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18 MARCH 2011 VOL 331 SCIENCE www.sciencemag.org
A t the October 2010 meeting of the
Convention on Biological Diversity
(CBD) in Nagoya, Japan, delegates
discussed a plan to reduce pressures on the
planet’s biodiversity. Key targets include
expanding coverage of protected areas, halv-
ing the rate of loss of natural habitats, and
preventing extinction of threatened species
( 1). For species whose habitat is severely
threatened, however, the outlook is so bleak
that the International Union for Conservation
of Nature (IUCN), the U.S. Endangered Spe-
cies Act, and the CBD (Article 9) recognize
that in situ conservation actions (i.e., in the
species’ natural habitat) will need to be com-
bined with ex situ approaches, such as captive
breeding in zoos, aquariums, and so on ( 2, 3).
Captive breeding may be the only short-
term practical conservation option for species
conﬁ ned to dwindling habitats ( 4). However,
captive breeding is absent or plays a minor
role in the policies of most governments, con-
servation organizations, and multilateral insti-
tutions. To shed light on the state of captive
breeding and its potential to contribute to con-
servation goals, we estimate the number of
threatened species already held in captivity.
Although ecosystem health should be a con-
servation priority, a recent evaluation of the
status of the world’s vertebrates ( 5) noted that
captive breeding played a major role in the
recovery of 17 of the 68 species whose threat
level was reduced [e.g., Przewalski’s wild
horse (Equus ferus przewalskii) ( 6), black-
footed ferret (Mustela nigripes) ( 7), and Cal-
ifornia condor (Gymnogyps californianus)
( 8)]. Captive breeding has the potential to
maintain targeted populations as an “insur-
ance policy” against threats like disease or
pressure from nonnative species [e.g., egg
predators on islands ( 9)] until reintroduction
into the wild is possible. A striking example
is the increase of amphibian collections in
zoos ( 10) as a response to chytridiomycosis,
a fungal infection responsible for precipitous
global amphibian population declines ( 11).
Captive breeding for reintroduction has
downsides. Sociopolitical factors can deter-
mine the success of programs. For example,
reintroduction of Arabian oryx (Oryx leu-
coryx) in central Oman was hampered by
poaching, partly because local communities
were insufﬁ ciently involved in conser vation
efforts ( 12, 13). Furthermore, captive breed-
ing is costly, and technical difﬁ culties can
arise such as hybridization [breeding among
different species ( 14), e.g., if current cryp-
tic species are managed as one species, but
are later split into several species according
to new taxonomic information]. The abil-
ity of individuals to learn crucial skills that
allow them to survive in the wild (e.g., fear
of humans or predators) may be compro-
mised. In many cases, these difﬁ culties have
been overcome by creative and species-spe-
ciﬁ c measures. For example, it was feared
that Puerto Rican parrots (Amazona vittata)
would be unable to escape predators in the
wild, but this problem was solved with a pre-
release aviary-based stimulation and exercise
program ( 15). Because ex situ conservation
programs can be challenged when called into
action at the last possible moment with only a
few remaining individuals of a species, cap-
tive breeding should not simply be seen as
“emergency-room treatment.” It is a tool that
should be considered before the species has
reached the point of no return.
Counting Threatened Species in Captivity
We used the International Species Informa-
tion System (ISIS) database to estimate the
number of threatened species already held in
captivity. ISIS is an organization that holds
the most comprehensive information on
animals held in zoos and aquariums world-
wide, with records of ~2.6 million individu-
als shared among ~800 member institutions
( 16). From the IUCN Red List of Threatened
Species ( 17), we obtained the threat category
of each terrestrial vertebrate species repre-
sented in ISIS ( 18). [See supporting online
materials (SOM) for details.]
One-quarter of the world’s described bird
species and almost 20% of the mammal spe-
cies are held in ISIS zoos (table S1). Only
12% of the described reptile species are rep-
resented and 4% of amphibians. Our primary
focus is on species of conservation concern;
for mammals, roughly one-ﬁ fth to one-quar-
ter of threatened ( 19) and Near-Threatened
species are represented in ISIS zoos (see
the ﬁ gure) (table S1). With the exception of
Critically Endangered species, which only
have a 9% representation (tables S1 and S2),
the picture is similar for birds. For amphib-
ians, the representation of threatened spe-
cies is much lower (~3%); this is a concern
because amphibians are a highly threatened
group, with 41% of described species listed
as threatened or Extinct in the Wild (EW) ( 5).
The IUCN threat-level assessment for rep-
tiles has not been completed, so our results
should be interpreted with caution, but of the
1672 species already evaluated, zoos hold
37% of threatened and 18% of Near-Threat-
Overall, zoos and aquariums hold roughly
one in seven threatened species (15%), but it
is important to consider also the number of
individuals held. Although individual zoos
might not have large populations of a par-
ticular species, collectively, zoos hold siz-
able populations of certain species, including
highly threatened ones (see the ﬁ gure). Zoos,
as a global network, should strive to ensure
that their populations of threatened species
can survive in the long term. However, each
zoo may make a larger conservation contri-
bution by specializing in breeding a few at-
risk targeted species, rather than aiming to
increase its species diversity, as specialization
increases breeding success ( 4).
Ultimately, success of conservation
actions depends on the extent to which birth
and death rates permit populations to survive
in the wild ( 8). Population viability analyses
(PVAs) are used to forecast the probability of
population extinction for conservation pro-
grams ( 20), but these require parameteriza-
tion with data on age-speciﬁ c birth and death
rates ( 21). Adequate data from natural envi-
ronments are often unavailable, especially for
threatened species ( 20). The zoo network has
large long-term data sets, including data such
as average litter size, interval between succes-
sive litters, and age at maturity, which could
be used to ﬁ ll these gaps. Of course, zoo data
should be used with caution because they
An Emerging Role of Zoos
to Conserve Biodiversity
D. A. Conde,
1 * N. Flesness, 2 F. Colchero,
1 O. R. Jones,
1 A. Scheuerlein
Roughly one in seven threatened terrestrial
vertebrate species are held in captivity,
a resource for ex situ conservation efforts.
*Author for correspondence: email@example.com
1Max Planck Institute for Demographic Research, Rostock
18057, Germany. 2International Species Information Sys-
tem, Eagan, MN 55121, USA.
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on September 28, 2012www.sciencemag.orgDownloaded from
www.sciencemag.org SCIENCE VOL 331 18 MARCH 2011 1391
Number of species
Number of individuals
pecies per interval
NT VU EN CR EW
25% 24% 23%
21 27 25 27
Species (ranked by number of individuals)
NT VU EN CR EW
840 29 23
NT VU EN CR EW
28% 51% 0%
640 32 22
NT VU EN CR EW
6% 4% 2% 3% 50%
24 10 18 48
NT: Near threatened VU: Vulnerable EN: Endangered CR: Critically endangered EW: Extinct in the wild
do not necessarily reﬂ ect the situation in the
wild, such as population ﬂ exibility in the face
of changing conditions.
Despite their current and potential contri-
butions to species conservation, ISIS zoos are
concentrated in temperate regions, whereas
most threatened species are tropical ( 5, 22)
(ﬁ g. S1). This mismatch between the areas
where captive populations are held and their
native range poses a challenge for imple-
mentation of effective conservation actions.
Acclimatization to a new home is likely to be
faster for animals raised in conditions similar
to those where they are to be released. This
is one reason that it is suggested that captive
breeding be done in the country of the spe-
cies’ origin ( 2).
There are large parts of the world with high
biodiversity value, yet whose zoos are not
well represented in a global network (ﬁ g. S1).
Given the importance of having data avail-
able for design of conservation programs,
policy-makers must encourage and facilitate
the participation of zoos from regions with
high levels of biodiversity threat in global
networks, such as ISIS and the World Asso-
ciation of Zoos and Aquariums (WAZA).
The potential for zoos to contribute to
conservation is not a new concept for the zoo
community. Zoos and aquariums have devel-
oped conservation projects in the wild, along-
side research and education programs ( 23).
For exam ple, mem bers of WAZA collectively
spend ~U.S. $350 million per year on conser-
vation actions in the wild, which makes them
the third major contributor to conservation
worldwide after the Nature Conservancy and
the World Wildlife Fund global network ( 24).
Given the scale of the biodiversity challenge,
it is vital that conservation bodies and policy-
makers consider the potential that zoos as a
global network can provide.
References and Notes
1. D. Normile, Science Insider, 29 October 2010; http://
2. Convention on Biological Diversity, Article 9, United
Nations—Treaty Series, pp. 149 and 150 (1993).
3. IUCN, IUCN Technical Guidelines on the Management of
Ex Situ Populations for Conservation (IUCN, Gland, Swit-
zerland, 2002), p. 4.
4. W. G. Conway, Zoo Biol. 30, 1 (2011).
5. M. Hoffmann et al., Science 330, 1503 (2010).
6. M. C. Van Dierendonck, M. F. Wallis de Vries, Conserv.
Biol. 10, 728 (1996).
7. J. Belant, P. Gober, D. Biggins, in IUCN Red List of Threat-
ened Species, Version 2010.4 (IUCN, Gland, Switzerland,
8. V. J. Meretsky, N. F. R. Snyder, S. R. Beissinger, D. A. Clen-
denen, J. W. Wiley, Conserv. Biol. 14, 957 (2000).
9. J.-C. Thibault, J.-Y. Meyer, Oryx 35, 73 (2001).
10. Amphibian Ark, www.amphibianark.org.
11. L. F. Skerratt et al., EcoHealth 4, 125 (2007).
12. J. A. Spalton, M. W. Lawerence, S. A. Brend, Oryx 33, 168
13. V. Morell, Science 320, 742 (2008).
14. R. Barnett, N. Yamaguchi, I. Barnes, A. Cooper, Conserv.
Genet. 7, 507 (2006).
15. T. H. White, J. A. Collazo, F. J. Vilella, Condor 107, 424
16. International Species Information System, www.isis.org.
17. IUCN, IUCN Red List of Threatened Species, Version 3.1
(IUCN, Gland, Switzerland, 2009); www.iucnredlist.org.
18. ISIS and IUCN information were matched on the species
level using the Catalogue of Life (F. A. Bisby et al., Eds.);
19. Threatened species are those listed as Critically Endan-
gered (CR), Endangered (EN), or Vulnerable (VU) by IUCN.
20. T. Coulson, G. M. Mace, E. Hudson, H. Possingham,
Trends Ecol. Evol. 16, 219 (2001).
21. J. M. Reed et al., Conserv. Biol. 16, 7 (2002).
22. R. Grenyer et al., Nature 444, 93 (2006).
23. WAZA, Building a Future for Wildlife: The World Zoo and
Aquarium Conservation Strategy (WAZA, Berne, Switzer-
24. M. Gusset, G. Dick, Zoo Biol., 6 December 2010 (http://
25. We thank J. Vaupel, M. Gusset, C. D. L. Orme, D. Levitis,
D. de Man, W. van Lint, K. Zippel, S. Möller, J. Runge, E.
Brinks, G. Fiedler, P. Kutter, and F. Quade. We also thank
three anonymous referees.
Endangered species in zoos. (Top) The number of
species with IUCN status, globally described (color
bars) and in ISIS zoos (black bars). (Bottom) The
number of individuals in ISIS zoos for species listed
by IUCN—for mammals (142 species), birds (83 spe-
cies), reptiles (90 species), and amphibians (29 spe-
cies). The vertical broken lines show the boundaries
by 250, 50, and 10 individuals. The large numbers of
individuals classiﬁ ed as Vulnerable and Near Threat-
ened are omitted for clarity. See SOM for details.
Supporting Online Material
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on September 28, 2012www.sciencemag.orgDownloaded from