Episode published: Tuesday 01/21/2025
Michael: Hi everybody, welcome to Every Day is Groundhog Day (Except for the Days When It's Not), the only podcast devoted to the holiday, Groundhog Day. I'm your host, Michael. Hope you enjoyed our last episode about The Happy Groundhog Studio.
On this show, we've spoken a bunch about groundhog prognosticators like Woodstock Willie, Gertie the Groundhog, and Buffalo Bert. But have you ever wanted to learn more about groundhogs in general and their hibernation habits? Well, if so, you're in luck because today I'm speaking with Dr. Stam Zervanos, who has been studying groundhogs for years at Penn State University and has authored a number of publications detailing the results of these studies. I had an opportunity to speak with him about his methods and what he learned. Hope you enjoy the interview.
Michael: Today I'm here talking to Dr. Stam Zervanos, a Professor Emeritus of biology at Penn State, specifically the Berks campus, who is an expert on groundhogs and their habits, and who has performed a number of studies on groundhogs over the past 20 years. Welcome, Dr. Zervanos.
Dr. Stam Zervanos: Glad to be here.
Michael: So, I want to talk about groundhogs and your studies. But first, could you give me a little background on yourself, how you became interested in biology?
Dr. Stam Zervanos: I grew up very interested in nature and the environment. I was a city boy, but I was a boy scout so that got me interested into things like outside, camping, and just enjoying the environment that we have. So, when it came time to make a decision about a career, I decided to go into biology and get my PhD and study physiological adaptations of animals to their environment.
So, I started at Albright College as an undergraduate, went to Penn State for my master's, and then to Arizona State for my PhD. In Arizona, I studied collared peccaries, which are desert mammals that are adapted to a very dry environment, came back and got a job at Penn State, and started all sorts of studies, eventually ending up with groundhogs about 20 years ago, which is a study I actually started as a master's student at Penn State. So, I had some knowledge about hibernation and their life cycle. We've been fortunate enough to have a particular study site that has or had about 40 groundhogs living in a 140-acre farm, a university farm. And I can tell you more about what we found out or what we learned as we go along here.
Michael: Yeah, I'd love to hear about that. So, is that what kind of led to the interest in groundhogs? You had that site available so that's kind of what you focused on? Or is there is there a particular reason other than that?
Dr. Stam Zervanos: That's part of it really. In the early 1980s, I got involved as an administrator, as an academic dean, which took me away from doing any studies at length. And then after 12 years, I decided to go back to teaching and that's when I started the groundhogs because they were fairly plentiful in the area, and I knew a little bit about them.
Michael: It looks like there's a number of publications that you have associated with groundhogs, starting about 20 years ago. And it seems like you've done a lot of work looking into the hibernation or the torpor habits. So, first question, is there a difference between hibernation and torpor?
Dr. Stam Zervanos: Yeah, there is a difference. Torpor is the ability of an animal to decrease its body temperature to a certain degree and go into a torpid state. Hibernation is a period of time that an animal spends going in and out of torpor. Mammals that hibernate don't stay at a low body temperature throughout the whole winter. They go through what are called torpor bouts, where they go into… For example, the groundhogs. Normal body temperature is similar to ours. It's 38 degrees centigrade, which is about 98 Fahrenheit. But they go from 38° centigrade all the way down to 5° centigrade, which 0° is freezing. So, they're pretty close to freezing. By doing that, they save a lot of energy, metabolic energy, so they can survive the winter.
The problem with that is that it puts a lot of stress on their physiology so they can't stay at that low temperature for long. They may stay in that low temperature maybe for five days, maybe even a week. But they arouse, they come back up to 38° centigrade, maybe for a day. We’re not sure exactly why they have to go through this process, but I'm pretty sure it's to deal with their physiology, the stress that a low body temperature puts on the body. So, they arouse, maybe get their metabolic processes geared up again. And then once they do that, they go back into torpor. So, the hibernation period is the period of going in and out of this torpor process. Torpor is really the lowering of your body temperature.
Michael: I saw that you, in the slides you had sent, said something about the latitude determines when exactly they go into torpor.
Dr. Stam Zervanos: Yes. The key to survival for a hibernating animal is to maintain a normal body temperature as long as possible. So, if you're in the South, groundhogs usually live all the way down into northern Alabama and all the way up into Maine and Canada. So, they have a wide range of environments. The shorter the winter, the shorter the hibernation period for them. So, one population we looked at was in South Carolina, they had a short hibernation period. I think if I remember correctly, it started in late November, early December, where groundhogs in our area here in Pennsylvania are starting right now. So, they're about a month ahead. And if you go further north, then you're looking another month ahead. So, the shorter they can avoid hibernation, the better. So, there's a variation; it's a variation in latitude and also altitude, depending on the winter.
Michael: So, you said in Pennsylvania, they're starting now.
Dr. Stam Zervanos: Yeah, beginning of October, middle of October. They'll rouse and come out beginning of February, but they go back into hibernation until March.
Michael: I'm sure we've touched on it a little bit. Did you want to talk about your study and what you found a little more in-depth?
Dr. Stam Zervanos: We surgically implanted telemetry units that gave us body temperature and a little bit of activity and heart rate. We also use what we call data loggers, they’re tiny, little quarter-sized temperature loggers that we implant in the animal and then looked at the data they collected. And we're able to look at a whole year worth of data in terms of the body temperature. And our groundhogs in Pennsylvania, as I said, go into hibernation… Their first torpor bout is right around now, October, first week of October, second week of October. And then they go through these bouts in and out of torpor. In February around Groundhog Day, they emerge out of their burrows, spend a little time getting together.
First of all, I should mention that the males and females live separately throughout the year. The only time they get together is February and March for mating. So, what's going to happen in early February is the males come out of their burrows, and they go around trying to find out where the females are because they haven't seen them all year. I call it the "kiss and make-up period" because the males go to the burrows of the females and maybe they spend a day or two there. They don't mate at this time, it's a period where the reproductive systems are starting to gear up for both males and females. After he's done maybe visiting the females in his territory, he goes back into hibernation, into torpor, and so does the female, until early March when they come out and actually mate.
The females are what's called induced ovulators. That means that they don't ovulate at a certain time; they ovulate when copulation occurs, when they actually mate with a male. So, that almost guarantees fertilization. The males leave never to be seen again, and the females spend the rest of their time in March in their burrow. They give birth in early April, about 30 days later, and then they lactate and feed the young until, well, mid-May when food is available for everybody, and then the young come out and they start feeding them. The females start feeding and so forth.
The key to the survival of these animals, why they do this? They do it because it's a way of making sure the young survive not only the summer but also the winter. And for the females and males to gain enough energy to survive the winter, but also have enough energy left over to mate in the spring. Because in March, there's very little food available for either the males or the females so they have to have stored energy when they come out of their hibernation. They spend about 25% of their energy in hibernation and have maybe another 10%, 15% left over to mate until they're able to start feeding in late April or early May.
So, the strategy is to mate at a specific time, not too early because then the young will be weaned too early in the spring when there's no food for them to eat, and not too late because they need the summer to gain enough weight to survive the winter. So, it's a matter of timing. You need to make sure that your young survive. And the only way you can do that is to make sure they're not born too early or too late and they can feed enough during the summer to gain weight to survive the winter hibernation. That's the whole strategy.
The study now has, as you said, started 20 years ago. I retired about 12 years ago, been doing a little bit with it, but we've been able to publish and get data that matches a lot of what other people are finding. That's basically the study that we've done. We looked at over 40 groundhogs over the years and have enough data to make some really good conclusions.
Michael: So, this is, like, an ongoing study? Is this something that's continually going over the past 20 years? Do you have a constant sample of groundhogs that you're looking at year after year? Or is it something that you start up again every so often? Or is it just consistently going?
Dr. Stam Zervanos: Well, since I retired, I really have initially kept going with the study. I have an office, and I still maintain a presence in our study site. And I've had some students come through that wanted to do a study with groundhogs and we've been doing that. But other people have picked up on the study, not at our location, but at other locations, other universities. And basically, hibernation is a very, I would say, a very interesting thing to look at. Why do animals and how do they do it?
Actually, I attended a meeting up in Canada just this summer and a lot of research on hibernation has gone to the molecular level. What I have done is basically showing what happens but now we're looking at what is the molecular level? What's going on in the body that the animals are able to go and do this? There are people looking at the genetics, there are people looking at the molecular level, for example, in the brain. If you decrease your body temperature to 5° centigrade, that can cause some very severe damage to your nervous system, to your brain.
One study that I learned about going to the meeting in Canada is that there is a group in Holland that is working on this issue has found that these animals, once they arouse, they can regenerate and re-stimulate their nervous system to be functional. Very important. If we would decrease our body temperature to 5° centigrade, we won't survive; our brain will completely shut down and be damaged. What we're trying to find out, or what they're trying to find out, is what allows these woodchucks or any hibernator to survive this very low body temperature. And there could be some applications to humans, really. If we can figure out how hibernation works, I'm sure, I'm one of the ones that believes that humans have, or still have, the genetic makeup, have the genes that allow for hibernation. Based on our evolution, our first ancestors were able to go into this torpor cycle. So, I'm sure that we still have the genes. And if we can figure out how to turn them on, we can actually go into some hibernation for humans.
Now, why is that important? It's important, maybe, for trauma. When a person's in an accident, loses a lot of blood and needs to survive, if you can decrease a person's body temperature, you're able to slow down their metabolism to a point where the loss of blood or any damage to the system, for example, trauma to the brain, can be minimized by lowering body temperature. Certain surgeries that take a long period of time for them to proceed, lowering body temperature to, let's say, even 30° centigrade, you can lengthen the period of surgery. In fact, some surgeries today are done by lowering the body temperature a couple of degrees in order to perform the surgery. There are a lot of adaptations. Weight loss; there are certain things that go on in the ground, for example, or in any hibernator, that increases or decreases their appetite and there may be some ways that we can do that for humans that we can learn from the hibernator. Well, there's a couple of other things that can help us with being able to decrease our body temperature.
Michael: Yeah. I think I saw on your slides, you said something about space travel, too, that's a possible future application.
Dr. Stam Zervanos: Yeah. If anybody saw 2001, the movie about space travel, going to some of these locations could take months or maybe even years. If you can decrease the energy required for a space traveler to travel at that distance, they don't have to carry as much food along and be able to be aroused when they get there and survive. Now, I think that's a little bit down the road, if at all possible.
Michael: A little bit.
Dr. Zervanos: We're finding out more and more each year about the process, the physiology of hibernation.
Michael: You have the groundhogs in Pennsylvania. I see you have this slide, which has a few other locations, South Carolina, Maine. Were those other universities that did the same study? Were you involved in that or is that where you're saying they kind of were picking up on the research?
Dr. Stam Zervanos: We got together. Chris Maher up at the University of Southern Maine has been doing studies with groundhogs up there and we just joined together to do this particular study about the latitudinal differences in hibernation. Down in South Carolina, I joined with a group down there that was actually not doing hibernation studies but doing some behavioral studies on groundhogs. We got together with them down there and I went down there, did the surgeries, and then they did the data collection and were able to get data down there.
Michael: So, in Pennsylvania at least, the groundhogs are coming out around Groundhog Day. I think you had, like, February 4th maybe you would start seeing them emerge or come out of torpor for that brief period?
Dr. Stam Zervanos: The average date for us in our study site is February 4th. A little bit about how the Groundhog Day emerged. When the German settlers came over to Southeastern Pennsylvania, they noticed that groundhogs were coming out around February 2nd, so they put two and two together and said that Groundhog Day is similar to what we had in Europe. Because they emerged at this time, that's how we got the Groundhog Day here in the United States, in America.
Michael: Right. And in Europe, it was badgers or hedgehogs or maybe even bears.
Dr. Stam Zervanos: Yes.
Michael: That was the original animals that they were kind of observing.
Dr. Stam Zervanos: Yeah, particularly the hedgehog. But yes, the tradition of celebrating the middle of winter, which is between the winter solstice and the spring equinox, the first week in February is halfway between those two events. And the celebration goes back into ancient times, the Greeks and the Romans celebrated this period and it was picked up by Northern Europeans. It got connected with Candlemas Day, which is, it is February 2nd. The two ideas joined together, and we have Groundhog Day here.
Michael: Did you have any connection to Groundhog Day before starting to study groundhogs? And then follow up, like now, do you have more of a connection to it?
Dr. Stam Zervanos: [chuckles] I mean, I've known about it ever since, you know, always growing up in the part of Pennsylvania where I grew up in, southeastern Pennsylvania, that's a big holiday, really, and you know about it from young. Never had a big interest in it until I started studying the groundhogs and learning more about the tradition. I've never been to Punxsutawney, but that's something that I'm not particularly interested in doing. It's a celebration and so forth, but that's what it is. It's just a celebration.
Michael: Yeah, I've never been there for the celebration. I went to the town once and just checked it out to see what they had but it also seems like it would be very crowded and very cold, particularly that time of year.
Dr. Stam Zervanos: So, I guess you've seen the movie, too.
Michael: Yes. How about you? You a fan?
Dr. Stam Zervanos: Yeah, I have. I have a video that I watch every once in a while.
Michael: Yeah, I try and watch it every year on the holiday.
So, I know you mentioned that the male groundhog will go and visit with female groundhogs. Do they generally have one mate during the season or are they potentially having multiple partners, multiple litters during the same year?
Dr. Stam Zervanos: Yeah, in our area, and this could be different. In fact, I think Chris Maher has a little bit of difference up in Maine, the males are territorial. In other words, they maintain a certain area that includes maybe three or four females. And that's pretty much what is involved in the mating. They're induced ovulators so once they mate in terms of copulation, that's it, that male gets the credit. And since there's only one male in that territory, we're pretty sure the young of that year in that area are his. That's as far as we know. It's probably an area that we should spend more time in and make sure that that's the case. But from what we know from our telemetry, that's what happens. We have cameras set up to take pictures every time a male or somebody comes to the burrow, like a fox. We have predators too to worry about.
Michael: So, the lifespan of groundhogs is, like, what? Three to three to five years in the wild? Is that correct?
Dr. Stam Zervanos: That's probably correct. We've had some groundhogs that have only been around a year or two and others that have been around for four years, maybe one or two at five. As I said, we have predators in our study area. We have foxes that love groundhogs, we even have a coyote that comes through every once in a while, and of course, the hawks and eagles pick off the young. So, the average survival would be maybe two, three years for our area.
Michael: And you said it's about 30 days after they mate that the babies are born. So, that's a pretty short gestation period. I was actually curious about that because I don't know if you saw Punxsutawney Phil apparently had children for the first time, him and his mate this past season, and it seemed to come as a surprise to his handlers and I was curious how that was possible. But if it's only if it's only 30 days, then I guess it's possible they wouldn't know that the female groundhog was pregnant in that time.
Dr. Stam Zervanos: I don't know how true that is. But as I said, they're induced ovulators, so all you have to do is do it once and she's pregnant. Groundhogs are rodents, and rodents have a very short gestation period in general. So, 30, actually it’s 31 to 32 days average, who's going to argue about one or two days?
Michael: Right.
Dr. Stam Zervanos: Yeah, I can see that happening if they’re together at the right time.
Michael: I think we've covered most of what I wanted to talk about.
Dr. Stam Zervanos: I think we've gone over the general information, the basic information. Obviously, there's a lot of details. Over the years, we've published a lot of papers on different parts of the hibernation of these groundhogs, you know, circadian rhythms. A colleague of mine in Colorado has been working on some of the basic digestive processes and how the digestive system adapts to hibernation and how they turn on and off the appetite process to get ready for hibernation. One of the things that has to happen is you can't start hibernation with food in your digestive system, intestines, and so forth. So, they basically have to stop eating maybe three to four weeks before they enter hibernation. Why do they do that? How do they know when to turn it off? So, there's looking at the hormonal process, Lipton, for example. Anyway, we can go into these details. It's just something that I gave you the basic idea. All the studies that have been done over the last 10 years can fill a couple volumes.
Michael: Are these studies all available online? Your publications, if someone wants to take a look at them further?
Dr. Stam Zervanos: My publications are online from various sources. The newer studies, some are out already, and some are in the process of coming out. I'm talking about the studies of other people that are working on the molecular and genetic processes. I know that at least one of them or two of them are out now. I haven't had a chance to really look at some of the other studies, but I'm sure they're coming out soon.
Michael: I noticed your shirt. Is that a groundhog with a heart balloon?
Dr. Stam Zervanos: Yeah, that's a groundhog. [chuckles]
Michael: Is that your everyday wear or is that special for this discussion?
Dr. Stam Zervanos: Special for this. I wear it on February 2nd. One of my students gave it to me a few years back on Groundhog Day.
Michael: Great. Well, I think that's everything I have unless there's anything else you want to mention, anything we didn't cover or I didn't ask about?
Dr. Stam Zervanos: I think you have the basics. I think you understand a little bit more about what we did. And if there's interest out there to get started on this topic, there's a lot of publications that are out there. I've been wanting to get together with a couple of colleagues and publish sort of a summary, maybe even a book, but that's time-consuming and I'm retired. [laughs]
Michael: Right, yeah. Well, I mean, if you do, if you ever do put out a book, just let me know and I'll definitely let other people know.
Dr. Stam Zervanos: Yeah. Well, thank you.
Michael: Okay. So, thank you so much for talking to me and talking about your study. Hope you enjoy the coming Groundhog Day season.
Dr. Stam Zervanos: Yeah, it's coming pretty soon.
Michael: It is. Thank you.
Dr. Stam Zervanos: Thank you, Michael. Enjoy it.
Michael: Thanks. Bye.
And that's the interview. If you want to learn more about Dr. Zervanos's work, I'll link to where you can find his papers in the show notes. Music for the show was written by the Stupendous Breakmaster Cylinder. Show artwork is by Tom Mike Hill. Transcripts are provided by Aveline Malek at TheWordary.com. If you want to learn more about Groundhog Day, visit CountdownToGroundhogDay.com. Any feedback or voice messages can be sent to podcast@countdowntogroundhogday.com. Thanks for listening, speak to you next time
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Transcribed by Aveline Malek at TheWordary.com