Squirrel Observations for the Fall 1999 Semester

Dan Campbell
Pat Hoban
Ecology 408

The eastern gray squirrel Sciurus caroliensis is found throughout the eastern U.S., ranging from northern Canada all the way down to Florida, and extending west where the deciduous forests meet the grasslands. Grey squirrels most commonly occur in two color phases, gray and black, which often leads people to think that there are two different species. Fortunately, the black coloration is most commonly found toward the northern limits of the species’ range, and the in the United States the black phase is less common or not found at all.

The most notable physical appearance of the gray squirrel is the large bushy tail, which is quite fitting since the Latin definition is derived from the Greek words skia, meaning shadow, and oura, meaning tail. The tail itself is an integral part of the animal, acting as a rudder when the animal jumps from high places, as a warm covering during the winter, and as a signal to others in order to indicate an individual’s mood. Finally, the tail can be used to distract a pursuing predator, and if necessary the squirrel can loose its tail sheath and some vertebrae in order to escape a predator’s grasp.

In natural conditions the gray squirrel can live to 7 or 8 years of age and tend to be larger in the northern part of their range than in the southern, most likely a result of the weather conditions that they are exposed to. They have both a summer and winter coat, and therefore molt twice a year. The spring molt begins in March when temperatures start to increase, while the autumn molt begins in September. It is interesting to note that the tail only molts once a year in July.

Eastern gray squirrels have a highly adapted sense of sight, even in dim light, as well as a wide field of vision. This trait, along with their tough curved claws and the ability to reverse their hind foot 180 degrees (to permit headfirst descent) makes them highly adapted for climbing trees. They are excellent climbers and can leap considerable distances using their powerful hindlimbs.

The gray squirrel spends most of its life in trees, where it is able to move about with great agility. They are active year round, predominantly during the daytime but can also be seen foraging at night. In summer, activity is greatest early in the morning and in mid-afternoon. During the winter, their activity peaks around midday, most likely to take advantage of the warmest temperatures. Peak hours are 2 hours after sunrise and 2-5 hours before sunset.

Grey squirrels are non-territorial, with overlapping home ranges that average in size of 5 hectares. Here the animal does most of it’s foraging for food, makes it’s nest, and rears its young. Due to an increase in their range during the breeding season, males have a slightly larger range than females, but there is little territorial behavior and many home ranges overlap. Although individual squirrels are often seen feeding close to each other without any aggressive activity, their acceptance of others is dependent upon food supply and squirrel population density. These densities are highest in habitats composed of tree species that produce foods suitable for storing over winter such as oak, hickory, and walnut. Due to variability in seed production on different years, a diversity of nut trees is important to support high densities. Our studies show that food density is the most important determining factor in squirrel population, with areas of high food availability (i.e.- around the dorms of Bellarmine’s campus) rating the highest.

Squirrels are generalist feeders, with eighteen plant species accounting for 87% of their diet. This ability allows them to live in a wide variety of habitats. Their diet includes (but is not limited to) nuts, flowers, and buds of 24 oak species, and 10 species of walnut, hickory, and pecan. Other foods include the fruits, seeds, or flowers of maples, mulberry, hackberry, elms, buckeyes, horse chestnuts, wild cherries, dogwoods, hawthorne, hazelnut and ginkgo. Pine tree seeds and pollen cones are readily eaten including cedar, hemlock, pines, and spruce. Food consumption peaks in summer and decreases in winter, with autumn rates of food consumption exceeding energetic needs by 32% so that the animals can increase their weight before the onset of winter.

Objective:
The objective of this project was to observe squirrel activity and determine if time of day as well as human population has any effect on squirrel behavior. These two determinants were also included in observations to determine the factors responsible for territory. Basically we wanted to see whether human contact affected squirrel behavior, and squirrel territory. Other things we were interested in seeing was how food supply affected territory size, and if this also had anything to do with the type of area as well.

Procedure:
The sites of observation included a suburban back yard, areas in both Seneca Park and Beargrass Creek, as well as on Bellarmine’s campus around the dorms. Hours were divided into several time periods, including from 8-12, 12-3, 3-5, and after 5 o’clock. Basically the squirrels were observed during these time periods over a two-month period at least once or twice a week. Also food was offered to the squirrels several times during observations to see if they would respond. Squirrel counts were taken to compare, as was a synopsis of food sources and tree density.

Suburban observations:
While squirrel density was moderate, consisting of roughly seven to ten individual squirrels the activity of each remained quite high, particularly in the morning hours when activity peaked. The squirrels had a variety of food sources to choose from, including open trash cans, sugar maple, pine, and (the most popular) a large walnut tree. Activity included chasing other squirrels, breaking open nuts and chattering at humans or other nearby animals.

Campus observations:
This site was chosen because there is both human contact within the site as well as numerous trees and cover for the squirrels to inhabit. This particular site had by far the most activity on the ground and in the trees, and the number of squirrels seen throughout the day almost doubled that of any other site. Close contact with humans was seen frequently and food that was offered was often taken several yards away from the observation point.

Seneca observations:
In the park, morning activity was the norm, with two to four squirrels foraging in the site between the hours of 8 and 12. After noon, the squirrel activity slowed down, and remained mostly in the trees at this point. When returning later in the evening, it was often difficult to find any activity at all, and was non-existent after 8 at night.

Beargrass observations:
This site was located across from Bellarmine College, yet far enough away so that very few humans disrupted observations. The squirrels in this area were spread out and harder to find, but nests were observed within the trees after the leaves fell. While the telltale clumps of hanging leaves showed us that the squirrel population was there, it was seldom that more than two squirrels were observed at one time. There was no squirrel/human interaction even when food was offered, and many times upon return the food would still be present.

Conclusions (Activity Hours):
Plotting the activity of the squirrels throughout the day, in could be seen that the most activity occurring in all of the areas was between the hours of 8 and 12 in the morning. This time was followed by the hours of 3 and 5, and the noon to 3 segment filled in the third position. The least amount of activity occurred after the hour of 6 (or around sunset). This was interesting because even though squirrels according to our research were shown to have adapted eyes they did not move around at night. We felt this was due to predators hunting at night like owls, possums, and house pets.

Conclusions (Human Contact):
Judging by the information collected, the ability to withstand human contact seems to be an acquired trait. The areas in which the squirrels accepted food from humans (Bellarmine’s dorms and the suburban site) were areas where humans had resided for quite some time, suggesting that these squirrels had lost their fear of humans due to their close living quarters.

Conclusions (Home Range):
Our results show that territory size is directly related to the amount of food available within the given space. The greatest number of squirrels were found at Bellarmine’s dorms, which had the greatest source of both manmade food as well as the most nut producing trees.

Final Conclusion
Our final conclusion was that we found answers to all of our questions. However we felt that research on why squirrels do not like the night could be done. Also a GIS on the movement of squirrels, an accurate count of squirrels in each area by marking, and a nest count could have better backed up our data