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The eastern chipmunk (Tamias striatus) is found in wooded habitats across North America (Snyder, 1982). Specifically, the Eastern chipmunk inhabits deciduous areas of southeastern Canada and eastern USA (Dunford, 1970). These chipmunks are classified as urban and wilderness species since it is not uncommon to find them in local parks or other public places, near human settlement (Snyder, 1982). Snyder found that fur colouration varies in chipmunks based on geographical distribution. For example, fur colouration shifts to grey in the northern geographic ranges whereas chipmunks inhabiting the southern range have a more reddish hue. Perhaps these traits may have evolved to due climatic reasons; to blend in the environment based on seasonal cues. These chipmunks reside in complex overlapping burrow systems underground (Snyder, 1982). Dominance areas in these burrows are maintained by both males and females (Dunford, 1970). The eastern chipmunks live in a loose territoriality system meaning that even though agnostic behaviour is displayed to assert dominance and maintain distance between two chipmunks, sharing can also occur between the groups although it is often unwanted (Dunford, 1970). For example, if a chipmunk discovers a rich food hoard in a nearby burrow, it will risk its chances of being chased by the dominant chipmunk several times just for food, despite the fact that running away is very energetically costly.

Physical Description and Lifespan

On average, eastern chipmunks are 225 to 269 millimeters in length. Their tails range from 72 to 101 millimeters, and skull size is anywhere from 39.4 to 43.6 millimeters (Snyder, 1982). According to the National Geographic Society, the eastern chipmunk can weigh anywhere from 28 to 142 grams and can live 2 to 3 years in the wild.

Diet

Diet of the eastern chipmunk mainly consists of seeds, nuts, and acorns (Snyder, 1982). These chipmunks also feast on small invertebrates (insects), fruit, as well as fungi which are crucial in the growing season (Snyder, 1982). According to the National Geographic Society chipmunks do not store fat in the winter months during hibernation. Instead, they slowly consume feed collected during the late summer/early fall season throughout the winter. Evidence from research conducted by Munro & Humphries in 2005 suggests that feeding behaviour during the hibernation period is different for male and female chipmunks. The chipmunks do not truly hibernate (National Geographic Society, 1996-2016). Instead, they enter extended periods of mental inactivity or lethargy, known as torpor (Munro & Humphries, 2005). Male chipmunks benefit the most by regularly feeding during the winter months to ensure they reach their maximum energetic potential during the mating season (Munro & Humphries, 2005). Displaying agnostic behaviour to gain access to female chipmunks is very energetically costly therefore it is important that the males are prepared to do so (Dunford, 1970). Females benefit the most from maintaining deep torpor phases during the winter months to save their food hoards for pregnancy and lactation (Munro & Humphries, 2005). Spending too much time foraging for food in those conditions may be detrimental to both the females and their newborns.

Reproduction and Communication

The eastern chipmunks reach sexual maturity at 11 months of age (Pidduck & Falls, 1973). Male adults come into breeding condition in March and remain that way until June (Smith, 1972). Female adult chipmunks are polyestrous meaning they annually experience two breeding seasons (Pidduck & Falls, 1973). Female breeding seasons are from March to April, and again from June to July (Smith, 1972). During breeding season, males become active early in the morning to guard burrow entrances and remain close to females in estrus (Snyder, 1982). When a mating bout takes place, dominant males copulate with the female by preventing access to other males and continue to remain in contact with the female until the session is completed (Snyder, 1982). When large amounts of males are present, the dominant male never gets a chance to copulate with the female since he spends all his time chasing away other males (Snyder, 1982). Litter size varies from 3 to 5 offspring (Pidduck & Falls, 1973). After giving birth, it is common for the mothers to transport their young to a different burrow and establish a new home away from male activity (Snyder, 1982). Chipmunks grow rapidly and reach full adult size at three months (Smith, 1972). Most young stay close to their home range as they grow. Even after reaching sexual maturity, these chipmunks display short distance dispersal movements (Snyder, 1982). To maintain spatial organization within the burrows, agnostic behaviour, as well as various vocalization techniques, are used (Dunford, 1970). To keep other chipmunks away from their core area, a chipmunk can chase others away for distances as small as 3 meters to as large as 15 meters (Snyder, 1982). Vocalization techniques are a less energetically costly method of keeping invaders out of their territory; however, it is less persuasive than chasing (Dunford, 1970). Vocalizations can also be used to attract female mates as well as warning others of nearby predators (Dunford, 1970).

Predation

Predators of the eastern chipmunk include snakes, hawks, weasels, foxes, coyotes and bobcats (Snyder, 1982). Chipmunks are more capable of outrunning predators in familiar places than places which are unfamiliar (Clarke et al., 1993). Chipmunks are intelligent animals since they can use celestial objects and other landmarks as navigational cues (Snyder, 1982). In unfamiliar areas, trees are often used as “safe sites” to out run or mislead predators (Clarke et al., 1993). When exposed to areas of danger, near predators chipmunks feed faster or quickly fill their cheek pouches to carry food to safety before consumption (Kieffer, 1991). As the risk of predation increases, number of seeds collected and time spent feeding decreases (Kieffer, 1991).

Conservation Status

According to the IUCN Red List of Threatened Species, the Eastern Chipmunk (Tamias striatus) is listed under least concern since it is an abundant species currently facing no major threats (ICUN, 2016).

Did you know?

The eastern chipmunks are infamous for being nest predators (Reitsma et al., 1990). According to an Artificial Nest experiment done by Reitsma et al., eastern chipmunks prey on eggs inside unguarded birds’ nests and bring their nest material back into their burrows for their young. This type of predation causes nest failure and this particular experiment observed the impact of nest failure in black-throated blue warblers (Reitsma et al., 1990).

References

Clarke, M., Da Silva, K., Lair, H., Pocklington, R., Kramer, D., & McLaughlin, R. (1993). Site Familiarity Affects

Escape Behaviour of the Eastern Chipmunk, Tamias striatus. Oikos, 66(3), 533-537. doi:1. Retrieved from http://www.jstor.org/stable/3544949 doi:1

Dunford, C. (1970). Behavioral Aspects of Spatial Organization in the Chipmunk, Tamias striatus.Behaviour, 36(3),
215-231. Retrieved from http://www.jstor.org/stable/4533329

Kieffer, J.D. (1991). The Influence of Apparent Predation Risk on the Foraging Behaviour of Eastern Chipmunks
(Tamias striatus). Canadian Journal of Zoology, 69(9): 2349-2351. Retrieved from http://www.nrcresearchpress.com/doi/abs/10.1139/z91-330#.WA1ezPkrLX4

Linzey, A.V. & NatureServe (Hammerson, G.). 2008. Tamias striatus. The IUCN Red List of Threatened Species
2008:e.T42583A10713654. Retrieved from http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T42583A10713654.en.

Munro, D., Thomas, D., & Humphries, M. (2005). Torpor Patterns of Hibernating Eastern Chipmunks Tamias
striatus Vary in Response to the Size and Fatty Acid Composition of Food Hoards. Journal of Animal Ecology, 74(4), 692-700. Retrieved from http://www.jstor.org/stable/3505449

National Geographic Society. (1996-2016). Chipmunk: Tamias. National Geographic. Retrieved from
http://animals.nationalgeographic.com/animals/mammals/chipmunk/

Pidduck, E., & Falls, J. (1973). Reproduction and Emergence of Juveniles in Tamias striatus (Rodentia: Sciuridae)
at Two Localities in Ontario, Canada. Journal of Mammalogy, 54(3), 693-707. doi:1. Retrieved from http://www.jstor.org/stable/1378968 doi:1

Reitsma, L., Holmes, R., & Sherry, T. (1990). Effects of Removal of Red Squirrels, Tamiasciurus hudsonicus, and
Eastern Chipmunks, Tamias striatus, on Nest Predation in a Northern Hardwood Forest: An Artificial Nest Experiment. Oikos, 57(3), 375-380. doi:1. Retrieved from http://www.jstor.org/stable/3565967 doi:1

Smith, L.C., & Smith, D.A. (1972). Reproductive Biology, Breeding Seasons, and Growth of Eastern Chipmunks,
Tamias striatus (Rodentia: Sciuridae) in Canada. Canadian Journal of Zoology, 50(8): 1069-1085. Retrieved from http://www.nrcresearchpress.com/doi/abs/10.1139/z72-145#.WA1dnPkrLX4

Snyder, D. (1982). Tamias striatus. Mammalian Species, (168), 1-8. doi:1. Retrieved from
http://www.jstor.org/stable/3503819 doi:1