Squirrels are mammals that belong to the Sciuridae family, which is included in order Rodentia (rodent) (Macdonald 2009). They are among the most common and widespread mammals and are found in almost all regions of the world, excluding the arctic, Madagascar and desert areas. These large-eyed, bushy-tailed, diurnal (active during the daytime) animals are relatively unspecialised, instantly recognisable and can often be quite clever (Macdonald 2009). Tree squirrels always descend tree trunks head first, digging their sharp claws into the bark like an anchor (Macdonald 2009). As they are generally perceived as attractive or “cute” animals, most people do not consider them pests like other rodents. For example, their distinctive way of feeding by squatting on their haunches and holding food in their forepaws can be considered very amusing.
Popular conceptions have led many to believe that squirrels hibernate. However, most species, including the ones found in the Morgan Arboretum, stay alert during the winter and rely on the nuts they have stored in the autumn (Macdonald 2009). Shockingly, a single squirrel can bury several hundred nuts every year. Individuals can smell nuts buried as deep as thirty centimeters, but many are never found which results in inadvertent tree seed dispersal (Steele & Al. 2006). Instead of hibernating like many other mammals, they must exit their nests to dig up the nuts they have stored in the previous months. Tree squirrels cannot spend more than two days inside their nest without having to exit and forage in the cold (Macdonald 2009).
Eastern grey squirrels (Sciurus carolinensis) and red squirrels (Tamiasciurus hudsonicus) are the two species of rodents found in the Morgan Arboretum of McGill that construct perched tree nests, also known as dreys (McGill Arboretum 2013). Spherical shaped dreys are constructed with small branches, twigs and grass, and are insulated with dry grass, moss and fur (Macdonald 2009). The number of dreys is a good indicator of the abundance of squirrels, but grey and red squirrels have very similar nest building strategies (Don 1985). This makes it nearly impossible to differentiate to which species a drey belongs (Gurnell et al. 2004). Red squirrels tend to prefer coniferous forests since they prefer to feed on pine cones over the fruits of maple, oak and hazel trees that make up the majority of the grey squirrel diet (Riege 1991). These nests allow the squirrels to function at a very low metabolism during most of the winter (Reynolds 2008) and are so well insulated that temperatures inside are usually around twenty degrees celsius higher than the outside temperature (Macdonald 2009).
Is there a relationship between squirrel nest abundance in the Morgan Arboretum and the forest types and tree species they are found in?
To test our research question, we sampled within seven 75×75 meter plots in the Morgan Arboretum. We tried to sample a variety of forest types, such as maple-dominated forest, beech-dominated forest, and coniferous forest. To create our sampling area, first a tree in the type of forest we wanted to test was marked with a piece of flagging tape. Two lines forming a right angle from this tree were then made, using two people walking 75 meters from the tree and marking a tree at the end of their lines with flagging tape. They then each turned 90 degrees towards each other and walked another 75 meters, marking the point they meet with flagging tape to make the final corner of the square. We then recorded the GPS location and forest type of the site.
The research group would then walk around the perimeter of the square, stopping every time a squirrel nest was spotted to record the species of the tree and the diameter of the tree 1.5 meters from the ground. A picture was then taken of the nest, and the tree was marked with flagging tape to avoid counting the same trees more than once. This procedure was repeated until the entire perimeter of the plot had been surveyed. Finally, a diagonal cross section was made through the plot, walking from one corner to its opposite to record any nests that resided in the middle. A final walk through was then done to remove all flagging tape from the area.
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Gurnell, J., Lurz, P.W.W., Shirley, M.D.F., Cartmel, S., Garson, P.J.,Magris, L. and Steele, J. (2004). Monitoring red squirrels Sciurus vulgaris and grey squirrels Sciurus carolinensis in Britain. Mammal Review, Vol. 34, No. 1-2, pp.51-74. DOI: 10.1046/j.0305-1838.2003.00028.x. Retrieved from: http://onlinelibrary.wiley.com/doi/10.1046/j.0305-1838.2003.00028.x/full
Macdonald, D. (2009). Squirrels. In The encyclopedia of mammals (New ed., p. 151). Oxford: Oxford University Press.
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Steele, M. A., Manierre, S., Genna, T., Contreras, T. A., Smallwood, T. D. and Pereira M.E. (2006). The innate basis of food-hoarding decisions in grey squirrels: evidence for behavioural adaptations to the oaks. Animal Behavious, Vol. 71, No 1, pp.155-160. DOI: 10.1016/j.anbehav.2005.05.005. Retrieved from http://www.sciencedirect.com/science/article/pii/S0003347205003374