The role of Zoos in the reintroduction of animals: myth or reality?


In here we present an analysis of the contribution made by Zoos for the conservation of threatened species of wild animals through the practice of reintroduction, on a discussion of the beginnings of this practice and the main critics which are aimed at it.


Lucília Tibério - Biologist in Lisbon Zoo



The potential reintroduction of animals born and/or raised in captivity is one of the major arguments pointed out by actual Zoos to justify their specific business. The conservation of endangered species and their habitats plus the raising of awareness and the environmental education of the several hundred million people who annually visit the Zoos’ animal collections all over the world – at least 600 million visitors each year in the Zoo members of the World Association of Zoos and Aquariums (WAZA) – is regarded by many current Zoos as much more than a spontaneous consequence of a nice leisure day in the Zoos’ premises made available for people of almost every socioeconomic and cultural backgrounds.


Nature conservation, environmental education and scientific research are identified by many of the actual Zoos as the strongholds of their mission statement, for which they actively invest a great deal of their human and financial resources, especially in the case of those institutions who work cooperatively with conservation organisations, such as the International Union for Conservation of Nature (IUCN), through international associations of Zoos and Aquariums, such as the European Association of Zoos and Aquaria (EAZA) or the Association of Zoos and Aquariums (AZA), besides the already mentioned WAZA.


In fact, if we take a quick look at the current WAZA Conservation Projects or check the comprehensive list of the 163 conservation projects branded by WAZA since 2009 we will find that a great number of these projects aims for the reintroduction of endangered species into the wild and/or for environmental education initiatives among the local communities from where these endangered species are native.


However, can we consider the reintroduction in nature of animals born and raised in Zoos as really feasible and, if so, is it really worthy and effective? And in which circumstances?



Reintroduction has made a long way

The practice of releasing wild caught or captive born animals into an area in which they have declined or disappeared has gathered general acceptance among the scientific community as a potentially relevant measure for conservation – for instance, captive breeding is considered a tool of critical importance for the intended recovery in the wild of the mostly endangered cat of the world, the Iberian lynx (Lynx pardinus), in Spain and Portugal.


Fig. 1 – CNRLI – The Iberian Lynx Breeding Centre in Silves (Algarve), Portugal


A reintroduction project can involve (a) the translocation of wild caught animals to other areas of suitable habitat preferably within the historical range of the species or (b) the release of captive born animals and/or wild caught animals raised or maintained in captivity, these latest either captured as infants or juveniles or as adults, and eventually confiscated from the illegal traffic by the local authorities to be released in the wild after a suitable process of rehabilitation.


Looking carefully into the past we can state that the reintroduction into the wild of animals born or raised under human care has already made a long way, especially since the beginning of the second half of the XX century. We could mention for instance the very slow, difficult and controversial process of recovery of the European bison (Bison bonasus) in Eastern Europe, or the combined conservation efforts made by several zoological institutions in the USA and Europe for the reintroduction and habitat preservation of the highly endangered Lion tamarins (Leontopithecus sp.) of the Atlantic forest in Brazil. The successful recovery of the nearly extinct Mauritius kestrel (Falco punctatus) and Mauritius pink pigeon (Nesoenas mayeri) populations in the wild (although this latest is still completely dependent on human support) are only two further examples to follow, here accomplished through the intensive effort, among many other institutions, of the Durrell Wildlife Conservation Trust, which besides being a foundation is one of the most internationally acknowledged zoological parks for its long time efforts in in situ conservation (i.e. of wild populations and their habitats).


Fig. 2 – Mauritius kestrel (Author: jmittermeier)


But many of the first attempts of animal reintroductions from captivity had a very low success rate. These failures combined with the general knowledge that the reintroduction of captive animals in the wild has still many obvious restrictions has made this subject often regarded as controversial, and also often negatively criticised by conservation biology scientists and professional conservationists all over the world.


Criticism over the reintroduction of captive animals by Zoos

Among the sharpest criticism against the role of Zoos in the reintroduction of animals into the wild we can point out the following:


The exotic animals kept in captivity, especially after many generations, suffer a weakening or even suppression of their “wild” traits, and eventually show the negative physical results of inbreeding depression in consequence of the bottleneck effect which occurs in the small animal populations usually kept and bred in captivity.


The first part of the argument is clearly fallacious, because many of the physical and behavioural traits necessary for the survival in the wild are genetically inherited and so cannot simply be “overwritten” by the acquisition of “domestic” traits in captivity. In other words, let’s imagine the artificial selection of tigers for a genetic repertoire better “adapted” to life in captivity (selection of genetic traits for more docility, for instance) – the truth is that we couldn’t ever erase many of their “wild” traits, even after a very high number of generations. The domestic cat’s competences for hunting – which greatly appreciates the comfort of a house heater in winter regardless of its excellent cover of fur – can be an eloquent image of the previous statement. On the other side, it is true that some behavioural traits which are also important for the survival in the wild of many endangered species (especially mammals and birds) must be “learned” during the juvenile stage, either through the interaction with one or both parents or with the animals’ birth group. For instance, a leopard “knows” instinctively that it is a carnivore, and even a predator, but it doesn’t necessarily know the best strategies for hunting successfully, which are learned by watching its mother during its juvenile period.


Fig. 3 – Leopard female hunting an impala


And this is why that one of the main goals of the environmental enrichment programmes which are developed on a daily basis for Zoo animals all over the world is to give them the possibility of performing their full repertoire of natural behaviours. Through an array of different stimuli – physical (type and placement of the physical components of the enclosure, such as logs, etc.), sensorial or feeding (for instance, using the smell of other animals or changing the way of presenting the feeding items), among others, it is indented to create opportunities for the animals to fulfil their natural behaviours in captivity as much as if they were really living in the wild. For the animals, this may signify being included in an adequate social group, or being stimulated to find food according to the animals’ specific skills.


The second part of the argument might well become true if the captive breeding programs leaded by Zoos aren’t sufficiently managed, as they should be according to the ethical and normative standards of WAZA and other associations of Zoos all over the world, namely through (a) the establishment of a managed captive population based on a sufficient number of genetically diverse wild founders, (b) the maintenance of a pedigree and demographic database (which is named the Species Studbook) as complete as possible, at least since the establishment of the captive breeding program, (c) a good analysis of the population genetics and demography in order to make the best recommendations for transferring breeder animals between the Zoos involved in the captive breeding program, and (d) a sufficient size of the ex situ metapopulation – considered as such for being globally managed as several interconnectable reproductive units which are distributed between the different Zoos involved in the captive breeding program – in order to sustain as a whole a stable demography, a high level of genetic diversity and a long term viability. These are in fact the ultimate goals of the responsible captive breeding programmes conducted by Zoos – and are being effectively achieved for an increasing number of species.


In this context it might be relevant to consider that inbreeding depression is also a serious issue in many wild animal populations which have been intensely fragmented by habitat occupation and/or destruction and excessive hunt. This is the case of the global wild population of Amur tiger (Panthera tigris altaica), according to a recent paper published in the journal Mammalian Biology: although the current wild population sums about 500 individuals, the effective population (a measure of its genetic diversity) is now fewer than 14 animals. So, at least in their best potential, some captive populations can be (or become) more genetically sound than some wild populations.



Fig. 4 – Female of Amur Tiger in the Nuremberg Zoo (Author: Calliopejen)


According to the previous reasoning, the affirmation that the responsible captive breeding programmes conducted by Zoos can constitute a genetic safety deposit for the reintroduction of wild animals whenever it becomes necessary and viable can congregate supporters. And this was in fact one of the conclusions of the latest Convention of Biological Diversity (COP-10), in Nagoya, Japan, in October 2010.


The exotic animals kept in captivity acquire a high level of human imprinting, in consequence of their frequent contact with the keepers and the public, especially in the case of animal presentations.


This is a strong argument in many aspects. First, the human presence is in fact insurmountable, because captive animals need daily husbandry and regular veterinary care. However there are always a certain number of animals in the zoological collection that may be pointed out at any time as the most genetically suitable for a reintroduction in the wild and thus the husbandry guidelines for many endangered species kept in Zoos recommend a reasonable emotional distance between the keepers and the animals kept under their care. Moreover, many Zoos advise their visitors to avoid direct contacts with other animals besides the farm and show animals not only for safety and sanitary reasons but also to avoid creating a behavioural imprinting in the animals. Of course these guidelines are not so often respected as they should, maybe because of our highly interactive biological condition as primates, and especially because these same Zoos promote a great number of interactions between the animals and the public, thus generating a somewhat confusing attitude among the visitors.


Surely, we could also counterpart that many wild animals in wildlife parks and reserves all over the world are nowadays more exposed to the direct contact with the public, and to the potentially lethal consequences for those animals, than the animals maintained in some pre-release facilities created for the adaptation of the individuals for their future release in the wild as part of a specific reintroduction program.


Secondly, the reversion of an imprinted behaviour is obviously very difficult, if we count ourselves among those who even consider it possible. However, a well managed reintroduction programme considers a pre-release period of acclimation and behavioural adaptation of the animals to their future life in the wild, with the preferable release of the descendants raised by their parents and/or inside a social group in the pre-release facility.


And the experience has been showing us a wide range of positive reintroduction initiatives, from the hard release of animals into the wild (without a pre-release adaptation period) – such as the release of the Alpine ibex (Capra ibex) in Austria – to the prolonged periods of pre-release conditioning (soft release), including many trial and error attempts in the case of the already mentioned long and difficult reintroduction process of the Lion tamarins in Brazil.


The reintroduction of captive animals into the wild can be considered an inhumane strategy on the perspective of animal welfare.


This is a very interesting argument, considering the many critical voices raised against Zoos and their practice of keeping wild animals and their descendants in captivity, thus restricting their opportunity to live freely in nature.


Fig. 5 – Release of a condor in a pre-release facility (Author: Pearson Education)


The reintroduced animals will indeed be submitted to higher levels of stress – e.g. from physical discomfort associated to hunger, thirst, disease or predation – than their captive counterparts maintained in ethically responsible Zoos, which is a contradiction to the Universal Declaration of Animal Welfare. But this discussion would definitely lead us outside the scope of this document.


The number of captive animals reintroduced into the wild until today is very low compared to the total number of animals kept and bred in Zoos worldwide.


According to a study conducted by Beck et al. for the Reintroduction Specialist Group of the World Conservation Union’s Species Survival Commission (IUCN/SSC), in a total of about 145 projects that released captive bred animals to re-establish or reinforce wild populations during most of the XX century, more than 70 000 mammals, birds an reptiles have been reintroduced, and Zoos were involved in at least 59 percent of the 129 reintroductions in which the animals could be sourced. In other words, it isn’t a great figure comparing to the huge number of captive animals which are held today in Zoos all over the world.


A more recent perspective, however, published recently by the IUCN/SSC Re-introduction Specialist Group, is more encouraging and probably more representative of the modern tendency in the practice of wild animal’s reintroductions much possibly thanks to the continuous development in scientific and technological knowledge which accompanied the turn of the century. It is also pertinent to add that many of the results of the scientific studies conducted in Zoos, in the latest years, on the fields of animal behaviour and veterinary medicine, have been used as crucial tools for the correct planning, execution and post-release monitoring of the introduced animals.


In spite of the above, however, the cold true is that most of the animals kept and bred in Zoos won’t probably ever be reintroduced into the wild. This could be for a good reason, meaning that it was not necessary. But, in spite of the arguments that the captive breeding programs lead by Zoos aim for the cooperative management of long term viable populations with high levels of genetic diversity, whose animals are physically and behaviourally suitable for a potential reintroduction programme, the more common destination of the animals kept and bred in the captive breeding programmes managed by Zoos is not the reintroduction into the wild but the supply of animals between Zoos, attending to the fact that their capture in the wild is no longer accepted either ethically or even legally in most of the cases. So, as many Zoos would argue, these animals live their lives as nature ambassadors for the preservation of their conspecifics in the wild, for instance through the Zoo’s educational programmes and public exhibitions. And in this context, another relevant argument used by Zoos is the importance of intentionally promoting a strong emotional bond between the visitors and the animals, which at least in theory could lead to a more proactive attitude towards their conservation in nature. But as puzzling as this may seem this human-animal bond should precisely be avoided for the reintroduction sake. There isn’t a simple cut for this closed circuit. This is why many Zoos are starting to understand and consider the need for specific breeding programmes intended for release, which must be managed in a more strict way than the general breeding programmes regarding isolation from public, environmental and behaviour management, proximity to the release site, etc.


Fig. 6 – Facility for common hippos in the Sedgwick County Zoo (Wichita, USA) (Author: Alamy)


At last but not least in importance we can also add a few generic restrictions to the reintroduction of captive animals in nature (either born in captivity or not), namely: (a) funding shortage for the necessary long term investment – and here we could point out the high importance of the EAZA conservation campaigns, launched since 2000, as fund raising initiatives capable of gathering hundreds of thousands Euros which are reverted to in situ conservation programmes, including reintroduction projects; (b) lack of enough scientific knowledge to support the several stages required for the reintroduction process – unfortunately this is an important prejudice for some highly endangered taxonomic groups, for example with many reptiles and amphibians; c) weak support from the local authorities and/or local inhabitants – and this is probably the second most important factor to consider before attempting any in situ conservation project, for if there is no local support for the preservation of a determinate wild animal species (either in consequence of human-animal conflicts, illegal captures for traffic, superstitious beliefs, or other) there is also no way of guaranteeing a long term viable population; that is why the local environmental education and the reinforcement of the local laws for nature preservation are crucial to the success of any conservation in situ project; at last and probably the greatest factor against the reintroduction of animals in nature besides the risk of disease propagation (d) there is simply no more space left by the human occupation and the human activities in which the animals can find a suitable natural habitat, wide enough for the needs of a self-sustainable long term population.



A spark of hope

So, is the reintroduction of Zoo animals valuable and effective? In sum, we can say that Zoos have an excellent potential for keeping well managed captive breeding programmes, capable of supplying genetically and behaviourally healthy wild animals for reintroduction. We can also state that the more recent events are showing us that the reintroduction in nature of animals provided by Zoos has been at least partially successful in more than a few situations. We could even risk saying that for some highly endangered (and not always charismatic!) species all over the world the strong commitment of some Zoos all over the world has been one of these species main strongholds against extinction since the second half of the latest century and especially in recent times.


Fig. 7 – Golden-Lion Tamarin (Leontopithecus rosalia)  – a well succeeded example of reintroduction of animals from captive breeding programs (Author: WAZA)


So, in spite of all the good reasons that we could point out against the translocation of wild animals and/or the release in the wild of captive raised animals (and/or animals kept in captivity) to re-establish or reinforce the wild populations, the fact is that the world’s biodiversity is diminishing at a such very high rate and the human overtake of the natural resources is expanding in such a chaotic way, that we simply cannot afford to throw away the opportunities that the responsible Zoos can offer to biodiversity conservation.


Note: The views expressed here are exclusively from the author’s responsibility.



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