Orion is a 21-month old white-handed gibbon living at the Philadelphia Zoo. The author observed Orion's interactions over the summer to study how they changed as he approached the end of the typical 20-month weaning period. The results showed that over the summer, Orion spent less time with his parents and more time alone or with his brother. Specifically, the percentage of time spent with parents decreased from 35% to 22% over the course of the summer. This supported the prediction that Orion would become more independent as he neared the end of the weaning period.

1. Bruce 1
Rachel Bruce
Philadelphia Zoo – Summer 2015
Environmental Education and Animal Behavior Internship
Weaning and Interaction Behavioral Study of Orion, White-Handed Gibbon

2. Bruce 2
Introduction
White-handed gibbons, or Hylobates lar, as their scientific name deems them are arboreal
primates who live in areas of southeast Asia such as southwest China, Thailand, Burma and parts
of Sumatra. Their habitat consists of primary and secondary tropical rainforests and they spend
most of their time visiting the canopy of the trees where they use their agile bodies to swing from
tree to tree. Gibbons are known as the best aerialists of all the primates. White-handed gibbons
are considered frugivores because their primary source of food is fruits, however they also eat
leaves, insects, and occasionally small birds or eggs. Generally males will weigh anywhere from
11 to 17 pounds whereas females are slightly lighter and will weigh 9 to 15 pounds. In the wild,
gibbons often live up to 25 years old, however captivity longevity is nearly doubled at a
maximum age of 50 years. Currently the Philadelphia Zoo is home to a white-handed gibbon
family consisting of four members: Phoenice (26 y.o.), her mate Mercury (25 y.o.), and their two
sons Leo (4 y.o.) and Orion (21 m.o.).
For my behavioral analysis, I decided to focus my attentions on Orion, the youngest
gibbon, and observe his interactions with his family group. Family structure is very interesting in
white-handed gibbons as it is made up of a normally monogamous pair of mated gibbons and
their children. Thus both parents play a role in the development and upbringing of their young.
However, as with most mammals, there is a period of weaning that the young go through before
they branch out on their own to gather, scavenge or hunt for food. The weaning period for white-
handed gibbons lasts approximately 20 months to about a full 2 years. Because Orion will be
turning 2 years old on November 2, 2015, I wanted to spend the summer observing him in his
last few months of the weaning period and determine whether his interactions with his parents,
but most particularly his mother were decreasing over the course of the summer.

3. Bruce 3
Methods
My methods began with a prediction that over the course of the summer, Orion would
spend increasingly more time by himself or engaged with his brother, Leo, and less time with his
parents, especially mom, Phoenice. My dates of observation ranged from May 31st to July 25th.
For the first two weeks, my methods consisted of taking note of Orion’s location, behavior and
any interactions every minute. However, I later revised my methods to focus more on the
interactions between Orion and the other gibbons by noting and tallying behaviors underneath
columns associated with each gibbon, including one for Orion himself whenever he spent time
alone. I recorded the behaviors using one minute intervals and observed Orion for an average of
40 to 55 minutes three days a week.
Results
When I compiled the data in excel, I condensed the behaviors into the number of
interactions with each individual gibbon. Figure I shows an example of the type of ethogram I
used to record the behaviors and interactions as well as the total interactions after one day. Then
I combined the data shown for Mercury and Phoenice together and the data for Leo and Orion
himself together. Thus my results show Orion’s interactions with his parents versus without his
parents over the course of the summer. As shown in Figure III, the results of my behavioral study
indicate that over the course of the summer Orion spent less time with his parents and more time
on his own or engaging with his brother Leo. The total number of interactions per individual
over the course of the summer was 126 with Mercury, 176 with Pheonice, 189 with Leo, and 414
by himself which equates to time spent by Orion as 14%, 19%, 21% and 46% respectively.
Finally, when the data was broken into four periods of the summer (as in Figure II), the
percentage of time spent with parents ranged from 35%, 41%, 31% and 22%. While these

4. Bruce 4
percentages already started on the low end, this makes sense since Orion is already past a year of
weaning.
Conservation Action
According to the IUCN, white-handed gibbons are an endangered species. A decline of
approximately 50% of the population has occurred in the past 30 years. One of the major threats
to the gibbons is habitat loss due to deforestation and lack of protected forested areas. However,
gibbons also face the threat of hunting and the rampant illegal pet trade. Even within their own
countries, white-handed gibbons are used as entertainment for tourists and for personal pets.
Most undergo maltreatment and abandonment as they reach sexual maturity and become much
harder to care for. My conservation action includes two steps. First step is to raise awareness of
deforestation especially for items such as palm oil which are found in almost all the items we use
each day and to make smarter purchases. The second step includes doing research before
deciding on a new pet and withholding support from companies and industries which exploit
these wild animals.

5. Bruce 5
Data
Figure I. Example of Ethogram
Date 6/3/2015
Time 9:35 - 10:26 AM
Location Outside/Trail
Gibbon Type of Interaction Count Total Daily Interactions
Mercury
E 1
14
S 9
JG 0
I 0
C 0
F 4
Phoenice
S 8
16
CA 0
E 0
JG 0
UT 0
F 8
Leo
FI 0
12
P 0
F 5
S 6
C 1
JG 0
Himself
O 0
18
R 1
S 2
IP 0
SW 0
EX 2
JG 5
H 1
CL 1
E 3
UT 3
P 0
** P = Playing, UT = Using Trail, E = Eating, CL = Climbing, H = Hanging, JG = Using Jungle
Gym. EX = Exploring, SW = Swinging, IP = Interact with People, S = Sitting, R = Running, O =
Observing, C = Chases, F = Follows, FI = Fight, CA = Carry, Instigates = I

6. Bruce 6
Figure II.
First
Quarter
Second
Quarter
Third
Quarter
Fourth
Quarter
Total
Interactions
Total
Percentages
With Parents 35% 41% 31% 22% M – 126
P – 176
M – 14%
P – 19%
Without
Parents
65% 59% 69% 78% L – 189
O – 414
L – 21%
O – 46%
Total 100% 100% 100% 100% 905 100%
M = Mercury, P = Phoenice, L = Leo, O = Orion (Himself)
Figure III.
Bibliography
Gibbon, White-Handed Species Profile 2011. Philadelphia: Philadelphia Zoo, 2011. Print.
Gray, Shalana. "Conservation Difficulties for Hylobates Lar: White-Handed Gibbons and the
Illegal Pet Trade." Conservation Difficulties for Hylobates Lar: White-Handed Gibbons
and the Illegal Pet Trade. Academia, 2015. Web. 10 Aug. 2015.
<http://www.academia.edu/1503391/Conservation_Difficulties_for_Hylobates_Lar_Whit
e-Handed_Gibbons_and_the_Illegal_Pet_Trade>.
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
First Quarter Second Quarter Third Quarter Fourth Quarter
Time Spent with Mercury and Phoenice during Summer '15