Scientific name: Tamias striatus
Common name: Eastern Chipmunk
(Information for this Species Page was compiled in part by Andrea Boysel for Biology 220M, Spring 2001 at Penn State New Kensington)
Chipmunks are eight to ten inches long and weigh two and a half to four ounces. Males are slightly bigger than females. Both sexes have the five prominent dark-brown to black stripes that run down their sides and backs. Their blunt heads also have black stripes that seem to run through the middle of their eyes and two light-colored outline stripes around each eye. They have light-colored bellies and brown feet with five toes on each hind foot and four toes on each forefoot. Their tails are flattened and furry.
The eastern chipmunk is found abundantly throughout the middle and eastern sections of the United States. Its North American range extends northward into southern Canada and south into the mountains of Mexico. It lives in a great variety of human generated ecosystems including fence rows, city parks, gardens, cemeteries, and even college campuses. The optimum natural habitats for the eastern chipmunk, though, are open deciduous woodlands containing abundant stumps and logs. Chipmunks are seldom found in swampy areas or in marshlands.
Within their forest habitats both the male and the female chipmunks occupy home ranges of a quarter to a third of an acre. Immature individuals have much smaller home ranges of a fifth of an acre. These home ranges extensively overlap and typically include those tree species that provide abundant and seasonally predictable sources of food. White oak trees (sources of the extremely palatable white oak acorns) are found in the larger, mature chipmunks' home ranges, while less palatable acorn producing oaks (like black and red oaks) are most commonly included in the smaller, immature chipmunks' home ranges.
Chipmunks construct two types of burrows within their home ranges: shallow burrows with many entrances and complex networks of interconnected tunnels, and deep burrows that have extremely complicated systems of tunnels and entrances within which food storage areas and a central, leaf-filled nesting chamber are located. The shallow burrows function as temporary refugia for the chipmunk during the day, while the deep burrows are the overnight and overwinter sleeping locales. Burrows are often located on sloping ground, a feature that contributes to efficient water drainage.
Longevity and Reproduction
Chipmunks live for two to three years in the wild and five to eight years in captivity. Females have two estrus cycles per year: one in March or early April, one in late July or early August. Males make long trips out of their home ranges to locate females and check on their reproductive condition.
Females raise their litters alone. No pair bonding between individuals takes place. Gestation is about thirty days after which the female gives birth to a litter of four to six young in the nest chamber of her deep burrow. The young (which
weigh about 3 grams at birth) are born toothless, furless and with closed eyes and ears. Fur (and stripes) becomes visible 10 days after birth
along with the emergence of the teeth (incisors at one week, first molars by three weeks, adult molars by three months). Ears open by twenty-eight days and eyes open a few days later. Juveniles starting at four to six weeks leave the nesting burrow during the day to forage and
frolic. Mortality rates for these frolicking juveniles (primarily due to predation) is approximately thirty percent.
Chipmunks are omnivorous. They consume roots, seeds, mushrooms, berries, corn, fruit and garden vegetables. They also eat bird's eggs, insects, earthworms, snails, salamanders, small snakes, frogs, young mice and young birds. Females especially consume high protein foods, while males consume materials that are rich in carbohydrates.
Most of the foraging activities take place on the ground although chipmunks are known to ascend into trees to gather food. They are not good climbers (smooth barked trees like beeches are climbed with great difficulty if at all). Often to get up into the crown of a beech tree a chipmunk will climb a rough barked adjacent tree (like a red oak or a cherry) and jump from crown to crown. This leaping can lead to frequent falls and injuries or even death.
From the end of July through October, chipmunks gather large quantities of seeds and nuts which they cache in the food storage tunnels of their deep burrows. The chipmunks go underground with the onset of winter where they will enter into a fluctuating state of torpor (not physiological hibernation) for the duration of the cold season. Periodically, the chipmunks wake up from their sleep, consume some of their stored food, and then re-enter their torpid sleep state. Males emerge first in the spring followed one or
two weeks later by the females.
Eastern chipmunks are solitary animals with limited inter-specific interactions.
Although they are solitary creatures, they do extensively communicate via vocalizations. A wide variety of "trilling, "chipping", and "chucking" calls indicate awareness, alertness, and alarm. Alteration of pitch and frequency are used to communicate information on predator types, and on the degree and timing of the alarm event. Familial warning calls are especially used by females to alert juveniles of dangers.
Chipmunks can have both stimulatory and inhibitory impacts on ecological succession processes. Their extensive gathering and burial of seeds and nuts increases the probability of germination and sprouting. Their affinity for certain acorn and nut types (like their amazing appetites for white oak acorns), though, may drastically reduce the germination rates for certain species of trees.