Chipmunks Everywhere!

by Steve Blight

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Last weekend I took a long walk in the bush, and it seemed to me that there were chipmunks everywhere. I had brought our dog Poppy along with me for company, and as part terrier, this was as close to dog heaven as can be found on Earth. For three solid hours she was on high alert, chasing down every “chip” call from the woods until the chipmunk it belonged to had neatly escaped down a hole under a rock or log. The final outcome of the dog-chipmunk showdown was chipmunks many, dog no score. But I’m not sure this mattered very much to Poppy – since for her the chase is everything.

Why are there so many chipmunks around at this time of year? This main answer is that this is the time of year when chipmunks are busy gathering as much food as possible for the winter. This makes them particularly easy to see as they go about their important fall work. The four – six young that are born to each female in spring have grown up and have joined the adults in the hunt for winter supplies, roughly doubling the chipmunk population that had emerged the previous spring. Although chipmunks usually forage on the ground for seeds and other food, they can also climb trees and shrubs to harvest nuts and fruit – and to escape single-minded dogs, as I saw first hand.

When foraging, chipmunks use their cheek pouches as temporary storage. When they become full, the chipmunk deposits the seeds in its nest or buries them in shallow holes that it digs in the ground and then covers with earth, leaves, and other litter.

In spring, chipmunks diligently search the ground for any seeds that remain from the previous summer as well as young leaves and shoots. Throughout the spring, summer, and autumn, the chipmunk’s diet is supplemented with insects, earthworms, flowers, berries, mushrooms, and occasionally eggs and carrion. Rare instances of chipmunks preying on birds or small mammals have been observed.

Chipmunks gather food in the fall because they are hibernators. By October, each chipmunk has accumulated enough seeds to enable it to survive the winter. With the onset of winter in November, chipmunks disappear below ground.

There are different ideas about what happens when chipmunks retire to their burrows for the winter. The first is that they immediately go into a state known as torpor, where the body temperature, rate of breathing, and heart rate drop to very low levels. This reduces the amount of energy required to keep the chipmunk going. Periods of torpor last from one to eight days or perhaps longer, and between them chipmunks wake up and consume part of their food supply. The other main view is that chipmunks don’t begin hibernation until their food supply has been exhausted.

With the first warm days of March, chipmunks begin to emerge, sometimes burrowing through snow to reach the surface. Scientists believe that it is important that a chipmunk make its burrow deep enough underground to reach below the frost line – the level to which freezing temperatures penetrate the ground in the winter. If the frost reaches the hibernating chipmunk there is a good chance that the animal may freeze to death in its burrow before spring arrives in the forest.

There is a second possible explanation, which could explain why Poppy seems to have more chipmunks to chase this year. In good years with plenty of food, chipmunks have the ability to produce a second litter in the fall. I noticed that several of the chipmunks I saw last weekend were very small, suggesting that this may be the case this year. Whatever the reason, I certainly know one four legged part-terrier that is more than happy with this year’s abundance of chipmunks.

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Please feel free to report any observations to Lorraine Julien at naturewatching@gmail.com  or Steve Blight at natureobservations@rogers.com