Introduction

Reviewing recorded observation from previous observations of Sciurus carolinensis, eastern gray squirrels, behavior, I had noticed that the squirrels were never seen grooming themselves on the ground. Other behaviors such as foraging, feeding, scanning the surrounding area occurred both on the ground and in trees. Grooming behaviors, however, had only been observed in trees. I was curious to know if squirrels do not engage in these behaviors on the ground or if I had simply not observed it yet. A literature search did not yield conclusive evidence on this specific topic, but I did discover an article finding success using YouTube videos to study squirrel behavior (Jagiello, Dyderski, & Dylewski, 2019). I decided to watch videos of squirrels grooming. After viewing numerous videos, I found no instances of wild squirrels grooming while on the ground. My goal is to watch gray squirrels grooming to see if they would only do it in trees which provide concealment and may be inaccessible to some predators. I assume that grooming behaviors are risky behaviors as they likely decrease the awareness of the squirrels and require the squirrel to be immobile. To mitigate the risk, it seems reasonable that they would only groom in areas that provide concealment or are otherwise comparatively safe S. carolinensis seems to already make attempts to reduce the chances predation in another risky behavior, foraging. (Lima, Valone, & Caraco, 1985) found that squirrels seem to weigh costs and benefits of where to consume foods based on travel time to cover and required handling time. A squirrel is more likely to carry food items requiring long handling times into a tree for processing than quick to handle items (Lima, Valone, & Caraco, 1985). Squirrels are also more likely carry all food items when distance to a tree was reduced (Lima, Valone, & Caraco, 1985). In my prior observations, grooming behaviors occurred up to several minutes at a time. For a behavior such as grooming that requires a squirrel to be stationary and is a considerable time investment, a squirrel should be more likely to perform this behavior in a place of lower predation risk. I hypothesize that squirrels will favor not engaging in risky grooming behaviors on the ground, therefore, most grooming observations will occur when squirrels are in trees.

Methods

Visual observations of S. carolinensis were made in small community park in Beaver, Pennsylvania. Several small patches of black walnut and maple trees as well as the surrounding area was selected as the observation site, as it contained at least six individuals and was easily observable without disturbing the squirrel. Best effort was made to not affect the squirrel's behaviors with human interference. Squirrels were observed on twelve occasions in the late afternoon between October 11 and December 1, 2019. Each observation lasted for 30 minutes in which a squirrel was observed and its behaviors (Table 1.) were recorded at one- minute intervals. Behaviors which persisted for more than one minute were recorded again for each interval in which they were observed. A focal sampling technique was employed as only single individuals were present on most occasions. During each observational period, an attempt to follow one squirrel was made. If this individual was no longer observable, another squirrel in the area was observed if possible.

The total number of each grooming behavior and the location of the squirrel while performing these actions was recorded to determine if squirrels would only engage in grooming when they are in the relative safety of a den or tree. Identification of specific grooming behaviors was done using visual depictions from (Steiner, 1973) as reference. Photographs and videos recordings were taken if possible when squirrels exhibited grooming behaviors.

After all observational data was collected, the total occurrences of each behavior were compiled and recorded in Table 2. A pie graph was used to display percentages of each recorded behavior for all observations. The total number of instances in which grooming behaviors were observed was compiled in Table 3. The total occurrences of grooming behaviors observed in trees versus on ground was compared and tested for significance.

Results

Results (Table 1., Figure 2.) show the number of behavior appearance per recorded interval. In most observations, the squirrels had been foraging or eating, and these two behaviors often occurred simultaneous. In instances when food items which took a considerable amount of time to process, such as opening walnut shells, squirrels would discontinue foraging and move into a tree to begin processing. There were no observations in which squirrels processed larger food items on the ground, whereas they did with easily processed foods such as maple seeds.

Different grooming behavior types were often performed together, but the total number of separate observations for grooming behavior was seven. Only self-grooming was observed (Table 2.), and grooming using the mouth (Figure 2., Figure 3., Figure 4) was observed in all seven instances. During all intervals of grooming behaviors observed (n = 38), squirrels only engaged in grooming behaviors while on tree branches.

Figure 4. Sciurus carolinensis grooming posterior and tail by nuzzling and chewing

Discussion

The breakdown of observed S. carolinensis behaviors (Table 2.) revealed that squirrels searched for or ate food in greater than 50% of the observation intervals. As observations were made in autumn when squirrels engaging in caching and building fat stores in anticipation of winter months (Smith & Reichman, 1984), many observations of foraging are expected. Another behavior with greater representation was grooming.

Grooming behaviors between two squirrels was a behavior that was looked for (Table 2.), but no occurrence of such behaviors was seen, and few direct interactions between squirrels were observed overall. As these behaviors were not seen at in either squirrels on the ground or in trees, they were not included in Table 3.

A total of seven unique observations of grooming behavior occurred, and in no cases did squirrels groom themselves on the ground. There seems be a clear preference by squirrels to groom in trees versus on the ground (p = 0.047) which supports the hypothesis. Squirrels behaviors are affected by risks involved with predation (Jayne, Lea, & Leaver, 2015). It is likely that squirrels can in some way evaluate the costs associated with possible predation while engaging in grooming behaviors and find grooming sessions to be too risky to do on open ground.

Squirrels would only groom in trees while being observed in my study, but I wonder if this is always true. In the location where my observations were made, there were ample trees within proximity to each other, meaning squirrels never needed to travel a great distance to retreat to one. Like how (Lima, Valone, & Caraco, 1985) saw that distance affected how likely a squirrel was to process larger food items in a tree compared to not, it is a possibility that this could be a factor in grooming behaviors as well. Squirrels in my study may have never groomed on the ground because a tree was always nearby. Perhaps if traveling a significant distance to tree was required, squirrels may instead choose to groom on the ground. This could be something to investigate in future studies.

Something to note about the recording of observed behaviors (Table 1.) is, ground traversal was recorded only when a squirrel was moving between two locations without any other behavior being apparent. The categories of ground traversal and non-ground traversal are not indicative of the actual amount of observed time squirrels spent in each location. Most of the squirrels' searching time was spent while on the ground rather than in trees.

A major limitation of this study would be the human element. While the was an attempt to avoid affecting the behavior of the squirrels during observation, there were some instance where my presence conspicuously attracted squirrel behavior which often caused them to run away. While proximity was necessary to observe the squirrels at the location used in this study, it may be beneficial for future observations to be conducted in areas where squirrels can be observed remotely perhaps using binoculars and higher fidelity cameras.

Another limitation would be the time when observations were made. All observations were made between late afternoon and early evening during only a 30-minute period. While no instances of grooming behaviors were observed by squirrels of the ground during these brief observation periods, it cannot be determined that squirrels would never do this. Increasing the observation periods or also making observations at different times of the day could lead to a better representation of how squirrels spend their time. It could be that squirrels' behaviors change based on time of day.

In conclusion, S. carolinensis does show a strong preference against grooming on open ground, first moving into a nearby tree before engaging in the behavior.

References

Jagiello, Z. A., Dyderski, M. K., & Dylewski, Ł. (2019). What can we learn about the behaviour of red and grey squirrels from YouTube? Ecological Informatics, 51, 52-60. doi:10.1016/j.ecoinf.2019.02.006

Jayne, K., Lea, S. E. G., & Leaver, L. A. (2015). Behavioural responses of eastern grey squirrels, sciurus carolinensis, to cues of risk while foraging. Behavioural Processes, 116, 53-61. doi:10.1016/j.beproc.2015.05.002

Lima, S. L., Valone, T. J., & Caraco, T. (1985). Foraging-efficiency-predation-risk trade-off in the grey squirrel. Animal Behaviour, 33(1), 155-165. doi:10.1016/S0003-3472(85)80129-9

Smith, C., & Reichman, O. (1984). The Evolution of Food Caching by Birds and Mammals. Annual Review of Ecology and Systematics, 15, 329-351. Retrieved from www.jstor.org/stable/2096952

Steiner, A. L. (1973). Self- and allo-grooming behavior in some ground squirrels (sciuridae), a descriptive study. Canadian Journal of Zoology, 51(2), 151-161. doi:10.1139/z73-023