The tradition comes from Germany. On an old religious holiday called “Candlemas Day,” the Germans paid attention to the badger. Candlemas Day was the midpoint between the winter solstice and the spring equinox. If the badger saw its shadow, it meant a “second winter” was coming.
When the practice came to the US in 1887, the groundhog was chosen, because badgers aren’t native to eastern North America. While it may seem random, there is some logic to turning to the groundhog for weather predictions.
Like badgers, groundhogs, also known as woodchucks or whistlepigs, are considered “true hibernators.” When they emerge from hibernation, it means winter is almost over. In winter months, their body temperature drops 62 degrees. Comparatively, if a human body temperature drops just four degrees, it goes into hypothermia.
A groundhog’s hibernating heartbeat is only five beats per minute. In warmer months, its heart beats 80 times per minute. Their breathing slows down in winter too. It can go from 16 breaths per minute to about two during hibernation.
However, the idea that groundhogs are predicting the weather when they come out of hibernation may be a bit of a stretch.
The real reason groundhogs come out of their holes in early February is to look for mates. Mating season is in March, so they wake up a little early to scope out potential partners and then return to their burrow to wait out the winter. Whether the groundhog sees its shadow on February 2 has more to do with the weather that day, than the groundhog itself.
After all, Punxsutawney Phil has only been right about 30% of the time.