I see a frog! Where was it all winter?

I have noticed a lot of activity outside over the last few days.  The Sandhill Cranes, Canada Geese and Mute Swans have all returned to our neighborhood.  Songbirds seem to be more abundant and flying around with purpose.  I even found a couple of frogs hopping among the grass, dirt and snow.  The question in my mind is this.  How do animals know that spring is coming?  Do they have a complex network of secret communication?  I know for a fact that they do not have a calendar like I do.  So, there must be something that is signaling them.

Animals pick up on what are called "environmental cues".  Warmer temperatures and an increase in the length of daylight are the two main cues that get animals moving and active as spring approaches.  Birds for example respond to the change in the length of daylight, also called photoperiod.  Along with warmer weather, photoperiod promotes changes in the color of fur and feathers, migration, reproductive behavior and exit from hibernation.

My mind turns specifically to the frogs that I saw this weekend.  Where were they all winter and why am I seeing them now?  I know they are cold-blooded, so their body temperature is directly effected by the temperature around them. This past winter was so brutally cold, why didn't they freeze to death? 

                                             (Photo credit: Naturenorth.com)

OK, here is where the biology geek in me takes over.  There must be a logical explanation for this.  Let me explain to you what I refer to as "the frogsicle".

In the fall, frogs and toads will burrow into the bottoms of ponds or lakes or in mud.  Since they are cold-blooded and take on the temperature around them, they actually go through freeze and thaw cycles.  Do they have antifreeze in their blood?  No, but their blood does contain what are called nucleating proteins, which act by causing the water inside of the frog's blood to freeze first.  This action causes the remaining parts of the frog to dehydrate.  At the same time, their liver starts producing large amounts of sugar in the form of glucose.  This glucose packs itself into the cells of the frog, which keeps its body and organs in their current shape and form and puts the frog into a state of suspended animation.  No brain activity and no heart beat....their bodies filled with a sugary syrup, their internal organs and structures protected, they are able to make it through the subzero temperatures that they endure all winter.

As spring gets close, sunlight increases, temperatures warm and things around us begin to thaw, so does the frog.  The water is restored to the cells, their brain function turns back on and their heart begins to beat once again.

So, as you begin your spring thaw, and you begin moving around outdoors a bit more.  Maybe cleaning out your garage, cleaning up after your pet's winter happenings, talking to neighbors who have also been locked inside for the last several months, take a little walk.  Maybe visit a nearby park.  Michigan has a lot of parks with trails just waiting for you to hike.  See if you can notice things around you that are changing.  Keep your eyes out for frogs.  I hope the next time you see one, you will have a little more understanding and appreciation for the fact that they made it through the winter.

Check out this cool video from Nova which shows a frog freeze and thaw!