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B io Factsheet
Number 208
Captive breeding and the role of zoos
Many animal species are threatened by habitat degradation,
fragmentation and destruction. The complex causes of these are
not going to be addressed quickly enough to prevent some animal
species becoming endangered or extinct.
Breeding successes in captivity have increased in range and
frequency, partly because of:
• environmental enrichment improving animals’ physical and
mental well-being, and their readiness to breed ( e.g. the social
grouping of lowland gorillas in the John Aspinall wild animal
parks in Kent has made them the most successful breeding
colony in the world )
• increased understanding of reproductive physiology ( e.g. an
appreciation of oestrus cycles in rhinoceros has improved
breeding success of both black and white rhinos at Whipsnade
Park )
• the International Species Inventory System ( the Stud Books)
set up at Minnesota Zoo and designed to reduce the genetic
dangers of inbreeding (e.g. Arabian Oryx at Whipsnade and
Golden Lion Tamarin at the Durrell Institute in Jersey have
benefited from contrived matings with distantly-related animals
• the ‘frozen zoo’ concept - the maintenance of banks of sperm,
ova and even embryos until such time as finance or habitat
availability makes breeding a reasonable proposition
• embryo transfer and surrogacy - involves obtaining ova from
a captive female treated with reproductive hormones, fertilising
these ova in vitro and implanting the resulting embryos into a
surrogate mother of a closely-related but more common species
The World Conservation Union (IUCN) estimate that only 3% of
the planet is designated as a protected reserve and that, on average,
one mammal, bird or reptile species has been lost each year for the
last hundred years. Certain groups of species are particularly at risk
– those with a restricted distribution, those of high economic value,
those at the top of food chains and those in climax habitats.
Zoos, or zoological gardens, are areas of confinement keeping
samples of species alive under varying degrees of captivity. Many
‘zoos’ or animal collections in Britain have closed down, and many
have tried to change the public perception of their activities by
changing their titles to, for example, ‘Wild Animal Parks’, but the
fact remains that they have been accused of animal exploitation on
the grounds that:
• Animals are exhibited on the basis of their ‘crowd-pulling’ power,
rather than on their endangered status
• Animals are kept under inappropriate conditions, both in terms
of their physical environment ( poor substrates in cages, for
example ) and their mental and social well-being ( limited feeding
stimuli, or atypical social grouping )
However, there are also difficulties..
• Capture of animals for exhibition may seriously deplete wild
The problems of captive breeding
• Re-introduction of species to the wild cannot be successful
Some of the arguments for and against the maintenance of animal
collections in ‘zoos’ are summarised in Box 1.
Box 1
Captive breeding and re-introduction
is an example of ‘ex-situ’ conservation
since the species are being protected
outside of their normal (‘wild’) habitat.
‘In situ’ conservation – the
management of species within their
natural habitat is to be preferred, but on
a worldwide scale it is thought that 800
species of mammal, 800 species of bird,
400 species of reptiles and amphibians
and as many as 80% of all Lake Malawi
cichlid species could disappear if there
were no captive breeding.
The species must retain its ability to survive in its original habitat
and this becomes more unlikely the longer an individual is kept
in captivity.
Some aspects of behaviour are learned and some are innate.
Advancing from primitive invertebrates to fish to reptiles to
mammals, the proportion of learned behaviour increases. Thus,
primates such as the Golden Lion Tamarin must be given the
opportunity to spend time with and learn from experienced adults
when they are young. If they are not given the opportunity to
learn that snakes or poisonous figs are dangerous, for example,
their release into the wild could have negative consequences.
Captive breeding often only begins when the wild population
has fallen to very low levels. The genetic diversity of the captive
population is therefore usually very low.
Captive breeding is very expensive. Leader-Williams (1990)
reports that the cost of keeping African elephants and Black
rhinos in captivity is 50 times that of maintaining equivalent
populations in national parks in Zambia. In addition, he argues,
money spent on captive breeding does nothing to help conserve
threatened habitats and the many other species that live there.
Bio Factsheet
208. Captive breeding and the role of zoos
A zoo that wants to maintain a breeding population of, say, Mountain oryx, cannot just keep two or three animals. It will need to keep 30
– 50 and this is expensive. Unfortunately, the general public are unwilling to pay more to see 30 oryx than they are one or two; they are more
excited by seeing lots of species rather than a lot of any one. Zoos that want breeding programmes must raise finance and this is what
prompts zoos to charge each other for exchange or loan of animals.
The problem may be made worse because zoos are in competition. A zoo that uses its visitor profit to maintain captive breeding
populations can be harmed if a competitor decides to use its profits in a price war (Fig. 1).
Fig. 1 Competition between zoos
Zoo 1
of animals to
Zoo 2
Uses population
of animals to
generate profit
used to
Zoo 2
used to
Critics of captive breeding in zoos also claim that, even if the breeding
programme is a success, this may lead to more problems (Fig. 2).
resources for
zoo considers
Fig. 2 Problems associated with captive breeding
Transfer to existing zoos
Build new zoos
Kill individuals
The main stages and problems involved in captive breeding are
shown in Fig. 3
Fig. 3 Stages and problems in captive breeding
Points to consider
Could it be reduced?
Habitat loss,
Overall problems:
• There are far more endangered species then can be
saved by captive breeding.
• Captive breeding reinforces species bias (in mammals,
• Ethical issues.
• Cross-fostering eggs or young, translocation, habitat
preservation, predator control.
Capture part
of population
How many?
vertebrates –
prebreeder or
Return to
Low survival
In existing zoo?
New zoo?
How to avoid inbreeding?
How to deliver appropriate
Encourage natural mating
or use artificial insemination
or embryo transplant?
Captivity does not exert the
same selection pressure as
in the wild.
Imprinting on zoo keepers
Much of the work on species preservation carried out in Britain is co-ordinated by BIAZA (British and Irish Association of Zoos and
Aquariums), with its headquarters at Regent’s Park in London. The work of BIAZA can be accessed at
Key points in species management in zoos:
• Zoos and aquariums cannot work in isolation, but must co-operate with one another.
• Co-operation is essential if captive populations are to be successfully maintained without taking more individuals from populations in
the wild.
• Animals in separate zoos should be managed as part of one single population, and this population must have the greatest possible
genetic variation.
• Zoo managers must change their management strategy from keeping few individuals of a wide range of species (very popular with the
fee-paying public) to keeping breeding groups of fewer species (often not so popular with the zoo accountants!)
• It would be dangerous to keep all the individuals of one species in a single location: the entire population could be lost to disease or
to a natural catastrophe. However, populations benefit genetically if they are managed as one single, global population. This management
is the job of organisations such as BIAZA.
Bio Factsheet
208. Captive breeding and the role of zoos
Captive breeding successes
Père David’s deer
(Elaphurus davidianus)
First made known to Western science in the 19th century, the only surviving herd was in a preserve
belonging to the Chinese emperor. After the remaining population in China was lost the remaining deer
in Europe were transported to England :The current population stems from this herd. Two herds of Père
David’s Deer were rentroduced to China in the late 1980s. In spite of the small population size, the
animals do not appear to suffer genetic problems.
Przewalski’s horse
(Equus przewalskii)
The wild population in Mongolia died out in the 1960s; a program of exchange between captive
populations in zoos throughout the world was started to reduce inbreeding. In 1992, sixteen horses were
released into the wild in Mongolia, followed by additional animals later on. These reintroduced horses
successfully reproduced, and the status of the animal was changed from “extinct in the wild” to
“endangered” in 2005. In October, 2007 scientists at the Smithsonian Institution’s National Zoo
successfully reversed a vasectomy on a Przewalski horse : scientists realized the animal in question was
one of the most genetically valuable Przewalski horses in the breeding programme.
Arabian oryx
(Oryx leucoryx)
Eliminated in the wild by hunting: restocked in Oman and Jordan from populations in London, Phoenix
and San Diego zoos.
Mauritius kestrel
(Falco punctatus)
Severe decline was in the 1950s and 1960s due to indiscriminate DDT use and invasive species like cats,
mongooses and crab-eating macaques which killed the kestrels and their eggs. Breeding programme
began at Durrell Wildlife preservation Trust - now up to 800 individuals in the wild.
Golden Lion Tamarin
(Leontopithecus rosalia)
Poipulation decline due to deforestation in western coastal forests of Brazil. In the 1970s the Brazilian
government provided zoos with Golden Lion Tamarins which were successfully bred and disseminated to
zoos around the world (especially jersey Zoo and Smithsonian Zoo in Washington, USA). Over the next 10
years the government succeeded in establishing forest reserves in Brazil that allowed reintroduction of the
Tamarins. In this case then, the captive breeding programme effectively bought the time needed for the
original habitat to be conserved. There are now an estimated 1000 wild Tamarins and 600 in captivity.
Lowland Gorilla
(Gorilla gorilla gorilla)
Critically endangered by war and by bushmeat trade: breeding at Port Lympne Zoo in Kent has released into
special reserves in the Gabon and the Congo. First ‘wild’ births to these reintroduced animals in 2008.
Zoocheck: Campaigning group who lobby government to strengthen the 1981 UK Zoo Licensing Act. The Act presently emphasises
safety of public and zoo workers; Zoocheck want emphasis on animal welfare. Zoocheck would like most zoos to close and for the
monies to be used to conserve habitats. They argue that zoos are an expensive waste of money, that most zoos do not contain
endangered species and that most endangered species are not represented in breeding programmes.
Zoos And Conservation
Captive breeding programmes
form a part of the work of even the smallest zoo
e.g. Lowland Gorilla at Howlett’s Sumatran Rhino at Port Lympne,
Cheetah at Whipsnade, Golden Lion Tamarin at Durrell Institute
Jersey and, eventually, should lead to reintroduction to the wild
how can zoos be justified?
Attraction to visitors
• generates REVENUE which:
1. can be used to keep animals under optimum conditions
2. can provide funding for academic research, particularly
into reproductive physiology and nutritional biology
3. might be used to pay for fieldwork and reserve management
and may stimulate INTEREST and CONCERN
(a) in conservation issues
(b) in the “world of wildlife” ( > 50% of zoo visitors are
children )
What about the animals?
they are usually well-fed and receive veterinary care so are
longer-lived than wild relatives
• they may suffer inapprpriate social grouping and
limited sensory stimulation
Thus much current research centres on behavioural enrichment
ACADEMIC RESEARCH is carried out by many zoo-based
organisations, e.g. the Royal Zoological Society of London (RZL ).
e.g. reproductive physiology of the Asian rhinoceros gene-pool
make-up of the Arabian Oryx nutritional requirements of the Giant
Security : appropriate den/nestbox to act as a retreat
Species-specific behaviour : mud-baths for wallowing ( rhinos)
deep litter for foraging (gorillas )
Foraging : hiding food, or presenting it in a challenging form
e.g. termite sticks, marmoset gum-trees
Locomotory challenge : climbing animals such as Tamarins and
monkeys require “challenges”rather than “safe” substrates
social stimuli : “calls” for Gibbons and Tamarins help them
to develop social and hierarchical skills and some
researchers also recommend
Selective challenges e.g. predators, severe climatic changes
Stud books and gene banks
the family history of all captive animals can be compared so
that matings between close relatives can be discouraged
frozen sperm and/or embryos may be kept at - 197oC for long
periods until breeding techniques are improved
Bio Factsheet
208. Captive breeding and the role of zoos
a. that genes from the original founder population (probably taken
from the wild) are retained and are equally represented, so that
b. individuals that breed poorly in captivity must be encouraged
to breed, and those that are particularly good breeders should
be limited in their breeding opportunities.
c. as a result of a. and b. the maximum genetic diversity, behavioural
characteristics and geographic origins are maintained.
Conserving genetic diversity : The importance of
How genetic variation is lost. Genetic drift is a change in allele
frequencies over time. This may be simply due to chance, as in
small populations some alleles may not be passed on to offspring.
Fig 4: Genetic drift
Two important points to note:
1. the modern approach is very different to that of zoo managers
50 years ago, who simply increased their stock of animals by
continually breeding the best breeders (and so reduced genetic
2. this type of programme is almost the complete opposite of
artificial selection methods amongst domestic animals, in which
certain characteristics are favoured even though these may be
harmful to the animal in the wild (and so reduced genetic
T, t and S
are alleles of
the same gene
i.e. one allele may
be 'lost' from
the gene pool
Case Study: Mauritius Kestrel
Genetic drift leads to a reduction in genetic variation.
Inbreeding depression
In a small population, for example in captivity in a zoo or wild animal
park, there is an increased chance that closely-related individuals
will mate (there simply aren’t so many partners to choose from).
This inbreeding reduces the proportion of heterozygotes in the
population: there are more homozygous recessives as individuals
receive recessive alleles from both parents. Many recessive alleles
have harmful effects on the phenotype, so inbreeding depression
results: the individuals are less reproductively ‘fit’. They may be
smaller, less able to cope with disease and the females may produce
fewer eggs.
Conservation ‘in situ’ to maintain the size of wild populations is the
best way to prevent genetic drift and inbreeding depression.
However, ‘ex situ’ conservation can play a part if the genetic history
of breeding individuals is known.
Keeping studbooks: Computer Dating for animals!
Since animals were first domesticated, breeders would note
differences between individuals and might use them selectively to
improve stock e.g. for milk yield, beef production or speed. The
first official studbook was the ‘General Studbook for Thoroughbred
Horses, set up in England in 1791. Modern studbooks
• are a collection of the genetic history and location of all the
captive animals of a particular species in the collections that are
cooperating in the overall breeding plan.
• include data on the species’ status in the wild
• usually include specialised software e.g. the ARKS (Animal
Record Keeping System) includes species, sex, parents, birth
date, birth location, current location and transponder chip
Studbooks provide the raw data on which the breeding plans are
based: the plan must ensure
Once widely distributed over the
island, the kestrel hunts in closed
canopy forest, feeding on geckos,
large insects and small birds.
Population decimated by forest
destruction for construction
timber, fuelwood, food crops and, in
the 1950s and 1960s, by the use of
organo-chloride pesticides. The
spread of non–native plant species,
introduced as seeds by other birds,
also contributed to the decline of the
native forests.
By 1974 only 6 birds remained, 2 of these were in captivity.
Cooperation of Mauritius government, Jersey Wildlife
Preservation Trust, Mauritian Wildlife Foundation and the
Peregrine Fund. Captive breeding successfully carried out
at Gerald Durrell Endemic Wildlife Sanctuary.
Eggs taken from wild nests stimulated wild kestrels to lay
second clutch. The eggs that were removed were hatched
in incubators and hand reared.
Some young kestrels were returned to the wild nest and
adult birds reared them.
Others were placed in artificial nest boxes and fed by
humans until they were old enough to hunt and avoid
predators. This allowed the breeders to exploit new, safe
areas of forest.
Over 400 kestrels have now been bred and released and
the wild-population now exceeds 800.
Ironically, in 1994, a Mauritian kestrel ate a newly hatched
chick of a recently reintroduced pair of Mauritian pink
pigeons, the world’s rarest pigeon!
The Mauritian kestrel is listed in Appendix 1 of CITES.
Mauritian Kestrels can be seen at Chester Zoo, Durrell
Wildlife Preservation Trust, Jersey and Paignton Zoo. and
Bio Factsheet
208. Captive breeding and the role of zoos
Case Study 4 : Ne-ne
Unfortunately, however, the reintroduction of Ne-Ne to Hawaii
and the neighbouring island has not yet been a complete
success (captive bred animals are less successful at feeding
themselves, and at avoiding predators) but at least its status as
a species has been ensured by the captive breeding programme.
It seems that the habitat of the Ne-Ne (the slopes of volcanoes)
is a difficult one for them to do well in: it is likely that this
habitat was ‘forced’ onto the Ne-Ne population, by pressures
from Humans and other animals, at just about the time
conservationists became aware of the declining numbers.
There are those who believe
that breeding animals in
captivity often results in
breeding them for captivity,
and that reintroduction to the
wild is rarely successful.
The Ne-Ne, or Hawaiian Goose (Branta sandvicensis) is often
quoted as an example of the success of captive breeding
techniques, since a wild population which may have been as
low as 12 breeding pairs has been supplemented by more than
3 000 captive-bred individuals.
The case of the Ne-Ne does emphasise a most important point reintroduction is unlikely to prove successful if the conditions
which caused the animal to become endangered have remained
unchanged. Once again, the importance of conserving a
habitat as well as preserving a species is illustrated: ‘in situ’
conservation and ex situ’ conservation are very closely linked.
The credit for this outstanding breeding programme is largely
due to the Wildfowl Trust in Slimbridge who developed
techniques in incubation, hatching and rearing of goose eggs,
and who ensured the introduction of ‘wild genes’ from geese
still living in Hawaii.
Key Words And Phrases
Captive Breeding
The breeding of species in confinement, usually zoos, with the aim of reintroducing the animals back to their
original habitat once it is safe to do so
Convention for Trade in Endangered Species: controls the transfer of wildlife and wildlife products between
member countries
a species whose continued existence is deemed unlikely if the factors that are causing its decline continue e.g.
Black rhinoceros
‘Ex situ’ conservation
Maintaining species outside their natural environment, in zoos or wildlife sanctuaries.
A species for which there has been no confirmed sighting for 50 years.
Genetic diversity
Maintaining the range of alleles present in the wild (founder) population.
‘In situ’ conservation
Maintaining species in their natural environment. This may include management of a Nature Reserve or
National park.
Inbreeding depression a reduction in reproductive fitness caused by matings between closely-related individuals (reduced
International Union for the Conservation of Nature and Natural Resources
A species with localised distribution but in no immediate danger
Red Data Book
List of all those species at risk: includes categories such as ‘vulnerable’, ‘at risk’, ‘rare’, endangered’ or
‘critically endangered’. An international register that is updated every three years
Stud Book
Awritten record (now computerised)of the genetic status and location of all of the individuals in a breeding
The release of animals taken from the wild into a new area in an attempt to re-establish or augment natural
A species which is likely to become endangered soon if the causes of its decline continue
Useful sources of information
Captive species breeding group of World Conservation Union (IUCN) Under “Reports” you can download summaries
of management action plans for species and habitats for news, campaigns and management plans for habitats and species such as the black rhino
World Zoo Conservation strategy
International Zoo News Lots of interesting articles
Reintroduction of Californian Condors
This Factsheet was researched and written by Ron Pickering.
Leader-Williams N et al (1990) Illegal exploitation of black
Curriculum Press, Bank House, 105 King Street, Wellington, Shropshire, TF1 1NU.
Factsheets may be copied free of charge by teaching staff or students, provided that their school is a registered
rhinoceros and elephant populations. J. Appl. Ecol 27:1055-1087 Bio
subscriber. No part of these Factsheets may be reproduced, stored in a retrieval system, or transmitted, in any other
form or by any other means, without the prior permission of the publisher. ISSN 1351-5136