In celebration of this glorious spring, I beseech thee, McQuaid. Why do some animals hibernate during the winter, and others (like squirrels, which you would think would hibernate) donâ€™t?
Wow, I’m answering a question in the same season it was asked in. That, my friends, is progress!
(The picture you see is a marmot, ready to hibernate. Marmots hibernate for up to 7 months of the year.)
Animals hibernate in general to avoid burning energy that they can’t replace in the winter. For example, black bears (which are not “true” hibernators, by the way) will enter a period of inactivity where the body temperature drops, the heartbeat slows, and activity ceases. A true hibernator will allow its body temperature to drop to extremely low temperatures (like 60 degress) and will not wake easily. A torpid animal (like the bear) will drop to maybe 85 degrees and can be woken up fairly easily.
In any case, the question is why do some animals hibernate and others do not. The answer is a combination of evolution and chemistry. As far as evolution goes, some animals who have become accustomed to life in warmer climates have lost the ability to hibernate. A good example are pet hedgehogs, which are based on an African breed. While local hedgehogs do hibernate through the winter, a pet hedgehog cannot. It can enter a hibernation-like state if it gets too cold, but it no longer has the ability to safely come out of it. This is true for other animals as well; if the animal has evolved to match the surroundings, and they are warm most of the time, it will have lost the ability to hibernate.
Another point is that hibernation is only one of the ways that nature has come up with to deal with winter food shortages. Some animals (like the squirrels we have around here) have evolved a different mechanism – instinctual food storage. This allows them to survive the winter since they have a food supply ready to go. Other animals migrate when it gets too cold and food is scarce. The point is, there’s more than one way to survive the winter, and it’s not likely that all animals evolved towards the same method.
On to chemistry. It turns out that some squirrels do, in fact, hibernate, and that a substance known as “Hibernation Induction Trigger” (HIT) can be extracted from the blood of the hibernating animal. When injected into another squirrel, the squirrel will go into hibernation. This has been shown to be extremely useful, because hibernating cells don’t need much oxygen; they are kind of suspended. Hence, organs that have been donated and are being transported can last longer if they are infused with HIT. Neat, eh? Anyways, animals that have the ability to generate HIT can hibernate; others cannot. This goes back to the “different methods to solve the same problem” discussion.
NASA is interested in HIT and hibernation in general, since it would be useful to hibernate the crew during a flight time of years.
I hope this answers your question to your satisfaction.