What Are Some Of The Challenges To Treating Exotic Animals Particularly In Zoological Settings

• Periodical Listing
• Animals (Basel)
• v.ix(half dozen); 2019 Jun
• PMC6616422

Animals (Basel). 2019 Jun; 9(6): 318.

Dilemmas for Natural Living Concepts of Zoo Animal Welfare

Received 2019 Apr 9; Accepted 2019 Jun iii.

Abstract

Unproblematic Summary

This ethical discourse specifically deals with dilemmas encountered within zoological institutions, namely for the concept of natural living, and a new term—wilding. Wilding refers to extrapolation of the natural living concept to treating an fauna equally wild, residing in a wild habitat. The problems associated with wilding are detailed. Complexities of natural living versus natural aesthetics as judged by humans, every bit well equally the possibility of innate preference for naturalness inside animals are examined. Information technology is argued that unintended and unavoidable genetic and epigenetic migrate favouring adaptations for life in a captive environment may even so occur, despite zoos all-time efforts to prevent this from occurring. This article further discusses the blurred lines between natural and unnatural behaviours, and the overlaps with more than important highly-motivated behaviours, which may be better predictors of positive affective states in convict animals, and thus, meliorate predictors of positive well-beingness and welfare. Finally, as we are now in the Anthropocene era, it is suggested that human-animate being interactions could actually be considered natural in a way, and notwithstanding, exist very important to animals that initiate these interactions, especially for "a life worth living".

Abstract

This ethical discourse specifically deals with dilemmas encountered inside zoological institutions, namely for the concept of natural living, and a new term—wilding. It is agreed by some that zoos are non ethically wrong in principle, but there are currently some contradictions and ethical concerns for zoos in do. Natural living is a complicated concept, facing multiple criticisms. Not all natural behaviours, nor natural environments, are to the benefit of animals in a captive setting, and practical awarding of the natural living concept has flaws. Expression of natural behaviours does not necessarily bespeak positive well-being of an animate being. Herein it is suggested that highly-motivated behaviours may be a better term to properly explain behaviours of more significance to captive animals. Wilding refers to extrapolation of the natural living concept to treating an animate being as wild, residing in a wild habitat. This definition is intrinsically problematic, equally quite literally by definition, captivity is not a wild nor natural environment. Treating a convict animal exactly the same as a wild analogue is practically impossible for many species in a few means. This article discusses complexities of natural living versus natural aesthetics as judged by humans, besides as the possibility of innate preference for naturalness inside animals. Zoos nobly strive to keep wild animals equally natural and undomesticated every bit possible. Here it is argued that unintended and unavoidable genetic and epigenetic migrate favouring adaptations for life in a convict environment may still occur, despite our best efforts to prevent this from occurring. This article farther discusses the blurred lines between natural and unnatural behaviours, and the overlaps with more important highly-motivated behaviours, which may be better predictors of positive affective states in captive animals, and thus, better predictors of positive well-beingness and welfare. Finally, as we are now in the Anthropocene era, it is suggested that homo-animal interactions could actually be considered natural in a style, and notwithstanding, be very important to animals that initiate these interactions, particularly for "a life worth living".

Keywords: animate being ethics, natural living, wilding, zoo animals, homo-animal interactions, animal welfare

ane. Introduction

To preface this article, I would acknowledge and address the implicit assumptions about animal welfare science and philosophy that have brought us to the ethical position herein. I would refer the readers to other published manufactures which explore the history of animal welfare and ideals in much depth, equally these are used as a footing for our understanding and arguments [1,2,3,4,five,half dozen,7,8,9,10]. This commodity specifically deals with competing ethics of optimal fauna welfare within zoological institutions, namely concepts of natural living, and a new term—wilding. This discourse does not necessarily apply to other captive animate being industries such equally farms or laboratories.

As other ethicists have written, I concord that zoos are not ethically incorrect in principle, simply at that place are currently some contradictions and ethical concerns for zoos in practice [5]. It should be understood that I am a supporter of zoological institutions and their edification, although I may disagree with some zoo practices, and between myself and other researchers in upstanding views of the specific dilemmas herein. It is too best-selling that zoos are not going away whatever fourth dimension soon (see [5]), so it is the pragmatic duty of researchers and philosophers to work with zoos constructively. I would as well like to acknowledge the positions of other researchers in the field, such every bit Weary and Robbins [9], and Yeates [ten]. This article is not intended as a refutation of these other contempo articles about natural living and holistic welfare, but rather to present an alternate formulation of one office of overall animal welfare that may accept been misconstrued in certain zoo environments, leading to in practice incongruence and dilemmas. I acknowledge that my arguments are formulated from my moral and upstanding position that humans have an obligation for special protection of captive animals, particularly zoo animals, and I subscribe to many (but not all) elements of compassionate conservation upstanding theory of gimmicky philosophers such every bit Bekoff [11] and Gray [12] over purely commonsensical or consequentialist approaches. At the moment compassionate conservation remains very anti-zoo in its position, yet, as Grey [12] posits, in that location is much merit in using this ethic to work with zoos constructively, to raise zoos' ethics and practices.

I acknowledge the currently accepted academic focus on the 3 conceptual frameworks (orientations) of creature welfare: biological operation, affective states, and natural living [2,13]. This is how the science of beast welfare is commonly taught to undergraduate and postgraduate learners in our subject area. It is acknowledged, withal, that this non the only style to conceptualise the unabridged moving-picture show of captive creature welfare [three,nine], and that these 3 conceptual frameworks practise not encompass all relevant information in all situations. I admit that a predominant model for characterising and assessing good welfare, especially inside zoos, is the 5 Domains Model of Mellor and Reid [14] and Mellor and Beausoleil [15]. Whilst incorporating pluralistic scientific elements of welfare, at its cadre the Five Domains Model assumes a hedonistic priority of beast welfare, that is, what the animal feels about its life and environment is the most important gene in holistic welfare. In this article a pluralistic basis of welfare is best-selling, though for the sake of argument a hedonistic ground is prioritised. Information technology is understood, however, that a hedonistic priority besides misses some of the whole picture [iii]; hedonism-based welfare conceptions are non dogma. The two scientific concepts of biological functioning and affective states volition only exist touched on in this article, every bit my primary focus is to polish a light on how the concept of natural living may accept been pushed by its useful bounds in zoo situations.

It should be stated that whilst hedonistic conceptions of welfare are mostly concerned with "how the lives of sentient animals are going, for the sake of, and from the perspective of, the animals themselves" [six], it is strongly suggested here that (as written by Weary and Robbins [nine]) relationships thing. That is, not only are the self-derived internal states of the individual highly important, merely besides those emotion-inducing relationships that are important to the individual—such as relationships to conspecifics, other animals, and humans including carers and visitors—and some relationships that others have with that individual may also be important to welfare outcomes (for example, the specific values and attitudes a person holds will bear upon their relationship with an private beast, and reinforcers to this relationship create a bi-directional, perpetual feedback loop). These relationships may then be reflected by the internal affective states of both (or all) agents in that interaction [sixteen,17]. This has been characterised by the full general Hemsworth-Coleman model of human-animal interactions [18,xix]. The general model has been specifically adapted for zoo visitor-animal relationships [20], pictured below (Figure 1). A very like model has been proposed for zookeeper-animal interactions as well [20]. Human values and attitudes towards animals, and the relationships formed between them, tin can strongly influence subjective (hedonistic) experiences of welfare.

Proposed visitor-animal interaction model (adapted from Hemsworth-Coleman model (2011) by S. Chiew and Fifty. Hemsworth, pers. comms., 2016) [xx].

ii. Natural Living

Natural living is a (sometimes) useful key concept in the assessment of creature welfare, often defined as "providing opportunities for animals to engage in natural, species-specific behaviours" [ane,2,10]. Every bit a concept, it suggests that animals' well-beingness may be considerably improved if they are able to perform species-specific behaviours from their natural repertoire, especially innate behaviours. In practice, this has oftentimes been achieved past removing restrictions to these behaviours (whether they are physical or environmental restrictions) and past providing advisable objects, resources or enclosures with/in which to perform the behaviour(s). Frequently, definitions of the concept as well include phrases about housing animals in natural environments. Notwithstanding, not all natural behaviours, nor natural environments, are to the benefit of animals in a convict setting, and applied application of the concept has many flaws. A main criticism of the use of natural living has been that "the concept of natural is normally too poorly defined to provide a sound basis for animal welfare assessment, and thus when applied uncritically it may atomic number 82 to poorer welfare instead of an improvement" [21]. This criticism has been expressed quite normally in the by few decades [1,2,10,19,22].

Joint of the concept, and its transposition to practical application in many captive settings have somewhat missed the betoken entirely. Natural behaviour, natural living and naturalness are poorly-defined key terms that are too often conflated with other concepts and measures of an brute's overall well-being, such equally feelings (melancholia land) or office (biological operation) [x]. Expression of natural behaviours does not necessarily betoken positive well-being of an animal; likewise absenteeism of some natural behaviours does non necessarily indicate suffering [23,24]. Nor should the term natural behaviour be used when actually referring to other conceptual types of behaviours, such equally highly-motivated behaviours, which may be natural or unnatural, however there is often pregnant overlap between these ii terms. Herein I will suggest that highly-motivated behaviours may exist a meliorate term to properly explain behaviours of more significance to captive animals, and hash out where boundaries betwixt harmless and harmful highly-motivated behaviours may lie (as we still take an ethical obligation to protect animals from harming themselves, whether intentionally or accidentally, in captivity).

3. Wilding: The Natural Living Dilemma

Natural living has been a useful tool for improving welfare, but its practical application, particularly within zoos, has been extended across its theoretical usefulness, and in many instances has been misinterpreted equally what I will herein refer to as wilding. Wilding is a new term created to refer to extrapolation of the natural living concept to treating an animal as wild, residing in a wild habitat. Wild here refers to "living or growing in the natural surroundings; non domesticated or cultivated" [25]. From a decade of first-hand experience within the zoo manufacture, this wilding conception of natural living has been encountered frequently enough to be considered pervasive amongst many zoo personnel's implicit beliefs and taught knowledge about how zoos should approach fauna welfare, though bodily prevalence rates accept not been systematically investigated. Indeed, many welfare cess and monitoring tools deployed by zoos focus somewhat on natural environments and natural behaviours [26]. This wilding conception is intrinsically problematic for any captive creature industry (especially zoos) every bit, quite literally by definition, captivity is non a wild nor natural surround [27]. To place a wild brute in an bogus environment (no matter how authentic a recreation of a natural setting) and still assume to care for information technology exactly the same as a wild counterpart is practically impossible for many beast species, in a few obvious means.

Firstly, truly wild animals in nature are not treated by humans in a particular style—they are not under the directly care of humans, however, they may yet exist influenced by humans [28]. These wild animals may be exposed to humans in multiple situations, and even have interactions with humans, but their lives are not solely dictated by humans as captors/guardians. This does non preclude the possibility of interactions (both positive and negative) or conflicts arising between humans and animals, animals venturing into "human being spaces", or encroachment of humans into an animal'southward native space [28]. Even so, as before long as an animal is placed in captivity, no matter how wild its behaviours or instincts, its intendance (and indeed its survival) is then determined and controlled past those humans that placed it in that location. A person cannot place an animal in a captive surroundings and so refrain from providing basic cares or resources (such as food, water and shelter), and yet wait the creature to survive, let alone to thrive. Even in a highly authentic recreation of a natural environment, those bones resource must even so be provided by the decision-making humans—that is, the environment has been created and curated to provide those resources for the beast, through natural or artificial structures.

Secondly, even if it were the instance that humans could provide a perfect replica of an animal's wild environs with wild conditions, would information technology be morally or ethically permissible? Would information technology be (morally) right? Forgetting for a 2nd that this perfect replica would still have been constructed upon another natural or wild surround (thereby destroying a natural habitat and causing displacement of many native species), if truly a replica of natural atmospheric condition, then the animals placed in this surroundings would exist subject field to both the boons and significant hardships of nature. Nature is often bountiful and has immune the rising of an amazingly various array of living beings, merely has also borne witness to countless extinctions and ecological changes. Wildlife often must endure very harsh conditions to survive—conditions that objectively lead to periods of very poor welfare, when measured through scientific welfare concepts (biological functioning and affective states) [10,28,29,30]. Inclement conditions and natural disasters such equally droughts, fires or floods, are all common occurrences in nature. Animals must suffer a lack of shelter, food or water in many areas; they must avert predation, injury, and affliction; they may experience miscarriages, offspring mortalities or reproductive issues; they often have to compete with other animals (both of their own and other species) for access to resources; and they accept to navigate oft-unfair social interactions and hierarchies. Often, living in nature leads to prolonged suffering and ends in premature death for individuals.

Many wild-blazon or natural behaviours are also maladaptive in a convict environment (such equally fratricide or infanticide for farthermost examples; to significant inbreeding in airtight populations; group ostracism of certain individuals; or unfulfillable migratory behaviours/motivations) [12,30,31]. Thus, if it was indeed the objective of convict fauna industries, such as zoos, to perfectly replicate natural environments so their animals may live wildly, it follows that all of the hardships of nature would as well occur, or would accept to be imposed. This is not a tenable ethical position that whatever zoo organisation is known to advocate. Instead, natural recreations of wild environments in zoos try to focus mainly on positive elements of nature, without imposition of events or states that may significantly diminish the animal's well-being [five,26,xxx,32]. Ethically, one will not notice much (or whatsoever) opposition to this mode of handling of the captive animals. This too provides a pro-captivity statement against some anti-captivity, animate being freedom-based philosophies—captivity does indeed curtail some liberty of the captive animal, simply it also provides solace and shelter from significant welfare-affecting hardships, which may be particularly of do good to those animals whom are nearly vulnerable to suffering. Indeed, if captivity is providing all of the needs and wants of an animate being (including positive affective experiences), but without freedom, then liberty is not necessarily a basic interest of the animal [5]. Zoos are frequently the concluding breastwork of promise for many endangered species, every bit their wild homes take been irreparably damaged or overtaken by ever-expanding human populations [12,28,30,33]. This is an always more than salient indicate subsequently the United Nations Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) released a 2019 report which estimates that anthropogenic influences may cause the extinction of 1 1000000 species of animals and plants [33].

Information technology should be noted that whilst zoos tend to focus mostly on recreating positive elements of nature and reducing negative circumstances, many zoos as well understand the impossibility of complete elimination of all negative circumstances, events, or negative feelings inside an animal. In fact, many zoos will impose slight negative circumstances if it is believed that they may be of benefit to the animals' health, fitness, or feel of life [34]. That is, harmless or minimally harmful negative circumstances are sometimes imposed to increase stress resilience and/or physiological arousal of an animate being [35,36]. For example, it has been reported that reliably signalling startling husbandry events tin improve stress resilience and welfare of zoo-housed capuchins (Sapajus apella), whilst still leading to physiological arousal within the animals [37]. Still, where is the distinction drawn between harmless, minimally harmful and very harmful negatives? And who makes these chiselled judgements?

Through collaborative practices shared between many zoos, a few common circumstances for imposing minimally harmful negative events include: rotational predator-prey housing (where predatory species and casualty species are rotated into the same enclosure at separate times); predator-prey adjacent housing with visual proximity; olfactory proximity between predator-prey species or dominant-subordinate species (sometimes in the class of "enrichment", like calculation predator bedding material to a prey enclosure); or auditory proximity between predator-prey species (such as housing prey species within earshot of vocalising predators or dominant species, or playing recorded audio of predator/ascendant fauna vocalisations nearly casualty/subordinate species) [26,31]. These circumstances are idea to confer some resilience to animals through arousal of certain fear and vigilance responses, which can have a wide range of beneficial physiological effects, if non experienced for prolonged periods (acute stressors versus chronic stressors) [35,36]. Therefore, some mild harms are really of loftier instrumental value within a captive environment. All the same, there should be a trepidation of pushing such stress responses also far in prey species, or causing inadvertent frustrations to these animals, for example in adjacent predator-prey housing where predators can visually meet prey in very close proximity, merely non actually accomplish them. Repeated frustration of consummatory outcomes may lead to development of negative melancholia states, as indicated by frustration-type behaviours [24,34]. More evidence is needed of the overall effects of the imposition of these stressors on individual animals, to ensure that the intended arousal and stress resilience is existence achieved whilst avoiding unintended frustrations or development of negative affective states in these animals.

4. Natural Living, or Just Natural Looking?

Sometime, when because and implementing positive natural enclosures, zoos may tend to focus only on those that, aesthetically, atomic number 82 people to believe that the environment is natural. For example, lush constitute-life (or well-designed barren/desert habitats), water features, painted backdrops or "mock-rock" walls, absenteeism of artificial structures, and/or limiting contact with visitors (or even staff/keepers) whether the limitations are visual, tactile or proximal. Much of the fourth dimension, considerations of what is aesthetically pleasing may eclipse considerations of what is functional and advisable, with respect to evidence-based practices [31]. More than just looking natural, zoo animals' enclosures must be able to provide necessary features and structures to allow animals to brandish a range of important behaviours, provide admission to perform positive husbandry practices, and allow ease-of-access for emergency procedures to be adhered to (for both animal emergencies, and other visitor or human emergency situations which may occur). If a natural expect is considered forefront, this may atomic number 82 to functional inadequacies in many enclosures. Sometimes artificial structures in enclosures may exist more appropriate to facilitate specific animal behaviours—whereas natural structures may weaken, deteriorate or break (such as tree branches or vines), suitable artificial replacements may provide the necessary environment for the behaviour and be a considerably more durable, sturdy or make clean provision, which would crave far less maintenance (and therefore monetary toll). Every bit is condign apparent in novel melancholia state research, interactions with humans may actually be beneficial and rewarding for some zoo-housed species in some situations [38,39,40,41]. If a zoo is too focused on wilding their animals, opportunities to truly provide the all-time positive welfare conditions for the convict animals may exist missed or ignored. Therefore, mixed natural/artificial enclosures for animals in zoos, that consider role, aesthetics, appropriate contact with humans, and practicality, may exist much more than fitting than the natural-simply enclosures of the recent past. Ii questions nosotros might ask ourselves of mixed natural-artificial environments are as follows:

1. Does the animal take the capacity to know that the environs is (partly) bogus?

2. Does the animate being care if the environment is (partly) artificial?

These are open-ended questions that might be addressed in a divide paper, drawing from current knowledge of animal neurobiology and cognition, and their needs and wants for a "life worth living" [iv,42]. At that place is some evidence that some species do indeed brandish an innate preference for naturalistic "enriched" enclosures equally opposed to basic artificial environments without many features (barren environments) (Box Turtles [43,44]; Coal tits and blueish tits [45]), suggesting that some animals may indeed have a chapters to identify natural environments. Alternatively, perhaps they just innately adopt non-barren, enriched environments—perhaps these animals would be just as likely to select enriched artificial environments over any basic or barren environments. Utilising electric current brute welfare research and expert consensus a new era of bear witness-based enclosure blueprint, natural or not, which consider the animals' needs foremost, should be the next step forrad for zoo institutions [46]. Equally volition be explored later on, unnatural or artificial environments can even so be compatible with promoting the expression of natural behaviours.

A dilemma with wilding, and so, is that attempts to treat captive animals every bit wild are partly or wholly incongruent with their bodily situation. Every bit has been said in this article before, captive animals are not, nor will they be, wild animals living in a wild environment. Their living environment is completely curated by humans, who must make many decisions for the animals for their all-time interests. This does not mean that we should try to treat all captive animals as we would extensively domesticated animals such as livestock or companion animals (i.due east., dogs and cats). Zoos indeed strive to keep their wild animals as "undomesticated" as possible [12]. This, however, may exist an unattainable ideal, due to unintended and unavoidable genetic and epigenetic drifts favouring adaptations for life in a captive environment, despite our best efforts to otherwise forbid this from occurring. Indeed, in a human being-animal interaction review affiliate, Hemsworth et al. [xviii] write about the possibility of unintended domestication in zoos, citing enquiry such as Price [47,48]—"While zoo animals are more often than not non considered to exist domestic animals, domestication tin can obviously occur with wild animals kept and bred in captivity, such as zoos, but the extent of the domestication process will depend on the charge per unit of bogus selection" [18]. The chapter as well highlights the distinction between domestication of a group of animals, and taming of an private animal—domestication can be defined as "a process by which a population of animals becomes adjusted to man and to the captive environs by genetic changes occurring over generations and environmentally induced developmental events reoccurring during each generation" [48]; whereas taming is simply "an experiential (learning) phenomenon occurring during the lifetime of an individual animal" [47]. Domestication is a process most likely to happen to animals that are purposefully kept in captivity, and artificially bred or selected, or genetically contradistinct, by humans. Individual taming may more than oft occur in both convict and wild animals that are in regular contact with humans.

To unpack this, we should consider other historical animal domestications. The domestication process has taken thousands of years for those animals that nosotros now consider domesticated. In that time, these animals have been bailiwick to multiple selective pressures including artificially imposed selective breeding, turning them from a "wild-variant" into domesticated animals, specifically called for their desirable adaptations. A strong statement against the concept of natural living for these domesticated animals, therefore, is that these animals don't actually represent or reflect any animal which may be plant in the wild or in nature [10]. They have transformed into animals that don't fill any natural ecological niche, whose existence is solely reliant upon human being intervention and intendance, and their persistence is reliant upon humans' continual propagation of that lineage. Of grade, if all human interference or interaction were to cease, these "unnatural" animals are still a part of the biotic customs of Earth, and they would be able to freely breed and propagate themselves. Even so still they would not exist a function of the current natural ecosystem, they yet would not have a natural ecological niche, and many cases of costless-living livestock or pets (feral animals) in many inappropriate locations accept led to irreparable habitat deposition or even ecosystem collapse [28,thirty].

Many researchers posit the co-evolution of wolves and humans, rather than the ane-way domestication of the animal [49]. Both species adapted to working with each other (for the benefit of both) over tens or hundreds of thousands of years. Wolf-homo co-evolution is now suggested to accept happened at multiple historical intervals in different geographical regions, leading to the rise of an entire species (or sub-species), dogs (Canis familiaris, or Canis lupus familiaris), and a multitude of breeds [49]. This co-evolution theory may plausibly explicate the domestication process of nigh modern livestock and pets. Novel research also suggests that the co-evolution of humans and many of our domestic species may have been modulated and propagated by the shared experience of bonding, through the ubiquitous neurotransmitter oxytocin [50,51]. While general consensus would not consider zoo-housed animals as domesticated, nosotros must consider that humans have unintentionally started these animals down a similar domestication pathway, as we now approach the third century of keeping animals in zoos, with many convict brute lineages able to be traced back over 100 years in captivity [12]. This generational convict convenance (including artificial choice of mates) will certainly accept profound effects on the prevalent adaptations of these captive animals—adaptations to life in a convict environment and in close proximity with humans. Speculatively, information technology is possible that shut contact with humans may be activating oxytocin pathways in many convict zoo species, leading to positive affiliative (or bonding) human-animal interactions. Indeed, some researchers are starting to focus on reported keeper-animal bonds in zoos [52,53]. All the same, 300 years is still a shorter timespan than the domestication process for almost other animals we keep today (with exception for some farmed species, such as chop-chop "domesticated" mink and foxes), and most animals displayed in zoos still resemble and carry like their wild counterparts far more than than any newly bred type of domesticated animal.

One of the core tenets of zoos is to brandish wild animals that accept, and volition retain, a certain wildness to visitors, non to brood new types of domesticated animals [12]. Therefore, many practices and safeguards are employed by zoos to try to maintain this wildness. However, the efficacy of our attempts to retain wildness may somewhen be mooted by uncontrollable selective pressures of generational life in captivity. If zoos exist g years from now, zoo animals may have significantly drifted from truthful representations of their wild counterparts (many of which will be extinct in the wild). Just, zoos will still strive to maintain wildness. And for many animals, zoos' conscientious management volition at least succeed in slowing the charge per unit of domestication, but inevitably some genetic or epigenetic drift (mitochondrial drift), or even morphological drift, might still occur regardless of our procedures and safeguards. Thus, these convict animals that still resemble wild species must take specific requirements for care and housing that may differ from common practices for domesticated animals. This is the intendance that zoos should, and do, provide. Only zoos must also make many upstanding judgements and decisions which will benefit the creature for a full and rich life in captivity, whether wild or domesticated or somewhere in-betwixt.

There is significant pressure level on zoos to exist to advance both creature welfare and wildlife conservation priorities. Indeed, the World Association of Zoos and Aquariums (WAZA) cite conservation equally zoos' core purpose, simply fostering positive fauna welfare is their core activity [32]. Yet, this animal welfare strategy document also quite plainly acknowledges that oftentimes conservation priorities may compromise optimal welfare, but zoos should e'er endeavor to minimise welfare-reducing conditions [32]. A potent priority of zoos is to avert genetic drift towards domestication of their captive held wild animals, just, as explained higher up, at that place is still a run a risk that time will modify these animals in unknowable ways. This is not written intentionally as an inflammatory argument against genetic selection and multifariousness processes utilised by zoos, but merely as an acknowledgement of the inherent entropy of many natural systems, and an acknowledgement that humans do non take absolute command of natural processes. But, nosotros do our best with the scientific discipline and technology that we have available. This ethical wildness dilemma has been explored in context of other arguments, such as human being-controlled facilitated adaptation to climatic change impacts [29]. It should also be considered that at that place may be negative impacts of zoos maintaining wildness in their non-releasable captive animals, specially in species known to have depression behavioural plasticity [xxx]. For example, some wild animals may be very prone to negative welfare states due to captivity, manifesting in fearfulness or anxiety responses and behavioural patterns [24,30], whereas domesticated or semi-domesticated species (or wild species with loftier behavioural plasticity) may potentially cope meliorate in captive environments [30].

v. (Un)Natural Behaviours

Function of the natural living concept is a focus on assuasive animals to express natural behaviours. As has been pointed out by many, all the same, the definition of natural behaviour is problematic, especially when referring to domesticated species with no natural or wild equivalent animal, and therefore, no known natural behaviours (for review, run across [10]). Once more, wilding runs into problematic territory here, by over-emphasising or reinforcing only those natural behaviours that are generally displayed by the species in the wild. Academics have suggested multiple culling terms for natural behaviour that may better ascertain what is intended, such every bit normal behaviours or species-typical behaviours [1,10,18,34]. However, these terms still struggle to clear which behaviours are definitely included as natural, and behaviours classified in this style may exist adaptive or maladaptive for a captive environment. For example, migratory behaviour would be considered normal or typical for a migratory bird species, just is maladaptive in captivity as the brute tin not fulfill that motivation [thirty]. Many behaviours that are displayed by a species in nature accept no function or purpose in a captive setting. Simply considering a natural behaviour is non displayed in captivity does not infer that the animal is in a state of distress or suffering. If a natural behaviour serves no purpose for the animal in its captive environment, the motivation to perform the behaviour may be very depression or non-existent [19,23,24,34].

Therefore, more important measures of welfare-positive behaviours for captive animals are highly-motivated behaviours, and highly-rewarding behaviours. These behaviours may be part of a natural repertoire, or wholly unnatural—only displayed in captivity. So-called unnatural behaviours may be the nigh adaptive for the animal'south captive surround, and may be important for positive affective experiences for that creature. Unnatural behaviours do not fit with the ethos of the concept of natural living or wilding, and attempts may be fabricated to extinguish these behaviours. However, this may actually exist of more harm to the animal than benefit—if the behaviour is highly motivated, frustration of that motivation may pb to a negative affective country, and possibly a negative welfare land [24]. Restricting an fauna'south behaviours to only those which are considered natural may also significantly reduce that animal's power to make choices (reducing self-determined agency), which in turn leads to a perceived lack of control over their situation, which is known to negatively impact coping efforts and welfare of captive animals [31,54,55,56].

Another curiosity of nature is what I will term unexpected natural behaviours. These are behaviours that will be performed by wild animals in specific unnatural situations, such equally interacting with artificial running wheels or mirrors placed in wild environments. Quite a few "pop scientific discipline" documentaries and online videos show the furnishings of placing these sorts of objects in nature. Often animals in these videos volition run in the bogus wheel, or stare at their reflection for long periods [57]. These are wholly wild animals that are interacting naturally with artificial (unnatural) objects. Following from this, many behaviours in captive animals may exist incorrectly classified as unnatural, as they are behaviours that are also displayed past wild animals with admission to the same or like unnatural objects.

To increment well-beingness and help positive welfare outcomes for captive animals, focus needs to shift from a fixation on what are considered natural behaviours to those behaviours which the fauna appears highly-motivated to perform. Thus, rather than focus on treating animals as though they were wild, it would be more than pertinent to focus on assuasive animals to express highly-motivated behaviours, particularly if deprivation or frustration of these behaviours results in pregnant stress, reduced fitness and/or a negative melancholia state [24]. Expressing highly-motivated behaviours may as well beget the animals more bureau and choice within their environments [54], which should be allowed within reasonable limits—the allowed behaviours must not compromise the safety or wellness of the individual performing the behaviours, or of the other animal(s) or man(due south) involved (i.e., assuasive a predator to hunt for alive prey does not consider the ethical obligations for the prophylactic of the intended prey animal). This may be categorised into harmless and harmful wants of an brute. Harmless wants may include highly-motivated behaviours such as foraging, climbing, playing or resting. Harmful wants may include highly-motivated behaviours such every bit feeding, hunting or fighting without restriction. The important cistron hither is that harmful wants without brake can pb to harmful consequences (negative, self-injurious or self-destructive outcomes) for the individual performing the behaviour, or for individuals that are the target of the behaviours. A classic instance is allowing Labradors access to nutrient advertisement libitum volition often result in excessive overeating causing multiple long-term health problems, such equally obesity and other related conditions. These limits demand to be examined carefully and thoroughly, every bit they volition exist very species- and individual-specific behavioural limitations. Many zoos are already doing this, however consensus for an ethical and practical realignment towards promoting highly-motivated behaviours instead of natural behaviours needs to exist agreed to and endorsed by zoological institutions, associations, workers and allies.

6. Are Man-Animal Interactions Natural?

Whether zoos focus on natural behaviours or highly-motivated behaviours, both of these may still include straight interactions with humans. Information technology is oft supposed or causeless that homo-fauna interactions in zoos are an unnatural phenomenon, however, in that location is i clear style to counter this presumption. In nature, wild fauna encounter many other species effectually them, to which they must conform, and frequently interact with, in positive, negative and neutral ways (from symbiotic relationships to parasitic or predatory relationships). Most wild animals at present have to conform not but to their historically natural ecosystem conspecifics, only too to a multitude of invasive species that were previously unknown to them or their ancestors [28,30]. Also, every bit we now alive in the Anthropocene era, wild animals increasingly have to adapt to the ever-growing and ever-encroaching human population, in an increasingly human-affected world [28,thirty,33]. In captivity, then, are not humans 1 of those species to adapt to, and to interact with? Humanity often assumes some removal of our species from the residue of nature, that we are somehow a step apart from other animals. It is doubtful that this is how other animals view humans, however. Often i of the corking curiosities of the natural world is how competing animal species may form symbiotic balances that benefit all, and actively help each other in interactions. These would be deemed natural behaviours. Therefore, if many species actively interact with other species as a mode of adaptation to their environment, would it not follow that man-creature interactions in zoos could actually be considered quite natural adaptations? And if those interactions are highly-motivated in the animal, should nosotros encourage them?

Whether these interactions are deemed natural or unnatural, allowing for positive human-animal interactions may be ane avenue of increasing positive affective experiences for animals, especially if those animals are highly motivated to interact with humans (whether it exist zookeepers or zoo visitors) [39]. These interactions must be subject to rigorous safety evaluations for all participants, of course. However, the electric current condition quo of wilding frameworks often view these interactions equally undesirable in any and all situations, regardless of the animal'due south motivations behind the intended behaviours. Again, frustration of these motivations may actually exist detracting from an creature's well-being. If an fauna is highly motivated to collaborate with humans in or effectually its environment, and if those interactions are considered safe for all participants, then those interactions should be allowed to occur, or even promoted (through supervised offerings of such interactions). Obviously some interactions are exempt from these stipulations, when considering an beast'south overall wellness or all-time interests (such every bit veterinary procedures or restraint for medical handling), though positive reinforcement training schedules tin oftentimes remove some of the harshest penalties to the animals these state of affairs might present (such as training for quick, mildly-aversive hand-injections, blood sampling, or "crate grooming" for restraint and send) [37,58].

An animal's motivation to engage in positive homo-interactions may vary from 24-hour interval-to-day, based on other internal and external factors, but the animal should never be bars to, or negatively coerced into, an interaction scenario. The choice to interact should always be on an creature's own terms. This may not exist the instance for all human being-animal interactions currently deployed past zoos beyond the world. Often, many "run across" or "interaction" animals are not afforded a selection of whether to participate or not, or are housed in inadequate areas that may increase their desire to escape that area, even if it means having to interact when they are unwilling [59,60]. Nearly industry-accredited zoos accept their own welfare charter, and take processes and policies implemented to safeguard encounter beast well-being, and to endeavour to offer every bit much option as possible to the animals before being handled for interactions. Indeed, the guidelines published by WAZA [32] state that: "Interactive experiences should be not-invasive, safe and not-stressful for animals. Monitoring of all animals involved in interactions must exist ongoing and have professional person oversight. Risks to animal welfare should be minimised by carefully considering whether interactive experiences are appropriate, and if they are, by accommodating the animals' item needs" (p. 74).

7. Conclusions

Natural living may be a useful concept for developing robust measures of holistic zoo creature welfare, only care must be taken to avoid the pitfalls and dilemmas explored in this commodity. Specifically, wilding is a concept that may not truly exist providing zoo personnel with an advisable ethical or conceptual basis for optimizing evidence-based fauna welfare. Zoos volition continue existing well into the futurity, so more appropriate measures of what is important to an animal for a "life worth living" in captivity should tend towards highly-motivated behaviours rather than just natural behaviours. Homo-animate being interactions in zoos are a source of fence and controversy, all the same, if implemented accordingly, they may significantly enhance animal well-being and holistic animal welfare (which may still be distinctly different concepts, even though the words are at present often used interchangeably [ten]), every bit they are often relationships of great importance to captive animals. Farther exploration of what might found positive human-animal interactions, both scientifically and ethically, as well equally ways of implementing such interactions without leading to unintended or "undesirable" human behavioural patterns emerging (such every bit an increased desire to "ain" exotic wildlife) shall be forthcoming as a follow-up to this article.

Acknowledgments

The writer wishes to acknowledge the immense assist of Peter Sandøe in testing and tempering the ethical arguments presented within. Thank you lot, Peter. The author also wishes to thank Paul Hemsworth, Sally Sherwen and Jenny Gray for their critique, comments and guidance. This paper represents an upstanding chapter of a broader ethical and experimental PhD thesis conducted through the University of Melbourne, Australia.

Funding

This research was supported by an Australian Authorities Research Training Program (RTP) Scholarship.

Conflicts of Involvement

The author declares no conflict of interest.

References

1. Fraser D. Toward a global perspective on farm creature welfare. Appl. Anim. Behav. Sci. 2008;113:142–149. doi: 10.1016/j.applanim.2008.01.011. [CrossRef] [Google Scholar]

two. Hemsworth P.H., Mellor D.J., Cronin G.M., Tilbrook A.J. Scientific assessment of brute welfare. Due north. Z. Vet. J. 2015;63:24–thirty. doi: 10.1080/00480169.2014.966167. [PubMed] [CrossRef] [Google Scholar]

3. Keeling Fifty.J., Rushen J., Duncan I.J.H. Agreement animal welfare. In: Appleby One thousand.C., Mench J.A., Olsson I.A.S., Hughes B.O., editors. Brute Welfare. 2nd ed. CAB International; Oxfordshire, Britain: 2011. pp. xiii–26. [Google Scholar]

4. Mellor D.J. Enhancing beast welfare by creating opportunities for positive melancholia engagement. N. Z. Vet. J. 2015;63:3–8. doi: 10.1080/00480169.2014.926799. [PubMed] [CrossRef] [Google Scholar]

5. Palmer C., Morrin H., Sandøe P. Is it ethically defensible to keep animals in zoos and aquariums? In: Fisher B., editor. The Routledge Handbook of Animal Ethics. Routledge; New York, NY, USA: 2019. [Google Scholar]

6. Palmer C., Sandøe P. Animal Ethics. In: Appleby M.C., Mench J.A., Olsson I.A.S., Hughes B.O., editors. Brute Welfare. 3rd ed. CAB International; Oxfordshire, UK: 2018. pp. 1–fourteen. [Google Scholar]

7. Sandøe P., Jensen K.G. Veterinary & Animal Ideals: Proceedings of the Showtime International Briefing on Veterinary and Animal Ideals, September 2011. Universities Federation for Animal Welfare; Hertfordshire, U.k.: 2011. The thought of brute welfare—Developments and tensions. [Google Scholar]

viii. Veasey J.S. In pursuit of peak brute welfare: The need to prioritize the meaningful over the measurable. Zoo Biol. 2017;36:413–425. doi: 10.1002/zoo.21390. [PubMed] [CrossRef] [Google Scholar]

nine. Weary D.G., Robbins J.A. Understanding the multiple conceptions of animal welfare. Anim. Welf. 2019;28:33–40. doi: 10.7120/09627286.28.1.033. [CrossRef] [Google Scholar]

eleven. Bekoff One thousand. Ignoring Nature No More than: The Instance for Compassionate Conservation. University of Chicago Press; Chicago, IL, U.s.: 2013. [Google Scholar]

12. Gray J. Zoo Ethics: The Challenges of Compassionate Conservation. CSIRO Publishing; Clayton, Australia: 2018. [Google Scholar]

13. Fraser D., Weary D.M., Pajor Due east.A., Milligan B.Due north. A scientific formulation of animate being welfare that reflects ethical concerns. Anim. Welf. 1997;6:187–205. [Google Scholar]

fourteen. Mellor D.J., Reid C.S.Westward. Concepts of fauna well-being and predicting the bear upon of procedures on experimental animals. In: Baker R., Jenkin G., Mellor D.J., editors. Improving the Well-Beingness of Animals in the Research Surroundings. Australian and New Zealand Council for the Care of Animals in Research and Education; Glen Osmond, Australia: 1994. pp. three–eighteen. [Google Scholar]

15. Mellor D.J., Beausoleil N.J. Extending the 'V Domains' model for animal welfare assessment to incorporate positive welfare states. Anim. Welf. 2015;24:241–253. doi: 10.7120/09627286.24.3.241. [CrossRef] [Google Scholar]

16. Charles Due north. Animals just love y'all as you are: Experiencing kinship across the species barrier. Sociology. 2014;48:715–730. doi: 10.1177/0038038513515353. [CrossRef] [Google Scholar]

17. Whitham J.C., Wielebnowski North. New directions for zoo beast welfare scientific discipline. Appl. Anim. Behav. Sci. 2013;147:247–260. doi: 10.1016/j.applanim.2013.02.004. [CrossRef] [Google Scholar]

18. Hemsworth P.H., Sherwen S.L., Coleman G.J. Human contact. In: Appleby M.C., Mench J.A., Olsson I.A.South., Hughes B.O., editors. Animal Welfare. 3rd ed. CAB International; Oxfordshire, United kingdom of great britain and northern ireland: 2018. pp. 294–314. [Google Scholar]

19. Hemsworth P.H., Coleman Yard.J. Human-Livestock Interactions: The Stockperson and the Productivity and Welfare of Farmed Animals. 2nd ed. CAB International; Oxon, Great britain: 2011. [Google Scholar]

twenty. Chiew S., Hemsworth L. Proposed Visitor-Animal Interaction Model, Adapted from Hemsworth-Coleman Model of Stockperson-Livestock Interactions. Brute Welfare Science Centre, The University of Melbourne; Melbourne, Australia: 2016. [Google Scholar]

21. Mellor D.J. Positive animal welfare states and reference standards for welfare cess. N. Z. Vet. J. 2015;63:17–23. doi: 10.1080/00480169.2014.926802. [PubMed] [CrossRef] [Google Scholar]

22. Bracke Grand.B.M., Hopster H. Assessing the importance of natural beliefs for animal welfare. J. Agric. Environ. Ideals. 2006;19:77–89. doi: 10.1007/s10806-005-4493-7. [CrossRef] [Google Scholar]

23. Dawkins M.S. The science of fauna suffering. Ethology. 2008;114:937–945. doi: ten.1111/j.1439-0310.2008.01557.10. [CrossRef] [Google Scholar]

24. Mason M.J., Fire C.C. Behavioral Restriction. In: Appleby M.C., Mench J.A., Olsson I.A.S., Hughes B.O., editors. Animal Welfare. 2nd ed. CAB International; Oxfordshire, United kingdom of great britain and northern ireland: 2011. pp. 98–119. [Google Scholar]

26. Sherwen S.Fifty., Hemsworth L.Grand., Beausoleil N.J., Embury A., Mellor D.J. An animal welfare hazard cess process for zoos. Animals. 2018;8:130. doi: 10.3390/ani8080130. [PMC free article] [PubMed] [CrossRef] [Google Scholar]

28. Sih A., Ferrari Chiliad.O., Harris D.H. Evolution and behavioural responses to human-induced rapid environmental alter. Evolut. Appl. 2011;four:367–387. doi: 10.1111/j.1752-4571.2010.00166.x. [PMC free article] [PubMed] [CrossRef] [Google Scholar]

29. Palmer C. Saving species but losing wildness: Should we genetically adapt wild creature species to help them respond to climate change? Midwest Stud. Philos. 2016;40:234–251. doi: 10.1111/misp.12058. [CrossRef] [Google Scholar]

30. Stonemason K., Burn C.C., Dallaire J.A., Kroshko J., Kinkaid H.M., Jeschke J.M. Plastic animals in cages: Behavioural flexibility and responses to captivity. Anim. Behav. 2013;85:1113–1126. doi: ten.1016/j.anbehav.2013.02.002. [CrossRef] [Google Scholar]

31. Maple T., Perdue B.M. Zoo Animate being Welfare. Springer; New York, NY, U.s.a.: 2013. [Google Scholar]

32. Mellor D.J., Hunt Due south., Gusset M., editors. Caring for Wildlife: The World Zoo and Aquarium Animal Welfare Strategy. WAZA Executive Function; Gland, Switzerland: 2015. [Google Scholar]

33. Díaz Southward., Settele J., Brondízio E. Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services; Advance Unedited Version; Proceedings of the IPBES 7th Session; Paris, France. 6 May 2019; Paris, French republic: UNESCO; 2019. [Google Scholar]

34. Stonemason Chiliad.J. Species differences in responses to captivity: Stress, welfare and the comparative method. Trends Ecol. Evol. 2010;25:713–721. doi: ten.1016/j.tree.2010.08.011. [PubMed] [CrossRef] [Google Scholar]

35. Lyons D. Developmental cascades linking stress inoculation, arousal regulation, and resilience. Front. Behav. Neurosci. 2009;3:1–6. doi: 10.3389/neuro.08.032.2009. [PMC free article] [PubMed] [CrossRef] [Google Scholar]

36. Parker K.J., Maestripieri D. Identifying key features of early on stressful experiences that produce stress vulnerability an resilience in primates. Neurosci. Biobehav. Rev. 2011;35:1466–1483. doi: 10.1016/j.neubiorev.2010.09.003. [PMC gratis article] [PubMed] [CrossRef] [Google Scholar]

37. Rimpley K., Buchanan-Smith H.Grand. Reliably signalling a startling husbandry upshot improves welfare of zoo-housed capuchins (Sapajus apella) Appl. Anim. Behav. Sci. 2013;147:205–213. doi: 10.1016/j.applanim.2013.04.017. [CrossRef] [Google Scholar]

38. Bloomfield R.C., Gillespie Thou.R., Kerswell Thou.J., Butler Yard.L., Hemsworth P.H. Result of partial covering of the company viewing surface area window on positioning and orientation of zoo orangutans: A preference test. Zoo Biol. 2015;34:223–229. doi: 10.1002/zoo.21207. [PubMed] [CrossRef] [Google Scholar]

39. Claxton A.M. The potential of the human-beast relationship as an environmental enrichment for the welfare of zoo-housed animals. Appl. Anim. Behav. Sci. 2011;133:1–10. doi: 10.1016/j.applanim.2011.03.002. [CrossRef] [Google Scholar]

40. Jones H., McGregor P.K., Farmer H.L.A., Bakery K.R. The influence of visitor behavior on captive Crowned Lemurs (Eulemur coronatus) and implications for welfare. Zoo Biol. 2016;35:222–228. doi: 10.1002/zoo.21291. [PubMed] [CrossRef] [Google Scholar]

41. Todd P.A., Macdonald C., Coleman D. Company-associated variation in captive Diana monkey (Cercopithecus diana diana) behaviour. Appl. Anim. Behav. Sci. 2007;107:162–165. doi: 10.1016/j.applanim.2006.09.010. [CrossRef] [Google Scholar]

42. Yeates J.W. Is 'a Life Worth Living' a Concept Worth Having? Anim. Welf. 2011;20:397–406. [Google Scholar]

43. Case B.C., Lobar G.A., Doerr P.D. The physiological and behavioural impacts of and preference for an enriched environment in the eastern box turtle (Terrapene carolina) Appl. Anim. Behav. Sci. 2005;92:353–365. doi: 10.1016/j.applanim.2004.11.011. [CrossRef] [Google Scholar]

44. Tetzlaff Southward.J., Sperry J.H., DeGregorio B.A. Captive-reared juvenile box turtles innately prefer naturalistic habitat: Implications for translocation. Appl. Anim. Behav. Sci. 2018;204:128–133. doi: ten.1016/j.applanim.2018.03.007. [CrossRef] [Google Scholar]

45. Partridge L. Habitat selection in titmice. Nature. 1974;247:573–574. doi: 10.1038/247573a0. [CrossRef] [Google Scholar]

46. Kagan R., Carter Southward., Allard Southward. A universal animal welfare framework for zoos. J. Appl. Anim. Welf. Sci. 2015;18(Suppl. 1):1–10. doi: 10.1080/10888705.2015.1075830. [PMC gratuitous commodity] [PubMed] [CrossRef] [Google Scholar]

47. Price E.O. Behavioural development in animals undergoing domestication. Appl. Anim. Behav. Sci. 1999;65:245–271. doi: 10.1016/S0168-1591(99)00087-8. [CrossRef] [Google Scholar]

48. Price Due east.O. Animal Domestication and Behavior. CAB International; Wallingford, Britain: 2002. [Google Scholar]

49. Pierotti R., Fogg B.R. The Start Domestication: How Wolves and Humans Coevolved. Yale University Press; New Haven, CT, USA: 2017. [Google Scholar]

l. Herbeck Y.E., Gulevich R.M., Shepeleva D.V., Grinevich V.Five. Oxytocin: Co-development of human and domesticated animals. Russ. J. Genet. Appl. Res. 2017;7:220–227. doi: 10.1134/S2079059717030042. [CrossRef] [Google Scholar]

51. Nagasawa G., Mitsui S., En Due south., Ohtani N., Ohta Thou., Sakuma Y., Onaka T., Mogi K., Kikusui T. Oxytocin-gaze positive loop and the coevolution of human-dog bonds. Science. 2015;348:333–336. doi: 10.1126/science.1261022. [PubMed] [CrossRef] [Google Scholar]

52. Ward S.J., Melfi V. Keeper-fauna interactions: Differences betwixt the behaviour of zoo animals affect stockmanship. PLoS 1. 2015;10:e0140237. doi: 10.1371/journal.pone.0140237. [PMC complimentary article] [PubMed] [CrossRef] [Google Scholar]

53. Hosey K., Melfi V. Homo-animal bonds between zoo professionals and the animals in their care. Zoo Biol. 2012;31:13–26. doi: 10.1002/zoo.20359. [PubMed] [CrossRef] [Google Scholar]

54. Špinka Thou. Animal bureau, animal awareness and creature welfare. Anim. Welf. 2019;28:11–20. doi: 10.7120/09627286.28.1.011. [CrossRef] [Google Scholar]

55. Špinka G., Wemelsfelder F. Environmental claiming and animal bureau. In: Appleby Yard.C., Mench J.A., Olsson I.A.Due south., Hughes B.O., editors. Animal Welfare. 2d ed. CAB International; Oxfordshire, Uk: 2011. pp. 27–43. [Google Scholar]

56. Mellor D.J. Updating animate being welfare thinking: Moving beyond the "five freedoms" towards "A life worth living" Animals. 2016;6:21. doi: 10.3390/ani6030021. [PMC gratis article] [PubMed] [CrossRef] [Google Scholar]

58. Weiss E., Wilson S. The use of classical and operant conditioning in training Aldabra tortoises (Geochelone gigantea) for venipuncture and other husbandry problems. J. Appl. Anim. Welf. Sci. 2003;6:33–38. doi: 10.1207/S15327604JAWS0601_03. [PubMed] [CrossRef] [Google Scholar]

59. Morgan One thousand., Tromborg C. Sources of stress in captivity. Appl. Anim. Behav. Sci. 2007;102:262–302. doi: 10.1016/j.applanim.2006.05.032. [CrossRef] [Google Scholar]

lx. Wells D. A note on the influence of visitors on the behavior and welfare of zoo-housed gorillas. Appl. Anim. Behav. Sci. 2005;93:13–17. doi: 10.1016/j.applanim.2005.06.019. [CrossRef] [Google Scholar]

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