Squirrels (Sciuridae)

Maurice Chen

Sciurus carolinensis. Photo credit to Maurice Chen.

Sciurus carolinensis. Photo credit to Maurice Chen.

I was walking through Madison Square Park earlier this week when I was stopped in my path by a rather outgoing bushy-tailed rodent. We stared at each other for several seconds, neither one of us willing to turn back down the road we traveled. After a short time time, I decided to circle around and continue along my path, the whole time being barraged with disgruntled chittering noises as I didn't pay the proper toll in nuts or whatever food I had on me. Because of my encounter, I decided that this month we honor the squirrelly members of the Sciuridae famly.

There are 286 known species within the Sciuridae family (Waldheim 1817) which can be further categorized into three groups. They are tree squirrels, ground squirrels, and flying squirrels.(Bradford 2014) The squirrels that we most commonly see in New York City are the tree squirrels, Sciurus carolinensis, or Eastern Gray Squirrels. Squirrels can be found throughout the world except in Australia. Squirrels primarily eat non-cellulose plant matter, such as seeds, fruits, and conifer cones, however they are also known to eat fungi and occasionally insects (Thorington & Ferrel 2006).

If you decide to enjoy your lunch in Madison Square Park, don’t be surprised if a squirrel casually walks up to you and patiently waits for a portion of your meal. It’s not uncommon to see squirrels in Madison Square Park perched on benches sharing french fries with a recent Shake Shack customer. However, you might notice that there is a particularly high population of squirrels running around compared to most years. This is the result of the 2016 mast year. A mast year is a period where oaks produce a much higher volume of acorns. Oaks can yield up to 10 times the amount they produce in an average year. Scientists hypothesize that masting developed as a way to guarantee propagation in the presence of high predation (Savage 2016). If acorns are produced in high quantities during certain years, some of the acorns will survive unscathed since the level of predators cannot consume the excess amount. This concept is called predator satiation. Mast years seem to occur irregularly and predicting when they might occur have eluded the best scientists. What makes squirrels special is that they can somehow predict when a mast year is about to occur and will also change their mating behaviors accordingly (Boutin et al. 2006). Before a mast year, female squirrels will produce a second litter of offspring since food sources will be plentiful in the upcoming mast. This allows squirrel to have an advantage over many of the other organisms that forage acorns.

Squirrels play an important role in genetic composition of oak forests due to their foraging behaviors. Squirrels are more likely to bury, or “cache” acorns from red oaks while immediately eating acorns from white oaks. Red oak acorns tend to have a higher fat content and will last the winter before germinating in the spring. White oak acorns tend to germinate soon after falling from their parent tree and are sweeter, thus making them more ideal for immediate consumption. Squirrels will therefore cache red oak acorns up to 150 feet away from its parent tree resulting in expansive red oak forests with tight clusters of white oaks (Line 1999).

While acorns are the preferred food source for storing for the winter, squirrels will resort to other sources when acorn yields are low. Interestingly, squirrels will actually harvest fungi and dry them out into a jerky (Bittel 2014). Squirrels will also tap maple trees for their sap, eating the sugary syrup once the water content has evaporated (Roach 2005).

References

Bittel, J. 2014. 5 surprising facts about squirrels (hint: they make jerky). National Geographic

Boutin, S., L.A. Waters, A.G. McAdam, M. M. Humphries, G. Tosi & A. A. Dhondt. 2006. Anticipatory reproduction and population growth in seed predators. Science 314: 1928-1930

Bradford, A. 2014. Squirrels: diet, habits & other facts. Live Science

Line, L. 1999. When nature goes nuts: an astonishing array of animals is linked in some surprising ways to the mighty oak and its bounty. National Wildlife Federation

Roach, J. 2005. No nuts, no problem: squirrels harvest maple syrup. National Geographic

Savage, J. 2016. When is a tree smarter than a squirrel? Society for the Protection of New Hampshire Forests

Thorington, R. W. & K. Ferrell. 2006. Squirrels: the animal answer guide. John Hopkins University Press 75

Waldheim, F. 1817. Scuridae. Integrated Taxonomic Information System