HOME: www.hiltonpond.org

GENERAL INFO

CONTENTS

RESEARCH

EDUCATION

PUBLICATIONS

MISCELLANY

UPCOMING OPPORTUNITY:
Join us for another
Winter Hummingbird Expedition to Costa Rica
in February 2006

Join Us for the
15th Annual
York/Rock Hill
Christmas Bird Count
19 December 2003
(Please note date change. Click on the link above for more information.)

CHEEKY LITTLE EASTERN CHIPMUNKS

In mid-September each year, there's a small but noticeable change in mammal activity at Hilton Pond Center. It's about that time when Eastern Chipmunks--seemingly absent from the property during the heat of summer--begin to reappear. Suddenly we see these little striped rodents scurrying everywhere, drinking from the bird bath, calling from logs, and gathering early acorns and hickory nuts. By early October they're even climbing trees to harvest crimson red berries from our Flowering Dogwoods. And this week at Hilton Pond they seemed especially frantic, dashing from one bird feeder to the next, gathering sunflower seeds the chickadees had dropped or stuffing cheek pouches with big dry kernels of yellow corn. This frenzy occurs shortly after dawn and again in late afternoon as the sun drops lower on the horizon (above and below); two hours before dusk we're almost guaranteed to see the short, erect ears and black, beady eyes of a chipmunk peering over the edge of a log or low rock wall, surveying its surroundings in golden sunlight before madly dashing out for another cheekload of seed.

All text & photos © Hilton Pond Center

No matter how many times the cautious chipmunk follows that exact same trail from burrow to rock wall to bird feeder, it always pauses five seconds or so before venturing into the open. Our wary little rodent never fails to first confirm the coast is clear--a remarkably constant behavior that enhances the animal's survival in a world full of predators whose primary goal is a belly full of chipmunk. Despite our never-ending supply of succulent seeds, the local chipmunks seem to fear us, too, so we have to work very hard to avoid alarming them as we take photos through the farmhouse window with our 400mm lens. If we make a sudden movement or accidentally tap on the glass the chipmunks scatter, disappearing for a quarter hour or longer while we twiddle our thumbs and hope for another chance.

Eastern Chipmunks, Tamias striatus, are true rodents, with two sharp upper incisors that match and slide against two more in the lower jaw; they are classified in the Sciurinae, the subfamily of Rodentia:Sciuridae that includes ground squirrels, marmots, and tree squirrels. (Flying Squirrels are in a different subfamily.) The Eastern Chipmunk's genus name comes from the same Greek word, tamias, which means a "treasuer" or "storer" and refers to the animal's penchant for hoarding large amounts of food. The species name--meaning "furrowed" or "striped"--is equally descriptive of an Eastern Chipmunk's most noticeable external characteristic. Most individuals are buffy beneath and more or less chestnut-colored dorsally (photo above), with bold longitudinal stripes that go from shoulder to rump but not quite to the base of the tail. Each flank bears a yellow-white stripe bordered by two that are brown-black, and on the head a pale white stripe begins at the nose and splits while passing over and under the eye before stopping in front of of the ear.

A fifth dark stripe--quite narrow--runs down the spine of the Eastern Chipmunk, with fur to either side appearing gray but actually being "agouti," a term used when individual black-tipped hairs have alternating light and dark bands. (Agoutis are South American forest rodents whose bodies are covered by this banded hair.) A chipmunk tail--somewhat flattened, hairy, and a little less than half the animal's total length of about 8"-10"--is also agouti. In our experience, juvenile Eastern Chipmunks tend to be paler with less-distinct stripes; there is also considerable color variation among populations across the species' range.

Eastern Chipmunks thrive from the Great Plains eastward from southern Canada to the Gulf Coast, except for the Atlantic Coastal Plain from Virginia southward (see range map at left). In North Carolina the species occurs throughout the Piedmont and Mountain Regions, but South Carolina chipmunks are found primarily in the northwestern portion of the state and barely enter Piedmont proper. In all, there are 22 chipmunk species in the U.S., 21 of which occur in the Midwest or West. The unstriped rump of the Eastern Chipmunk is useful in separating it from other chipmunk species such as Least Chipmunks, Eutamias minumus, in northern and midwestern locales where their ranges overlap.

As its scientific name implies, the Eastern Chipmunk is noted for compulsive food-gathering and food-storing behaviors, both of which are facilitated by fur-lined cheek pouches that swell to the size of half a pingpong ball when full of seed. Solitary by nature, the chipmunk uses stout claws on its five-toed feet (above right) to dig a burrow in firm, often rocky soil. The entryway--about two inches in diameter (two adjacent holes are shown below)--is always level with the substrate; i.e., there is no mound of earth around the hole. Often the immediate vicinity of the opening is scattered with whole acorns and fruit from walnut, hickory, or pecan, along with half-eaten or empty nut shells.

The portal leads to a tunnel that may be three feet deep and ten feet long, including a nest cavity lined with dry, partially chewed leaves. In addition, there are usually a couple of spacious pantry chambers in which an industrious chipmunk can store a true bushel of seeds, berries, and nuts gathered during fall harvest. This nonperishable food supply is crucial, because no matter where they live, Eastern Chipmunks go into some level of winter torpor that lasts from a day to a week or two or even longer. Unlike long-term hibernators that put on prodigious amounts of fat and sleep all winter, most chipmunks snooze for short periods, wake up, nibble on select items from the larder, and then go back into torpor. If winter weather is particularly mild, a chipmunk may exit its burrow to explore the outside world; there are even occasional reports of Carolinas chipmunks cavorting in the snow during our traditional but short-lived January thaws.

An Eastern Chipmunk's burrow system typically has a main entrance and one or more other openings that remain plugged with soil. We suspect a chipmunk can quickly dig through these plugs, using an auxiliary entrance as an escape route if a potential predator enters its burrow. Such a predator would need to be long and skinny to follow a chipmunk down its tunnelwea; weasels and snakes happen to fit that configuration. Although we're not aware of any weasels at Hilton Pond, we're certain local serpents help keep our chipmunk population in check. On several occasions we've seen a large, 6-foot-long Black Ratsnake ascend a dogwood tree just outside our office window, its arboreal progress impeded somewhat by a large chipmunk-sized bulge halfway along its otherwise slender body. Despite such predation by snakes--and weasels, hawks, foxes, and feral cats--marked and recaptured Eastern Chipmunks have been known to live up to eight years, an amazing age for any small wild mammal.

In the Carolinas, male Eastern Chipmunks come into breeding condition by early February, females a week or so later. After mating, both sexes may retreat to their respective burrows and go back into torpor for a few weeks. Across southern parts of their range, females breed in spring and again in summer, each time gestating 4-5 embryos for about 31 days. The female nurses within the nest chamber, from which her young emerge at about 60 days after birth--fully furred and ready to explore. Within a few weeks each surviving chipmunk will have begun excavating its own burrow and defending a quarter-acre territory, sometimes physically and aggressively but more often by an incessant series of relatively low-pitched barks or chips--the same note repeated over and over. Although we always thought these vocalizations gave rise to the word "CHIPmunk," the name is actually derived from the Algonquian Indian atchitamon, meaning "one who descends trees headlong"--an apt description of what the chipmunk does after stealing dogwood berries from topmost branch.

Eastern Chipmunks prefer deciduous woodlands but also occur in open scrub if there are rocky areas with crevices in which to hide and/or stumps and logs from which to survey and proclaim a territory. They are almost never found in grasslands or wet, marshy areas. When we first moved to the Hilton Pond property in 1982, we had no Eastern Chipmunks, likely because our 11-acre tract was completely open but for a few mature trees; mostly it was a monoculture of native Broomsedge grasses growing in nutrient-depleted red clay. As natural succession progressed, local habitat might have become more attractive to Eastern Chipmunks, particularly with its bountiful seed and berry crop being produced on fast-growing shrubs and trees. This new vegetation also supported a broader assortment of items eaten by Eastern Chipmunks, including beetles, earthworms, and fungi (see the chipmunk-nibbled mushroom above). Individual chipmunks also may develop a taste for snails and slugs; small amphibians, snakes, and mice; bird eggs; or even birds themselves. On average, however, stomach analyses reveal plant matter makes up 90-95% of a chipmunk's diet, except in spring when animal components may increase to 30%--possibly an attempt to quickly replenish protein lost during winter torpor.

Sooner or later we might have acquired a local chipmunk population at Hilton Pond, but we hastened colonization in the mid-1980's when parents of one of our high school students in Rock Hill SC offered us several live-trapped chipmunks. His parents' yard in southeastern York County--at or near the edge of the species' range--was a hotbed of chipmunk reproduction, and their garden was overrun by fecund terrestrial rodents. Back in those days we were less educated about potential pitfalls of moving native animals from one site to another, so we welcomed the opportunity to release a half-dozen of our furry gifts near the Hilton Pond farmhouse. Those original chipmunks--and perhaps some immigrant cousins from neighboring farms--seem to have done quite well over the past two decades. Today we have a thriving Eastern Chipmunk population that is forever stealing food from our bird traps, stuffing seed after seed in their chubby little cheeks while keeping an eye out for predators--and for people taking photos through the window glass.

All text & photos © Hilton Pond Center

POSTSCRIPT: Outdoors writer Jim Casada of Rock Hill SC tells us his 96-year-old father--who was a teenager in the days just before American Chestnuts were essentially wiped out by the blight--used to raid chipmunk dens to get chestnuts gathered by the industrious rodents. Jim says this was common practice for folks in the Great Smoky Mountains and guaranteed an additional peck (quarter bushel) or more from each burrow. Jim also notes that people seldom hunt chipmunks for food because they're too small to make much of a meal.