog scientist in the state and to tour his study area. Stam Zervanos describes himself as a physiological ecologist, and for the past six or seven years his research has focused on the biological rhythms of woodchucks, a.k.a groundhogs, a.k.a. Marmota monax. Berks campus grew up around a couple of old farms, and it includes a mixture of habitats ideal for the ecotone-loving marmots. Thanks to the efforts of Dr. Zervanos’s incredibly dedicated assistant, June, the grounds crews at Berks have learned to tolerate groundhog burrows just about everywhere, including in the flower beds and right next to the library. The 60-acre study site currently supports a population of about 30 chucks.

The heart of the study area is in a wildflower meadow adjacent to the horticulture department’s experimental garden. Several woodchucks have had their privacy permanently violated by the implantation of radio transmitters in their abdomens and the installation of motion-triggered cameras outside their burrows. Body temperature information is collected every hour throughout the hibernation period, which in Pennsylvania lasts from early November to early March.

There are two types of mammalian hibernation, Dr. Zervanos explained. Woodchucks, like chipmunks and jumping mice in our area, go into deep torpor, meaning that body temperature goes down below 20 degrees Centigrade. Black bears, by contrast, maintain a body temperature between 25-30 degrees, and can rouse fairly easily.

The data collected so far show a pattern of regular awakening every week to ten days throughout the winter. Males are lighter hibernators than females, waking up more often and maintaining slightly more elevated temperatures. Some speculate that this periodic reawakening may be related to a need to maintain muscle tone. But at this point, how animals in hibernation or estivation maintain muscle tone remains a mystery.

The regular arousals appear to have social benefits. Groundhogs are the only solitary marmots, although June showed us one, rare exception – a burrow currently shared by two young males. When they rouse in early to mid-February, male woodchucks do much more than check for a shadow. They pay social visits to all the females within their territories – re-acquaintances made necessary by the fact that woodchucks do move around, whether as a result of juvenile dispersal, or simply to acquire better real estate. The high ratio of females to males that drives this annual peregrination stems partly from the increased exposure of male woodchucks to predators, especially in late winter and early spring when cover is scarce and predators are hungry. I can’t help wondering if monogamous co-habitation wouldn’t be a more sensible approach. But doubtless that would merely result in over-population, as it has for humans.

Following this rare burst of sociality they return to their burrows and go back to sleep; mating only commences after final emergence in March. So it seems that having biorhythmically timed arousals and emergences helps keep local populations on the same wavelength, so to speak – males can be reasonably certain to find females awake when they make their February rounds, and again during mating season.

However, up to ten percent of Pennsylvania woodchucks don’t hibernate at all. This is surprising, since the main reason for going into deep torpor is to make it through the long months when forage is unavailable. Apparently, southern groundhogs may never hibernate, though this remains to be verified by scientists. But during a severe drought back in 1999, Dr. Zervanos and his assistants found that their study animals were going into deep torpor on a daily basis in the middle of the summer to conserve water and energy.

A new theory holds that torpor patterns in mammals can be traced back to our reptilian ancestors. Some lineages that subsequently lost the ability to hibernate, such as primates, may still posses genes that could be switched back on, if they haven’t already mutated too much. The study of hibernation may yield some medical insights or applications, Dr. Zervanos told us, since deep torpor apparently interrupts the activities of viruses, and possibly of internal parasites as well.

June showed us the burrow of one female in the middle of a small woodlot who only hibernated for the first time this year. The previous two winters she had stayed awake, and not coincidentally, didn’t bear a litter in the spring – her body was probably much too weakened. This made me wonder if perhaps skipping hibernation wasn’t a deliberate attempt at avoidance of estrus? June did say that this was an unusually anti-social individual.

Image Hosted by ImageShack.usWoodchuck personalities can be quite diverse. June told us about some that are completely placid, and seem to enjoy their periodic captures once they find out about the fine marmot cuisine she whips up for them. Others remain unremittingly hostile. These personality differences seem mirrored by their divergent choices of home burrows. Some groundhogs nest right in the middle of cornfields, which are as devoid of forage as woodlots. Dr. Zervanos was surprised to hear about the groundhogs we occasionally find living deep in our wooded hollow, but it is apparently not uncommon for them to share burrow complexes with other species, such as skunks, porcupines, raccoons and opossums. This is the situation under my house, which has more things that go bump in the night than you can shake a stick at. Regular readers may recall my occasional descriptions of animals fighting viciously right under the floorboards where I type. In many cases, these are probably male woodchucks in a territorial dispute.

It occurs to me that such diversity in personality and choice of home site is probably highly advantageous for a habitat-generalist species. How much of our own vaunted individualism stems from our ecological role as highly adaptive, edge- or savanna-dwelling scavengers?

Various woodchucks were out and about during our visit. While the sight of a distant chuck is nothing out of the ordinary for us, it was interesting to see how attentively the researchers watched them. “I’ve developed a groundhog eye,” June said when we marveled at how easily she picked out a brown animal against a brown background from several hundred yards away. “I’m always spotting them from my car now, everywhere I go.”

It’s always inspiring to meet people who are keenly observant and deeply involved in the study of something for its own sake. We were also impressed by how generous both researchers were with their time. My mother plans to incorporate much of what we learned into her “Naturalist’s Eye” column in Pennsylvania Game News magazine. I hadn’t really planned to blog about our visit, so I wasn’t particularly well prepared, and didn’t write down any good quotes. I didn’t even think to ask some of the most obvious questions, such as: How much wood would a woodchuck chuck? Are there any plans for a woodchuck webcam? And what was up with that strange, vaguely groundhog-shaped megalith behind the sheep barns?

One Reply to “Marmota monax”

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.