Chipmunks Cherish Their Solitude
Living alone underground
by Bob & Jorja Feldman
From the October, 2017 issue
For years, we have enjoyed the antics of chipmunks as they dart around the yard, occasionally standing on hind legs to survey their surroundings, and often dipping into the grape jelly we put out to attract orioles.
If you've noticed more chipmunks lately, you're not alone--Scott Purr of Critter Control of Ann Arbor says he's seen a big surge in calls about uninvited visits by these small rodents in the past few years. Cody Thompson, the mammal collections manager at the U-M's zoology research museum, and Ben Dantzer, an assistant professor of ecology and evolutionary biology, helped us learn more about them.
Like prairie dogs, chipmunks are burrowers. But unlike prairie dogs, who are highly social, chipmunks live alone and are quite territorial, particularly around their burrows. Chipmunks mark their territories and generally don't encroach on others' turf. The size of a territory depends on available food sources; they may be smaller in town, where landscaped yards offer more food than their native deciduous forests.
Chipmunk burrows are less than three feet deep but can be as much as thirty feet long, with multiple rooms, including sleeping quarters and a food larder. Members of our local species--the widespread and common Eastern chipmunk--carry food to that larder in cheek pouches, each of which, when full, can bulge to a size bigger than their heads.
Their accommodations have a separate latrine and, for females, a cozy nursery chamber lined with soft leaf material to coddle tiny pups (a female raising pups is only exception to the one-burrow, one-chipmunk rule). Chipmunks have litters in the spring, and, if enough food is available, additional litters in the summer. They're promiscuous; each of the pups in a litter may have a different dad.
Come winter, chipmunks head down into their subterranean homes for long naps. They go into torpor, a state of reduced body temperature and slowed metabolic rate, but do not put on enough body fat to hibernate through the winter. Instead,
they wake up hungry from time to time and go looking for food in their underground larders or, in milder weather, in caches scattered around their territories. They also are known to steal from other animals' caches and to raid platform bird feeders, or scrounge for spilled seed on the ground.
Though they live alone, we often see two chipmunks chasing each other around the yard. What is going on there? Dantzer's answer: "They are either trying to have sex or are engaged in a territorial dispute." We think it's more often the latter, because we see these chases outside the mating seasons.
Chipmunks avoid burrow-unfriendly swamps and wetlands, but otherwise are pretty flexible about where they live. Ann Arbor, with its many trees and parks and backyards, is great habitat.
We had always thought that squirrels were squirrels and chipmunks were chipmunks. It turns out that all species of chipmunks, from the scientists' perspective, are ground squirrels. This makes them cousins to another of our backyard residents: the roly-poly woodchuck who lives in the wild part of our backyard is actually a giant ground squirrel.
[Originally published in October, 2017.]
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