Estrus in Female Chimpanzees
WHY THEY SWELL
Females have an estrus cycle which lasts approximately 36 days. During the course of this cycle, as
her hormone levels change, a female experiences changes in the size, shape, and color of her genital
skin. As circulating estrogens increase during the follicular phase of the cycle, the size of the swelling
increases. When the anogenital skin is fully engorged, it is typically bright pink, and can measure
from 938 to 1400 cc. The state of maximal tumescence (swelling) is of variable length in different
individuals and at different stages of maturity, but lasts an average of 6.5 days. It is during this time
that females are sexually receptive and that the bulk of copulations with mature males occur.
Every day the chimp keeper is responsible for scoring the females stage of the cycle. The attached
chart is filled out each day, for each sexually mature female.
SCORING
The scoring range is 0 to 4, below each stage is described. Ovulation occurs near the end of the
swelling, which is two days prior to decrease from maximum tumescence.
0
1
2
3
4
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Complete Detumescence:
Partial Tumescence:
Labial Occlusion:
Significant Tumescence:
Maximum Tumescence:
Minimum size, extensive wrinkling
Slightly enlarged labia
Medial surfaces of labia pressed tightly together
Slight wrinkling, tissues raised significantly above anus
All tissues taut and pink, no wrinkling, anus deeply recessed
Chimpanzee Keeper Chat Information
EXHIBIT OVERVIEW
 The Chimpanzee Forest opened in 1995
 All primates on exhibit are in the chimpanzee forest
 Visitors can also experience the world of aquatic reptiles
 The chimpanzees have both an indoor and outdoor exhibit
 Mixed species exhibit with Black and White Colobus, Red-Tailed Guenons, African Crested
Porcupines and Rock Hyrax
NATURAL HISTORY
Range
 Chimps are found in West and Central Africa
 They are divided into 3 subspecies depending on where they are found geographically and the
numerous physical differences that have emerged within each of the 3 major populations
Diet
 Fruit makes up the majority of their diet in the wild, but they also eat leaves, bark, insects
 They have also been known to hunt and eat meat
Life Expectancy
 35-40 years in the wild
 Can live into their 50s and 60s in captivity
 Chimp life expectancy in the wild is affected by many factors such as disease or illness, fatal
injuries from fights, and the bush meat trade (humans)
 Chimps in captivity obviously have a safe environment, healthy diet, and medical care that
prolongs his/her life
Physical Characteristics/Adaptations
 Digigrade (knuckle-walking)
 Arms are longer than legs
 Opposable thumbs and big toes (which make tool use possible)
 Fingerprints and toe prints that can be used for identification
 Occasionally walk upright (especially when carrying objects)
 Shoulder joint flexibility making brachiation possible (swinging from branch to branch)
 Vision is their primary sense and they can see color (just as we do)
 Tool use (twigs to extract insects/hammer and anvil to crack nuts)
 Hunting (cooperative)
 Incredible strength (3times that of a human male) even though they only weigh up to 130
pounds (with the exception of Rustie)
Differences between monkeys and apes
 Overall body size; apes are larger than monkeys
 Monkeys have tails; apes do not
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Apes have arms that are longer than their legs; most monkeys have limbs of equal length
Apes have wider range of motion in shoulder joints
Apes can recognize their own reflections in a mirror
Size and function of brain; apes have larger brains and it is thought that apes are more
intelligent
Apes are capable of completing more complex tasks
Social Structure
 Groups of 20 to 200; many separate into smaller groups (such as natal groups)
 Very complex
 One dominate adult male with all other males being subordinate and one dominate female
and all other subordinate females
 Dominance is sometimes obtained and secured by elaborate displays such as
breaking/dragging branches, fighting, chasing, banging on different surfaces to make as much
noise and appear as threatening as possible
 Dominance doesn’t always mean being the strongest, it also requires brains. It can be
whatever it takes to obtain the fear and respect of the others in the group
 Female dominance works differently and is often times influenced by parturition. The alpha
female may have the most offspring in the group and thus the most support/numbers
 Many times adolescent chimps, females more so than males, venture off or are driven out of
their natal group to find another group in which to establish themselves. This ensures a
healthy gene pool
 Males patrol borders of territory
Breeding
 Sexual maturity at about 8 years of age, but may be 12 or older before giving birth for the first
time
 Sexual swellings
o synchronous with ovulation (most swollen and bright at peak); cycle -35 days
o acts as an invitation to mate, very attractive to male chimps
o male-male competition to mate can be intense, which insures that most successful
male gets to mate
 Both males and females initiate copulation
 Sexual behavior can also be a social behavior (ex. Gain favor, ease tensions)
 Consortships but not monogamous
 Gestation is 230 days (8 months)
 One offspring; twins are possible, but rare
 Mother may nurse for 3 years or more
 Very strong bond between mother and offspring
 Males will tolerate and even play with youngsters
INDIVIDUAL HISTORIES
Kasoje
 Came from Little Rock Zoo in Little Rock, Arkansas
 Pronounced Kah-SO-Jee, named after the Kasoje Forest in the Mahale Mountains of Tanzania
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Louie
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Jack
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Joice
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Carole
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Bunny
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Currently the dominant male in the troop
Large, broad shouldered, muscular
Tightly bonded with Jack and Louie
Playful with younger chimps
Demonstrates strong male dominance displays, very acrobatic
Joined the troop in the summer of 2010, from Auburn California
He is a retired entertainment chimp, that appeared in commercials and movies
He is half brother to Jack, they have the same mother but different fathers
Louie is often seen sucking his thumb
He will clap his hand or kiss his lips when he really wants something
He is tightly bonded to the other 2 males in the troop, and plays well with the juveniles
Jack joined the troop in the summer of 2010, from Auburn California
He is a retired entertainment chimp, that appeared in commercials and movies
He is Louie’s half brother, sharing the same mother but different fathers
He is very intelligent and playful, enjoyed interacting with keepers and plays well with
juveniles
He is most often seen with the other males in the troop or the kids
Dominant female
Mother of Renee and Jambo
Came to us from Yerkes in Atlanta in 1995 when the Chimpanzee forest first opened
Hand raised
Has lighter colored neck and chest with liver spots, silvery back and dark face
Loves to eat the peels of fruits
Often heard making a loud, buzzing/grooming noise
Came to us from Yerkes
Hand raised
Has white beard, smaller in stature from Renee and Bunny
Very intelligent, but also mischievous
She will whistle when she really wants something
Often seen sitting or laying in a black tub with a large amount of blankets
Came to us from Yerkes
Has light colored face, despite age (face usually darkens with age)
Hand reared
Mostly deaf
Lowest ranking female
She interacts with keepers and guests at the windows and holds up her hand as if sharing food
with you
Renee
 Joice’s daughter, so she is one of the more dominant females in the troop
 Came to us from Yerkes when very young
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Raven
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Rozi
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Asali
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Mother reared
She is large in stature and very dark
Very playful and protective of her younger sister Jambo
Rustie’s daughter (Rustie has since passed away), lost rank within the troop once her mother
died
Born here shortly after mother arrived from Yerkes in 1995
She is the first chimp to be born at the Maryland Zoo
Mother reared with the help of “aunts” Bunny and Carole
Very intelligent, great at tool use and enrichment puzzles
Rustie’s daughter (Rustie rejected her after several attempts to reintroduce, Rustie has since
passed away)
Hand reared here at MZIB
Name is Swahili for FLOWER
Hair is very poofy
Very playful with the boys and often seen wrestling with Jambo and Asali
Came here from Sedgwick County Zoo in Kansas at 4 mos. old after her mother died suddenly
from heart failure
Hand raised here at MZIB with Rozi
Has darker face and more smooth/sleek looking hair than Rozi
Large ears and close set eyes with a very pronounced eyebrow area
Name is Swahili for HONEY
Very observant and mindful of adult chimps
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Jambo
 Joice’s youngest child
 Born here at MZIB on Jan. 20, 2006
 Name is Swahili for HELLO
 Since she is the daughter of Joice and the sister of Renee, she has more dominance in the
troop than others
 Very playful with the other kids and males in the troop
INTERESTING TIDBITS
 Station training (show prop) breakfast in the morning
 Chimps are moved to the yard, exhibit or empty cages so that their night cages can be cleaned
 Chimps are fed a variety of fruits and vegetables, anything from asparagus to mango to
zucchini, periodically throughout the day. (AM/PM in holding areas and scatter or hand fed on
exhibit several times)
 Keepers change produce regularly so they do not get bored of an item and so that they are
always getting something new and different. The commissary at the zoo offers several
different items each month to choose from, based on what is in season.
 Fruit items are usually the favorite (Joice doesn’t care for any type of melon and Joe loves any
type of lettuce)
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In addition to the fruits and vegetables, the chimps get a dry chow called Primate
Maintenance Biscuits and are also offered
Personality/Common Behaviors
 Each chimp has their own unique personality
 They all know and respond to their names when they want to 
 Joice and Bunny get very excited when they see their keepers in the morning
 Carole craves attention and will do anything to get it; she likes to spit on unsuspecting new
people because they give her the best reaction
 Bunny is very interesting and interactive with the zoo guests; she pretends to share food and
is fascinated by new objects
 Renee has a short attention span; very closely bonded with Joice and tends to get away with
bad behaviors; also very nurturing to Rozi and Asali
 Raven grew up here and has been trained from early on; cooperative during training and is
very food motivated; known to investigate; very good at tool use and manipulating objects to
get food or get into things she should not get into
Chimps In General
 Intelligent-think/plan/manipulate
 Can be/act impulsively
 Mischievous
 Social
 Expressive-can easily tell when they are excited, upset, sad, annoyed etc. (explain facial
expressions they make)
Grooming
 Very common but very important chimp behavior
 Social
 Can calm nerves, ease fears or tensions
 Show status-subordinates will seek dominants and want to groom to gain acceptance
 A male might groom a female if he is interested in mating with her
 Mothers attentively-sometimes obsessively groom infants
Displaying
 A common chimp behavior, more so with males then females
 Periodically throughout the day, our dominant male will display, which may involve throwing
toys, screaming/hooting, punch/kick glass or mesh, etc. He will do this to remind the chimps
in the troop that he is in charge.
CONSERVATION (CAPTIVE POPULATIONS)
 Approximately 200 individuals in the North America population
 Breeding is managed by the SSP/TAG
TRAINING AND ENRICHMENT PROPS
Enrichment Items
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Puzzle feeders
Honey dipper (show parts and talk about it)
Fire hose feeders
New ropes and branches/hanging toys
Paper
Balls
Variable feeding schedule
Social groupings
Training as enrichment
Training
 Stationing
 Injection
 Blood sleeve
 Body exams daily
 Nail trimming
 Wound treatments
 Medicines
Artifacts To Show
 Honey dipper parts
 Clicker
 Station poles
 Photographs
 PMB (biscuit)
 Training supplies (artificial needle, swabs etc…)
POINTS FOR CHIMP TRAINING INTERPRETATION
Why do keepers train the chimps?
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Intellectually and psychologically stimulating/enriching for the chimps
Helps to build care bond between keepers and each individual chimp.
Aids in husbandry
o Trained to shift between different exhibits and rooms in their night quarters
o Trained to station for feeding or visual examination
o Trained to present body parts for nail trims or wound checks, etc.
Medical Care
o Allows keepers/vet staff to get a better look at wounds/injuries
o Administer voluntary injections for vaccinations or procedures involving anesthesia
o Perform ultrasound and other behaviors involved in managing successful breeding and rearing
of offspring
o Collect urine samples to monitor health & test for pregnancy
o Oscilltation (monitoring of heart and lung sounds with stethoscope)
Do the chimps have to participate in the training sessions?
It is up to the individual chimp how a training session goes. If he/she is not interested then
they simply do not participate. Some chimps seem to really enjoy interacting with keepers
(and getting rewards!) but other individuals would rather ‘do their own thing.’
Why do the keepers have the chimps sit down to eat?
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“Cooperative feeding”
o A dominance hierarchy exists in all chimp groups including ours.
o More dominant chimps may steal the food of subordinate chimps.
o Keepers have trained the chimps to take their meals sitting down on the ground in a specific
spot to prevent this [food stealing] from happening.
 This minimizes any stress and insures that each chimp gets his/her portion.
Specific behaviors and fun facts to go along with them
OPEN
 Chimpanzees and humans have the same number of teeth
o Note that the chimpanzees’ canines are much larger
 Being able to look into a chimp’s mouth allows keepers to monitor oral and dental
health.
EAR
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The keepers may ask for ear to take a chimpanzee’s temperature using an ear
thermometer.
HAND
 Keepers use this command to check hand injuries, clip and file nails and position
hands at a certain height in order to perform other behaviors.
o Chimpanzees have opposable thumbs.
o Chimps have unique fingerprints.
o Chimps walk on their knuckles.
FOOT
 Chimps have an opposable big toe that they can use to grasp branches when climbing.
They can also hold objects with their feet if their hands are full!
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Chimps walk on the soles of their feet (and knuckles of their hands).
They sometimes stand up for short periods to get a better view of something in the
distance or if they are carrying an object with both hands.
BELLY
 This behavior is useful for performing ultrasounds on pregnant chimps
o Joice presented her belly for the vet staff as they performed an ultrasound for
infant Jambo.
o Chimp gestation is approximately 8 months.
HIP/SHOULDER
 Chimps present hip/shoulder to receive an injection for a vaccine or anesthesia.
BUTT
 Chimp present their butt so that keepers can check wounds in this area
o During chimps fights, the genital area is a prime target for wounds
 Chimps also present their butt to assess female swelling/estrus cycles
o Keepers score (0-4) female swelling size, which are tracked on a monthly basis
o 4 is the largest swelling size and this means the female is sexually receptive
o Most copulations happen when the female is at maximum tumescence
(swelling)
TRADE
 Chimps know to trade certain contraband items for rewards.
What is enrichment?
Enrichment is the process of creating a novel and challenging environment to address an
animal's social, psychological, and physical needs. Enrichment aims to enhance animal
activity, provide psychological stimulation and even improve the success of captive breeding
of endangered species.
Why is enrichment important?
 Chimps are extremely intelligent and need to be psychologically stimulated and offered
a challenging environment.
o We try to encourage species typical behaviors such as foraging, tool
use/manipulation, social interactions, stimulation of the senses, and locomotion.
o Chimps receive enrichment daily (several times per day)
o All food enrichment is carefully considered. Our veterinarians and enrichment
coordinator calculate calories and nutritional value and decide on appropriate
items and portions to ensure that the chimps stay healthy.