Curious Chipmunks

by Nancy Olmstead

A month ago I was walking in the woods and it seemed like I couldn’t go more than a few feet without disturbing another chipmunk.  The little brown stripe-y streaks were running all over the place, stopping to chirp and chatter at me as I passed.  Don’t worry, buddy, I don’t want your nuts.

We’re having a mast year in the northeast.  The oaks, beeches, and other masting trees are making a bumper crop of seed, which chipmunks eat and store by the cheekful.  This probably explains the superabundance of chipmunks.  The eastern chipmunk, Tamias striatus, can tell when the fall harvest is going to be good.  So they go all out making babies over the summer.  Some of the animals I’m seeing now are probably this year’s offspring, rushing to find, secure, and fill their burrows before settling down for their long winter rest.

Scientists have also studied this phenomenon in red squirrels, and chipmunks may be similar.  After all, chipmunks are a kind of squirrel.  They belong to the family Sciuridae, the sciurid rodents, which includes chipmunks, ground squirrels (e.g., prairie dogs), marmots (e.g., woodchuck), and tree squirrels (e.g., gray and red squirrels and flying squirrels).  Red squirrels are also known to anticipate high seed crops and reproduce accordingly.  Females may even have a second litter in the summer that precedes a big fall.

But how do chipmunks and red squirrels know that it’s going to be a good year?  The jury is still out on that question.  It’s hard to measure what individual animals are using as a cue to guide their reproductive “decisions.”  (And by using the word “decisions,” I don’t mean to imply that chipmunks and squirrels have consciousness, just an instinct to reproduce when certain cues are present.)

Scientists involved in these studies have suggested that the visual stimulus of an abundance of flowers may clue the squirrels in, but that explanation is less convincing for chipmunks, who spend more time on the forest floor than up in the tallest trees.  Chipmunks may be able to smell the upcoming bounty by homing in on the subtle scent of all those beech, oak, and maple flowers.  However they do it, it’s pretty cool.