Scientific & Common Name:
This particular species of squirrel is commonly known as the “Eastern Grey Squirrel” and has the scientific name; Sciurus carolinensis (IUNC, 2016).
Habitat and Geographic Range:
The eastern grey squirrel is native to North America, in the United States it is prevalent in areas west of the Mississippi River, in Canada it inhabits the southern; more temperate provinces (Koprowski, 1994). The eastern grey squirrel is also exists as an invasive species; in Ireland, Scotland, England and northern Italy (Gurnell, Wauters, Lurz, & Tosi, 2004). Naturally, the eastern grey squirrel inhabits areas that consist of dense and continuous forests, in particular woodlands that are able to provide these squirrels with produce that can be cached and subsequently consumed; through the winter (Oak and Hickory). Additionally, these critters are commonly found in parkland areas, situated in suburban and even urban landscapes (Lawnizak, 2002). Eastern grey squirrels reside in two kinds of structures; in the winter they live in dens—holes constructed in large trees, these structures are often used as brood chambers by females. The second structure squirrels may dwell in are; nests—densely packed collection of sticks and leaves, often situated atop high-rise trees. The eastern grey is a very adaptable species and as a result; it is able to survive and prosper in an extensive number of habitats (The Pennsylvania State University, 2002).
Size/Weight and Lifespan:
According to Koprowski (1994) the eastern grey squirrel ranges from 380 to 525 mm in total length, with their tails measuring about 150 to 250 mm in length. Depending on their respective size; these squirrels have a mass of about 300 to 710 g. On the high end, these squirrels have a life span of about 12 and half years in the wild, this life span, depends on the abundance of food, the prevalence of disease/parasite and the severity of the climate (Lawnsizak, 2002) . In captivity, where the aforementioned variables are desirably controlled, the eastern grey squirrel experiences great longevity, living for about 23 and a half years (Lawnsizak, 2002).
The eastern grey squirrel can be described as an omnivorous opportunist, which is what allows it to thrive in a plethora of environments and thus enables it to exist as an invasive species (Thompson & Thompson, 1980). As the seasons change and the type of food that is available changes, so does the eastern grey squirrel’s diet, consequently, it is able to thrive on whatever fauna and flora its habitat has to offer (Bosak, Moore, Masino & Klein, 2013). In the spring time; the squirrel will feed primarily on the buds of trees and tree flowers, in the summer it will feed on wild fruit, mushrooms, seeds and nuts. When the aforementioned sources of food are not abundantly available, these squirrels resort to feeding on insects, smaller rodents, smaller birds, bird eggs and frogs (The Pennsylvania State University, 2002). In the fall time; the eastern grey squirrel eats hard nuts like, acorns, walnuts and beech nuts, the organism will also begin to cache these nuts for the winter—in which the abundance and availability of food becomes scarce (Bosak et al., 2013).
Communication and Reproduction:
The eastern grey squirrel uses vocalizations and postures to communicate with one another, these tactics are especially intensified and utilized in the mating seasons, when communication is of paramount importance (Lawniczak, 2002). Furthermore, the squirrels use their strong sense of smell to detect physiological changes in other squirrels, males often use this tactic to find estrous and receptive females (Koprowski, 1992). Koprowski’s (1994) study found that the eastern grey squirrel practices polygynandry—where multiple males have relationships with multiple females, as many as 34 males can be be attracted to a single estrous female. According to Koprowski (1992) males choose between two strategies when attempting to find a mate: satellite or active pursuit. Satellite males disperse themselves around estrous females. Active pursuit males defend close proximity to estrous females, though both strategies have their benefits, the latter of the two tactics is generally more successful (Koprowski, 1992). Moreover, males reach sexual maturity at around 11 months of age and females reach sexual maturity at around 5 and half months to 1 year of age. Breeding season occurs twice a year, from December to February and also from May to June. Therefore, females may bear young two times in a given year, with each litter consisting of 2 to 4 juveniles (Barkalow & Soots, 1975).
Due to its relatively small size, the eastern grey squirrel is a desirable prey for a multitude of larger species. These species include but are not limited to; grey wolves, red foxes, coyotes, skunks, weasels, bobcats and owls (Lima & Valone, 1986). When the eastern grey squirrels sense predators in close proximity, they often use vocalizations to warn other squirrels in the area of the imminent threat (Lima & Valone, 1986). In addition to the aforementioned cooperative behaviour, eastern grey squirrels are able to use their great burrowing ability, agility in trees and shear speed to evade their larger and slower predators (Lima & Valone, 1986).
Taking into account that the eastern grey squirrel is relatively populous in North America and exists as an invasive species elsewhere, it is currently regarded as “Least concern” according to “The IUCN Red List of Threatened Species”—meaning that the species of interest is not threatened and populations are stable (IUNC, 2016).
Did you know?
Since the eastern grey squirrel’s primary predators owls and hawks, the species actually has its eyes angled slightly upward, this is thought to have evolved to help the organism watch out for any avian predators in close proximity (The Pennsylvania State University, 2002).
Barkalow, F.S. & Soots, R.F. (1975). Life span and reproductive longevity of the gray squirrel, Sciurus c. carolinesis Gmelin. Journal of Mammalogy. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/1141781?dopt
Bosak, L., Moore, A., Masino, C., & Klein, A. (2013). Foraging and feeding behavior of the Eastern Squirrel (Sciurus Carolinensis). Journal of Applied Ecology. Retrieved from http://www.life.umd.edu/classroom/bsci338m/MdMammalogy/Bosak_et_al_2013.pdf
Gurnell, J., Wauters, L.A., Lurz, P.W., & Tosi, G. (2004). Alien species and interspecific competition: effects of introduced eastern grey squirrels on red squirrel population dynamics. Journal of Animal Ecology. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2656.2004.00791.x/full
IUNC, (2016). The IUNC Red List of Threatened Species. International Union for Conservation of Nature and Natural Resources. Retrieved from http://www.iucnredlist.org/details/42462/0
Koprowski, J.L. (1992). Alternative reproductive tactics in male eastern grey squirrels: “making the best of a bad job”. Behavioral Ecology. Retrieved from http://beheco.oxfordjournals.org/content/4/2/165.short
Koprowski, J.L. (1994). Sciurus caronlinesis. Mammalian Species 480: 1-9. The American Society of Mammalogists. Retrieved from http://www.science.smith.edu/msi/pdf/i0076-3519-480-01-0001.pdf
Lawniczak, M.K. (2002). Sciurus carolinensis. Animal Diversity Web. Retrieved from http://animaldiversity.org/accounts/Sciurus_carolinensis/#c901aaf88eddc5c36c8c6803a2b0cfad
Lima, S.L., & Valone, T.J. (1986). Influencie of predation risk on diet section: a simple example in the grey squirrel. Animal Behavior. 34 (2). Retrieved from http://www.sciencedirect.com/science/article/pii/S0003347286801221
The Pennsylvania State University, (2002). Eastern Gray Squirrel. Virtual Nature Trail at Penn State New Kingston. Retrieved from http://www.psu.edu/dept/nkbiology/naturetrail/speciespages/graysquirrel.htm
Thompson, D.C., & Thompson P.S., (1980). Food habits and caching behavior of urban grey squirrels. Canadian Journal of Zoology. 58. Retrieved from http://www.nrcresearchpress.com/doi/pdf/10.1139/z80-101
Scientific and Common Name(s):
The common name attributed to the animal in the pictures provided is the “Eastern Grey Squirrel” and the scientific name is Sciurus carolinensis. This animal belongs to the Rodentia order and is further classified into the Sciurus family (Cassola 2016).
Habitat and Geographic Range:
The Eastern Grey Squirrel is mostly found in large hardwood or mixed forests (usually greater than 40 hectares of land) and also in urban and suburban areas (Lawniczak 2002). The squirrels prefer more mature deciduous and mixed forests because of the abundant diversity of mast (like acorns and hickory nuts) and conversely a more mature forest is better capable of providing for a denser population of squirrels. They also inhabit city parks and floodplains and are usually within small distances of water sources (Cassola 2016). The Sciurus carolinensis are believed to have originated from North America and they generally inhabit regions in the USA stretching from Eastern United States to just West of the Mississippi River and slightly North into Canada. Introduction of this species has been discovered in more Western regions of USA and other non-native regions of Canada as well as in Italy, England, Scotland and Ireland (Lawniczak 2002). They are also quite disruptive to the native red squirrel populations in England, Wales, Scotland and Ireland (Morris 1997).
Size /Weight and Lifespan:
The Eastern Grey Squirrels are considered mid-sized tree squirrels relative to their closely related ancestors, and range anywhere from 380-525mm in length, and a good portion of their size is contributed by the length of their tails which generally range from 150-250mm in length. They can weigh anywhere from 338-750g but the average mass is 540.33g. In general the average lifespan trends show that in the wild these squirrels have a life expectancy of approximately 12.5 years and in captivity they can live to be more than 20 years old (Lawniczak 2002).
The Sciurus carolinensis is an omnivorous species and they feast on a vast variety of nuts and plants and are also known to consume other small mammals. In terms of vegetation they feed on nuts, seeds, flowers, buds and certain crop and this consists of the majority of their diet. There have been reports of cannibalistic behavior and they are often spotted ingesting the carcasses of other animals, bird eggs and even frogs (Lawniczak 2002). Since their diet is so heavily un-restricted, they generally do not have many issues foraging for food. These squirrels are considered Scatterhoarders, which means that they bury their nuts and acorns in the Fall for later consumption in the Winter and Spring (this is the very stereotypical quality that we often see portrayed in cartoons and the likes) (Cassola 2016).
Reproduction and Communication:
The female squirrels are capable of bearing children as young as 5.5 months of age and in general they are fertile for more than 8 years of their lives. The female vagina is closed in anestrous and pubescent females but during estrous phases (which last around 8 hours) their vagina will allow penetration and their vulva turn pink. The breeding seasons for these squirrels are quite seasonal and tend to occur during two distinct periods between December and February and also May through June. Approximately five days before estrus in the female, males can identify that there is a female available for reproduction and will actively seek her out (they can identify her from distances up to 500m). Copulation lasts for less than 30 seconds and the male mounts the female dorsally, and it is also possible and even likely that the female will have multiple mating partners (Koprowski 1994). On average they produce about 3 offspring and are capable of giving birth of up to 8 babies, and the average time for gestation (being carried in the womb) is 44 days followed by a 3 week interval of weaning. Sciurus carolinensis are known to communicate with one another through a variety of vocalizations and also physical gestures like tail flicking and are also known to warn fellow species of the presence of potential predators. They also have a very keen sense of smell which comes in handy when trying to determine the stress levels of neighboring animals (determine whether they are a threat or not) and they can also smell whether any nearby females are ready for reproduction (Lawniczak 2002).
Eastern Grey Squirrels are subject to predation by a wide host of predators including weasels, red foxes, bobcats, lynxes, coyotes, and birds of prey like the eagles and the red-tailed hawk. They are however extremely agile creatures and trees provide excellent cover from most predators (Lawniczak 2002).
Sciurus carolinensis is not an endangered species and they also occur naturally in a number of protected areas (Cassola 2016).
The Eastern Grey Squirrels are actually quite cunning and intelligent creatures; they are often wary of on looking animals trying to steal their stashed food and so they will create bogus food burial spots (these sites do not actually contain food) in the hopes of tricking potential thieves. Also there tend to be more black Eastern Grey Squirrels in Northern regions (like Canada) because apparently black furred squirrels have 18% less heat loss in colder climates and a lower baseline metabolic rate.
Eastern grey squirrel
Habitat & Geographic Range:
Eastern grey squirrels are native to North America, specifically southeastern Canada and the eastern and mid-western United States (Lioy, Mori, Wauters, & Bertolino, 2016). This species of tree squirrel commonly lives in highly wooded areas, although some may be found in cities. In general, their populations are the densest in areas that include nut-producing trees, such as oaks, since nuts are easily stored for the winter (Koprowski, 1994).
In the 1800s, grey squirrels were brought to Europe from North America, specifically to Britain, Ireland, and Italy (Lioy et al, 2016). The species was later introduced to both South Africa and Australia via Britain. However, the eastern grey squirrel became locally extinct in Australia by 1973 (Koprowski, 1994). These squirrels are considered an invasive species in Britain because they threaten native red squirrels, Sciurus vulgaris, through competition for resources. They are also a threat to regional plant life, as they are known to strip bark from trees in the UK (Nichols, Drewe, Gill, Goode, & Gregory, 2016).
Size & Lifespan:
The eastern grey squirrel is generally medium-sized relative to other species. Adults weigh between 400 and 720 grams and grow to be approximately 42 to 55 centimeters in length including their tails (Lioy et al., 2016). The life expectancy of a newborn grey squirrel is only one or two years. However, if they reach adulthood, their life expectancy increases to approximately six years. Eastern grey squirrels are known to live much longer, on average, in captivity than in the wild due to the absence of predators and fluctuations in food availability (Koprowski, 1994).
The diet of the eastern grey squirrel consists mostly of nuts, fruits, and seeds. They commonly consume both acorns and hazelnuts. These squirrels often eat fungi and berries to supplement their diet, while other items such as bird eggs, small invertebrates, tree bark, and lichen act as secondary food sources. Overall, their food consumption varies by season due to changes in availability, especially in the spring and summer when nuts from the previous autumn are more scarce. For example, lactating females have been known to gnaw on the bones and antlers of other animals as a source of calcium (Nichols et al., 2016). There is a peak in activity among these squirrels at feeding sites around midday and dominant squirrels tend to monopolize food sources by keeping smaller competitors away. Eastern grey squirrels compete for the same food sources with other small animals, such as corvids (Jayne, Lea, & Leaver, 2015).
Reproduction & Communication:
Little or no sexual dimorphism exists between male and female grey squirrels in terms of size and colour. Most females are not able reproduce until they are over a year old, while males reach sexual maturity at around 10 to 11 months old. Females tend to mate with several males and can reproduce for more than eight years after reaching sexual maturity. A hierarchy exists among males, with some viewed as more dominant than others (Koprowski, 1994). There are two annual breeding seasons in winter and summer, and population sizes fluctuate each year according to food availability and the cold temperatures in winter months (Nichols et al., 2016). Each litter consists of two or three young on average, but litter size decreases when food is scarce. Newborns do not have an fur and weigh between 13 and 18 grams (Koprowski, 1994).
Grey squirrels use several different vocalizations to communicate, which differ according to their purpose and context. While foraging, they may use alarm sounds and body language to warn others of predators. Squirrels also use cooing noises for communication between males and females during breeding, as well as between mothers and their young to show affection. The species has a number of other communication methods that involve both gestures, such as tail movements, and facial expressions (Koprowski, 1994).
Some of the main predators of the eastern grey squirrel include larger rodents, large birds such as hawks and owls, snakes, foxes, and domestic animals such as dogs (Jayne, Lea, & Leaver, 2015). Grey squirrels make up approximately five percent of the diet of timber rattlesnakes, which reside in the same region of North America (Pomento, Perry, Denton, Gibbs, & Holding, 2016). The risk associated with predators weighs heavily on decisions about foraging location and time span. Squirrels often participate in social foraging to reduce their vulnerability to predators. Although some individuals will choose areas that are more exposed to predators in order to avoid competition for resources, foraging in the company of others increases safety and is often seen as beneficial. Alarm behaviours include standing on the hind legs, waving of the tail, and barking (Jayne et al., 2015).
The eastern grey squirrel is listed as “Least Concern”, the lowest level of conservation. Grey squirrels are not currently threatened by extinction. On the contrary, populations are thought to be growing in number (Lioy et al., 2016).
Did You Know?
Eastern grey squirrels may be able to evolve a resistance to the venom of the western diamond rattlesnake, C. atrox, which is present in the southwestern regions of the squirrel’s native geographic range. Serum-based inhibitors resist hemorrhagic activity in the blood of the grey squirrel after they are exposed to the bite of a rattlesnake. This serves as a useful defense mechanism, as rattlesnakes are one of the main predators of the grey squirrel (Pomento et al., 2016).
Jayne, K., Lea, S. E. G., Leaver, L. A. (2015). Behavioural responses of Eastern grey squirrels, Sciurus
coralinensis, to cues of risk while foraging. Behavioural Processes, 116, 53-61.
Koprowski, J. L. (1994). Sciurus carolinensis. Mammalian Species, 480, 1-9. Retrieved from
Lioy, S., Mori, E., Wauters, L. A., Bertolino, S. (2016). Weight operated see-saw feeding hoppers are not
selective for red squirrels when greys are present. Mammalian Biology, 81, 365-371.
Nichols, C. P., Drewe, J. A., Gill, R., Goode, N., Gregory, N. (2016). A novel causal mechanism for grey
squirrel bark stripping: The calcium hypothesis. Forest Ecology and Management, 367, 12-20.
Pomento, A. M., Perry, B. W., Denton, R. D., Gibbs, H. L., Holding, M. L. (2016). No safety in the trees:
Local and species-level adaptation of an arboreal squirrel to the venom of sympatric
rattlesnakes. Toxicon, 118, 149-155. http://dx.doi.org/10.1016/j.toxicon.2016.05.003