What the Wild Squirrels Do: Ethogram of Sciurus carolinensis
Eric Falck Course: EEOB 440-Ethology 14 October 2009
Abstract:
An ethogram is provided of Sciurus carolinensis (Gmelin), termed eastern grey squirrel.
The eastern grey squirrel is a common arboreal rodent that is native the eastern and central
United States and southeastern Canada. All the data collected was in situ observations, mostly
located at Whetstone Park Clintonville, Ohio. Activities of subjects were collected with relation
to space, speed, direction, duration, and all notable environmental factors. Categories of
Foraging, Grooming, Social, and Movement and Postures emerged and suggested as major
components of behavior during the season of study, autumn. Each category was then broken
down into specific behaviors, usually 3-4 behaviors existed within each category, and patterns
emerged for individuals’ behavior. Patterns suggested a highly dynamic relationship with
environmental factors such as competition and predation. Comparative approaches to other
ethograms like this one may find more relationships of behaviors and the evolution of them.
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Introduction:
The eastern grey squirrel, Sciurus carolinensis (Gmelin), is a common species of the
rodent family sciuridae, native to eastern and central United States as well as to southeastern
Canada. There range is associated with their preference for hardwood/mixed forests, which
span their entire region, as well as their ability to prosper in suburban and urban areas.
Deciduous trees provide eastern grey squirrels with their favored foods, such as nuts, seeds,
buds and flowers. Grey squirrels may also consume eggs and nestlings of native birds within
their area (Reid, 2006). Grey squirrels have a moderate body size, 300-700g, usually reached by
nine months of age of their twelve-year lifespan. They have evolved a long, bushy tail for
balance as well as communication to other organisms, squirrels and predators alike. Their
coloration on their backs is dark grey/brown, which aids in blending into the darker ground
cover, and they have a lighter, whitish belly to blend into the lighter sky (Steele & Koprowski,
2001).
Grey squirrels have diurnal activity patterns and are most active around sunrise and
sunset (Gurnell, 1987). The have acute eyesight and a heightened sense of smell, but the
habituation to human activity makes grey squirrels easily observable within relatively close
distances (Steele & Koprowski, 2001; Cooper et al, 2008). Eastern grey squirrels noted to be
solitary but home ranges usually overlap, and group nesting is common. Notably though,
pregnant and lactating females are territorial to protect their altricial young; young are weaned
around 70 days of age (Steele & Koprowski, 2001).
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Environmental context also plays a role on behavioral repertoire, changing how much
food is being stored, what kinds of food, and how much time spent foraging is based on
competition as well as food availability (Hopewell et al, 2008 ). Also seasonally, activity
patterns as well as feeding patterns alter. The two breeding season generally starts in
December and May with good food conditions, and February or August if food sources are
unfavorable during the beginning of the season (Gurnell, 1987). Keeping a behavior inventory
is an important way to reflect on the changes in the environment. Altering environments,
temperature and declining favorable habitats for both predators and conspecifics, will affect
organisms whose plasticity in behavior reflects the biotic and abiotic factors in their
environment.
Methods:
Duration and Conditions- Observations started 4 October 2009 and ended 4 November
2009. I recorded a total of 7.183 hours of observations with average time per period being
47.89 minutes for the nine periods. The majority of the observation times occurred between
either 9:00-12:00 or 16:00-1900 though some observations took place during the 14:00-16:00.
The periods attempted to achieve a complete record of eastern grey squirrel behavior
throughout a day, but it was constrained by scheduling conflicts.
Before each period, the Weather Underground website provided temperatures, wind
speeds, and sky conditions documented (Weather Underground): average temperature for the
study was 11.44 ˚C, standard deviation ±3.20 ˚C; average wind speed was 9.39 kph, standard
deviation ± 5.19 kph; sky conditions described equally as clear, partially cloudy or overcast.
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Observation Areas and Techniques- Observations occurred at either Whetstone Park in
Clintonville Ohio (Figure 1) or at The Ohio State Campus (Figure 2). Whetstone Park
observations are broken down in Figure 1 into three distinct areas based on the type and
amount of vegetation present. Site A was a brushy area with wooded shrubs and moderate
cover. Site B was an open area with only grass and large deciduous hardwood trees spaced out
through the area. Site C, which was used less because of difficulties keeping visual contact, was
a densely forested area; the area is less trafficked. The site on the Ohio State University
campus was a moderately trafficked area with a couple medium-sized hardwoods and some
wooded shrubs.
Observations started at least 6.06 m away from subject individual and written in a small
notebook. However, movement of subject resulted in varying distances of observations ranging
from 1m to 10m. Observer noted squirrels awareness of the observer with behavior still
recognized as a potential predator or intruder. The subject remained the subject as long as the
observer never lost contact with the subject squirrel. To decide if subject was novel, the
observer made a best guess to decide to label the squirrel as a new or original subject when
visual contact disconnected briefly with multiple squirrels in the area.
Behaviors- Being aware of the season, projected plastic behaviors for squirrels relevant
for the autumn period was caching, building nests and courtship within two hours after sunrise
and two hours before sunset. Expected non-plastic behaviors that would occur at throughout
all seasons included walking, climbing, eating, grooming, and social behaviors (Grunal 1987).
After completion of the observations, patterns were determined significant by a chi-squared
test assuming a null hypothesis that there should be no difference in occurrences of a behavior.
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Results:
Ethogram- The list of behaviors consists of four main categories: Foraging, Grooming,
Social, and Movement and Postures. Figure 3 shows the time allocated during the observation
hours of each category, illustrating the importance of each category during the study period.
Each category is then broken down into a list of behaviors and definitions and descriptions are
defined (Table 1).
Foraging- The foraging category implies all behaviors relating to nutrition of the eastern
grey squirrel. For the autumn season, eastern grey squirrels exhibited three main behaviors:
Searching, Caching, and Eating. Searching was noted when an individual used their face or
hands against the surface of the ground and followed by acquiring food. Eating, the
consumption of food, was recorded when an individual chewed on the acquired food for a
length >30 seconds. Caching, defined as storing food, documentation occurred if an individual
cared around a piece of food and proceeded to bury in soil or leaf litter.
Grooming- The grooming category combines all of the behaviors documented by an
individual that gave attention to the maintenance of an individual. Observed behaviors include
Scratching, Rubbing, Gnawing, and Licking. Segregation of the behaviors resulted from either
the body part that the individual utilized. Scratching used the claws of either the anterior or
the posterior manus. Rubbing utilized the palms of the anterior manus and sliding them across
portions of the body. Gnawing came from the use of the individual’s incisors, but the use of the
tongue resulted in the notation of Licking.
Social- Social behaviors included any interaction between one individual and another,
inter- or intra- specific interactions. Chasing, by the subject, describes a rapid charge at
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another individual. Notably this only occurred once with an individual of a different species, an
unknown species of bird. Flight, movement away from a potential conflict, however, resulted
from both interspecific and intraspecific individuals. Tail Waving was recorded when the
subject’s tail would ungulate two or more times and recorded as either to a direct individual or
an ambiguous recipient. Vocalization, recorded with no direct relationship to a particular
individual because deciphering of the signaler proved futile, refers to different shrills made by
any individual within the area being observed.
Movement and Postures- Major types of locomotion and positions executed by subjects
compile into the movement and postures category even though they occurred during other
behaviors because they took place during multiple activities. The five types of movements
were consequences of the speed, directionality and location of movement that are more than
aptly described in Table 1; as well, the postures besides resting are represented in Figure 4.
Patterns- Three different statistically significant patterns occurred within the
documented behavior: Time of Day and Behavior Category Preferred (Figure 5), Foraging Area
and Time of Day (Figure 6), and Tail Waving in Relationship to Predators
The graph in Figure 5 shows the number of occurrences of a behavior category on the Yaxis dependent upon the time of day, x-axis. A simple chi-squared test assuming time of day
had no effect on the occurrence of a behavior resulted in a X2 value of 9.125 for 8:00-11:00,
1.454 for 11:00-1600, and 13.40 for 16:00-20:00 (p=.05, df=2, x2= 5.99). The only significant
pattern in the data for Figure 6 is in the hours of 16:00-20:00 with X2= 4.167 (p=.05, df=1, x2=
3.84), but there was a slight significance during the hours of 11:00-16:00 with an X2= 2.667.
This suggests that there is a preference for different foraging area type between the hours of
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11:00-16:00 and 16:00-20:00. For patterns with tail waving during the scanning posture, tail
waving performed with scanning posture occurred only if a potential predator was apparent or
the individual had just responded to a confrontation with another individual, inter- or intraspecific.
Discussion:
Behaviors- Multiple sources compiling behavior of eastern grey squirrels presented the
same behaviors found during observations (Grunel 1987; Steele & Koprowski, 2001). However,
this research lacked behaviors directly related with mating, though there may have been some
interactions found during observations that possibly suggest courtship. Spitzer (2002) noted an
increase in mating activity and foraging as a reason for a peak of squirrel activity to be in
November. Therefore, it is likely that careful observations would create a mating behavior
category in the future.
Patterns- Predation and competition are likely causes of the resulting patterns of
foraging time and site. Highest human activity at Whetstone Park was during the early
afternoons from 12:00-15:00. This relates to the significant difference in foraging behavior
being favored during the early morning and evening. Cooper et al (2008) found an increased
flight distance for squirrels in less trafficked areas, which suggests the cost associate with
human interaction. Individuals in this research appear to be lowering the possible costs of
foraging on the open ground by utilizing less active times of potential disturbances; that a food
area was more available at certain times (Hopewell et al 2008).
Predation probably had an effect on the site area chosen for foraging during the time of
activity; however, competition could be equally an influence. Site A, documented as a brushy
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environment, provided more cover during high activity times of humans, birds, and
eavesdroppers, while Site B contained more open space between large hardwoods. The
smaller nuts and berries from the herbaceous woody plants at Site A suggested a lower nutrient
value, but the large walnuts and acorns from the hardwoods in Site be suggested a higher
nutrient content. Lima and Valone (1986) documented, eastern grey squirrels will alter food
choices and body position, including spatially, depending on the presence of a potential
predator, or Schmidt and Ostfelt(2008) reporting that the value of caches decreases if the
squirrel anticipates a cache robber present.
Visual signals in response to predators is absent in scientific literature on grey squirrels.
It would be advisable to see experiments done to check movement’s ability to illicit a response
from a sight-based predator. This could possibly explain the use of tail waving in the scanning
position after/during time with a potential predator. If a predator would more likely attack the
moving tail and spare the entire squirrel, results would favor this behavior spreading through
the population. Eastern grey squirrels, as mostly solitary creatures, could be the next model
organism for interspecific interactions because all behaviors seem to be a response from their
environment.
Acknowledgments:
I would like to thank Jessica Hall, GTA for the Department of EEOB at The Ohio State
University, for all of her help throughout this research process, and I would like to acknowledge
Professor Douglas Nelson for teaching EEOB 440, without which I would have never done this
project.
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Literature Cited:
Cooper, C.A., Neff, A.J., Poon, D.P., and Smith, G.R. 2008. Behavioral Responses of Eastern Gray
Squirrels in Suburban Habitats Differing in Human Activity Levels. Northeastern
Naturalist. 15:619-625.
Lima, SL & Valone TJ (1986) Influence of predation risk on diet selection: a simple example in
the grey squirrel. Animal Behavior. 34:536–544.
Gurnal, J. 1987. The Natural History of Squirrels. London: Christopher Helm.
Hopewell, L.J., Leaver, L.A., & Lea, S. E. G. 2008. Effects of competition and food availability on
travel time in scatter-hoarding gray squirrels (Sciurus carolinensis). Behavioral Ecology.
19: 1143-1149
Reid, F. 2006. Peterson Field Guide to Mammals of North America. 4th edn. New York: Houghton
Mifflin Company.
Schmidt, K.A. & Ostfeld, R. S. 2008. Eavesdropping Squirrels Reduce Their Future Value of Food
under the Perceived Presence of Cache Robbers. American Naturalist. 171: 386-393.
Steele, M. A. & Koprowski, J. 2001. North American Tree Squirrels. Washington, D.C.:
Smithsonian Institution Press.
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Table 1. Categories and List of Behaviors of Sciurus carolinensis with Descriptions
Behavior
Description
Category of Behavior
Foraging
Caching
Eating
Searching
Grooming
Scratching
Rubbing
Gnawing
Licking
Food Related Activities.
Activities for food storage: looking for
cache site while holding food, digging site,
and covering site.
Acts of consuming food.
Looking on ground for food, includes
testing potential food.
Cleaning or maintenance activities.
Scraping either front or back claws against
skin.
Moving manus across body usually on
head after licking palms.
Using mouth to chew on body.
Using tongue to clean body.
Social
Chasing
Flight
Tail Wave
Vocalizations
Traveling at another individual.
Fleeing from another individual.
Movement of tail in ungulations or flicks.
Sounds produced through vocal cords.
Locomotion and Stationary Positions.
Standing
Sitting
Stationary with body extended vertically.
Stationary with body at a less than 180˚ to
gorund.
Upside down on tree with head
perpendicular to vertical axis.
Stationary with body against surface
below.
Locomotion upwards on surface.
Medium paced locomotion parallel to
ground.
Locomotion by passing through the air
between branches
Locomotion with light elevation off ground
multiple times in succesion
Movement and
Postures
Scanning
Resting
Climbing
Walking
Jumping
Leaping
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Figure 2. Map of Whetstone Park Observation
Areas
Site A Brushy Area. Site B Open Area. Site C
Dense Forest
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Figure 3. Site of Observation on The Ohio State University Campus.
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43.13
48.49
3.39
Foraging
Social
Grooming
Movement and Locomotion
4.99
Figure 3. Percent of Time Allocated to Behavior Category.
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Figure 4. Postures of Sciurus carolinensis
A. & B. Two types of sitting: arms on ground and arms off;
C. Scanning posture; D. Standing Posture
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30
Occurrence of Behavior
25
20
15
10
o
5
Foraging
0
8:00-11:00
11:00-16:00
16:00-20:00
Time of Day
Figure 5. Occurrence of Behavior Category and Time of Day
Grooming
Social
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18
Number of Times Site Chosen
16
14
12
10
Site A
Site B
8
6
4
2
0
8:00-11:00
11:00-16:00
Time of Day
Figure 6. Choice of Foraging Area and Time of Day
16:00-20:00