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Reptilian ethology in captivity: Observations of some problems and an evaluation of their ætiology

Part II: Findings and Discussion

Clifford Warwick, Applied Animal Behaviour Science, 26, (1990) 1-13


General behavioral restrictions
Spatial requirements and restrictions
Persecution from other occupants
Disposition-related environmental temperature preference
Interaction with transparent boundaries


Findings And Discussion
Many behaviours which occurred among captive reptiles during this study presented problematic or potentially problematic conditions. In this paper, however, particular attention is given to a few examples not only because these are relatively common (yet largely unrecognised) but also because they broadly embrace numerous other EEMB/EIT (environmentally encouraged modified behaviours (EEMB) and environmentally induced trauma (EIT) and general principles of ætiology.


General behavioural restrictions
Certain behavioural restrictions in artificial environments warrant concern because they result in physical injuries while others are primarily related to inhibited ethological expression.

Many medium to large, colourful and imposing lizards, for example water dragons (Physignathus), are popular among collections. An extremely common sight on these reptiles are lesions at the tip of the snout. These injuries are often very recent, or they may be infected or serious necrosis may have already occurred or may occur. With treatment, the condition usually heals quickly but considerable permanent scarring or defacement may remain. Occasionally, such injuries may be accompanied by anorexia.

Being largely arboreal species, the provision of branches or other climbing facilities is desirable and such additions are well utilised by the occupants. When startled, or even voluntarily, the lizards frequently dive from a raised position. They plunge into a shallow pool of water or on to a substrate, neither of which is of sufficient depth to absorb the energy of impact. Dives into concrete-based water containers are a particular problem. Concussions and bone fractures arise from such falls. For practical reasons of general maintenance deep natural substrates are uncommon and deep water requires unusually large enclosures and thus is rarely seen.

The reason for the diving behaviour among these reptiles is not difficult to locate. Physignathus and similar lizards naturally forage or rest in trees, often high above ground. When threatened in a tree, they commonly dive into deep water from the overhanging branches or on to a thick terrestrial substrate, both of which greatly cushion the fall.

Being a common flight reaction, it is not surprising that sudden disturbances result in injurious drops from a height in captive situations. The fact that unprovoked descents and incurred injury may be repeatedly performed presents a more interesting case and this aspect is discussed under "Adaptability".


Spatial requirements and restrictions
The difficulties of assessing the spatial requirements of captive animals are well known. Certain dimensions which do not even permit basic locomotive exercise are critically restrictive environments (CRE) and would be widely recognised as unacceptable. Other enclosures permit locomotion, swimming and climbing, for example, but do not allow a large, startled, fast-moving lizard (e.g. a monitor (Varanus)) to accelerate, decelerate and stop without impact with the enclosure walls. A similar case exists for other reptiles capable of relatively rapid locomotive movement, such as crocodilians and aquatic chelonians. Such space-limited environments are perhaps best referred to as overly restrictive environments (ORE).

Clear physical problems can result from CRE and ORE type enclosures, including physiological imbalances, loss of condition, overgrown claws and accidental collisions with enclosure walls. Problematic ethological restrictions are also incorporated into these environments.

Moderate to large enclosures which allow for reasonable exercise, permit the occupants to accelerate, decelerate and stop well within the available area, and which accommodate good furnishings without saturation of space, may prevent many primarily physical problems for the occupants. Some behavioural problems however are often not overcome with larger size environments.


Although many reptiles in captivity appear sedentary, others are highly active. Such activity often seems purely related to attempts at escape, and this can be frustrating for the occupants and observers alike. Animals showing these levels of activity are often described by casual observers as "hyperactive", commonly intended to imply an "overactive" individual. What constitutes true hyperactivity may be clouded by the relaxed use of this term since most of the captive reptiles in this study did not exhibit greatly differing mobile activity periods (MAPs) than those of conspecifics in the wild. Therefore, it could be said that these reptiles are engaging in normal levels of activity and thus are not hyperactive. It is, however, not unreasonable to suggest that because considerable activity in the captive environment is behaviourally unwarranted, in comparison with requirements in the natural environment, that "high" activity is effectively redundant and therefore could be reclassed as hyperactivity with some justification.

Whilst physically some reptiles may not need as much activity as they often display, ethological demands may be being presented which Maps type behaviours go some way towards satisfying. High activity is probably largely attributable to two areas: (a) innate drive states; (b) food and environmental searches. The former will be discussed under "adaptability". Numerous species of reptile, for example lizards (Varanus) and tortoises (Testudo), are natural wanderers and cover great distances. Other reptiles are far more sedentary in their habits, for example, certain crocodilians (Alligator) and chelonians (Terrapene).

The naturally wandering species in the study were the most common exhibitors of high activity in captivity. Although these animals are scavengers and thus casually presented food in the artificial environments is acceptable, they are also hunters and browsers. Therefore, particularly in the case of the carnivorous lizards mentioned earlier, live food searches are naturally an active pursuit. When food items (whether live or dead) are hidden in well-furnished enclosures, search behaviours are usually stimulated and, following food location (a series of successful food "recoveries" may be necessary), high activity is reduced or ceases altogether. High activity usually resumes after a period of digestion, although not infrequently lasting well after digestion.

When the lizards and tortoises were presented with an access to additional environments with differing furnishings, almost without exception they would voluntarily enter and make an initial examination of the "new" surroundings and then settle to more regular environmental interactions.


In the reptilia, where comparatively long periods of inactivity are common, it can be difficult to assess whether an individual is abnormally sedentary. However, occasionally specimens will seem hypoactive and a symptom which often accompanies this is anorexia. It is common to discover that inadequate furnishings and/or an ORE or CRE are involved. However, enclosures may be adequately heated, without unwanted cool areas, and well ventilated. The provision of larger, well-furnished enclosures gave valuable results in avoiding or remedying hypoactivity. Offering "favourite" foods would often reactivate individuals and encourage interest in their environment. It is of particular interest to note that hypoactivity usually occurs among those species which naturally æstivate to avoid environmental problems. In these cases, this kind of natural response may be being referred to the artificial environment. Furthermore, such behaviour is more commonly associated with non-aggressive species, for example tortoises, where energy may be directed "inwards" rather than outward through aggression.


Persecution from other occupants
Physical injuries among captive reptiles often arise as a result of persecution by co-habitants. In aquatic turtles in particular, persecuted animals typically avoid potential conflicts by inhabiting areas away from other specimens. In addition, there is a tendency for victimised individuals to recognise offenders and retreat. Hiding places may be sought in the substrate, secluded sites under water or on land where attack is less likely or less effective. Co-occupant aggression can have a profound effect upon the persecuted animals, and symptoms such as hypoactivity, anorexia and occasionally hyperactivity are observed.


Disposition-related environmental temperature preference
Being ectothermic, voluntary selection of temperature variants in order to achieve thermoregulation is normal for reptiles. Certain elements are known to affect typical thermoregulatory behaviour in reptiles. Diseases can influence thermoregulation wherein an individual may be inclined to maintain temperatures at the higher optimum. However, captive reptiles often seem to exhibit low temperature preferences (LTP) and inhabit the cool areas of an enclosure for unduly long periods. Accompanying this inactivity is often considerable disinterest in their environment and anorexia (alternatively, these latter two symptoms may arise afterwards). These manifestations occur despite the availability of appropriate temperature gradients. All-warm enclosures may deter the commencement of this type of lethargy. Once evident, though, the inactivity initiated during LTP behaviour will often not cease with the provision of all-warm enclosures. In addition, if successfully eradicated by the removal of cool areas, the underlying reason for the induction of the LTP behaviour may still remain. Several points are worth bearing in mind when considering this behaviour.

In natural environments of extreme climatic changes, for example, deserts, reptiles emerge from resting places after low scotophase temperatures encouraged by, then exploiting, higher photoperiod temperatures.

In captive situations, these reptiles may exhibit the same tendencies or, not uncommonly, indulge in relatively greater periods inhabiting the warmer areas of the enclosure. This may be considered as opportunistic behaviour in that the animals can generally benefit from longer activity periods. Such opportunities are utilised in the natural environment.

The selection and subsequent protracted occupation of the cool areas, however, is not typical in view of there being warmer facilities available. It could be said that the reptiles are responding to minor environmental or innate drive influences towards hibernation. Reptiles are, however, known to refrain from hibernation if warm conditions are provided, although they may be generally less active than in their natural active season, This behaviour also occurs among species which do not hibernate and therefore cannot be solely attributable to hibernative tendencies.

Species from extreme desert or near-constant tropical temperatures also display occasional preference for the cooler temperature in captive enclosures. In the desert species, there is a clear association with intermittent low temperatures. For those species from tropical zones, however, a link may seem more difficult to find.

Since environmental temperatures and thermoregulation are fundamental elements and influences of basic biological functions and normal behaviours, it is interesting to hypothesise that this system might operate in the reverse flow. That is to say that a reptile's disposition might influence its thermoregulatory behaviour and thus the selection of "appropriate" environmental temperatures results. In short, the animal seeks an environmental temperature to match its mood. A comparison can be drawn here with the example cited earlier where reptiles seek warmer temperatures to assist in the healing process. The main difference is, perhaps, that preference for higher temperatures during disease is pathologically related whereas for LTP it is largely ethologically related (although biologically the subjects can be more closely combined).

The tendencies towards temperature selection under these circumstances can perhaps best be described as disposition-related environmental temperature preference (DRETP). The term could effectively be applied to both "conditions", in the pathological/physiological sense, and "disposition", in the ethological sense. It is of particular interest, that the majority of reptiles which seem to constitute cases of DRETP are those with reputations as highly unadaptable to unnatural environments, for example certain lizards (Chamaeleo), certain chelonians (Kinixys) and certain snakes (Boiga). This suggests that DRETP occurs particularly in conjunction with "sensitive" species and individuals. Furthermore, certain environmental deficiencies in comparison with the natural environment regularly accompany DRETP. It is common, for example, to discover that for arboreal species there is little height to the enclosure along with poor foliage cover. For secretive species or those which simply occupy areas of dense vegetation (e.g. Kinixys), a lack of natural growing plant life and other furnishings often coincides, and for burrowing reptiles a lack of deep substrate. A lack of space is often also noticed. Persecution from other occupants can also contribute to DRETP or general hypoactivity.

DRETP behaviour is probably an indication of substantial dissatisfaction with the captive environment or specific elements within it. The adoption of this behaviour may be to reduce the metabolic rate similar to a rest period contrary to, for example, basking (which raises the metabolic rate) and may, therefore, be an attempt to cope with EIT by way of certain physiological and behavioural shutdowns. Improvement of the environment in the form of furnishings, space and food types usually remedy these situations.


Interaction with transparent boundaries
Transparent materials, for example glass and acrylic plastic (perspex/plexiglass), are widely used to form one or more boundaries in artificial environments. There are certain obvious advantages in using transparent boundaries (TBs) to contain reptiles over, for example, wire mesh barriers which are often used to contain mammals and birds, although in warm climates or during the warmer periods many keepers of reptiles will use wire structures as enclosures or parts of them. TBs have several useful functions: they allow for good observation; heat conservation; impermeability to water (for housing of aquatic species); and hygiene as thorough cleansing is practicable.

Many observers, however, will be aware of the considerable interaction which reptiles of any species engage in during attempts at penetrating a TB. This may take the form of rubbing of the snout against TBs, attempting to climb, applying pressure via the snout, or swimming directly against them. The period an individual spends interacting with a TB may constitute almost 100% of its total activity period. These activities can be reduced by masking (e.g. with vegetation) the TBs or completely replacing them with non-TBs. However, this is less effective than relocating the occupants to all non-TB surroundings because reptiles may remember the sites which were previously TBs and persist in their earlier activities.

The initiation of Maps/TB behaviour is probably attributable to two elements. Specimens which are introduced into enclosures may quickly discover a TB and commence their interaction. Otherwise, environmental inadequacies within the enclosure prompt environmental search behaviours whereby the occupants seek alternatives to surroundings which do not satisfy their biological needs.

Occasionally, within certain enclosure designs, parts of the artificial environment can be mirrored in the TB and thus the occupant may be attempting to reach a visually stimulated, yet non-existent habitat. In the majority of instances, however, MAP/TB behaviour probably relates to conflicts of environment over the innate programming of the reptile (see "Adaptability"). Here, the reptiles are presented with a barrier which is an impermeable obstruction but one which their natural education determines can be entered. Not accepting that the TB is impenetrable, the reptiles persist to the extreme.


Reptiles recently collected from the wild, recently replaced under "new" care and highly sensitive species and individuals, somewhat expectedly will display aggressive behaviours. Aggressive behaviours between individuals are not uncommon in captive conditions, Often, these are strongly related to natural ritualised courtship activities, e.g. in rattlesnakes (Crotalus spp.) and to territorial defence, e.g. in crocodilians (Alligator). There are, however, examples of aggression which arise largely as a consequence of inadequate housing and which, if unchecked, frequently result in fatalities. In addition, aggressive behaviour occurs among single-occupant cases which previously may have been placid. This energy may be directed at minor disturbances or familiar handlers.

While numerous reptiles, for example, cheIonians (Testudo spp.) And lizards (Chameleo spp.), display aggressive tendencies during breeding activities, these examples do not typically exhibit aggressive behaviours towards each other and have naturally non-retaliatory defence systems. Those species which are inclined to be aggressive towards each other and occasionally humans are, almost without exception, types which are capable of highly aggressive retaliatory/defence activities, for example, chelonians (Trionyx spp.), lizards (Varanus spp.) And snakes (Python spp.).

These behaviours often corresponded with poorly managed enclosures, for example, peculiar scotophase /photoperiods, insufficient or inappropriate furnishings (although there may be good space availability). A prime example of probably environmentally related aggression is to be found in the aquatic soft-shelled turtle (Trionyx sinensis). This turtle is naturally an aggressive reptile. In captivity, these turtles frequently attack, injure and kill co-occupants of an enclosure. Certain precautions are often taken by managers to prevent this problem, for example, by providing natural or artificial vegetation into which persecuted individuals can escape their attackers. This, together with spacious environments, can assist in avoiding many potential conflicts. However, whilst acknowledging that aggression in this species may be encountered in nature, an unsuitable artificial environment and involved EIT are probably important elements in exacerbating the aggressive habits. Turtles of this and other Trionychid species which were observed displaying hyperaggressive behaviour were almost always maintained in substrate-free surroundings. In nature, these turtles spend a great deal of their time buried in the substrate. A few enclosures had mock substrates of hard-based materials with inset sand and gravel but these were, of course, unusable by the occupants.

Once provided with deep (10-30 cm) substrate, typically of fine-grain sand or mud (or a combination of both), burrowing activities quickly commenced and hyperaggression (and not uncommonly the corresponding hyperactivity) rapidly diminished. The effect of substrates was enhanced by plant furnishings and underwater crevices (still allowing access to the burrowing material). Excessive utilisation of substrates however may indicate other problems, for example hypoactivity. It seems reasonable that hyperaggression is fundamentally related to natural offence/defence behaviours and is shown as a reaction to other hostilities (the environment).

In cases where hyperaggression and hyperactivity exist together in highly carnivorous reptiles, but environmental provisions and diet type and quality seem reasonable, the cause may be related to dead food items being offered. Natural predators of live food (e.g. Python spp.) And to a lesser extent opportunistic feeders upon live prey (e.g. Varanus spp.) are of considerable relevance here. Snakes and many lizards not uncommonly indicate signs of irritation at each other (mainly at any contact) and towards keepers. In snakes, examples of irritation are typically hissing, exposure of the tongue and its movement in a slow raising and lowering fashion (scent checking), retraction from contact and "loop-pushing" using coils of the body to nudge off contact and occasionally, or if persistently disturbed, striking out with the jaws. In lizards, signs are typically hissing, prolonged inflation of the body, a raised quadrupedal and sometimes bipedal stance, retraction from contact and occasionally, or if persistently disturbed, seizing with the jaws, lacerating with the claws or striking with the tail. One must, however, consider that in snakes hypersensitivity to approach and contact is also commonly attributable to the skin sloughing process and should therefore not be confused.

Occasional or regular offering of live food, for example, every 2-3 feeds or each feed, greatly reduces or eliminates symptoms of aggression. For practical reasons, such as the risks of prey injuring the predator, public disapproval or ethical reasons, many keepers refrain from offering reptiles live food items. An alternative to live food can be provided by attaching the "prey" to a narrow unobtrusive pole by way of a manually controllable noose and then mimicking activity in the dead animal. If not freshly killed, then gradual warming of the carcass may assist in imitating the natural body warmth and help to improve the offering's acceptability.

Once the food item has been seized, artificial movement should continue for a short period to reproduce being subdued and killed by the predator. The method is particularly successful when used for feeding dead animals to snakes. Since the aggressive tendencies decrease when predator/prey interaction and killing is simulated, it seems likely that a "struggle" with the prey animal is biologically anticipated and, as an innate drive mechanism, failure to properly fulfil this behaviour results in a biologically incomplete kill. It is largely the most aggressive aspect of the feeding process which is effectively removed. The regular failure to have greater predator/prey interaction probably leads to an accumulation of inhibited natural aggressive habits which are eventually directed at non-prey objects.


Although adaptability is cited towards the end of this paper, it is, in many respects, the most important subject. A general comparative assessment of reptilian, avian and mammalian adaptability to captivity can be found in Warwick (1987). The problems given so far in this paper and others cited in Murphy (1973) and Cowan (1980) are attributable to maladaptation to artificial environments. Whereas these aspects are studied in this and other references given later, the basic ethological and psychological reasons for poor adaptability or inability for even partial adaptation have not been even moderately assessed in the literature.

It is widely recognised that, in pure physiological terms, reptiles are very specialised within certain environments because of, for example, certain specific food sources and climatic requirements which thus make them less environmentally "versatile" than many mammals and birds. Among mammals and birds, more advanced central nervous system functions, such as modification of the environment and "intuitive thought", mean that certain "toys" or other environmental enrichment accessories can, although probably only temporarily, occupy individuals and relieve stress. Within the reptilia, however, such facilities are typically unrecognised by occupants and are thus of no value.

A fundamental difference between the natural ethological and psychological arrangements of mammals, birds and reptiles resides in the systems of natural education. Within mammals and birds, although some educational elements are received pre-birth, typically offspring education is parentally and socially transported. The consequences of this system are that not only do these animals not possess greatly specified expectations of an environment but that they are highly susceptible to general education. Within the reptilia however, education is primarily innately and not parentally or socially received. Reptiles are effectively born with sufficient predetermined cues and expectations for a certain life in the wild. In captivity, the strength of this system can be commonly observed. A marine turtle hatched from an egg in captivity and housed for 1 year in a clinical container was released to the natural environment and immediately put practical use to its foraging activities as if it was a typical "wild" specimen. The offspring of multi-generational captive-bred reptiles have been reported to indicate no significant (or any) behavioural variance from their conspecifics in the wild. Therefore the natural innate characteristics and requirements remain with reptiles for life and thus re-education beyond very precisely defined limits cannot be expected to occur. This therefore increases the emphasis on the necessity to provide appropriate and stimulating habitats for captive reptiles.

Many of the behaviours and activities exhibited by captive reptiles suggest that they are unable to cope with their unnatural situations. It might be argued that an exception to this is in certain cases of hypoactivity where individuals may be attempting to cope with environmental inadequacies by biological shutdowns. However even in these situations complete æstivation is not achieved as limited environmental and other stimulation continues. Therefore proper withdrawal from unsuitable surroundings does not adequately arise.

All of the problems cited in this paper are closely related to inabilities to adapt to environments which may, in many cases, be caused by subtle but extremely important deficiencies. Where maladaptation or non-adaptation occurs, stress probably is also involved (Cowan, 1980). Stress arising from inhibited ethological expression is by itself perhaps adequate reason for offering more appropriate conditions for captive reptiles or even to refrain from maintaining individuals in captivity. However, stress-related physiological and biochemical changes and pathophysiological consequences (Cowan, 1980) offer other considerations.

Snyder (1976) suggested that in high-stress environments energy is directed at maintaining internal stability at the expense of certain vital, though less immediate, functions like growth, reproduction and resistance to infection. In a ten-year study of 1300 mortalities among captive amphibians and reptiles, 11.6% were caused by "trauma" (Kaneene et. al., 1985). However, there was no cited attempt at assessment of any further relation between trauma and the causes of death by microbial agents (36.6%) and parasites (12.6%).

Symptoms may arise quickly or, as in some cases of anorexia, manifest after already considerable trauma. Cowan (1980) suggests that maladaptation may cause anorexia, wasting and emaciation (even though specimens may he feeding); fragility of tissues, resulting in ulceration of skin at points of friction or mild trauma; great increase in susceptibility to infection; infections with normally innocuous organisms; ulceration of the gut; overgrowth of parasites; impaction of the oviduct (egg binding) with peritonitis. To a lesser extent, poor growth and reproductive failure are also manifestations of maladaptation (Cowan, 1968). In personal studies, however, it was recorded that many examples of successful breeding among captive reptiles resulted, yet conditions were often highly inadequate and symptoms of stress would be clearly present. In these situations, breeding behaviour, as with occasional excessive food intake leading to obesity, may be related to a retreat from the environment to certain basic biological functions.

Personal studies of reptiles maintained under historically similar management practices, but later maintained under different conditions, revealed that resistance to disease is higher among specimens in the most naturally ecologically similar environments. Furthermore, diseased individuals from less natural enclosures indicated higher recovery rates when relocated to more natural surroundings, in particular when outdoor environments could be provided. This applies to both non-medically assisted examples as well as those undergoing treatment and which did not appear to be responding. In certain circumstances, though, clinical management may be favourable.

 To Part III: Conclusions and Reference

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