Wooly Monkey Behavior and Vocalizations
View the PowerPoint Presentation
Vocalizations
& Displays in the Common Woolly Monkey
(Lagothrix
lagothricha)
Lindsey Hughes
Abstract
Two troops of captive woolly monkeys were
observed with the aid of an 8 mm video camera and a proprietary Palm Pilot
program. My research up to the
present will be continued, but with modifications in equipment and methods of
data. The two troops differ since
Troop I consists of a family group with four members; the breeding male Corey,
his son Tomas and daughter Sara, and a non-breeding female named Sissi who is
the Corey’s sister. The mother of
Tomas and Sara died while giving birth to Sara.
Troop II consists of three unrelated males, with two more unrelated males
who are currently in isolation to be introduced in the near future.
Troop I is one of only two captive family troops of woolly monkeys in the
world; the other is located in London, England.
The video recordings were analyzed
frame-by-frame using a proprietary video digitization program.
The vocalizations were recorded by the video camera as well and analyzed
using Sound Forge to make sound spectrographs, or sonograms.
A programmed Palm Pilot was used to record the movement and behavior of
both troops in order to make ethograms to display patterns of behavior and
vocalization.
The following was anticipated: 1. vocalizations
would be correlated with visual displays; 2. display function would be
identified through context; 3 individuals would be identified through harmonics
in the sonograms; 4. the behavior and vocalizations of the two troops would
differ; and 5. the behavioral analysis would be useful for maintaining and
breeding captive troops.
Introduction
The common woolly monkey (Lagothrix
lagothricha), also known as Humboldt's woolly monkey, is found only in South
America in the Amazon River Basin of Brazil, Colombia, Ecuador, Peru, and
Venezuela. They range in all canopy levels of primary rainforest as well
as gallery forests, and have been found in mountainous areas and cloud forests
up to 3,000 meters. The
classification of the common woolly monkey is as follows:
Taxon |
Classification |
Kingdom |
Animalia |
Phylum |
Chordata |
Class |
Mammalia |
Order |
Primates |
Suborder |
Haplorrhini |
Family |
Cebidae |
Subfamily |
Atelinae |
Genus |
Lagothrix |
Species |
lagothricha |
The morphology of the common woolly monkey is similar to that of other
monkeys in the Atelinae subfamily. The
woolly monkey is the largest monkey in South America, with the female weight
averaging 11 pounds and the male weight averaging 15 pounds. They have a prehensile tail that can support their full
weight and is used for feeding and locomotion.
Woolly monkeys can have dark brown, pale brown, dark gray, pale gray,
reddish-brown, or black fur. The
limbs, tail, and head are usually darker than the back, with the face being
black and the palms of the hands and feet being pink.
Slight sexual dimorphism exists including the canines, body, and head in
the males being longer than females. However,
the female's tail is longer than the male's and the female's clitoris is longer
than the males' penis, which sometimes makes it difficult to determine the sex
in the wild.
Humboldt's woolly monkey is primarily frugivorous, but they also feed on
leaves, seeds, flowers, and some invertebrates and small mammals. In captivity they have been known to prey upon birds that fly
into their cages. The group size
for woolly monkeys averages 10-12 group members, but much larger groups are
known to exist. Subgroups sometimes
form and travel independently from the larger group.
Woolly monkeys are not territorial and allow group ranges to overlap and
have been known to forage alongside each other as well as other species in their
family. The woolly monkey travels
through the forest quadrupedally using its tail as a fifth arm.
They rarely come down to the ground and, therefore, are known to be
almost totally arboreal. They even sleep 150 feet above the ground in the canopy.
When on the ground, which is especially rare in the wild, they walk
bipedally, using their arms and tail to balance.
The tail is extremely important and is always anchored to something; it
is used to pick up objects and sometimes even allows the monkeys to rest by
hanging from just the tail.
The social structure of the common woolly
monkey is a multi-male-multi-female group in which a hierarchy exists between
the males in the group. The
dominance hierarchy is determined by play-fighting and age.
The species' mating system is polygamous because each receptive female
mates with every male in the group, with the most dominant males receiving the
most copulations. Because of this,
the male that succeeds in passing on his genes is the one that releases more and
better-fit sperm per session, with multiple sessions increasing the likelihood.
Therefore, every male mates with every female, but only one female is
copulated with at any given time. In
addition to receiving the most copulations, the most dominant males also receive
the most social grooming and are known to protect mothers and their infants from
others in the group. In general,
adult and subadult males are dominant over all other members in the group.
Male woolly monkeys are philopatric, which means that the males stay in
the group in which they were born, known as their natal group, while the females
leave their natal group. Female
dispersion usually occurs between the ages of five and a half years to six
years, the same ages that females begin to mate.
Although females begin to mate between those ages, they remain sterile
and do not conceive until one to three years after they leave their natal
groups. The gestation period
averages seven and a half months, or about 223 days, and the female gives birth
to one young about every two to three years during the birthing season, which
occurs between the months of August and December.
After birth, the infants nurse from sixteen to twenty months, traveling
independently by six months.
Little research on woolly monkeys exists, with the majority of the
research focused on ecology, morphology, location, social structure, and so on.
Research on the behavior and vocalizations of the common woolly monkey is
almost completely nonexistent. The
research on woolly monkey behavior and vocalization that has been done was
performed by M. Ramirez and published through the World Wildlife Fund in 1988.
His research was made into a "dictionary" that explained the
behavior or reason behind each vocalization, which he spelled out using human
phonetics. He also explained some
of the woolly monkeys' visual communication.
Although thorough in some respects, his research did not investigate
sequences of behavior and vocalization or analyze each individual separately
with respect to behavior and vocalization sequences.
Methods
My research on the common woolly monkey was
conducted at the Louisville Zoo, one of only two places in the world that have a
captive family troop. After being
formally introduced to the monkeys by the head veterinarian, I was able to begin
collecting data. Before starting
the data collection process, I decided to spend a few weeks observing the two
troops in order to become acquainted with the individuals.
During the three weeks of strict observation, I took notice of each
behavior and began compiling a list of the observed behaviors.
This list is located in the results and discussion section.
I also realized that not only could I tell the monkeys apart visually,
but vocally as well. After becoming familiar with the behaviors (displays) and
vocalizations of the monkeys, I began collecting data.
The data collection consisted of a variety of
methods including the use of an 8 mm video camera to record behaviors, a mini
disk recorder to record the vocalizations, and a proprietary Palm Pilot program
to record the movement and behavior of each individual in the two troops as well
as the overall behavior of each troop. At
first, I videotaped the woolly monkeys individually.
This method was not effective because the behavior of the other woolly
monkeys could not be seen and the monkeys move extremely fast and it is
difficult to follow them around the cage. I
then tried to videotape sections of the cage, but that did not work well either
because I could not differentiate between the monkeys because of the camera’s
bad resolution. After four hours of
recording over one month, I realized that I needed a much better video camera in
order to continue with the research. For
my future research I will have a video camera with superior resolution.
The video recordings that I had were used to learn and practice the
digitization process. The
recordings were digitized and transferred to compact disk for later analysis. The digitized version of the video recordings could be
analyzed at 1/10 of a second, with the potential advantages including the
ability to record the behavior at set intervals, allowing the viewer to record
the behavior of all the monkeys in view.
The mini disk recorder was used in conjunction
with the video camera. I
experienced multiple difficulties and problems with the mini disk recorder that
eventually led me to discontinue using it in this project.
This will be discussed further in the results and discussion section.
Because I did not have any vocalizations recorded, I decided to use the
sound from the video recordings for my vocalization analysis.
Sound Forge, a computer program used for the sound analysis, enabled me
to make sound spectrographs, or sonograms, on the woolly monkey vocalizations.
In order to analyze just the woolly monkey vocalizations and not all of
the background noise, adjustment was required. With Sound Forge, I was able to
delete all of the outside and background noise that included crickets, birds,
trains, human voices, and so on.
The proprietary Palm Pilot program used for recording the behaviors was
called Pen Recorder and the program used to analyze the recordings was called
Pen Reviewer. Below are diagrams of
Pen Recorder, Pen Reviewer, and View Data.
When
using Pen Recorder, I had to designate letters of the alphabet to the observed
behaviors. Once I started Pen
Recorder, I wrote the letter of every behavior that I observed an individual
doing until they went inside or went to sleep.
This method was difficult because it was impossible to keep up with the
behaviors while having to remember which letter went with which behavior as well
as write the letter and then keep going. The
collected data was viewed in Pen Reviewer under View Data, displayed above, and
then analyzed in the form of a graph, time line, and matrix, displayed below.
After
using this technique for a while, I decided to change my method of recording
because of the above stated reason as well as the fact that certain monkeys were
more active than the others and I had to start and stop recording for the
different individuals, which does not heed good results for analysis.
For my further research, I will be using a new method of recording
behaviors. Instead of using the
proprietary Palm Pilot program, I will be using a tablet PC with a voice
recognition program so I can just speak each behavior as it occurs.
Results &
Discussion
The individual woolly monkeys of Troop I each
have extremely different personalities, rank, age, relationships, etc.
The family troop consists of four related individuals:
Name |
Birth Date |
Age |
Corey |
11/13/91 |
11
years |
Sissi |
09/29/95 |
7
years & 2 months |
Tomas |
12/01/98 |
3
years & 11 months |
Sara |
12/07/00 |
1
year & 11 months |
Corey
Sissi
Sara
Tomas
Corey is the dominant breeding male and is father to both Sara and Tomas.
Sissi is Corey's sister and is the dominant non-breeding female.
Sissi has never had any offspring and is considered sterile.
The position of the second most dominant member of the troop is currently
being fought over between Sissi and Tomas. Because Tomas is a subadult male and Sissi is an adult
female, he and Sissi fight over everything, from food to where to sleep.
Thomas and Sara are siblings and fight and play in ways similar to human
siblings, but still show affection quite often, grooming each other and resting
next to each other.
Tomas and his father Corey appear to have the closest relationship within
the group. Tomas follows Corey
around, mimicking certain behaviors. When
Tomas and Sara are resting together or grooming each other, Corey generally
joins them. Strange to human
viewers, the family troop members are sexual with each other, especially Corey
and Tomas and Corey and Sara. Sexuality
between family members is surprisingly common in the primate world.
According to primate research, it is quite normal for a father and son to
feel on each other's genitals and have erections when around one another.
These behaviors are considered greetings and are meant to establish
friendly contact, usually occurring between adult males and juveniles of both
sexes. During my observations, I
noticed that Corey and Sissi rarely interact, while the same is true for Sara
and Sissi.
The monkeys in the family troop have differing personalities, with Corey
as the alpha male. He is the
largest monkey, with huge canines and constant eye movement that indicates a
neurological disorder, though not apparent in any other way. Corey never plays and is always pacing the cage, eating,
grooming himself or others, staring at outside disturbances, or resting.
Only after about a month of observation Corey appeared not to consider me
an outside threat anymore, showing behaviors indicating a friendly greeting and
then calming down other group members through appeasement behaviors.
This meant that I could now observe their behavior undisturbed by
outsiders. Tomas is more of a loner
for the majority of the time; shy toward outsiders, he never makes eye contact
with me, which is unlike all the others in the group.
When not off by himself, Tomas is playing or play fighting with Sara,
fighting with Sissi, or grooming or resting with Corey and/or Sara.
Corey
staring Tomas hiding
Sissi & Tomas Sissi
walking
Sara eating
fighting
Sissi is the most unsocial member of the group, only interacting with the
others when fighting with Tomas. She
is, however, active toward me, cage shaking, which is a sign that she feels
threatened, and intense staring sessions at me, most likely indicating that she
does not approve of my presence. When
not interacting with Tomas or me, Sissi rests high up in the top of the cage,
far away from everything and everyone else.
Sara on the other hand is the most active and social member of the group.
Sara is always doing something, whether watching me, playing with Tomas,
resting with Corey and/or Tomas, eating, playing by herself with toys, or just
running around bipedally on the cage floor.
The youngest, most curious and loving of the group, she is the one that
has tried to make contact with me the most and is the most affectionate toward
others.
Below is a table listing the observed
behaviors, their description, and the individuals in which the behaviors were
observed.
Behavior |
Description |
Individuals
In Which The Behavior Was Observed |
Eat |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Play |
Self
explanatory; includes biting, running, climbing, rolling around, etc. |
Sara,
Tomas |
Chestrub |
Rub
object against chest to scent mark; usually only done by males |
Corey,
Tomas, Sara |
Swing |
Self
explanatory; on ropes or around the cage |
Corey,
Sissi, Sara, Tomas |
Walk
Quadrapedally |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Fight |
Self
explanatory |
Sissi,
Sara, Tomas |
Groom |
Each
other or themselves |
Corey,
Sara, Tomas |
Walk
Bipedally |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Teeth
Chatter |
Dominant
male moves jaws up and down rapidly, chattering his teeth; threat display
or sexual arousal display |
Corey |
Jump |
Self
explanatory; on floor, up to cage or rope, etc. |
Corey,
Sissi, Sara, Tomas |
Climb
cage |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Climb
Rope |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Cage
Shake |
Use
all four limbs to shake the cage; threat display |
Corey,
Sissi, Sara |
Rub |
Use
hands to rub on each other’s bodies; brings appeasement and strengthens
close relationships |
Corey,
Sara, Tomas |
Bite |
Self
explanatory |
Sissi,
Sara, Tomas |
Grasp
With Tail |
Use
“5th limb” to hold on to objects or pick up objects |
Corey,
Sissi, Sara, Tomas |
Stare |
Self
explanatory |
Corey,
Sissi, Sara |
Hump |
Self
explanatory |
Corey,
Tomas |
Copulation
Attempt |
Attempt
to copulate with another individual; practice for actual copulation;
occurs between males and females and between males |
Corey,
Tomas, Sara |
Run |
Self
explanatory |
Sissi,
Sara, Tomas |
Yawn |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Lick |
Themselves,
each other, or various objects including the floor and the cage |
Corey,
Sissi, Sara, Tomas |
Masturbate |
Self
explanatory |
Corey,
Tomas |
Feel
On Genitals |
Feel
on own or another individual’s genitals; display of friendship and is
thought to bring appeasement |
Corey,
Tomas |
Reach
For Me |
Self
explanatory; reach out of cage to try to touch me |
Corey,
Sara |
Rest |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Sneeze |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Drink |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
Scratch |
Self
explanatory; usually themselves |
Corey,
Sissi, Sara, Tomas |
Hang |
Upside-down
with tail grasping object and supporting entire body |
Corey,
Sissi, Sara, Tomas |
Reach
Out Of Cage |
Self
explanatory; usually to get leaves, sticks, or other food dropped outside
of the cage |
Corey,
Sissi, Sara, Tomas |
Sit |
Self
explanatory |
Corey,
Sissi, Sara, Tomas |
In
addition to using the video recording of the woolly monkeys for behavioral
analysis, it was also used for sound analysis.
I used a computer program called Sound Forge, which enabled me to make
sound spectrographs, or sonograms, of the woolly monkey vocalizations. In order
to analyze just the woolly monkey vocalizations and not all of the background
noise, adjustment was required. Using
Sound Forge enabled me to delete all of the outside and background noise
including crickets, birds, trains, human voices, and so on.
I was able to produce several sonograms from the data collected by
listening to the sounds while watching the screen and marking where I heard
common sounds of the woolly monkey. These
common sounds included shrieks, squeaks, and grunts.
I
then performed a spectrum analysis, an option in Sound Forge, in order to view
the vocalizations in the form of a sound spectrograph.
Although this analysis is not yet complete, it will be continued in the
future. After more spectrographs
are made and analyzed, I will be able to differentiate between individuals just
by looking at their sonograms because it is my hypothesis that each individual
produces different sound spectrographs although they make the same
vocalizations. The human ear might
not be able to differentiate between individuals when they are making the same
sounds as others so this data will be useful in further vocalization research in
woolly monkey populations.
The
sound spectrograph below is of a squeak.
The next sound spectrograph is of
a screech.
The last sound spectrograph is of a grunt.
For
my further research, I will be using a new method to record behaviors. Instead of using the proprietary Palm Pilot program, I will
be using a tablet PC with a voice recognition program so I can just speak each
behavior as it occurs. The program
is called Dragon records what I say and analyzes the data in a similar manner to
that of the proprietary Palm Pilot program.
I will also be using an Elura 40 digital video camcorder, which has
superior resolution and sound quality combined with the ability to take digital
photographs. The camera also has a
steadier that eliminates most of the shakiness from holding the camera.
The observation of Troop II will begin when the two new unrelated male monkeys are introduced to Monkey Island. I will continue recording more vocalizations and perform more in depth analysis using Sound Forge. This research will be helpful in teaching zoo personnel and others interested in woolly monkeys about their behaviors and vocalizations, as well as being useful for maintaining and breeding captive troops.