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Backyard Chipmunks Living the Good Life

March 1, 2010

The Eastern Chipmunk ran back and forth from my bird feeders to his den every fall day. He’d appear with a skinny face and disappear with fat cheeks filled with black sunflower seeds. When it disappeared I imagined its network of tunnels and chambers several feet underground and perhaps a yard long with its hoard of sunflower seeds stacked for the winter in a food chamber.

They live off their hoard all winter long. Unlike other mammals like bats, Eastern Chipmunks do not lay on the fat for winter. Instead, they rely on good food stored in the pantry. All winter long chipmunks eat and chill out, eat and chill out. I am not just using “chill out” to be cool. They really do chill out falling into torpor for up to eight days. Torpor is characterized by reduced body temperature, oxygen consumption, heart rate and breathing which all lead to much lower energy use. It makes a mouth full of sunflower seeds go a long way.

Many animals enter torpor during times of serious resource scarcity. But torpor can have serious physiological costs. It’s not easy on the body long run, but it does allow short term survival. Individuals that have good energy reserves may not enter torpor as much as those that may need to stretch their food stores a bit more. The duration and depth of torpor is regulated by the size and the fatty acid composition of their food reserves.

The chipmunk in my backyard feeding on sunflower seeds has a diet far higher in fatty acids than those in the woods eating acorns and beechnuts. Because nut crops wax and wane over the years, they may also have a smaller hoard some years too. The backyard chipmunk is guaranteed a steady supply of sunflower seeds each fall.

Dietary studies found that chipmunks fed sunflower seeds reduce both the depth and duration of torpor bouts. Even when chipmunks were provided with natural fatty acid supplements rather than high-powered sunflower seeds, they spent half as much time in torpor and their skin temperatures (indicating torpor was not very deep) were almost twice as high as those on a normal diet. With the pile of high fat seeds that our backyard friend has, he must be living large in his underground castle.

Source: Journal of Animal Ecology (2005) 74, 692–700 doi: 10.1111/j.1365-2656.2005.00968.x

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