If you are familiar with Snapshot Wisconsin’s crowdsourcing website hosted by Zooniverse, you likely have heard of the term #SuperSnap used by volunteers to denote especially captivating photos. Recently a slight typo, #SuperNap, not only gave Snapshot staff members a good laugh – but also a potentially catchy new phrase for hibernation? In this blog post, we will dive into the science behind slumbering wildlife in winter.

What is hibernation?

When winter rolls around, critters get creative with how to stay alive! In some cases, animals combat the considerable metabolic challenges of winter by entering into a state of temporary hypothermia, such as the black-capped chickadee. The ruby-throated hummingbird migrates south to Central America to avoid the entire winter thing all together. Others avoid the perils of induced hypothermia and the exertions of migrating by going to “sleep”, or hibernation. During this state of sleep the temperature, breathing rate and heart rate of animals drops significantly. To survive harsh winter conditions and scant food availability, animals can quite literally shut off for a few weeks at a time. If you’ve lived through a Wisconsin winter, you understand the appeal of this!

Not all sleep is created equal

There are two main sleep survival strategies that animals use in the winter. True hibernation is a voluntary state that animals enter induced  by day length and hormone changes. These conditions indicate to an animal that it’s time to go into a truly deep, long sleep. Hibernation can last anywhere from several days to months depending on the species. Animals still need to wake up to drink water every one to three weeks. Waking up from hibernation every few weeks is a good idea to improve your immune system by removing those pesky parasites.

Torpor, similar to hibernation, is a sleep tactic animals use to survive the winter. Unlike hibernation, it is involuntary and induced by outside temperatures and food scarcity.  Torpor can reduce an animal’s normal metabolic rate by 40 times in as short as two hours. In contrast to hibernation, torpor only lasts for a short period of time, sometimes just the night or day depending on the activity of the animal. Torpor can be considered “light hibernation”. To awake from torpor requires ample amounts of shivering and muscle contractions to return to a normal metabolic rate!

Torpor or hibernation?

Whether an animal goes into torpor or hibernation is usually based on body size. The smaller the body size, the more likely an animal is to enter into a state of hibernation over torpor. A large body requires removing higher levels of excess body heat which would make light bouts of torpor energy inefficient. Smaller bodied animals can adjust to winter conditions more quickly.

Based on what we now know about the differences between torpor and hibernation, can you take a guess as to what type of sleep the below animals use to get through the winter?

Quiz

A.

B.

C.

D.

Results

A. The black bear (Urus americanus)  enters a state of TORPOR. Contrary to widespread belief, black bears go into torpor in the winter! They can turn their pee into protein through a urea recycling process and the females will wake up to give birth and go right back into a state of torpor! (source).

B. The chipmunk (Tamias spp.) uses HIBERNATION to survive the winter. A chipmunk can bring its heart rate down from 250 beats per minute (bpm) to as low as 4bpm.

C.  Raccoons (Procyon lotor) enter into a state of TORPOR, along with species like skunks.

D. The common poorwill (Phalaenoptilus nuttallii), native to the western United States, is the only bird species known to truly hibernate in the winter (source). Birders may be familiar with their Wisconsin relative nightjars – the common nighthawk and eastern whip-poor-will!

Additional Sources:

• Hibernation and Torpor
• The truth about bears
• Do bears actually hibernate?
• Scottish Wildlife Trust