IMPROVING FERTILITY IN CAPTIVE GORILLAS
Lois J. Miller
B.A. Metropolitan State College, 1982
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Master of Arts
Department of Anthropology
This Thesis for the Master of Arts Degree by
Lois J. Miller
has been approved for the
Miller, Lois J. (M.A. Anthropology)
Improving Fertility in Captive Gorillas
Thesis directed by Professor Duane Quiatt
Feral gorilla populations are declining primarily due to
human encroachment on existing land with poaching for meat and
trophies as a contributory factor. If present trends continue the
wild gorilla may be extinct by the year 2000. Successful
reproduction of captive gorillas may be the only means for
preservation of the species. Unfortunately, captive gorillas do not
reproduce well as evidenced by a three percent annual decline in
captive population numbers. Male captive gorillas appear to suffer
from serious infertility problems that include low sperm counts and
testicular pathology. Captive pairs do not always breed, and even
when productive breeding occurs females in many cases refuse to care
for their offspring. Zoos throughout the world are concerned about
improving the reproductive rates of their gorilla collections. The
Denver Zoo in conjunction with anthropologists and medical
specialists has initiated a Gorilla Breeding Program that includes
breeding loans, behavioral studies, and detailed physical
examinations of gorillas to determine reproductive states and
potentials. In conjunction with the behavioral studies a special
program was established in 1982 which involved daily physical
examination of one regularly cycling female gorilla to assess her
status with regard to the timing of menstruation and
estrus. To aid in determining estrus the Sub-Human Primate Pregnancy
Test was used. This test affords detection and qualitative
assessment of LH, the lutenizing hormone which peaks just prior to
Accurate prediction of estrus has two major applications
toward improving reproductive records in gorillas. In a non-breeding
female the optimal time for medical intervention such as artificial
insemination or laparoscopy can be determined. In a breeding
situation environmental conditions can be manipulated at the time of
estrus to provide maximal protection from stressful events which
otherwise could prove detrimental to mating activity. Efforts
utilizing a variety of methods and approaches are necessary to
improve the reproductive success of captive gorillas and may benefit
efforts toward preservation of the species.
I am grateful to my thesis committee: Duane Quiatt, Lorna
Moore, and Graham Sterritt. I especially thank Duane Quiatt, for
allowing me to pursue my interests with his characteristic quiet
encouragement and steadfast moral support. I extend special thanks
to the Denver Zoo, especially to Clayton Freiheit, Director, who
allowed me access to the back areas of the gorilla compound and to
Dr. Richard Cambre, Zoo Veterinarian, who initiated the project and
who never hesitated to listen to my latest ideas. I am deeply
grateful to Ann Rademacher, Vince Carbone, Bob Hamill, Mike Kinsey,
and Fred Jacobs who shared information and friendship. I thank my
family, for understanding the time constraints imposed by this
project. Thanks to Bonnie Thorne who participated in the original
phase of this program. Special thanks, with great affection, to
Maguba, Bibi, Thomas, Max, and Kisoro, my gorilla friends, who made
I. INTRODUCTION............................................ 1
History of Gorilla Studies ........................... 1
Current Status of Gorilla Populations................ 3
II. INFERTILITY IN CAPTIVE GORILLAS......................... 6
Reasons for Infertility............................. 7
Incest Inhibition................................... 8
Choice of Partners............................. 8
Spatial Constraints............................... 9
Lack of Stimulating Environments....................11
Organic Difficulties.............................. 12
III. GORILLA RESEARCH AT THE DENVER ZOO......................13
Study Methods....................................... 13
Breeding Loans.................................. 16
Behavior Studies............................. 17
Research Techniques............................... 21
Close Observational Setting......................21
Training Procedures............................ 26
Daily Assessment................................. 26
Phase 1 Maguba and Thomas........................29
Phase 2 Maguba and Max...........................32
Phase 3 Maguba and Kisoro...................... 34
IV. STRATEGIES FOR IMPROVING BREEDING SUCCESS..............40
Breeding Loans................................... 41
Improving Living Conditions..........................42
1. Gorillas at the Denver Zoo ..............................14
2. Summer 1980: A. Attempts (per 10-minute period) to
engage another gorilla in social interactions.
B. Episodes (per 10-minute period) of pounding and
3. Outdoor Gorilla Exhibit..................................22
4. Cross Section View of Gorilla Exhibit....................24
5. Position for Examination of Female Gorilla...............25
6 May 1982 Assessment Results..............................30
Urinanalysis for LH......................................30
7 June 1982 Assessment Results.............................31
Urinanalysis for LH......................................31
8. Sub-Human Primate Pregnancy Test Scoring................35
9. Spring 1982: Behavior-Test Results..................36
1. Behavioral Observations: Spring 1981.................. 19
2. Conjunctive Approach................................... 20
3 Dally Assessment.........................................27
History of Gorilla Studies
Early accounts from adventurers, hunters, and even
missionaries gave us lurid descriptions of a hairy beast, fearsome
and savage, that roamed the African rain forests searching for
human victims to attack and kill. Confusion prevailed as to the
specific status of this ape-creature which was given contradictory
names and descriptions; no less than 15 variations in nomenclature
can be found in documents between 1847 and 1905 (Maple and Hoff
1982). In the mid 1800's Thomas Savage and Jeffries Wyman wrote a
paper in which taxonimic confusion is triply confounded in the
title: "Troglodytes Gorilla, a New Species of Orang From the Gabon
River," (Willoughby 1978). This paper contains highly imaginative
and entertaining tales of an ape that:
"lies in ambush to kill passer-bys ..."
"builds a rude hut . sleeps outside on the roof ..."
"clubs elephants that come to feed where they be . ."
"carries off native women ..." (Willoughby 1978, pp. 35-
In the early part of this century chimpanzees, macaques,
and probably baboons were confused with gorillas. Even today, from
publications of dubious reputation (SUN: June 4, 1985) headlines
such as Gorilla Makes Girl Pregnant" can be found lurking in
supermarket aisles, conveying false and innacurate information
about the gorilla.
The proper taxonomic status of the gorilla shifted into
focus in the first part of the present century as trickles of
information concerning the ecology of the gorilla were published.
However, it wasn't until George Schaller's pioneer investigation in
1960 on the ecology and behavior of the mountain gorilla in Kabara
that reliable data collected by a scientist in systematic fashion
began to dispel previous myths. Schaller discovered that the
gorilla in fact was a shy and gentle creature who lived a peaceful
family life in the depths of the rain forest, with no natural
enemies other than man (Schaller 1963). During his 18 months in
the field, Schaller recorded his observations for a total of 466
hours. He collected the first reliable data on gorilla diet,
nesting, ranges, and social organization and behavior, as well as
compiling baseline census figures.
In 1967, Dian Fossey, under the tutelage of L. S. B.
Leakey, began a longterm field study of the mountain gorilla,
eventually establishing the Karisoke Research Centre which provided
the basis for numerous studies of the gorilla in nature. From
Fossey's book "Gorillas in the Mist" (1983), and still more from
scientific papers by Fossey and her co-workers (Harcourt et al.
1980) we now have a wealth of material about the wild gorilla.
Studies of captive gorillas beginning with those of Robert Yerkes
(1925) have added to our scope of information. Ironically, as our
knowlege of the gorilla expands, the gorilla himself recedes from
Current Status of Gorilla Populations
At a June 1985 conference on Primates: The Road to Self
Sustaining Populations," in San Diego, California, census figures
were presented which indicate that at present there may be 5,000
Eastern lowland gorillas (Gorilla gorilla graueri) in Eastern
Zaire, 5,000 Western lowland gorillas (Gorilla gorilla gorilla) in
forest areas near the coast, and only 230 mountain gorillas
(Gorilla gorilla beringei) in a 150 square mile preserve located in
Rwanda, Uganda, and Zaire. What is most significant and of great
concern is the rapid rate of decline. Using George Schallers
original computations (Schaller 1963) Dian Fossey reported a 50%
reduction in the mountain gorilla living in the Virunga mountains
during a 22 year period (Fossey 1983). According to Fossey, the
male/female ratio is presently 1:.92, down from a previously
reported 1:4, while the ratio of adults to sub-adults has increased
from 1.2:1 to 2:1. Of the births documented in her geneologies 16%
were the result of inbreeding (Kurland 1984:502). If present
trends continue the wild mountain gorilla will be extinct by the
year 2000, and no mountain gorillas have survived in captivity.
The other 2 subspecies are likely to follow suit.
There are a number of reasons for the downward spiral in
gorilla populations, beginning with the procurement of animals for
zoos, museums, and private collectors in the latter part of the
19th century. As a matter of practice, entire troups or family
groups were killed so that young animals could easily be taken.
For captured gorillas long sea journeys under devastatingly
unsanitary conditions, culminating in prolonged quarantines,
resulted in a 50% death rate for these captives. It has been
estimated that with all factors combined 20 gorillas died for each
one that reached its destination abroad (Erlich 1984). Recent
awareness of the need to conserve primate species all over the
world led to the enactment of various international laws
prohibiting capture, exportation or importation of gorillas. Legal
prohibition, however, has not eliminated these practices: in April
of 1984 the International Primate Protection League Newsletter
reported 7 young gorillas for sale by a French couple in
Sangmelina, Cameroun, who claimed they had "adopted" the gorillas
after local residents had killed their mothers for meat.
Gorillas often have been caught inadvertently in snares and
traps set for animals such as antelope and small game. They were
at one time captured and killed so that specific body parts could
be stewed to concoct a virility potion. They seem to have suffered
a great deal at the hands of poachers (Fossey 1983). Fossey's
moving account of the death of Digit, one of her favorite study
subjects, and the subsequent establishment of the Digit Fund, has
given worldwide attention to the poaching problem. In 1984 a
poacher apprehended by a patrol supplied the names of 94 other
poachers as well as the locations of their snares, traps, and
escape routes. Fossey stated at the San Diego conference mentioned
above that it is becoming increasingly difficult to locate snares
and traps, from which she infers that there has been a decline in
these illegal activities. Not all gorilla researchers agree with
Fossey's approach to conservation, but all agree that until animal
dealers no longer have a cash market for young gorillas poachers
will continue to take their toll on gorilla populations. Gorillas
are occasionally killed for sport, for trophies, and for meat, and
in Zaire they have been shot for crop raiding. At present, the
most serious threat to wild populations stems from conversion of
gorilla habitats. Expanding human populations have increased the
need for permanent agricultural land as has a rising market in
export crops such as rubber, coffee, and pyrethem. Forest areas
are being cleared at a rapid rate to satisfy the fuel requirements
of local populations. Increasingly, gorillas must compete with
cattle for habitat. It appears that the unchecked human population
expansion in all of Africa threatens not only gorillas but a
variety of wildlife as well as the ecological balance of nature.
The outlook is not promising for the gorilla dependent as it is on
humans control of resources necessary for its survival.
INFERTILITY IN CAPTIVE GORILLAS
With wild populations so severely threatened, successful
reproduction of captive gorillas, all of whom are believed to be
Western lowland gorillas and who may number about 400 worldwide may
be the only answer to preservation of the species. In spite of
breeding successes at some zoos, captive gorillas have a very poor
reproductive record and a high perinatal mortality rate so that the
viability and genetic diversity of this population is severely
threatened (Beck 1982). Indications are that the captive
population in North America decreases by three percent per year
(Bahl 1985). According to a survey by Beck in 1978-79 of 52 North
American Zoos and biomedical institutions, only 21% of adult male
gorillas sired offspring. In the period covered by Beck's study 34
of 55 males with access to females copulated with intromission, but
only 13 births were recorded (Beck 1982:8). Figures from the 1983
Studbook of World Gorillas reveal that in North America as of that
date 38 of 76 wild born female gorillas up to age 40 had given
birth compared with 8 of 55 captive born females. 27 of 58 wild
born males had sired offspring, compared with 2 of 37 captive born
males. It appears that captive born males and females
statistically have reduced chances to reproduce, so that it can be
expected that this population will continue to decrease in
numbers. There is some evidence to suggest that for captive male
gorillas fertility is maximal between ages 7-15 (Beck 198,2). An
unexplained phenomenon is a number of blackbacks who mated
successfully at an early age but stopped after age 12 or 13 (Foster
1982). In addition, many males tested for fertility have been
found to be organically sterile due to low sperm counts or abnormal
sperm morphology or both (Platz et al., 1979, p. 79). To make this
already dismal picture worse, primaparous gorillas exhibit a high
degree of maternal incompetence, indifference, and abuse, sometimes
with fatal consequences for their offspring. Conversely, if
maternal care is adequate and the infant remains in the group, the
birth interval of 4-5 years approximates that in the wild, which is
not conducive to rapid increase in population. It appears that
captive gorillas are not reproducing at a rate that will enable
them to sustain their numbers, and that inadequate parenting
confounds the problem, creating hand reared gorillas with their own
subset of difficulties.
Reasons for Infertility
Factors that inhibit reproduction in gorillas are numerous;
reproductive failure can be attributed to psychological,
physiological or behavioral inadequacies, with multifactor
causation in most cases. Foster (1982, p. 27) has proposed that
the inability of gorillas to reproduce in captivity is a result of
our failure to provide for their needs. Some pertinant factors are
Gorillas reared together in captivity often exhibit a lack
of sexual interest in each other during adulthood. A similar
phenomenon is seen in humans according to the well known
Westermarck hypothesis (McCabe 1983). It Is possible that a
similar "incest taboo operates in the wild, where according to
Harcourt (1978), inhibition of mating with specific individuals can
be predicted on the basis of early close familiarity. Furthermore,
there is a marked preference for mating with strangers.
Choice of Partners
Wild female gorillas leave their natal group at sexual
maturation to join a mature silverback and his troop. Males also
emigrate to establish a harem although they may inherit a troup
from an aging father if breeding opportunities are available. Zoos
have been prone to a "Noah complex in the past, acquiring pairs of
gorillas as infants or juveniles and waiting for the progeny which
unfortunately usually fails to materialize. Beck (1982) agrees
with Harcourt and has confirmed that maintaining pairs of gorillas
greatly reduces the probability of breeding. Yet today more than
50% of 133 institutions that house gorillas, display them in pairs
or, even worse, in solitary confinement. Using several case
histories Beck (1982) demonstrated the importance of individual
partner preference. In these instances paired gorillas that did
not mate were successful at mating when paired with new partners.
However, a choice of sexual partners is usually not available to
captives. Under the artificial conditions imposed by the captive
setting, gorillas may not be sexually attracted to their cagemates
and are therefore without breeding options.
In the wild, female gorillas tend to space themselves some
distance away from the silverback except during estrus (Nadler and
Collins 1984). The captive environment dictates unnatural spatial
relationships which can increase aggressive attacks by the male
without providing avenues of escape or concealment for the
females. The tension and occasional injuries which result
contribute to disharmonious relationships, including sexual
relationships. At the Yerkes Primate Research Center, 3 female
gorillas who had earlier failed to conceive during timed pairings
with males, conceived within one month after they were placed in a
large, outdoor compound with a male. In this enclosure they were
able to avoid or escape the male when they wished and were thus
able to control the occurrence and frequency of mating (Nadler
It is also possible that diet contributes to breeding
success in ways yet not completely understood. Good health, after
all, requires more than satisfying caloric needs. There may be
nutritional requirements for optimal fertility which captive diets
do not provide. Throughout the year, gorillas at the Howletts Zoo
Park in England, are fed more than 120 different fruits and
vegetables, many of which are imported, in addition to locally
grown hay and browse. John Aspinall, director and owner of
Howletts, has stated (1980) that a varied and changing menu is
essential to the health and well being of his gorillas, who perhaps
only incidentally have enjoyed breeding success. Maple and Hoff
(1982) reported on the "Cincinnatti love diet" at the Ohio zoo
where breeding commenced after the introduction of a new dietary
regime. No one would argue that reproduction can be increased
among captive gorillas by implementing any one simple measure, but
there may well be positive even if indirect benefits from an
improved and varied diet. Imagine the depressing effect of a
daily, unchanging, monotonous menu, however nutritionally sound, on
a species that under natural conditions chooses from over 200 food
items in a given year.
Sexual behavior is observed and subsequently practiced by
young primates in the wild. Social experience is also a primary
factor in the acquisition of appropriate mothering techniques
(Harlow 1971). In captivity, young gorillas are not often kept
with their parents or even in troops and so they may grow up
without appropriate age and sex role models. Captive primiparous
female gorillas who have not "aunted", that is who have not handled
and played with infants are likely to reject, abuse, or neglect
their own newborn offspring. Such inexperienced mothers too
frequently handle their infants awkwardly, play with them roughly,
and seem confused by the attempts to nurse. Maple and Hoff (1982)
believe that for an ape to achieve social competence he or she must
interact with peers, adults, or even humans. Thus in one way or
another, basic social experience and stimulation through all
sensory channels is required. General social competence is of
course a prerequisite of competent parenting. Maple and Hoff
maintain that even primiparous females can care competently for
their offspring if their learning experiences have been complex and
numerous. Unfortunately, the majority of zoos do not have
sufficient numbers of gorillas to provide group settings and varied
social situations, and few allow human-ape interactions for fear of
injury to staff members and fear of "humanizing" the gorillas.
Lack of Stimulating Environments
Boredom in the captive environment has contributed to
decreased libido in all the great apes. Coprophagy,
regurgitation/reingestion, stereotypic movements, fur plucking and
high levels of aggression are unfortunate consequences of
inadequate stimulation in captivity (Erwin, Maple, and Mitchell
1979). It seems reasonable to speculate that improvements in
gorilla compounds will have beneficial effects upon behavior in
general, including sexual and parental behaviors.^
^Preliminary analysis of my behavioral data from the Denver Zoo
;n 1982 and 1985, indicates a dramatic reduction in the frequency of
fitation/reingestion and coprophagy with the gorillas as well as
:ion of aggression during the main feeding time, with the implementation
liet plan whereby seeds, alfalfa hay, fresh spinach, and citrus fruit
are made available for foraging throughout the day.
Physiological infertility in female gorillas has not been
thoroughly investigated, so it is difficult to assess the scope of
this problem. In male gorills the "infertility issue is made more
complex by the fact that some males designated as infertile have
subsequently fathered offspring, while others with acceptable sperm
counts and no documented pathology have mated but failed to
reproduce. We still do not have baseline sperm counts or hormonal
analysis for wild gorillas to compare with those of captive males
so that at present designations of "infertile" or "sub-fertile"
applied to captive animals are based on a comparison with human
male values and may not be applicable to gorillas.
GORILLAS RESEARCH AT THE DENVER ZOO
The Denver gorilla collection originally included three
gorillas (Figure 1):
Thomas, a wild caught male who arrived at the zoo in
December 1970 at the estimated age of 2 years.
Bibi, a wild caught female who arrived in Denver in January
1971 at the estimated age of 2.5 years.
Maguba, a wild caught female brought to the zoo in July
1971 at the approximate age of 6 months.
Detailed information about breeding is not available, but
in 1975, at the approximate age of 6 years, Bibi gave birth to a
female infant who was removed to separate confinement because of
Bibi's incompetence and aggressive threats by Thomas. The infant
survived for 10 days, but unfortunately succumbed to E. coli
pneumonia and sepsis. Zoo records indicate that Thomas and Bibi
mated at regular intervals, while Maguba and Thomas mated only
occasionally. In 1978 a new gorilla compound was finished, but it
is believed that the new situation was stressful to Thomas for
breeding was never observed in this enclosure between Thomas and
either of the females.
1970 1975 1980 1985
Fig. 1. Gorillas in residence at the Denver Zoo from 1970 to the
In 1980, Zoo officials, concerned about the reproductive
fate of its gorillas collection, implemented a Gorilla Breeding
Program utilizing the special talents of medical experts, staff
members, and anthropologists. The program involved 3 main
1. Detailed physical examinations of all the gorillas to
assess potential fertility.
2. Breeding loans with the Cincinnatti, Topeka, and
Lincoln Park Zoos.
3. Behavioral studies correlated with daily physical
examination of one female gorilla (Maguba) to assess status of her
The focus of the plan when it originated was to
artificially inseminate one female and to achieve natural
insemination with the other by placing her in the Cincinnati Zoo on
breeding loan; however, subsequent events altered the nature and
direction of the plan.
Physical Examinations. All 3 gorillas were anesthestized
in April 1980 and given routine health checks that included dental
work, blood sampling, and tuberculin testing. All were examined to
determine possible impediments to fertility. Laparoscopy
examination of Maguba revealed numerous luteal scars on both
ovaries, including a fresh corpus luteum believed to be less than
three days old on her right ovary. Her uterus appeared healthy
with no detectable lesions (Cambre and Wildt 1980). Urine
collected for a 2 year period was analyzed by radioimmunoassay at
the San Diego Zoo Research Department. Results indicated that
Maguba cycled regularly at approximately 25 day intervals.
Indications were that Maguba was fertile and would be an
appropriate candidate for artificial insemination since she did not
breed voluntarily with Thomas. Laparoscopy of Bibi revealed
healthy reproductive organs without abnormalities but there was no
evidence of recent ovulation or any ongoing cyclicity (Cambre and
Wildt 1980). Since Bibi had previously given birth and was
technically a "proven breeder" she was considered an appropriate
candidate for a breeding loan with the hope that a new partner
would stimulate hormonal activity and an interest in mating.
Electroejaculation of Thomas indicated a total sperm count of
338xl06, a sperm count of 423x10^ per ml, with a 78% total abnormal
morphology. In addition bilateral, testicular dysfunction was
noted. Though sub-fertile by human standards, he would nonetheless
serve as a donor for artificial insemination. Administration of
Clomid was begun with Thomas in the hope of improving his total
Breeding Loans. Bibi was sent to the Cincinnatti Zoo in
June 1981. After almost a year she began to mate on a cyclical
basis with the resident silverback of the group, Atari, but
unfortunately she never conceived. She returned to Denver in
*After 6 months the percentage of normal sperm doubled and there was a
Eicant increase in his overall sperm count.
August 1984 having gained sexual experience as well as experience
interacting with gorillas of different ages, including
youngsters. It is hoped that Bibi possesses some knowledge of
infant care which will prove useful in the future.
Behavioral Studies. In the summer of 1980 students from
the University of Colorado, Boulder, working under the direction of
David Chiszar, conducted a behavioral study involving Thomas, Bibi,
and Maguba. A retrospective hypothes was that Maguba's attempts to
engage the other two gorillas in social interactions increased in
frequency during ovulation (projected on the basis of laparoscopie
findings). In addition, the students noted that the frequencies of
her chest pounding and running displays with chest pounding also
increased during this time period (Figure 2). The zoo requested
further involvement from the academic community.
In the spring of 1981, students from the University of
Colorado, Denver, began a series of behavioral observations under
the direction of Duane Quiatt. This work was designed to test the
possibility of correlating non-breeding behaviors with estrus. The
initial study was conducted blind with regard to Maguba's menstrual
cycle and involved behaviors such as chest displays, pounding on
the windows and doors, Maguba's proximity to Thomas and genital
examinations of Maguba by Thomas (see Table 1). Observations
commenced in April and included all three gorillas, but focused on
Fig. 2. Behavior of Maguba during summer, 1980. (A) Attempts (per
10-minute period) by Maguba to engage another gorilla in social
interactions. (B) Episodes (per 10-minute period) of chest pounding
and running by Maguba. (Chiszar and Caldwell, 1980).
BEHAVIORAL OBSERVATIONS Spring 1981
Summary of Index Behaviors
(Quiatt, Miller, and Cambre, 1986)
Maguba. Bibi left during June for Cincinnatti and the observations
of Thomas and Maguba continued through July with the help of zoo
docents. Results have been published elsewhere (Quiatt, Miller,
and Cambre 1986); in summary, correlations found between certain
behaviors and menstruation, helped to plot Maguba's cycle, but
ovulation could not be clearly determined.
In November 1981 an attempt was made to artifically inseminate
Maguba. Timing of the attempt was based on analysis of hormone
output, using urine samples. It was unsuccessful, perhaps because
ovulation was not accurately predicted (Albrect et al, in press),
but it is also possible that ovulation was suppressed as a
consequence of stress from manipulations while Maguba was under
anesthesia or from the drugs employed during the process. Lasley
(1982) has reported on two other unsuccessful artificial
inseminations in gorillas, stating that there seems to be a
prolongation of the follicular phase in both instances. With such
a small sample it cannot be stated for certain but preliminary
indications are that artificial insemination in gorillas may be
more difficult to achieve than in other primate species. In
humans, artificial insemination is performed 3-4 times during one
cycle to maximize the chances of conception, clearly not yet a
viable option with gorillas since it would require immobilization
and anesthesia each time.
At this point zoo officials decided that with Bibi still in
Cincinnatti and with Thomas and Maguba still not copulating, the
only recourse was to try a second artificial insemination, with
greater emphasis on accurate timing of the procedure. A plan was
developed to make continued behavioral observations of the gorillas
using a more inclusive and conjunctive approach (Table 2).
1. Prolonged observations and detailed records.
2. Close attention to monitoring and self monitoring.
3. Increased familiarity between Maguba and observer(s).
4. More input from keepers.
(Quiatt, Miller, and Cambre, 1986)
For reasons relating to the health of the gorillas, and in
accordance with zoo safety precautions it was decided that only one
observer would be allowed access to the back areas of the gorilla
exhibit with the rest of the students remaining in the visitors
section. It seemed reasonable to assume that if an observer could
manage to establish a friendly relationship with the gorillas she
could develop a clearer understanding of the individual
personalities so as to better interpret interactions and
behaviors. This inside observer could also record events in the
catch cages shut off from public viewing and would be able to hear
vocalizations not audible from the glassed-in visitors section.
Most important, inside observation would enable close,
uninterrupted study of the animals, unhampered by noisy crowds.
For the first several weeks I visited to the keepers area
behind the gorilla display cage for 2 hours every morning to become
familiar with the gorillas and their daily routine and to establish
contact with keepers. In time, the gorillas became accustomed to
my presence. Perhaps because Maguba had had a great deal of human
contact as a youngster she began to request tickling by pressing
her back against a steel mesh door and looking over her shoulder
towards me. Gradually Thomas learned to approach and trade pieces
of monkey chow for bits of fruit.
Close Observational Setting. When the weather permitted,
the gorillas were allowed to use their outdoor enclosure which is
an odd-shaped grassy area separated from visitors by a shallow moat
and plexiglass windows (Figure 3). On one end of the outdoor
exhibit, on the keepers side there is a cement wall with four
Fig. 3. Layout of outdoor gorilla exhibit at the Denver Zoo showing
steel mesh adjacent to keepers area.
continuous sections of steel mesh inserted. One morning as I stood
watching from one section Maguba unexpectedly stepped across the
moat and climbed up the mesh (Figure 4). The bottom of the mesh
grid connects with the concrete wall in such a way as to form a
narrow shelf, on which she could maintain her balance only by
grasping the mesh with her hands, arms extended above her head.
Her knees were bent and flexed laterally so that her bottom barely
rested on the shelf, just about at my eye level (Figure 5). After
reviewing reports by Nadler (1975, 1980) describing labial
tumescence in captive gorillas, i realized that the situation
afforded an opportunity to replicate Nadler*s observational
recording technique with Maguba. Nadler described the gradual
increase in labial tumescence on a 4 point scale which corresponded
to an increase in estradiol during the follicular phase of the
menstrual cycle. The 1-2 day period of maximum swelling appears to
be the optimal time for conception to occur. Maguba's perineum had
been shaved for the artificial insemination procedure, and this
afforded a relatively unobstructed view of her genitalia. After
consultating with the zoo veterinarian, Dr. Richard Cambre, and
other members of the Gorilla Breeding Program, I decided that I
would examine Maguba on a daily basis and monitor overt physical
change in detail; this would provide a fuller description of events
surrounding ovulation and seemed to be the most effective way of
pinpointing estruS. Other students continued their observations of
the gorillas with a refined checklist of behavioral categories. On
the day of suspected estrus the urine was to be collected from
Fig. 4. Cross-sectional view of the gorilla exhibit at the Denver
Zoo. The gorilla has jumped across the moat and is balancing on the
concrete shelf, facing the keepers area, allowing an examination
through the wire mesh.
Fig. 5. Female gorilla in position for examination by the
investigator through the wire mesh.
Maguba and rushed to the University of Colorado Medical Center for
analysis for LH. My goal was to bridge the gap between the
laboratory results and ongoing behavioral studies. If I could
accurately predict estrus, the insemination team could be ready
after confirmation from the laboratory.
Training Procedures. For several weeks I encouraged Maguba
to jump across the moat and climb the shelf by offering her pieces
of fruit, recording progress on a daily basis. On most days Maguba
was quite willing to cooperate; on occasion I found she was waiting
for me on the shelf. On other days she would sit stubbornly across
the moat with her back to the mesh, refusing to budge. At these
times I fed Thomas her share of the fruit and left the compound.
After 20 minutes I would return to repeat the process. Usually
Maguba then would be willing to cooperate, but on a few instances
she still could not be coaxed subsequently to submit to the exam.
I later determined that these instances of refusal to cooperate
regularly occurred a few days prior to menstruation.
The daily assessment included measuring the parameters
listed in Table 3. Each morning a chemical test strip (Hemastix,
Ames Co., Elkhart, Iowa) was used to detect occult menstrual blood
in a fresh urine sample which was then frozen for hormonal analysis
at a later date. I did not have access to the results of this test
at any time during the study period so that descriptions of overt
physical states were not biased.
Time transfer to shelf length of session
Nipple circumference 1-3
Uro-genital length 1-4 centimeters
cleft width 1-2 centimeters
Mucosal color light (1), Medium (2), Dark (3)
Cervical Mucous amount 1-3
Tumescence external perineal labia....,
Blood by visualization presence (+), absence (-)
Mucosal Color. A section of the mesh grid was removed in
order that I might reach through the bars and have physical contact
with Magubas genitalia. Adequate light for visual examination was
imperative and I experimented with several different light
sources. An inexpensive penlight was the only flashlight that
provided a small, solid spot of illumination of sufficient
intensity. To the end of the penlight I glued 3 small pink color
chips that corresponded to changes in the color of the vaginal
mucosa during the month. Color assessment was made by holding the
penlight next to Maguba's vagina and rotating it.
Uro-genital Cleft. A one centimeter square plastic grid
was cut into a T-shape and used as a scale to determine variations
in the uro-genital cleft, placing it directly over the vaginal
area. The grid was flexible, and inexpensive, and after Maguba was
given one to examine she showed little interest in trying to snatch
Nipple Size. A plastic circle template was used to measure
the circumferance and length of Maguba's nipples. This was pressed
over her nipple, while the longitudinal side measured relative
length. Cylindal changes were noted.
Labial Tumescence. The original focus of this daily
routine was on labial tumescence, which proved to be the most
difficult parameter to assess and the least reliable measurement of
those collected. During some months no detectable swelling
existed, at other times swelling was so slight so that it was
impossible to make an accurate estimate of any sort. This lack of
tumescence may suggest a hormonal basis for lack of breeding
(Nadler 1980), but it is equally possible that tumescence is
variable among individual gorillas since reports from other zoos
indicate that many females lack this indicator of estrus. Harcourt
et al. (1980) reported that a sexual swelling is only detectable
in nulliperous female gorillas.
Initially an assistant fed Maguba to distract her while I
conducted the examination, but Maguba became so accustomed to the
procedures that it eventually took me less than 5 minutes to
complete them working alone. In addition, the amount and quality
of her vaginal secretions were noted when possible. A daily
conference with the gorilla keeper provided information on Maguba's
emotional state, that is, how easily she transfered to her catch
cage, whether there had been any interactions between Maguba and
Thomas, etc. Occasionally, Maguba would smear or throw feces on
the walls, or she would toss it towards the staff. Since this
behavior occurred infrequently it was charted to test the
possibility that it corresponded to changes in her cycle. Maguba
eventually allowed me to touch her perineal area, parting her fur
for better visualization. She moved to either side if I motioned
to her arid she would press her bottom closer to the opening in the
mesh upon request. I began to accustom Maguba to digital
intromission and eventually insertion of a lubricated syringe.
Maguba's cooperation exceeded our expectations, so we decided as a
second goal to train her to allow artificial insemination without
anesthesia, thereby eliminating the stress factors that may have
been associated with the past failure.
Phase 1; Maguba and Thomas
Results of the examinations for May and June of 1982 are
given in Figures 6a and 7a. On the basis of my observations and
the changes noted with regard to nipple size, color change, length
and width of the vaginal opening, and the quality of vaginal
Fig. 6. Results of Daily Assessment of female gorilla Maguba plotted
with results of urinanlysis for lutenizing hormone (LH) May 1982.
* t .
15 20 25 30 day
Fig. 7. Results of Daily Assessment of female gorilla Maguba plotted
with results of urinanalysis for lutenizing hormone (LH) June 1982.
secretions, including the presence of blood, it was estimated that
Maguba menstruated on May 12 and 13 and June 4 and 5 and that she
ovulated on May 22 and June 20. On these dates, the highest values
were given for parameters measured. On May 21 and 22 some
detectable labial swelling was observed. Hemastix testing in the
zoo hospital confirmed the menstruation dates. A second artificial
insemination was scheduled for the fall of 1982 and it was decided
to spend additional time preparing Maguba for artificial
insemination without anesthesia. We hoped that she would become
increasingly tolerant of my intrusions so that we could make more
that one insemination attempt. We planned to use fresh semen
collected on the morning of the procedure as well as some
previously frozen samples. Unfortunately, Thomas died suddenly in
August 1982 of undetermined causes, thereby throwing the proverbial
monkey wrench into our project. At a later date, laboratory
analysis of urine collected during the study period was performed
at the University of Colorado Health Sciences Center. Results are
given in Figures 6b and 7b. The LH surge on May 21 and June 19
indicated that ovulation took place 12 to 24 hours after each of
these hormone surges, confirming our estimates. It appears that we
were able to determine estrus with some accuracy from the physical
Phase 2: Maguba and Max
After Thomas' death Maguba became lethargic, anorexic, and
appeared to be suffering from social deprivation. In December of
1982, Maguba was paired with Max (Kukuma), an adult male lowland
gorilla on breeding loan from the Topeka, Kansas Zoo. Max had been
born in captivity and spent most of his 15 years with a female,
Tiffany, approximately the same age. Max and Tiffany had never
mated and while a new gorilla habitat was under construction both
were sent out on breeding loans in the hope that new partners would
provide them with sexual stimulation. Almost immediately Maguba's
appetite improved and her behavior returned to normal. During
their 17 months together several clumsy, cyclical mating attempts
were made by both Max and Maguba but although they were monitored
carefully copulation with intromission was never observed. During
this period Max would initiate long play bouts, shadow-walking
close behind Maguba, occasionally sniffing and touching her
bottom. She would stare directly at him for long periods,
sometimes stamping her feet. Analysis of Maguba's solicitation of
her present cagemate gives evidence that she was in fact soliciting
Max, but her efforts were disjointed and ineffectual. Max's
attempts to mount her usually ended with one or both of the them
falling. I continued my daily physical exams of Maguba,
hoping to ascertain estrus so as to correlate findings with her
mating solicitations, but results were inconclusive due to a
reoccurring peri-vaginal infection that caused persistent labial
swelling and drainage. At this point to avoid reinfection, I
decided to employ the Ortho Sub-Human Primate Pregnancy Test which
uses small amounts of fresh urine and which has been used with
success to determine estrus in great apes. This test kit has been
modified to qualitatively detect the presence of LH which peaks 15-
30 hours prior to ovulation (Gould and Faulkner 1981; Figure 8). I
performed this test along with the Hemastix test every morning in
the primate house immediately after urine was collected from
Maguba. Results of the Sub Human Primate Pregnancy test with
regard to mating attempts are given in Figure 9. This test was
performed as early as possible each morning and the results were
available within two hours so that observations were scheduled
Phase 3: Maguba and Kisoro
During this third phase of the Gorilla Breeding Program
efforts focused upon more informal behavioral observations with an
emphasis on qualitative assessment of social interactions. In the
fall of 1984 Max returned to Topeka and Bibi was reunited with
Maguba. After a period of adjustment the females were introduced
to Kisoro, a silverback on loan from the Lincoln Park Zoo. Over
the years Kisoro has fathered 14 offspring with several different
females, primarily while on loan to Howletts Park Zoo. On the very
first morning of their introduction he mated twice with Bibi. For
3 months Kisoro and Bibi mated at regular intervals but for
unexplained reasons they then ceased. We assume that she is not
cycling. As of this writing, Kisoro and Maguba have mated at 25
day intervals for over one year without conception.
We have noted that any major changes in routine (e.g.,
isolation of one animal for medical reasons) will lengthen Maguba's
cycle. Kisoro does not permit Maguba to lend herself to
examination, so to prevent aggression on his part we have
0 >0 +1 +2 +3
Fig. 8. Diagrammatic representation of the scoring system used with
the Sub-human Primate Pregnancy Test (Gould and Faulkner 1981:678).
This test has been modified to detect the midcycle LH (lutenizing
hormone peak in apes and women so as to predict ovulation.
1 days 5
ub-Human Pregnancy Test
V** Non-Copulatory Sexual Interactions
Fig. 9. Correlations between behavior of Max and Maguba, the Sub-
human Primate* Pregnancy Test kit (detecting of LH), and menstruation
(Hemastix) during Spring 1984.
discontinued daily exams for the present. We carefully monitor the
behavior of all 3 gorillas and in doing so have discovered several
clues as to when mating is likely to occur. Normally, KIsoro Is
keenly vigilant of both females, positioning himself so that both
are in sight. If, for example, one female moves to the outdoor
enclosure Kisoro moves to the doorway between the outdoor/indoor
areas so that both females are in view. He constantly glances in
their direction while they feed or move about. In marked contrast,
when Maguba is in estrus he spends much of the time concentrating
on his food in a much more intense manner than usual. At these
times, he lies on his back with his legs raised at right angles to
his body often with his feet crossed. He plays with his toes, and
rubs his nipples. Instead of orienting himself with alert
attention towards his cagemates, he positions his body so as to
face in the opposite direction. His careful disregard of Maguba
makes her soliciting all the more obvious to the observers. Kisoro
fits Fosseys' description of a "pretentiously blase silverback
during courtship by a female (1982).
During estrus Maguba shows little interest in food, even
preferred fruits, and instead eats small amounts of monkey chow in
a offhand manner. Our first clue to estrus is sometimes an
overnight weight loss of 2-4 pounds. During the pre-weighing
period, while in the catch cage, she may throw feces at the wall,
smear it on the shelves and floor, or hurl it at the staff.
Instead of transferring easily to the weighing cage where she
leaves a urine specimen each morning, she is likely to be restless,
unwilling to cooperate, sometimes drinking 2 quarts of unsweetened
Kool-Aid before voiding. Also, the frequency of her displays
increases. Her solicitation of Kisoro (Miller and Quiatt 1986),
consists of a series of stereotypic postures and behaviors which
are repeated almost constantly during an estrus period that
normally lasts 2 days. Once behavioral cues indicate that Maguba
is approaching estrus, the keepers pay close attention to the video
monitor in their work area so as to record breeding behavior.
Arrangements are made so that I or other observers can be on hand
to record solicitation and mating bouts.
Although present circumstances have eliminated the original
goal of artificially inseminating Maguba, the program of
observations initiated in conjunction with this goal has led to a
much clearer understanding of gorilla behavior. Behavioral changes
in conjunction with changes in routine can be predicted, and more
precise prediction of reproduction behavior in general is now
routine. In addition, my research position has provided a bridge
between the administration and the keepers so that more
cohesiveness of effort has been achieved in the Gorilla Breeding
Program. Because Maguba has become so accustomed to daily
attention and contact it has been possible to detect and evaluate
physical problems such as a persistent vaginal infection and
various wounds and bites. Maguba is now quite willing to allow us
to examine closely an affected part, and to treat it with
antibilotic creams when necessary. An added bonus has been that
Bibi, in imitation of Maguba, will allow us to inspect her vaginal
area. This may prove beneficial if we decide to monitor Bibi in a
STRATEGIES FOR IMPROVING BREEDING SUCCESS
The widespread problem of non-sustaining gorilla
populations has been recognized for several years; and as the ages
of captive gorillas increase without imports from the wild,
concerns of institutions holding gorillas escalate. Some steps
have been taken to remedy the situation. Symposiums, conferences,
and workshops have identified many of the problems, and the
implementation of solutions is slowing taking place. In theory
there should be a variety of ways to improve fertility in captive
gorillas based on understanding gained from research in this field
in many other species of animals. Selective breeding in cattle has
long been a mainstay of the cattle industry. Under laboratory
conditions sheep, pigs, rabbits and mice have been manipulated to
produce desired strains and breeds. Artificial insemination has
been successful in monkeys, and Gould (1982) reports successful
insemination in chimpanzees. In humans there are multiple options
for infertile couples, ranging from artificial insemination to in
vitro fertilization and to surrogate mother programs. However, for
gorillas we do not have large numbers of animals to experiment with
nor can we apply methods successful in other species. It is clear
that we must seek ways to improve the low reproductive rate and the
high perinatal death rate in gorillas through ways that are
practical and feasible and specificially designed for gorillas.
Some of the possible ways to improve fertility in captive gorialls
are discussed below.
The basic problems of rearing young gorillas as "sibs and
the lack of role models in small groups could theoretically be
solved by breeding loans. Ideally some type of master plan would
afford arrangement of breeding loans among captive gorillas
worldwide, mixing the sexually experienced with the inexperienced
and the nulliparous with experienced mothers in enclosures that
could accommodate troops of up to 25 members. Gorillas reared
together as youngsters would be separated and sent out on breeding
loans. Zoos that temporarily relinquished their gorillas could
begin construction of more natural enclosures that would be ready
to accommodate offspring from those breeding loans. Breeding loans
involving gorillas have been arranged between institutions during
the past few years, and that translocation of gorillas can remedy
past copulatory failures is evidenced by the fact that in recent
years 13 loans have produced 26 offspring in North American Zoos
Through breeding loans potential sexual partners become
available to non-breeders while in breeding animals new variety is
entered into the gene pool. Breeding loans are not a panacea,
however. Transportation, especially across continents, is
difficult to arrange, expensive, requires anesthesia at least once,
and necessitates cooperation among officials who must be prepared
to insure the safety and proper handling of animals involved. With
a change in environment comes the exposure to new and potentially
harmful microbes. Injuries are frequently sustained during the
stress of introducing a gorilla to a new partner or group.
Conditions of a breeding loan may dictate removal of an infant from
its mother, disrupting the mother-infant bond, and that disruption
may affect the youngsters' social development at some indeterminate
later point. On a physiological level, lack of immunological
benefits from its mother's milk may compromise the health of a
gorilla. Breeding loans do not come with guarantees, either. At
the Denver Zoo after a total of three such loans there are still no
offspring. Furthermore, such a plan as is suggested here would
require close cooperative effort between institutions to a degree
not yet achieved, as well as financial resources seldom available
Improving Living Conditions
Given that all three great ape, species gorilla,
chimpanzee, and orang-utan, are fertile in the wild, it is not
surprising that zoos with spacious and naturalistic outdoor gorilla
habitats are breeding successfully. Woodland Park Zoo in Seattle,
Washington and the Apenheul Sanctuary in Apeldoorn, Netherlands are
two examples. Howletts Zoo Park in Great Britain and the Lincoln
Park Zoo in Chicago, Illinois have impressive breeding records and
in both great care has been taken to design enclosures that are not
only spacious but complex enough to provide nesting areas, play
apparatus, privacy and avenues of escape for females and
youngsters. All the aforementioned facilities house family groups
and appear to satisfy the gorillas' psychological, physical and
behavioral needs so as to elicit a wide range of natural species-
specific behaviors. Many more zoos have plans on the drawing board
for new facilities to be constructed as funds become available.
Hopefully these new facilities will give more attention to use of
vertical space, temporal complexity, and naturalistic components
Given the gravity of the situation perhaps an aggressive
approach is necessary whereby we turn to the laboratory
intervention and fertilization in vivo or in vitro. In theory we
should be able to harvest eggs and freeze semen for later
manipulation. In fact, the Denver Zoo currently is seeking funding
for in vitro fertilization of at least one of their female
gorillas. Plans are at a preliminary stage as it is recognized
that such an ambitious project is frought with inherent
difficulties. Anesthesia would be required twice as would
separation from cagemates for recovery periods. Both events have
proved extremely stressful to all the gorillas sharing a habitat,
which very well might have an inhibitory effect upon the success of
Artificial insemination in gorillas has been undertaken at
the Denver, Memphis, San Diego, and Los Angeles Zoos. To date one
questionable pregnancy has resulted but not a single surviving
infant gives testimony encouraging for this approach. Lasley et al
(1982) reports on two unsuccessful artificial insemination
attempts; in both instances there seems to have been a prolongation
of the follicular phase instances. With such a small sample it
cannot be stated for certain but preliminary indications are that
this technique may be more difficult to perfect in gorillas than in
Behavioral studies can be an adjunct to other approaches to
coping with the problem of infertility in gorillas. Information
concerning gorilla behavior from the wild is now being supplemented
with insight gained from careful studies of captive gorillas.
Institutions like the Woodland Park Zoo in Seattle, Washington have
developed programs designed to monitor and assess behavior and
interaction among their animals. In a recent study of a non-
breeding captive female lowland gorilla, it was concluded that
behaviors such as finger licking and smelling, nipple manipulation,
and grooming were indicators of reproductive status (Watson
1984). The particular female in this study, Koko, is paired with a
male but does not breed. Her reproductive cycle is carefully
charted however and this information will prove invaluable if
medical intervention becomes necessary. If behavioral observations
are combined with physical examinations of non-breeding female
gorillas it is theoretically possible to detect estrus.
From this project several recommendations can be made to
help institutions holding gorillas of any age.
1. Complete fertility evaluations should be undertaken for
both males and females, to evaluate fertility potential and aid in
future decisions regarding reproductive efforts. Inherent risks of
anesthesia should be recognized and emphasis placed on how to
accomplish procedures of artificial insemination with as much
caution and care as possible. Wasted efforts and false hopes could
be eliminated if any animal were to be found irreversibly
sterile. On the other hand, a non-breeding animal, if managed
properly, might ultimately mate successfully. Every male
anesthesized for any reason, should be electroejaculated, freezing
the semen sample for later use, thus building a sperm bank for
gorillas. Recently, at the Denver Zoo, five year old frozen semen
from Thomas was thawed to room temperature. Spermatozoa appeared
sufficiently viable for in vitro fertilization (R. Cambre, personal
2. For females, hormonal profiles are needed to determine
if and when cycling occurs. Policies regarding the collection and
storing of daily urine specimens should be established. This
necessitates cooperation with a laboratory that has the
capabilities of performing the necessary tests at an agreed-upon
cost to the zoo.
3. Hemastix testing and use of the Sub-Human Primate
Pregnancy Test by the keepers provides them with necessary
information concerning menstruation and ovulation early in the
morning. If this test is performed by other personnel there is a
lag time in interpreting results. It is advisable that only one or
two persons perform the test to insure uniform procedures and
reading of the results.
4. In institutions where staff members have physical
contact with female gorillas, training procedures should be
instituted along the lines taken by the Woodland Park Zoo with
"Nina." She was trained to allow vaginal swabbing so that
assesments could be made regarding her monthly cycle (Keiter and
Pichette 1979). Artificial insemination without anesthesia might
be possible in gorillas conditioned to these types of procedures.
It might even be feasible to make more that one attempt per
cycle. An added benefit in Nina's case was that after her
offspring Zuri was born the veterinarian and his assistant were
able to enter her enclosure and examine the newborn infant without
stress or elaborate preparations (Violet English, personal
5. Daily physical examinations as described herein can aid
in detecting estrus and can facilitate detection of other physical
conditions such as injuries and bites.
6. Establishing a permanent affiliation with a university
will provide interested students willing to devote time and energy
to behavioral study of gorillas without cost to the zoo. Keepers
often are more than willing to make observations but the demands of
their jobs may not allow regular time to do so. Plans modeled on
Jane Goodall's "Chimpanzoo project would insure that every gorilla
or gorilla group would be studied, adding to our bank of knowledge
of gorilla behavior.
7. Detecting estrus through non-invasive means such as
behavioral observations, daily examinations, and the Sub-Human
Primate Pregnancy Test has several advantages. In a non-breeding
gorilla, medical intervention such as laparoscopies or artificial
insemination could be more accurately scheduled. With a breeding
animal, to maximize the possibility of successful copulations, care
could be taken to maintain the normal routine, avoiding stressful
situations. For example, visitors regardless of their status could
be denied access to the back areas of the gorilla compound. Non-
critical repairs in the exhibit could be postponed during this
period. Video equipment could be set up to record for the entire
day to document breeding. If crowds seemed to adversely affect
mating, signs might be posted explaining that this was a day of
importance and care has to be taken not to disturb the gorillas by
loud noises or inappropriate behavior. Arrangements could be made
to bring in familiar observers either students, docents or staff.
If aggression has been associated with breeding, extra browse could
be made available along with large branches or plastic tubs to
serve as objects of displacement. The gorillas might be allowed
access to a back cage to afford privacy during this 1-2 day
There are some problems associated with detecting estrus,
none of which is insurmountable if anticipated. To collect urine
for analysis the animal must be separated from her cagemates, which
may require a training period for all the animals. In Denver it
took three months before the gorillas became accustomed to a
musical chair rotation through the back cages. Urine must be
deposited onto an area or in a container that has never been
cleaned with detergents since even trace amounts render urine
invalid for laboratory analysis. Also, the collecting syringe must
never have been washed with soap prior to sterilization. Use of
volunteers or others unfamiliar with these requirements can cause
errors in collection, as can lapses in memory on the part of the
keepers. Specimens can be inadvertantly mislabeled, lost, or
contaminated. Inevitably such accidents seem to occur on days of
To detect estrus by examination of the female's genitalia
as has been described may require separation from cagemates. When
I first began to examine Maguba at the Denver Zoo, she was housed
with Thomas who watched us nervously from the indoor display cage
but never tried to interfere. Max, when he was caged with Maguba
appeared curious about the procedure and would sit outside in close
proximity to her. She refused to climb the fence under these
circumstances, but for the sura of one kiwi fruit Max was easily
trained to move indoors where he agreed to remain locked in until I
finished my examination. Kisoro has refused all forms of bribery
and physically restrains Maguba from interacting in any way with
me; consequently, as mentioned, examinations have been
Conducting for the examination outdoors provides natural
lighting but means that during inclement weather the examination
cannot take place. Durings some months, on the days when I
suspected estrus, a disturbance in the visitors area or a repairman
in the primate house would upset Maguba to the point where she
refused to cooperate. Some disturbances are unavoidable which
suggests that we not rely on one method of detecting estrus but use
every method at our disposal.
This report covers a period of several years in which the
administration and other personnel at the Denver Zoological Gardens
have put considerable effort into developing a gorilla breeding
program appropriate for that facility. They are to be
congratulated for their effort even though rewards to date have
been small. Every zoo needs a gorilla breeding plan that is tailor
made to the reproductive status of its gorillas, the size of the
collection, the physical restraints of its enclosure, the amount of
financing available for changes in the compound, the basic
philosophy of the institution, and the number of dedicated
individuals willing to implement ideas and procedures. Having
compatible, mature males and females in quarters conducive to
mating is of first importance. Students or other individuals can
be employed in behavioral observational programs related to
breeding; when circumstances permit and qualified observers are
available, closer daily monitoring of a females reproductive
status can afford prediction of and special care-taking procedures
for days when mating is likely to occur.
In addition, cooperative efforts should be pursued at every
opportunity; the situation requires that preservation of the
species be granted priority over local program needs. With feral
gorilla populations declining at a rapid rate it is imperative that
all institutions holding gorillas plan for the reproductive success
of each and every animal. There is little time to be lost in this
effort if the species is to be preserved. Wild gorillas can no
longer be imported and captive gorillas have a poor reproductive *
record thus far.
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