A gray tree frog

We had an unexpected visitor in our garden office building this afternoon, a gray tree frog (Hyla versicolor).  I'd seen anoles inside before, but not a tree frog.  But my new office colleague (a keen naturalist) spotted it in the stairwell, and we took a look.  Gray tree frogs vary in color, depending on their surroundings, temperature, and humidity;  this one was a solid dried-leaf gray.

I was surprised to see a frog still out and about, maybe seeking warmth?  But, doing a bit of research, I learned that gray tree frogs survive the winter by hibernating 'on land' - under leaf litter, rocks, and logs; their bodies 'freeze' but are protected from damage by high glycerol levels in their tissues.

Cool!