Patterns in Squirrel Behavioral Ecology
Daily Activity Schedule of the Eastern Gray Squirrel (Sciurus carolinensis)
Andrew G. Watts
"Browntail", a gray squirrel from the UF campus
Photo by Andrew Watts
Abstract: The widely varied behaviors of gray squirrels (Sciurus carolinensis) make them an adequate research tool for the study of behavioral ecology. The main objectives in this study are to observe the behaviors of squirrels during different parts of the day, and how their behaviors vary with temperature. It is predicted that squirrels are least active during the afternoon, because it is the warmest part of the day. To test this hypothesis, 0/1 samplings were conducted for twelve 5-minute time intervals each hour for mornings, afternoons, and evenings. The results from the samplings show that squirrels indeed are less active in the afternoon when it is hotter. Additionally, squirrels rest much longer and more often in the afternoon than in the other parts of the day. In conclusion, squirrels generally avoid temperature extremes by resting.
Keywords: Sciurus, squirrels, activity, behavior, schedule, temperature, cold, heat
For a long time, the eastern gray squirrel (Sciurus carolinensis) has been an important research tool for the study of animal ecology (Spritzer 1999). Their genus name comes from Latin meaning "he who sits at the shadow of his tail" (Woods 1980). The gray squirrel is found in several habitats across the eastern United States, such as temperate forests, neighborhoods, city parks, and college campuses. Arboreality may be a primitive trait for squirrels (Thorington 1998). Over the past two centuries these mammals have been introduced to England, South Africa, parts of the western United States, and parts of Italy (Hartson 1999, Currado 1998).
Various factors determine the behavioral routines of squirrels. Metabolic constraints, weather, predators, competition, and food availability all play a part in the activity of squirrels. When it is hot or raining, squirrels may not be as active. However, Long (1995) states that squirrels may be more active during periods of light rain because the wet ground may bring out the scent of the stored food. When predators are in the area, squirrels will make a bark-like alarm call possibly to warn other squirrels. Intraspecific competition is common among the gray squirrel; therefore, chasing is frequent. To prepare for the possibility that food may be scarce in the future, squirrels are well known as hoarders of food.
The purpose of this experiment is to observe squirrel behavior by recording various activities at three different times of the day (morning, afternoon and evening). I hypothesize that gray squirrels will be more active in the morning than in the other parts of the day. One justification for this hypothesis is that the other parts of the day are warmer, causing squirrels to be less active. I also expect that the squirrels may exhibit different behaviors at different parts of the day. Since weather (excluding temperature) is indiscriminate to the time of day, it may influence the data. Temperature, however, is correlated with the time of the day, with the warmest part being the afternoon.
Similar studies on animal behavior have been conducted on California ground squirrels (Spermophilus beecheyi) (Fitch 1948). Additionally, studies on animal behavioral ecology comparable to my study have been conducted on Big Cypress fox squirrels (Sciurus niger avicennia) at the Big Cypress National Preserve in south Florida (Jodice 1990).
The study area for my experiment is located between McCarty Hall and the Reitz Union lawn on the campus of the University of Florida in Gainesville, FL. The area contains trees such as hackberry, palm, magnolia, pecan, oak, pine, and others. Gray squirrels are frequently encountered here, and are therefore easy to observe. The observations took place during March and April on Saturdays, Sundays, and other days when there was minimal human activity. The behavior of squirrels would be different if there are too many people moving through the study area.
The observations were recorded on twelve 5-minute intervals for a morning hour, an afternoon hour and an evening hour during each day of minimal human activity. A total of 13 morning hours, 13 evening hours, and 10 afternoon hours were sampled. I did 0/1 samplings of several squirrels on the following activities: foraging, chasing other squirrels, eating, standing alert, barking (alarm call), burying food, resting, running in trees (e.g. climbing), running on the ground, and miscellaneous activities. I also noted the weather at the time of the observations.
When squirrels forage, they are looking for food on the ground and on the trees, most often moving slowly and sniffing. Gray squirrels spend only 14% of their active time in the canopy of trees (Gurnell 1987). Chasing is aggressive behavior showing that gray squirrels exhibit intraspecific competition. Eating takes place both on the ground and on trees, the staple diet being acorns. Often squirrels will bury acorns and other food. When squirrels hear a sound that may be threatening, they stay still for a few seconds in an alert posture. Barking is also a result of a threatening sound, but it is mainly an alarm call used when squirrels see a predator. Resting may be confused with the alert stance, but it is much longer. In addition, resting squirrels are usually lying flat. Often squirrels will run in order to find food, avoid competition with other squirrels, or avoid predation. Running occurs both on the ground and in trees. Miscellaneous activities include (but are not limited to) jumping in an odd manner, playing with other squirrels, grooming, and pseudo-mating; most of which are done by juvenile squirrels. I compared the persistence of morning behaviors versus evening behaviors. Numbers were measured as mean time intervals per hour. A chi-square test was used to find out if occurrences of resting were inversely proportional to running on the ground.
There was considerable variation in the behavior of squirrels among different parts of the day. Figure 1 indicates that squirrels exhibit less activity during the afternoon than in other parts of the day. This holds true for all forms of activity. In addition, they rest most often in the afternoon (mean = 5.9 time intervals per hour) and least during the morning (mean = 0.46). Comparing between the morning and the evening, there was no considerable difference between occurrences of the alert stance (mean = 11.2), eating (mean = 10.5), foraging (mean = 11.3), or miscellaneous behaviors (mean = 4.6). All three activities where running was involved (chasing, running on the ground, and running in trees) showed a trend that was greatest in the morning (mean = 7.5, 10.4, and 9.9, respectively), intermediate in the evening (mean = 5.4, 9.8, and 8.5, respectively), and least in the afternoon (mean = 4.3, 6.8, and 5.8, respectively). Most running occurred on the ground. Figure 2 shows the relationship of squirrel behavior versus temperature. Regardless of the time of day, it is clear that there are hump-shaped trends in a majority of the activities for the following temperature ranges: cold (approximately < 13º C), mild (13-21º C), warm (21-29ºC), and hot (> 29º C). These activities are foraging (mean = 10.7, 12, 12, and 9.3, respectively), chasing (mean = 5.1, 6.7, 7, and 3.6, respectively), eating (mean = 8.6, 12, 11, and 8.3, respectively), alert stance (mean = 10.4, 11.7, 11.8, and 9.3, respectively), burying food (mean = 3.7, 7, 9.4, and 4.1, respectively), and running on the ground (mean = 8.4, 11.1, 11.4, and 7, respectively).
A chi-square test was conducted showing that the correlation between resting and running on the ground for the four temperature ranges is nearly opposite.
It was discovered that there is a strong correlation between the behavior of squirrels and the time of day. As predicted, most of the activity occurred during the morning and the evening, and least during the afternoon. This is most likely because the afternoon is the warmest part of the day, so it causes squirrels to rest longer and more often than they do in during mornings and evenings. The reason why squirrels rest during warm weather is because it too expensive energetically to forage when it is too warm (Gurnell 1987).
As it gets colder, squirrels seem to become increasingly active in the trees, but not on the ground. It is during intermediate temperatures when they are most active on the ground. An additional hypothesis is that squirrels might not get less active as it gets colder, but rather restrict their activity to the trees. If this is so, then the squirrels are most likely not avoiding the ground entirely, because they frequently uncover buried food items in the winter that they stored in the autumn. If it is not true that they restrict their activity in the trees when it is cold, then there may be possible sources of error influencing the data, such as rain or wind. These sources of error may have influenced the data supporting the original hypothesis as well.
In conclusion, it would appear that as squirrels get increasingly active on the ground, there would be less occurrences of resting. Mild weather is correlated with activity of squirrels on the ground, whereas hot weather causes squirrels to rest. Cold weather may also cause squirrels to rest, but the fact that resting was not observed as frequently as in hot weather does not mean it is less frequent. Gurnell (1987) states that squirrels will often huddle with one another in their nests (where they cannot be observed) during cold weather. This is another source of error. Although squirrels were observed to be slightly more active in cold weather than in hot weather, they generally tend to show decreased activity during both temperature extremes because it is energetically costly.
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Fig. 1. Mean number of time intervals per hour for different observed behaviors in the morning (n = 13 hours), afternoon (n = 10) and evening (n = 13).
Fig. 2. The relationship of squirrel behavior based on temperature. Cold weather is approximately 13ºC or below, mild weather is about 13-21ºC, warm weather is about 21-29ºC, and hot weather is over 29ºC.