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Feeding Habits of The Eastern Grey Squirrel in Urban and Forest Habitats

Squirrels are one of the most recognizable animals in Canada. According to The Natural History of Squirrels (Gurnell 1987), three different types of squirrels exist: flying, ground-dwelling and tree squirrels. They all evolved from a common ancestor living in North America during the Eocene epoch (54 to 57 Million years ago), and then spread out, colonizing other areas and evolving into a wide varieties of species.

In taxonomy, squirrels belong to the rodent (rodentia) order, inside the bigger mammalian group. One of the diverse rodent family is the Sciuridae family which contains the Sciurinae subfamily (as tree squirrels), which contains the Sciurus genus. This genus is then divided into twenty-eight species, S. carolinensis being one. The classification goes on, differentiating five subspecies of the S.carolinensis, also called Eastern grey squirrel (Lawniczak 2002).

Our attention will be focused on the Eastern Grey squirrel (Sciurus carolinensis), a medium sized tree squirrel species, that usually weights around 300-710g, found from the Gulf of Mexico to the southern parts of Quebec, and Ontario (Sandro 2008). This species can easily be observed in city parks and backyards, and is also found in wild deciduous forest at the Morgan arboretum.

Project

We are observing our study species at three site at the Morgan Arboretum (the experimental groups), and at one urban backyards located in Anjou (the control group). Grey squirrels make caches by carrying food in their mouth to a suitable location, sometimes digging in several places before selecting a site (Hopewell and Leaver 2008). However, proximity with humans (by deforestation and urbanization) sometimes denatures these foraging behaviors to such a point that some squirrels are now living in towns, and feeding on human garbage (Bowers and Breland 1996). The goal of our project is to try to analyze to some extent the impact of human activity on squirrels.

Figure 1. Squirrels found in a rural area (left) and an urban area (right).

Research Question

In the arboretum, the squirrels mainly have access to nuts like acorns, samaras and hickory nuts. Whereas the urban squirrels have access to diverse food choices, and do not have to cache as much food as wild squirrels considering that they can rely on garbage and bird feeders during winter (Thompson and Thompson 1980). We wanted to compare the different feeding behavior between wild and urban squirrels. We placed two feeders in three different locations in the Morgan arboretum and in one location in an urban backyard. Considering that acorns are a big part of the wild squirrel nutrition in the arboretum, if a new type of nut is introduced in the arboretum (the peanut), which the wild squirrels usually do not have access to in Québec, what type of nuts, the foreign (peanuts) or the native (acorns), will the wild squirrel choose compared to the urban one? This is relevant because, human activity such as the introduction of open garbage bins in cities could have possibly altered the foraging behavior of the eastern grey squirrel. Our research question is then: Does the feeding habit of Sciurus carolinensis differ between an urban and forest habitat?

 Methods and Materials

To construct the squirrel feeders, we first cut off the bottom of a clean two liter soda bottle. Two holes were then cut on the side of the initial hole to allow the squirrels to take the nuts. The bottle was then glued to a plastic plate; the plastic plate had three holes at each end to allow water to drain when it rained. A wire was attaches to the top of the bottle, around the cap, to allow the feeder to hang in the tree.

3Figure 2. An example of a feeder.

In the Morgan Arboretum we located three different environments (sugar maple forest, beech forest and mix beech forest) where two feeders were placed in each environment; one with peanuts and the other, acorns. To place the feeders in a tree we used a pulley system. To a 10m long rope was attached a counterweight that we threw over the shortest and most accessible branch on a designated tree. Once a feeder was full with either acorns or peanuts, we attached it to the end of a wire that was in turn attached to the 10m rope, and pulled the feeder close to the branch, about 3 to 4 m high, so that it was not easily accessible to other animals. The loose end of the wire was then wrapped and tied around a nearby tree so that the feeder was secure. To check the feeders, the rope was untied and the feeders were slowly let down, as to not let any nuts fall off. Once the recordings were done and the squirrel feeder refilled, it was pulled back up into to tree. Each feeder was checked 3 times a week by members of the group. The weight of the nuts that were left over in the feeders was recorded, as well as the new weight of the nuts used to refill the feeder. Each feeder originally had the same amount of nuts at the beginning of the experiment. The feeders were all refilled based on the amount of nuts gone from the last reading.

Team members carried observational analysis, sitting far enough from the feeders as to not disturb or scare the squirrel’s, but close enough to record their activity. The observation was completed in periods of two and a half hours, with teammates rotating between feeders at the Arboretum. The objective of this watch is to not only record squirrel activity, but to ensure that squirrels are in fact the ones foraging in the placed feeders, and not other species of animals.

Expected Results

Considering that the wild squirrel are used to the acorn that they can naturally find in the Arboretum we expect them to feed more on the acorn feeders than on the foreign peanuts. Furthermore, we expect to see a higher selection for the foreign peanuts in the urban control, than at the experimental sites of the Morgan Arboretum.

 

References

Bowers MA, Breland B. 1996. Foraging of Gray Squirrels on an Urban-Rural Gradient: Use of the Gud to Assess Anthropogenic Impact. Ecological Applications. [Accessed 2016 October 27]; 6:1135–1142. http://onlinelibrary.wiley.com.proxy3.library.mcgill.ca/doi/10.2307/2269597/abstract. doi: 10.2307/2269597

Gurnell J. 1987. The natural history of squirrels. New York, N.Y: Facts on File. 201 p.

Hopewell LJ, Leaver LA. 2008. Evidence of Social Influences on Cache-Making by Grey Squirrels ( Sciurus carolinensis ). Ethology. [Accessed 2016 October 26]; 114:1061–1068. http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2008.01554.x/abstract. doi: 10.1111/j.1439-0310.2008.01554.x

Lawniczak, M. 2002. Sciurus carolinensis. Animal Diversity Web. [Accessed October 27 2016]. http://animaldiversity.org/accounts/Sciurus_carolinensis/

Morgan arboretum [Internet]. [Updated 2013 November 15; Accessed 2016, October 26]. http://www.morganarboretum.org/nature-en/mammals.html

Sandro B. 2008. Introduction of the American grey squirrel (Sciurus carolinensis) in Europe: a case study in biological invasion. Current science. [Accessed 2016 October 26]; 95(7): 903-906. https://www.researchgate.net/publication/242084905_Introduction_of_the_American_grey_squirrel_Sciurus_carolinensis_in_Europe_A_case_study_in_biological_invasion

Thompson DC, Thompson PS. 1980. Food habits and caching behavior of urban grey squirrels. Canadian Journal of Zoology. [Accessed 2016 October 26]; 58:701-710. http://www.nrcresearchpress.com/doi/abs/10.1139/z80-101#.WBKijpPhDox. doi: 10.1139/z80-101

 

 

 

 

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2 comments on “Feeding Habits of The Eastern Grey Squirrel in Urban and Forest Habitats

  1. I’ll be excited to see what your research shows! I’m a fan of squirrels and think this is an interesting research project.
    A squirrel question for you: A friend of of mine, who, like me, is from an area further south of here, remarked that melanistic gray squirrels seem to be more common further north. We both agreed we never (or almost never) see black squirrels further south, but they are fairly common here. Do you have any idea why? Could coat color be related to temperature? I know there are some documented cases of rabbits developing black paws/ears in colder areas, while staying white in warmer areas. Could this be a similar idea?

    • Hi M. Harris, thanks for sharing your enthousiasm! We are still working on our results but we will upload them soon on our blog…
      You are right, melanistic gray squirrels seem to be absent in the southern regions. This color is indeed caused by a genetic mutation (a deletion of 24base pairs on the MCR 1 gene). Compared to eastern gray squirrels with grey coat, black squirrels are homozygous or another allele according to The Genetic Basis of Melanism in the Gray Squirrel (Sciurus carolinensis) (Helen McRobie et al. 2009). About their geographic distribution, we could indeed think of this allele as a temperature sensistive-allele expressing under particular environmental conditions (low temperatures), as for the Himalayan rabbit. This is still a question of research to scientists. However, recent researches have shown that, at some point, black squirrels are more resistant to cold temperatures. We could think that through time, being better fit to a range of habitat (northern regions) and the occurrence of natural selection (maybe black color is a lot less advantageous in southern regions), are the causes of such a pattern distribution.

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