The study that I am assisting this summer is part of a much broader long term line of research to better understand ground squirrel biology. It is not just about the squirrels, they merely serve as a model to understand how mammals and any vertebrate life form can adapt to extreme conditions. Several aspects of their biology are particularly interesting. For one, they are an integral part of the arctic ecosystem. Many animals depend on them as a food source, such as eagles, grizzly bears, fox, and wolves.
Last summer in Denali National Park, I watched this grizzly successfully dig up a ground squirrel.
Our project is interested in the physiology of these unique animals. Because they live in such an extreme environment, they have many adaptations. The tundra is a land where only a handfull of mammals survive. Any creature that lives in the arctic must be able to deal not only with below zero temperatures for several months of the year, but also, wind, snow, darkness, and limited food supply. Most of the animals I am seeing at Toolik cope with these hardships by migrating south in the winter. This is how most of the birds here (except ptarmigan) cope with the cold. Caribou also migrate north each summer from the milder boreal forest.
We found these caribou antler sheds near one of our field sites. The caribou have already migrated north through this area.
This squirrel is at the lab in Fairbanks. It's body temperature is about the temperature of ice- 0 degrees C!
For ground squirrels, migration is not an option. Their strategy for survival is to hibernate underground. Even this poses some major challenges. For one, the winter is long so they must hibernate as long as 9 months of the year. Even underground the temperature may drop as low as -23 deg. C (-10 F). To do this, they allow their body temperature to drop to as low as -2.9 degrees C. Their bodies are actually colder than ice! For all other known mammals this sort of extreme hypothermia would be fatal. For the squirrels, it appears to be a normal, annual part of their life cycle. While in hibernation, the squirrels have an approximately two to three week cycle of extreme cold, then they wake themselves up and rewarm their bodies through shivering. After 18 hours of near normal body temperature, they re-enter hypothermia for another two week cycle. They do this over and over during the winter.
This graph shows the body temperature of a ground squirrel during the course of hibernation. Note the fluctuations of temperature during the winter from sub-zero to normal every two to three weeks. Also notice that when bears hibernate, their body temperature drops comparatively little. (Williams, C.T., personal communication)
Because of the extreme arctic environment, any animal that lives here must evolve unique adaptations to survive the conditions. The goal of this project is to better understand how they do it. Along the way, we may learn to better understand how all life copes with extremes- including ourselves.
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