BIO 301 – LAB REPORT #2
Name: Matt Wilhelm
Date 4/18/12
Behavioral Tendencies of Gorilla gorilla
Abstract
In this study two sampling methods were used to observe the behavior of the organism Gorilla
gorilla and the effectiveness of each sampling method was assessed. The sampling methods used
were Focal-Animal sampling and Scan sampling. The organism of study was chosen because the
behavior of the gorilla and availability were favorable to the goals of the study. Two
observations sessions occurred. The first was used for a preliminary evaluation of the primary
behaviors of the gorilla. The observation data from this was used to develop an ethogram. The
ethogram was used to classify the behaviors of the gorilla for both the Focal-Animal and Scan
sampling parts of the study. The study revealed some interesting differences among the sampling
techniques used while also identifying some common behaviors of the gorillas. The gorillas
spent most of their time sitting in an inactive state or walking. As for the sampling methods, the
Scan sampling method was clearly more useful when evaluating the behavior of a group. The
Focal-Animal method was much more difficult to execute is more useful when focusing on
individual members of a group.
Introduction
Before any animal behavior experiment is executed a sampling method must be
established targeted to the goals of the study. An appropriate sampling method must address all
the behaviors of the organism of study and efficiently evaluate their behavioral tendencies during
the experiment. The sampling method must also accurately depict the behaviors of interest, this
includes things such as transition behaviors or overall behaviors. For this experiment two
methods of sampling will be utilized and explored, Focal-Animal sampling and Scan sampling.
Focal-Animal sampling is a method in which all occurrences of specified interactions of
an individual or group of individuals are recorded during each sample period and a record for the
length of each sample period for each individual is kept (Altmann, 1974). Focal-Animal
sampling is a useful method when an observer is interested in percentage of time, rates, durations
and nearest relationships of behavior interactions (1974). This method provides a general
storyline of the behavior of the organism of study and a complete record of the animal’s
interactions during the sampling period can be obtained. Focal-Animal sampling is great for
either state or event sampling. Events are instantaneous, while states have appreciable durations.
Scan sampling is a form of Instantaneous sampling, a technique in which the observer
records an individual’s current activity at a preselected moment in time (1974). Scan sampling
however is when Instantaneous sampling is utilized for all members of a group. This sampling
method can evaluate the behavioral states of the organisms of study at a particular time. This
method is useful when an observer wants to evaluate a group of organism’s behavior quickly and
efficiently. Scan sampling can provide the researcher with a percentage of time the organism of
study is involved with certain behaviors based on the number of scans taken and the number of
occurrences of a behavior.
The organism of study selected was Gorilla gorilla because the researchers both had an
interest in the gorillas, the exhibit set up was favorable to limit time-out time-in and the study
required the organism of study to be in a group in order to utilize both the Focal-Animal and
Scan Sampling. Basically, the gorilla was a favorable organism to choose based on the goals of
the study to evaluate Focal-Animal and Scan sampling. The gorilla resides generally in tropical
forest habitats in central Africa, it generally feeds upon the vegetation that is supplied in those
environments (SeaWorld, 2012). Gorillas generally live between 30 and 40 years in the wild and
up to 50 years in captivity (Cawthon, 2005). Gorillas can be found up in the mountains and also
in ravines or lowland areas. In the wild, all gorilla groups exhibit synchronized activities and,
throughout the day alternate between rest periods and travel or feeding periods (Cawthon, 2005).
Generally, Gorillas spend about 14 hours feeding and foraging and about 10 hours resting every
day (SeaWorld, 2012). In addition, Feeding/foraging activity peaks during the first three to four
hours of the day. Then there is usually an extended rest period during midday until mid-late
afternoon at which point feeding/foraging activity resumes (2012). Gorillas are also not known to
share food very often or compete for resources. For this study the gorillas will be observed in an
enclosed non-natural environment. It will be interesting to evaluate the behavior of the gorillas in
this environment and compare their behavior to that of a wild gorilla. It appears that in the wild
most time of activity is spent either feeding or foraging for food. The gorillas spend a good
portion of their day resting as well. These behaviors along with others will be observed and
evaluated using the methods of sampling explained above.
Methods
The study was executed over a two week time period. The first goal of the study was to
identify a study organism and the common behaviors of that organism. The organism of study
selected was Gorilla gorilla because the researchers both had an interest in the gorillas, the view
was favorable to limited time-out time and the study required the organism of study to be in a
group in order to utilize both the Focal-Animal and Scan Sampling. There were two observation
sessions. The purpose of the first observation session was to identify an exhaustive list of
common behaviors exhibited by the gorillas. Once this list of behaviors was established, the next
few days were spent developing an ethogram. The ethogram for this study was limited to eight
categories as shown in Table 1.
Table 1, Ethogram
Behavior
Sitting
Eating
Collecting
Walking
Playing
Sleeping
Grooming
Other
Description
Sitting down and in an inactive state
Eating process, injesting food, chewing and swallowing
Scavenging for food or other items
Active movement in horizontal direction
Climbing, interacting with other Gorillas and jumping around
Laying with eyes closed in an inactive state
Cleaning oneself or other Gorillas
Any other behavior that doesn't fit into above categories
Sampling Method
State
State
State
Event
Event
State
State
Either
*Table 1 portrays the ethogram used in this study to observe and record the behavior of the gorillas. The ethogram was
used for both the Focal-Animal and Scan sampling trials. There are eight categories based upon observations during the
first portion of the study.
The behavior categories selected were chosen because they represented a broad variety of
categorized behaviors which would be sufficient to record any behavior observed during the
study. The descriptions of the behaviors categorized are shown in Table 1. The ethogram was
used for the second part of the study, the actual observations which took place during the second
week.
As mentioned above, the study utilized both Focal-Animal and Scan sampling.
Observations for both sampling methods were to be 1 hour and 30 minutes, broken into
alternating 30 minute periods. Essentially, every 30 minutes the method of sampling was
alternated beginning with Scan sampling. Prior to the start of the study the focal animals were
selected for the Focal-Animal sampling. To randomize the selection of the focal animal the
gorillas were all labeled as A, B and C, and selected out of a hat. To start the experiment, one
researcher was the timer and one researcher was the data recorder, this was also rotated
simultaneously with the sampling method being done.
The data was recorded using data sheets created after the ethogram was established
(Appendix A). The sampling approaches being used in the study required the data sheets to be
very flexible as the intensity of behavior could not be predicted. For the Scan sampling, behavior
was observed and recorded every minute for each gorilla, there were three gorillas in the
enclosure labeled A, B and C. A key coding for the behaviors on the ethogram was listed at the
bottom of the data sheet. The data sheet consisted of 4 rows, an extra row in case there was
another specimen in the enclosure. This part of the study was to last 90 minutes, each minute had
a corresponding box on the data sheet for each gorilla. One observer watched the time while the
other assessed and recorded the behavior. After 30 minutes of Scan sampling, a switch to FocalAnimal sampling was made.
The Focal-Animal had been selected prior to data recording, Makari or gorilla C was the
first subject. The data for this portion of the study was collected for 30 minutes, the behavior and
length of each behavior was recorded. The data sheet was set up very simply. A row for time to
the left and then each behavior listed to the right. When the gorillas were partaking any of the
listed behaviors an “X” was placed in that category and the start time of the behavior was
recorded. Intuitively, the start behavior for a new behavior is the end of the previous behavior,
this allowed the length of time each behavior lasted to be recorded to the nearest minute. The
design of the data sheets was very simple and favorable for the goals of the study.
The study intended to compile three hour’s worth of observations. During the study a fire
hazard prevented this from being possible. The study was terminated prematurely as a result of
the unavailability of the gorillas. For Scan sampling data was compiled for 60 minutes and for
Focal-Animal data was compiled for 34 minutes based upon gorilla C and gorilla A.
Comparisons will be made based on the results of the data collected.
Results
The results for this study for both sampling methods were used in order to evaluate the
overall amount of time the gorillas were spending exhibiting each behavior. For the Focal-
Animal sampling, the data was organized with respect to total amount of scans. A total of 60
scans were taken for each animal as the Scan sampling portion of the study lasted 60 minutes.
This resulted in a total of 180 scan samples collectively. Azizi, gorilla A, spent most of his time
sitting, 37% of the time (Table 2). Tabibu, gorilla B, spent most time sitting as well roughly 62%
of the time. Azizi, gorilla C, spent most of her time sitting as well, 52% of the time. Overall, the
Scan sampling revealed that the gorillas were mostly sitting, walking or playing.
Table 2, Results Scan Sampling
Behavior
Sitting
Eating
Collecting
Walking
Playing
Sleeping
Grooming
Other
Total Scans
A
22
8
3
10
15
0
2
0
60
Gorilla
B
37
1
0
11
10
0
1
0
60
C
31
0
0
15
14
0
0
0
60
Total
90
9
3
36
39
0
3
0
180
Total Scan %
50%
5%
2%
20%
21%
0%
2%
0%
100%
*The data in Table 2 shows the quantity of scans recorded for each gorilla for each behavior during the Scan sampling.
The total percentage of scans spent performing each behavior is also listed.
The Focal sampling data was unfortunately limited due to the termination of the study.
Gorilla C was observed as the focal individual for a period of 30 minutes and gorilla A was
observed as the focal individual for a total of 4 minutes. As a result a majority of the FocalAnimal data is based upon gorilla C. During the study, gorilla C was generally more active or
constantly moving than the other gorillas. The amount of time for the two individuals observed
spent performing each behavior is shown in Table 3.
Table 3, Focal-Animal Data
Time Spent on Behavior (min)
A
B
C
Total
12
1
NA
13
3
0
NA
3
3
0
NA
3
11
2
NA
13
1
2
NA
3
0
0
NA
0
0
0
NA
0
0
0
NA
0
NA
30
4
35
Behavior
Sitting
Eating
Collecting
Walking
Playing
Sleeping
Grooming
Other
Total Time (min)
Total % Time
37%
8.3%
8.3%
37%
8.3%
0%
0%
0%
100%
*The data in Table 3 shows the time recorded for each gorilla for each behavior during the Scan sampling. The overall
percentage of time spent performing each behavior is also listed.
For the Focal-Animal portion of the study the focal individuals spent 37% of the time
either sitting or walking. There was no time spent sleeping, grooming or other. In addition, the
focal individuals spent 8.3% eating, collecting and playing. The data was limited for this portion
of the study due to the termination of the study. In Chart 1 and 2 the data for the Focal-Animal
and Scan sampling is summarized as an overall percentage of time the gorillas spent performing
each classified behavior.
Chart 1, Scan Sampling Data
Scan Data Behavior
50%
Percentage
20%
5%
2%
21%
0%
2%
0%
Behavior exhibited during study as a percentage
*The data above from the Scan sampling revealed the gorillas spent most time or 50% of their time either sitting.
Chart 2, Focal-Animal Sampling Data
Focal-Animal Data
37%
Percentage
37%
8.3%
8.3%
8.3%
0%
0%
0%
Behavior
*The data above from the Scan sampling revealed the gorillas spent most time or 37% of their time either sitting or
walking.
As portrayed in Chart 1 and 2, the data from both the Focal-Animal and Scan sampling
found that the gorillas spent a majority of the trial period sitting or in an inactive state. The
gorillas also spent a significant amount of time walking during both sampling periods. In
addition eating, collecting and playing were also activities they were involved in during both
sampling periods, this is more evident for the data of the Focal-Animal study at 8.3% of the time.
From the charts, it is clear that in both sampling sessions the gorillas were often sitting or
walking.
Discussion
The purpose of this study was to evaluate Focal-Animal sampling and Scan sampling
while observing the behavior of the gorilla. The gorilla group being observed consisted of three
individuals, two females and one male. There appeared to be no tension between the gorillas
which would appear normal as there is no competition for food and they didn’t seem to be
competing over space. With respect to the sampling methods, the Scan sampling was much more
effective in evaluating the overall behavior of the group, this method also was much easier for
the researcher to record the data. The Focal-Animal sampling method was also a useful tool,
although it was not as fluid of a process as the Scan sampling. Often the individual would be
inactive for long periods of a time and then perform many behaviors very quickly, this made it
hard to record all the observations accurately even when isolating one Focal-Individual. In
addition, for the Focal-Animal sample our group decided to break down the behavior durations
into minutes, I don’t feel this accurately reflects the behavior of the gorilla and in retrospect
would have broken down the record into seconds for more accuracy. For Scan sampling, a
constant record of the state of each individual was recorded throughout the trial period, I feel for
this study that the data constructed during the Scan sampling is more valuable as all individuals
were observed simultaneously and accurately for what was to be established. I feel that the
Focal-Animal study was not as successful because the time durations recorded were restricted to
minutes and in turn, were not flexible enough to accommodate the behavior of the gorillas. The
data recorded for each sampling method was fairly consistent with one another. The sitting
behavioral category was dominant during both sampling periods. Walking also was very
prevalent during both sampling periods. This suggests that the data and sampling methods are
likely efficient to evaluate animal behavior.
Once again, the goal of any study should be acknowledged before a sampling method is
established. In certain situations, multiple sampling methods may yield the most telling results
for an animal behavior study. For the gorillas, I would tend to favor the Scan sampling method. I
felt this method accurately described the behavior of the gorillas as it was intended. The process
of observing and recording was very smooth and errors can be held to a minimum. I don’t feel
the Focal-Animal method would be preferred in this situation because the gorillas move very
randomly from little movement at all to very quick and sudden spurts. In order to record these
behaviors as a timeline, multiple observers may be need so that observations and records can be
compared after the study to make sure all behaviors were accounted for. I feel the Scan sampling
method is best for groups of individuals that have the potential to be very active suddenly or in
short intervals. I believe the Focal-Animal sampling is best for very large groups of individuals
who behavior is not so sudden and random as this would allow for more accurate observations.
For the gorillas, a narrative of their behavior would seem to be more useful than Focal-Animal
sampling or at the least should be used in cohesion with Focal-Animal sampling.
The data from the experiment was fairly consistent with the literature regarding the
behavior of the gorillas. As shown in Chart 1, during the Scan sampling portion of the study the
gorillas spent 50% of the trial time sitting down and in an inactive state, 20% of the time walking
or in active movement in horizontal direction and 21% of the time playing, climbing or jumping
around interacting with other gorillas. This would conform to the literature that stated gorillas
spend most of their time during the day either resting or feeding and foraging if the time walking
and playing was considered active time. During the initial observations the gorillas spent more
time feeding and foraging than during the actual trial periods. This was classified as collecting on
the ethogram, they spent only 5% of time during the Scan sampling collecting, this is likely due
to their relative awareness of when food is or is not available based upon feeding times for the
zoo. With regarding to the Focal-Animal study, only one individual was studied for an entire 30
minutes as the study was prematurely terminated. But overall from the data in Chart 2, the
gorillas spent 37% of the time sitting or walking, and 8.3% of the time eating, collecting or
playing. This would conform more to the idea that gorillas spend a majority of their day eating
and collecting. The data is consistent with that of the Scan sampling, the gorillas spent a majority
of time either sitting in an inactive state or walking in the horizontal direction. In this study the
behavior of the gorillas appeared to be dominated by either sitting or in an inactive state or
walking, movement in the horizontal direction. When compared to the literature it would appear
that the gorillas should have spent more time foraging or collecting. The discrepancy in behavior
tendency can most likely be attributed to the reality that they are living in a zoo or enclosure. The
gorillas know when they are being fed and are aware that they don’t need to forage for food as
they will receive it anyway. Their behavior then in the zoo would most likely be a result of
boredom or a desire to remain active. The older gorilla, gorilla C, appeared to have the most
desire to move around. She was constantly walking around, there was never a clear reason for
this movement, it appeared to be simply boredom. If the gorillas were in a natural environment it
is likely they would spend more time foraging than was revealed in this study.
A question I developed during my observations was the motivation for the behaviors of
the gorillas. For instance, when people would get up close to the glass, gorilla B would often spot
these individuals, run up and pound on the glass to scare the onlooker. It appeared as this was a
form of entertainment for the gorilla. In addition, the constant walking of gorilla C with no
apparent cause suggest she was moving out of boredom. I supposed my question is what is the
motivation for their behaviors, they don’t appear to be simply seeking to feed, mate and rest. The
gorillas seem to have some sort of desire to ward off boredom or to seek entertainment. The
gorillas seem to be very human-like in that they have the desire for entertainment or amusement.
When the threat of survival is eliminated, essentially as it has been for humans, I believe the
behavior of the gorillas is altered significantly from survival tactics to that of entertainment. It is
also interesting to note that the gorillas always seemed to be thinking. Understanding the thought
process of a gorilla may be more of a psychology experiment, but the combination of behavior
analysis and maybe the psychology of the gorilla could give some great insight into the
evolutionary development of thought and the ability to reason that humans have developed.
Literature Cited
Altmann, J. (1974). Study of behavior: Sampling methods. Behaviour, Vol. 49, No. 3/4, pp.227267.
Cawthon Lang KA. (2005) Primate Factsheets: Gorilla (Gorilla) Taxonomy, Morphology, &
Ecology. http://pin.primate.wisc.edu/factsheets/entry/gorilla. Accessed 2012, April 14.
SeaWorld Parks & Entertainment. (2012). Gorillas. http://www.seaworld.org/animal-info/infobooks/gorilla/behavior.htm. Accessed 2012, April 14.
*Websites both list multiple scholarly references pertaining to the information they have
presented.