Wednesday, August 12, 2015

Squirrels can teach us a lot about science. Who knew?!

Today I want to take a look at a photograph that I've shared a couple of times in the past and actually explain what is happening in the photograph.

This picture of a Fox Squirrel (Sciurus niger) seems simple enough.  A squirrel lying flat on a branch.  

It must be tired, right?

Maybe, but that is not why it is stretched out flat on that branch.

This squirrel is keeping cool, but not just by being inactive. 

While inactivity does help, it is often not enough.

All mammals have sweat glands that help them cool, but many animals such as squirrels have too few of these glands to help them cool effectively.  (I on the other hand have lots of sweat glands that at times seem to work almost too well.)

So if an animal such as squirrel lacks sufficient sweat glands, how can it lower its body temperature enough to prevent overheating?  Some animals pant heavily (like dogs), expelling excess heat through their mouths and nasal passages.  Squirrels will sometimes pant to reduce heat, but this individual is using a more effective method.

This squirrel is using a technique know as conductive cooling.  Squirrels (and most other mammals) have less insulating fur on their chest and bellies than on their backs.  The skin of their chests/bellies also contains a complex network of small blood vessels called capillaries that carry blood from the core of the body to the surface.  When a body heats up it automatically pushed more blood to the surface  in an attempt to cool the core - this is why people look red when they overheat.

Some of this heat is carried away by the process of convection - air moving across the surface of the skin pulls heat from the blood near the surface, when the blood returns to the core of the body it is cooler than it was seconds before.  This is why fans feel so good on hot days.

Unfortunately for the squirrel, it didn't have a fan available for cooling and there was no cool breeze to pull heat away from its body.  Instead the squirrel places the hot skin of its body directly on a cool surface (the bark of the tree).  Heat is transferred directly from the squirrels skin into the tree bark; the blood leaving the surface is cooled by this heat loss and the squirrel prevents its core from overheating.  This principle of conduction (direct heat transfer) enables the squirrel to cool down rapidly and resume its normal activities.

You can try this principle.  If you have to be active outdoors on a really hot day, wet down a bandana (or rag) and tie it loosely around your neck.  Your neck contains many blood vessels.  These vessels will transfer heat into the cool bandana, reducing your core temperature when your now cooled blood circulates back to the interior of your body.

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