Small Arboreal Mammals of the St. Lawrence Lowlands

Small arboreal mammals, such as Eastern Gray Squirrels (Sciurus carolinensis), American Red Squirrels (Tamiasciurus hudsonicus) and Eastern Chipmunks (Tamias striatus), play important roles in forest ecosystems of the St. Lawrence Lowlands, including that of the Ste-Anne-de-Bellevue Morgan Arboretum. These species are essential to healthy forests because they distribute seeds from plants, as well as fungi and lichens (Carey and Harrington 2001). They also aid in mixing soil with decomposing organic matter (Carey and Harrington 2001). In addition, small arboreal mammals are a key prey of larger mammals and birds and act as an intermediate in the transfer of energy to higher trophic levels (Gurnell et al. 2001).

The Eastern Gray Squirrel (Sciurus carolinensis

Identification and Distribution:

Eastern Gray Squirrels are small mammal with a white belly and a bushy tail edged in white (Whitaker and Elman 1980). They are typically gray but have various colour morphs; they can also be black, white, brown and brown-red. These squirrels are native to Eastern North America, but can be found in Central and Western North America, as well as some areas in Europe (Whitaker and Elman 1980).

Eastern Gray squirrel

Black morph of Eastern Gray Squirrel


During a female’s single day of estrus, male Gray Squirrels congregate around her in an attempt to mate with her (Koprowski 1993). Most mating takes place from December to February and May to June. Gestation is around 45 days, with birthing happening either in February, at the same time spring buds appear, or in July, at the same time as nut crops ripen. Eastern Gray Squirrels do not parent their young (Koprowski 1993).


Their diet primarily consists of acorns, other nuts and seeds (Gurnell 1983). They are scatter hoarders that cache most of their food, but only hide one or two seeds underground at a time (Gurnell 1983; Wauters et al. 2002).


Gray Squirrels live and construct their nest in deciduous forests. They have three types of nests: the ground nest, the cavity nest and the drey, a leaf nest lined with dry leaves, grass, moss, and fur (Cudworth and Koprowski 2011). Gray Squirrels often choose tall trees with many interlocking branches to have multiple access points to their nests. They tend to place nests adjacent to the main trunk of trees for more stability, as well as near the top of the trees for the thick foliage that provides protection from wind and elements (Cudworth and Koprowski 2011).

Additional resources: enature.com and newyorkwild.org

The Red Squirrel (Tamiasciurus hudsonicus

Identification and Distribution:

American Red Squirrels are smaller than Eastern Grey Squirrels and their tails are not as bushy (Whitaker and Elman 1980). They have a white belly, which is bordered by a dark stripe in the summer. They can vary in colour from brown to an olive-red. These animals live in North America and are found higher north than other species of squirrels (Whitaker and Elman 1980).

Red squirrel. The dark stripe and white belly are very visible.


Red Squirrels have two breeding seasons in a year, the first from December to February and the second from May to June (Layne 1954). The average litter size is four and a half young. Young squirrels are born naked and do not open their eyes until 29 days after birth. The young venture out of their nest after several weeks and reach adulthood in approximately three months (Layne 1954).


The diet of Red Squirrels primarily consists of pinecones, although they eat a large variety of other foods as well (Gurnell 1983). They are scatter and larder hoarders that look for their food mainly on the forest floor, but also up in the trees (Guerra and Vickery 1998). Red Squirrels are known to have large hording sites where they hide great amounts of food (Gurnell 1983; Penner and Devenport 2011).

Red squirrel eating a nut.


Red Squirrels are found in similar habitats as Gray Squirrels, although they prefer coniferous forests to deciduous forests because they enjoy eating the pinecones that conifers produce (Riege 1991).

Additional resources: arkive.org and  waza.org

The Eastern Chipmunk (Tamais straitus)

Identification and Distribution:

Eastern Chipmunks are slightly smaller than American Red Squirrels and they do not have bushy tails (Whitaker and Elman 1980). They have prominent dark and light lines on their back, sides and face. They have a reddish-brown back, rusty coloured rump and flanks, along with a white belly. Eastern chipmunks are found in Eastern North America (Whitaker and Elman 1980).

Front view of Eastern Chipmunk

Back view of Eastern Chipmunk


Eastern Chipmunks have two breeding seasons, one between March and April and another between June and July (Smith and Smith 1971). They have a 31-day gestation period and litters consist of one to seven young. Young Chipmunks leave their burrows after six weeks and reach adulthood in three months, but do not reach sexual maturity until they are 11 months old (Smith and Smith 1971).


Eastern Chipmunks mainly eat seeds and nuts from trees, but are also known to eat fruit, insects, frogs and bird eggs (Guerra and Vickery 1998; Wrazen and Svendsen 1978). Like Red Squirrels, Eastern Chipmunks have large hording sites where they hide a large quantity of food (Gurnell 1983; Penner and Devenport. 2011).

Eastern Chipmunk foraging


Eastern Chipmunks dig burrows in which they sleep and store food (Bihr and Smith 1998). A Chipmunk’s burrow usually has more than one entrance, with tunnels connecting them all together. These entrances are often located under or near large objects, such as rocks, for structural stability, to act as barriers against predators and help conceal their location (Bihr and Smith 1998).

Chipmunk burrow

Much research has been done on squirrels and chipmunks over the years, ranging from competition with other species to general physiology and anatomy (Layne 1954; Wauters et al. 2002). Important research done by Reitsma et al. (1990) evaluates the impact of Eastern Chipmunks and Red Squirrels on avian nest predation in a northern hardwood forest. Their study consisted of trapping and removing sciurids from a six-kilometer area so they could estimate the importance of these mammals on nest predation. After removing a total of 49 individuals (23 Red Squirrels and 26 Chipmunks), they came to the conclusion that neither Chipmunks nor Red Squirrels are the most important predators on avian eggs in this forest system (Reitsma et al. 1990).

A paper by Koprowski (1993), underlines a study concerning the approach male Gray Squirrels have towards reproducing and the tactics they use. Traps were set to ear tag a group of squirrels, about 10 females and 20 males. The group of squirrels were observed, and when a bout of matting occurred, they recorded their findings. The results illustrate that males use two ulterior motive, active pursuit and satellite, to achieve copulation with females, but only one of the two was used in a mating bout. In active pursuit, males fend off any other potential male competitors and in satellite, males stay within the home range of a female in estrous (Koprowski 1993).

 Additional resources: animals.nationalgeographic.com and canadiangeographic.ca



Bihr K.J. and Smith R.J. (1998) Location, structure, and contents of burrows of Spermophilus  lateralis and Tamias minimus, two ground-dwelling scuirids. The Southwestern Naturalist. 43: 352-362.

Carey A.B. and Harrington C.A. (2001) Small mammals in young forests: implications for management for sustainability. Forest Ecology and Management. 154: 289-309. DOI: 10.1016/S0378-1127(00)00638-1

Cudworth N.L. and Koprowski J.L. (2011) Importance of Scale in Nest-Site Selection by Arizona Gray Squirrel. The Journal of Wildlife Management. 75: 1668-1674. DOI: 10.1002/jwmg.194

Guerra B. and Vickery W.L. (1998) How do Red Squirrels, Tamiasciurus hudsonicus, and Eastern Chipmunks, Tamias striatus, coexist? Oikos. 83: 139-144. DOI: 10.2307/3546554

Gurnell J. (1983) Squirrel numbers and the abundance of tree seeds. Mammal Review. 13: 133-148. DOI: 10.1111/j.1365-2907.1983.tb00274.x

Gurnell J., Wauters L.A., Preatoni D., Tosi G. (2001) Spacing behaviour, kinship, and population dynamics of grey squirrels in a newly colonized broadleaf woodland in Italy. Canadian Journal of Zoology. 79: 1533-1543. DOI: 10.1139/cjz-79-9-1533

Koprowski J. (1993) Alternative reproductive tactics in male Eastern Gray Squirrels: “making the best of a bad job”. International Society for Behavioral Ecology. 93: 1045-2249.

Layne J.N. (1954) The biology of the Red Squirrel, Tamiasciurus hudsonicus loquax (Bangs), in  central New York. Ecological Monographs. 24:226-268. DOI: 10.2307/1948465

Reitsma L.R., Holmes R.T., Sherry T.W. (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: 375-380. DOI: 10.2307/3565967

Riege D.A. (1991) Habitat specialization and social factors in distribution of Red and Gray Squirrels. Journal of Mammalogy. 72: 152-162. DOI: 10.2307/1381990

Smith L.C. and Smith D.A. (1972) Reproductive biology, breeding seasons, and growth of Eastern Chipmunks, Tamias strialus (Rodentia: Sciuridae) in Canada. Canadian Journal of Zoology. 50: 1069-1085. DOI: 10.1139/z72-145

Wauters L.A, Tosi G., Gurnell J. (2002) Interspecific competition in tree squirrels: do introduced Grey Squirrels (Sciurus carolinensis) deplete tree seeds hoarded by Red Squirrels (S. vulgaris)?. Behavioral Ecology and Sociobiology. 51: 360-367. DOI: 10.1007/s00265-001-0446-y

Whitaker J.O. and Elman R. (1980) The Audubon Society field guide to North American mammals. New York: Knopf.

Wrazen J.A. and Svendsen G.E. (1978) Feeding ecology of a population of Eastern Chipmunks (Tamias striatus) in southeast Ohio. American Midland Naturalist. 100: 190-201. DOI: 10.2307/2424789


About Christopher Ernst

Hakai postdoctoral scholar at the University of British Columbia and Simon Fraser University (B.C.)

2 comments on “Small Arboreal Mammals of the St. Lawrence Lowlands

  1. Great work! Very interesting!

  2. Hi there. Great post regards North American squirrels. I live in Toronto, Ontario, and earlier this year, my wife, Jean, and I were in Ireland where we came upon the rarely seen Red Squirrel. To us, they actually look somewhat like our American Red squirrels, but boy, do they have long ears! We were shocked to learn that U.K. and Irish Red squirrels are contracting the pox virus from Grey squirrels, and dying. We feel very lucky to have seen two Red squirrels in Ireland, and have posted some of our pictures and videos for anyone interested at: http://frametoframe.ca/photo-essay-red-grey-squirrels-canada-ireland

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