UNIVERSITY PARK – It began as a Northern European pagan holiday brought to Pennsylvania by German immigrants. Ever since the earliest settlers arrived, they have anxiously looked to the groundhog in early February to forecast the weather. According to legend, if he sees his shadow, there will be six more weeks of winter weather; if not, an early spring is predicted.
Scientists have always been skeptical that groundhogs are emerging from hibernation to help forecast the weather. But then why do they rouse at this time of year, a month before mating season and before there is anything around for them to eat?
The fact is that the dates of hibernation are variable based on latitude. The time for groundhog emergence in the spring depends on where you live, according to Stam Zervanos, emeritus professor of biology at Penn State Berks.
As a physiological ecologist, Zervanos studies how animals adapt physiologically to their environments. He has been studying the hibernation patterns of groundhogs since 1996.
His current research emphasis is on latitude variations in hibernation patterns. Working with researchers from Clemson University in South Carolina and the University of Southern Maine, he compared the hibernation patterns of northern and southern groundhogs. As expected, major differences have been observed. In Maine, they hibernate 175 days, from Oct. 19 to April 11; in Pennsylvania, 100 days, from Nov. 17 to Feb. 25; and in South Carolina, 67 days, from Dec. 13 to Feb. 18. Thus, depending on where a person lives, groundhogs emerge on different days.
The next step will be to determine if these variations are environmental or genetic in nature. The plan will be to send animals from the three populations to Colorado State University, where the three groups will be subjected to constant temperatures. The study will be valuable in understanding the effects of global warming on hibernation.
Groundhogs do not simply crawl into their dens and hibernate, but rather they experience a series of torpor (sleep) and arousal bouts throughout winter. During arousal bouts in the winter, they stay in their burrows; but in the spring, they emerge and move around above ground. They then return to the den for some more deep sleeping episodes before the final arousal for the hibernation season. In southeastern Pennsylvania, groundhogs do not exit hibernation for good until late February to early March, which is when they mate. The episodes of early emergence occur in early February; with the average date being Feb. 4. It does not appear that mating occurs during these early encounters.
“For males, these early excursions are an opportunity to survey their territories and to establish bonds with females,” said Zervanos. “For females, it is an opportunity to bond with males and assess food availability.”
“It would appear that the early bonding activity and establishment of territories in preparation for mating insure optimum conditions and timing for reproduction and offspring survival,” said Zervanos.
“The length of the hibernation season at a given location appears to be consistent for groundhogs and is characterized by a predictable timing of immergence and emergence. As expected, animals in colder climates spent more time in torpor, thus saving sufficient energy to survive the harsher climate. This is important, because if mating occurs too early, young would be weaned at a time in the spring when food is still limited. If mating occurs too late, young would not have sufficient time to gain their critical hibernation weight.”
The Penn State scientist studied free-ranging groundhogs over 10 hibernation seasons. Radio telemetry and data loggers were used to monitor hourly body temperature from the groundhogs. During the first two seasons, straw at the burrow entrances indicated if an animal had exited or entered a burrow, but for the last eight years of the study, infrared motion-triggered cameras were placed at the burrow entrances. These cameras recorded date and time of emergence and also supplied photographs and videos.
So the next time you see a groundhog emerging from his hibernation den, you will know that his motive is to find a mate, not predict the weather. Perhaps Groundhog’s Day should be observed on Feb. 14, rather than Feb. 2.
