Cold Blood in Cold Weather

In anticipation of a north country winter, humans bundle up in hats, mittens and wool sweaters before venturing out into the cold. Other mammals of New Hampshire also add insulation to keep warm- red fox thicken their fur and black bears get fatter. But have you ever seen an amphibian plump up for winter or a fish with a warm winter coat? While they don’t use the same techniques as mammals, New Hampshire’s cold-blooded residents have a number of clever tactics to avoid a deep freeze.

Most year-round residents without a warm coat, be it feathers or fur, hide out in locations away from the elements. Aquatic environments provide protection from extreme weather, but give little insulation from freezing temperatures. Cold-water fish such as lake trout, whitefish and bluegill, adjust to the changing seasons by producing new enzymes as the water cools. These “isoenzymes” function identically to their summer counterparts, but are not altered by the cold temperatures.Without isoenzymes in winter, fish would not be able to perform basic bodily functions like digesting food or contracting muscles.

In late fall, the turtles of New Hampshire begin their longest dive of the year. At this time, they take their last breath of fresh air before burying themselves in the muddy floors of lakes and ponds. Here they avoid freezing, but are faced with limited access to oxygen. Luckily, turtles are able to perform gas exchange through their skin. This alternative breathing mechanism in combination with reduced energy needs from dormancy allows turtles to quietly endure the winter months.


Spring peepers are best known in New England for their impressive spring chorus. Yet naturalists often find a frog’s winter survival mechanism even more extraordinary. Frogs of the north country hibernate in a burrow of leaves, tree roots, soil, and other materials known as a “hibernaculum”. As snow piles up, the hibernaculum protects the frog from predators and extreme weather conditions, but not from freezing temperatures. Instead of fighting the frost, these amphibians give in to it. The secret to this ice cube strategy of survival lies on the cellular level. Freeze tolerant frogs including spring peepers use chemicals naturally found in their body, like glucose, as antifreeze to prevent ice formation inside their cells. Additionally, these frogs promote ice formation between cells and allow up 65% of their total body water to freeze. By manipulating the location of ice formation, frogs successfully overwinter as ice cubes until spring thaw.

New England’s cold-blooded residents employ a variety of strategies for surviving cold winters. Because they cannot generate their own body heat, an extra layer of fat and fur will not provide insulation from the cold. By choosing the right environment and utilizing some unique physiology, fish, turtles, and frogs can bear the cold each year. That said, aren’t you glad you have that colorful holiday sweater to keep you warm?

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