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Rachel Bruce Philadelphia Zoo – Summer 2015

Environmental Education and Animal Behavior Internship Weaning and Interaction Behavioral Study of Orion, White-Handed Gibbon

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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.

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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

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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.

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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

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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