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Myths and reality of Groundhog Day that you may not have known

Anyone who has seen ‘ Trapped in Time ‘ knows well that in the town of Punxsutawney, Pennsylvania , they celebrate Groundhog Day every February 2nd. It is a festival of music and food that surrounds the superstitious central show. In it, Phil , a male groundhog, comes out of his burrow. Some people believe that it is the same year after year, since 1886, and that the groundhog is already more than 130 years old. Although in other places they have assumed out of necessity that the life expectancy of these animals is, in reality, much lower; This is how it was seen today in Miltown, New Jersey , where they imitate the same tradition with the groundhog Mel , who has died hours before going on stage.

But back to tradition. If when coming out of the hole, the marmot sees its own shadow, six more weeks of winter are predicted; and if it doesn’t, an early spring is forecast. He is the president of the so-called Inner Circle , which are the organizers of the festival, who warns the population what the marmot has seen, thanks to the fact that he listens to the animal in a language that we would translate as marmotes . Supposedly, he understands the animal thanks to a kind of ancient cane made of acacia wood. Ironically, the groundhog—or rather, his interpreter—gets it right only half the time, which is the same as tossing a coin heads or tails.

Superstitions and magical thinking aside, what we do know is that around this time groundhogs begin to wake up from their long winter sleep. Hibernation is a state in which a warm-blooded animal enters a kind of torpor in which its activity is reduced to a vital minimum and its entire metabolism slows to a near standstill. Strictly speaking, hibernation refers to the process experienced by animals that go into deep torpor , such as groundhogs and other rodents. A more superficial one, although it also lasts through the winter season, like the one we can observe among bears, is usually called torpor, although by extension, it is also considered a hibernation mode.

However, hibernate should not be confused with wintering . Despite the similarity in terms, it refers to very different behaviors. Wintering is not any type of lethargy, but a change of habits during the winter season; what storks did, at least until a few decades ago. Generally, from the Iberian Peninsula they migrated to sub-Saharan Africa in late summer, returning to their summer nests in late January or early February. And if all went well, they could already be seen during the proverbial San Blas day. But the metabolism of the stork does not fall to minimum levels for months.

Nor should hibernation be confused with brumation; both are very similar forms of lethargy that affect during the colder season. But the effects are very different. Hibernation, typical of warm- blooded animals, requires more sustained maintenance, in which the animal lives off its fat reserves, although with minimal consumption due to lethargy. On the other hand, brumation, common in reptiles , is an effect of inactivity induced by the cold itself, which causes a decrease in their metabolism, although they hardly accumulate reserves. Unlike animals that hibernate, those that brumate still need to drink water , so it is common for torpor to be broken by brief moments of activity to forage for water and occasionally some food.

But back to Phil . If it really is a groundhog, and it is, it should go into true hibernation . When they are in their natural environment, marmots dig a specific burrow to spend the winter, with a series of characteristics that differentiate it from a normal one. On the one hand, they dig it under the vegetation, never on barren land —because the vegetation helps keep the temperatures from being so extremely low— and on the other, they make it deep enough so that the frosts do not reach it.

When the time comes, the marmot, after a season giving himself good feasts, hides in his special burrow, and there he will spend as long as necessary. These times depend a lot on latitude and climate: in warmer areas, like South Carolina , they don’t go into torpor until December, and by February they’re coming out of it; on the contrary, in much colder regions, such as Maine , they are already hibernating in September and continue to do so until the end of March. In the Pennsylvania area where Phil lives, they typically wake up from hibernation during the second half of March. But then how come Phil is awake in early February to tell the man with the cane whether or not he has seen his shadow?


We might think that it is a premature awakening . In the wild, there is a time several weeks before hibernation ends when male marmots break their dormancy to search for females. The females do so shortly after to go around the burrow waiting for a male to find it. Once they meet, they return to their respective burrows to hibernate for a while longer, with a mental map of where to find their potential mate when hibernation is finally over.

But Phil ‘s case is even more extraordinary. For he does not live in a natural warren , but has his own fully heated human-made warren in the Punxsutawney library, from where he and his mate can be seen through glass . Not only does he not need to go out looking for a female, since he is already paired, but also, as we have said, hibernation is dependent on the weather, and as they are not under the rigor of inclement winter, neither Phil nor his partner get to hibernate . .



Hellgren, E.C. et al. (1990) ‘Serial Changes in Metabolic Correlates of Hibernation in Female Black Bears’, Journal of Mammalogy, 71(3), pp. 291–300. doi:10.2307/1381939.

NCEI (2017) Groundhog day forecasts and climate history, Nacional Centers for Environmental Information. Available at: (Accessed: 27 January 2022).

Zervanos, S.M. et al. (2010) ‘Latitudinal differences in the hibernation characteristics of woodchucks (Marmota monax)’, Physiological and biochemical zoology: PBZ, 83(1), pp. 135–141. doi:10.1086/648736.

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