29 Jan Frozen Frogs
Posted at 10:07h
in
Winter
by Andrew Prazar
Last week a colleague of mine, Cori Brauer, made an amazing discovery with her homeschool class at the Ipswich River Wildlife Sanctuary in Topsfield, MA. Encased in the ice of a vernal pool was the silhouette of a frog.
Frog Silhouette in Ice (Photo Credit: Cori Brauer) Copyright 2015
There are so many aspects of this that are fascinating. First of all, the frog outline was not at the bottom of the ice (where the ice meets the water), it was within a few inches of ice. So how did it get there? Where did the frog go? Why was there a frog active in the pond in the middle of winter? SO MANY QUESTIONS! Cori posted her pictures on Facebook and received a variety of hypotheses. Here’s the one I’m partial to: A frog “woke up” during the mid-January thaw and swam towards the surface looking for air. The frog then made contact with the ice, froze to it, and was briefly encased (perhaps overnight?). The next morning, the temperatures warmed, the frog loosened and swam back to the bottom of the pond. Ice then reformed around the impression the frog left in the ice and as the temperatures dropped over the next few weeks, became permanently encased. Not a completely satisfactory explanation, but I can’t think of anything else.
What makes this especially intriguing is that frogs should not be active in January. In the late fall, the vast majority of our frogs (green, bullfrog, pickerel, and leopard) will seek out a pond and bury themselves in the mud. As the temperatures continue to drop, they will enter a state of torpor. Their metabolic processes will be dramatically reduced and what little oxygen they need will be absorbed through their skin. Typically they will remain like this until the spring thaw when food once again becomes readily available. Clearly the frog in question chose not to play by the rules, and for some reason became active while there was still ice covering its pond.
Frog Silhouette in Ice (Photo Credit: Cori Brauer) Copyright 2015
There is, however, another possibility. There are three types of tree frogs that live in our area (spring peepers, wood frogs, and gray tree frogs) and they have a very different adaptation for surviving winter. When the first winter chill descends upon New England, wood frogs bury themselves under a shallow layer of leaf litter while spring peepers and tree frogs find a large piece of tree bark to wiggle behind. These frogs then FREEZE SOLID. How do they do this? First, special proteins in the frog’s blood (nucleating proteins) cause the water in the frog’s blood to freeze. This, in turn, draws water out of the surrounding cells. Meanwhile, the frog’s liver goes into overdrive converting glycogen into glucose, which gets pumped into the frog’s cells. This highly sugary solution prevents the cells from dehydrating and collapsing which would be catastrophic. Why the ice in the frog’s blood causes no damage, I’m not sure, but as soon as the cells are protected, the frog’s heart slows down and then stops. All brain activity ceases as well. The frog has essentially become a “frogcicle.” There reports that if you find a frog in this state and drop it on a hard surface it makes a “clink” sound. Crazy.
Wood Frog
Throughout winter, these frogs may freeze and thaw as temperatures rise and fall. Typically it takes the frog about an hour to get all of its systems back on-line. So in the case of an extreme January thaw (and if there was no snow cover), it is possible that there would be an active wood frog that could have left its impression in the ice of the vernal pool. However, I have never heard of wood frogs spending the winter at the bottom of a pond, and the ice silhouette provided by Cori looks much more like a “pond” frog than a wood frog. So the mystery remains unsolved.
Regardless, get outside and explore this winter! Who knows what you might find! Now that there’s deep snow covering the ground, keep an eye out for tracks. Follow them and who knows what you will find. Next week, I plan on logging an entry about coyote-deer dynamics in deep snow.
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