Two chipmunks vie for seeds on our front lawn. One lives
directly underneath the bird feeder. Another hails from the far
side of the house, address unknown.
The chipmunks appear identical to me: same size, same stripes.
Same interests, namely seed hoarding, aggressive chittering,
jumping into the bushes and back out again, and brazen stiff-tailed
standoffs with the dog.
However, some aspects of these chipmunks' behavior are probably
distinctive. Experiments have demonstrated that a chipmunks'
choosiness about what food they collect, how fully they stuff their
cheek pouches, and even how quickly they stuff food in there all
relate to the distance between a foraging site and a home
The eastern chipmunk, Tamias striatus, is a central place
forager. This means that, similar to the beaver and the honeybee,
the chipmunk carries food back to a central location. This time of
year, that location is the chipmunk's winter burrow. It's an
impressive feat of earthworks that includes a bedroom, bathroom,
several tunnels to the surface, and multiple larders.
In late autumn, the chipmunk retreats to its bedroom, tucks its
tail over its nose, and sinks into a deep sleep. However, unlike
many other hibernating mammals, the chipmunk doesn't sleep the
winter away. Because it lacks fat reserves, it has to wake up
frequently to feed.
In other words, chipmunks have good cause for their hoarding
But their intense foraging activity has a cost. The time and
energy that a chipmunk spends obtaining and hauling food from a
particular site, be it a birdfeeder or a patch of forest floor,
represent precious calories invested and other opportunities
As established food sites are depleted, chipmunks have to go out
and look for new ones, and this is an energy gamble. Long distance
foraging may offer access to more desirable food sites, but it
requires more travel time and increases the risk of predation.
Then there is the "loading curve" consideration. In general, the
more food a chipmunk stuffs in its cheek pouches, the slower its
subsequent stuffing, and therefore the greater its overall risk of
predation. Nor is every food item created equal. In addition to
issues of durability and nutritive value, some food is simply
easier to harvest and stuff than other food.
As if all these factors weren't enough to worry about, chipmunks
have another problem to manage: other chipmunks. Chipmunk
territories average about 5,000 square meters (a little more than
an acre) and they overlap. This means that rivals lurk nearby,
poised to Hoover up food at a forage site, or even steal from
So how does all this play out underneath the bird feeder?
Fortunately for the inquisitive, there has been extensive
research in central place foraging over the past few decades, and
the chipmunk has been the protagonist of numerous scholarly papers.
Some of these veer to the unintentionally funny. My favorite
example, a paper out of the Université du Québec, describes an
experiment assessing chipmunk reactions to sunflower seeds that had
toothpicks stuck to their shells with glue.
Out of all this research emerges what might be called the
guiding rule of chipmunk game theory. Chipmunks have evolved to be
energy maximizers. They seek to strike the optimal balance between
the energy gain per cheek pouch load and the highest possible
number of trips back to the burrow. In the absence of other
variables, a chipmunk that is near its burrow will have smaller
pouch loads and make more frequent trips than a chipmunk from a
distant burrow, which will stuff its cheeks full before heading
Of course, chipmunks' lives teem with other variables, and
studies show that chipmunk behavior adapts to take many of them
into account. Here are some basics from what might be called
Chipmunk Game Theory 101.
If another chipmunk is making a lot of noise, it might be
fussing at you, but it also may have spotted a hawk or a weasel.
Slow down pouch stuffing and look out for predators. If food is low
quality and far from home, seek another foraging site. If a site
has a dwindling supply of food, or if the food requires extensive
handling time (i.e, seeds covered with toothpicks and glue), take
time during your return trip to explore alternative sites. If a
dominant chipmunk temporarily vacates a food site, spend more time
there and stuff all you can. If another chipmunk is at the food
site, slow down stuffing and keep an eye on them. If a subordinate
chipmunk is intruding on your territory, chase them. Sure, it will
cost you energy, but it will cost them energy too, and maybe they
won't come back.
Of course, it's easy to imagine more factors: weather, steepness
of terrain between burrow and foraging site…how about pouch
fatigue? My small primate brain boggles at the complexities. It's
enough to make me want to chitter aggressively, jump into the
bushes, and jump back out again.
Elise Tillinghast is the publisher of
Northern Woodlands magazine. The illustration for this column was
drawn by Adelaide Tyrol. The Outside Story is
assigned and edited by Northern Woodlands magazine and sponsored by
the Wellborn Ecology Fund of New Hampshire Charitable Foundation: