Cold-blooded winter survival

As the cold is approaching us quickly here in Minnesota we bundle up in sweaters, hats, mittens, scarves and coats to keep warm. Many animals that stay active all winter such as white-tailed deer, fox and squirrels also add layers by growing in a thicker coat and building up a nice layer of fat. The majority of our bird species escape the cold by migrating to a warmer location. However, numerous animals do not have these options. So, how do they survive the below freezing temperatures and barren snow covered landscape of a Minnesota winter? They avoid it by going dormant.

Dormancy is a period during which there is a temporary pause in growth, development and/or physical activity as a response to unfavorable environmental conditions. It can either be consequential if conditions were unforeseen such as a drought, or predictive when the shorter daylight hours and cooler temperatures indicate winter is coming. The threat of harsh conditions triggers the biological reactions associated with dormancy, such as the slowing of heart rate, breathing and metabolism.

There are different forms of winter dormancy that various animals utilize for survival. Bears, woodchucks and other hibernating mammals eat more food throughout the fall to build up fat reserves they rely on during a deep sleep until the following spring. Reptiles like snakes and lizards may eat a little more than normal in the fall, but then find a crevice or abandoned den below the frost line to spend most of their time during winter. However once in the den, they do not enter into true hibernation. Their body processes will slow for short periods of time, but they need to wake and emerge on warmer days to find water in order to stay hydrated. During these excursions they are very slow and lethargic, quickly retreating back to their den when finished. This type of dormancy is called brumation. Turtles brumate as well, but do so under water, beneath log jams, submerged tree roots or by burrowing into the mud of lakes and river bottoms.

Minnesotan amphibians employ a variety of different dormancy styles. Toads burrow into the ground below the frost line adjusting their depth as temperatures change. True frogs such as Leopard, Bull and Green Frogs spend their winters underwater buried in lakebeds. The dormant state brought on by cold northern winters of some frogs is rather unique; they will actually freeze solid and then thaw in the spring! They are able to survive this by replacing the water in their cells with glycerol, which acts as an antifreeze so that large ice crystals cannot form and destroy the structure of the cells. Surprisingly, while most salamanders spend the winter burrowed under rocks and logs, a couple varieties stay active all winter long. Aquatic varieties such as Mudpuppies and some Eastern Newts don’t mind the chilly temperatures and go on with business as usual under the ice. Actually, Eastern Newts are a bit indecisive about whether they are aquatic or terrestrial. Their eggs are laid and hatched in the water and then most juveniles (efts) come up on land, becoming temporarily terrestrial before returning to the water and transforming into an aquatic adult. The strange thing is that some newts skip the eft stage, never go up on land, immediately becoming aquatic adults, which are active all year. While at the same time some of the land dwelling efts never return to the water and instead become terrestrial adults where they need to hibernate in burrows during the winter. The fact is that no matter how these cold-blooded critters spend the winter, they are pretty tough and have some amazing adaptations to help them survive our cold harsh winters here in Minnesota.

Get active and explore this winter by checking out snowshoes, binoculars or nature activity backpacks from the Kroening Interpretive Center. Test the kids’ winter skills with our winter break camps December 27-29 and January 2-5. Explore snow and ice with your little one by registering for our new play group series -Nature Nuts- for children under age six and an accompanying adult. Each series includes four sessions on Fridays from 11:30 a.m.-12:30 p.m.

December Free Public Programs (all ages): Dec. 2 – Early Birding: Search for birds while on a naturalist-guided hike, 9-10:30 a.m.; Dec. 9 – Nature Art: Ginger-bird Houses: Craft an edible snack house for the birds. 1:30-3 p.m., $10; Dec. 17 – All about Evergreens: Find out what makes these trees special. 1-2:30 p.m.; and Dec. 23 and 30 – Snowshoeing: Borrow a pair of snowshoes and hike the park, 11 a.m.-3 p.m.

Kids Winter Break Camps (ages 6-12): Dec. 27-29 Winter Whimsy: Discover the fantastical winter world around you. 8 a.m.-4 p.m., $90; and Jan. 2-5 Wild Winter Survival: Build shelters, track animals and trek on snowshoes, 8 a.m.-4 p.m., $120.

Find registration for these programs and more at or call 612-370-4844 for more details. Like us on Facebook to stay in the loop about what is happening at your park!

Written by Kelley Ekstrom, Minneapolis Park & Recreation Board Naturalist, North Mississippi Regional Park