For species which are more arboreal (tree climbing) in nature, for example, the green iguana and many snakes (e.g. the boa constrictor and Burmese python), the emphasis in cage design should be more on vertical height rather than horizontal space. For tortoises, however, the provision of too much vertical space is pointless. Barnard (1996) provided some minimum dimensions in Table 18.1.

Table 18.1 Some minimum vivarium sizes.

Cage materials commonly used include perspex, reinforced glass, sealed wood and fibreglass (Figure 18.2). Wood should be avoided unless it is sealed to prevent moisture damage and rotting. Glass and clear perspex are useful when showing off a collection, but care should be taken as many reptiles cannot see the tank sides, and so may continually rub their snouts along the inside of the vivarium, causing severe abrasions which can become infected. Often the provision of a tape strip on the outside of the glass at reptile level allows them to appreciate that a barrier exists and prevents this problem.

Figure 18.2 Vivarium made of moulded fibreglass.

Heating

Reptiles are ectothermic by nature, i.e. they rely on the environment to provide sufficient heat to warm them to their preferred body temperature (PBT). Their PBT is the body temperature at which their organs and biochemical processes function optimally. To maintain their PBT, the reptile must be provided with a preferred optimum temperature zone (POTZ) within which it may position itself. This necessitates the provision of some form of artificial heating within the tank/vivarium to create a temperature gradient within which the reptile can place itself to either cool down or warm up.

Two main forms of heating are advised. A background, continuous heat source is important to raise the vivarium temperature above the background room temperature. This is often provided in the form of a radiant heat mat, a mat which emits heat continuously, and is placed on the outside wall of the vivarium (Figure 18.1). It then radiates heat through the tank wall. Placing it on the outside of the tank avoids the possibility of the reptile chewing, urinating or defaecating on it, so increasing hygiene and safety. The size of available mats varies, but a rough rule is that one-third to one-half of the longest side of the tank should be covered with the mat. Some form of insulation on the outside of the mat, increasing reflection of heat into the vivarium, is also useful.

In addition, the vivarium requires a focal hot spot, which may be provided in the form of a ceramic, infrared heat or combination heat/UV bulb. This should be suspended from the ceiling of the vivarium, and should be protected from the reptile to avoid the risk of burns. The bulb should be attached to a thermostat, which will allow maximum and minimum tank temperatures to be set. A form of heated, plastic molded rock has been used to provide a basking point for reptiles. These should be avoided as should the thermostat break within such a device it can overheat and the reptile will injure itself.

The importance of a focal heat source is that it provides a temperature gradient, allowing the reptile to bask underneath the heat source or to escape to a cooler end of the tank when overheated. The reptile can then maintain its PBT by positioning itself at different points in the tank during the course of the day.

The temperatures required for different species of reptile will naturally differ. A list of some species and their temperature requirements is given in Table 18.2.

Table 18.2 Preferred optimum temperature zones and relative humidity for selected species of reptile.

Humidity

Humidity is also important. Many species of reptile come from dry desert regions, but equally many originate in tropical rain forests. Therefore, their tolerance of water moisture in their environment will vary. A water dragon, basilisk or garter snake, all used to living near or in water, will require a 75–90% humidity level. This may be difficult to maintain in a heated environment; as the hotter the air, the more water droplets the air can hold, and so the relative humidity levels drop. Thus, spraying the enclosures frequently, using a hand-held plant mister, with previously boiled and then cooled water is useful. Alternatively, the provision of water baths or damp substrate within the tank can be used to increase humidity. Care should be taken over hygiene levels though, as a too damp and soiled substrate can lead to skin infections such as blister disease, a common problem in garter snakes. In the case of reptiles from more arid climates, a relative humidity between 25 and 50% is often adequate (see Table 18.2). This is around the normal level of the average centrally heated home. However, at certain times even these species require increased levels of humidity. One such example is during the shedding cycle when the old skin layer is sloughed. At this time an increase in humidity is essential to prevent the old skin drying out before it has a chance to peel off and so resulting in constrictions around extremities such as the digits. This is a very common problem in leopard geckos and many adults have lost the ends of their toes through avascular necrosis. To prevent this, it is useful to provide a hide that has an increased humidity level in addition to a normal hide. This can be achieved by placing a shallow dish of water with some cotton wool in it within the hide.

Ultraviolet lighting

Lighting is particularly important for the growing juveniles of many species. In the wild, many of these reptiles live in parts of the world where the intensity of the sun’s ultraviolet rays is high. These ultraviolet rays stimulate a number of functions in the reptile; often encouraging mating at certain times of year, and may act as a general appetite stimulus. This seems to be the role of the A section of the ultraviolet waveband.

The B waveband of the ultraviolet spectrum is important in all species in encouraging the production of vitamin D3 from precursors in the reptile’s skin. Vitamin D3 is intimately involved in the metabolism of calcium and bone growth within the juvenile reptile. Therefore, a lack of ultraviolet light can be responsible for the presence of metabolic bone disease in several species, particularly the green iguana and the Mediterranean tortoises (see chapter 21). Many terrestrial chelonia are kept in open-topped, plastic or wooden enclosures with suspended heat/ultraviolet lamps.

Artificial ultraviolet lighting is therefore important in these species, and should be provided on the inside of the vivarium. This is because glass and perspex will filter out the UV rays if the light is placed on the outside of the tank. In addition, the light source should be positioned close to the reptile, i.e. within 30–45 cm. This is because the intensity of these artificial lights is relatively low, and the inverse square rule tells us that the intensity of the light diminishes with the square of the distance from its source (e.g. the intensity at 2 m from the source is a quarter of that 1 m from its source).

Some species are not so susceptible to ultraviolet deprivation, including more nocturnal species such as the leopard gecko and many snakes. The theory is that these species gain sufficient preformed vitamin D3 in their diets to cope. This is important if the owner is not feeding them correctly, as metabolic bone disease may then be seen.

It is also worth noting that the type of UV lighting should be tailored to the species. Some species prefer to bask in full sunlight and so a ‘sunbeam’ method of providing lighting with a high UVB mercury vapour or metal halide light ideally in combination with an incandescent lamp to produce the equivalent of a sunbeam in the basking zone. This should be big enough to get the whole reptile inside the basking zone. This is most suitable for reptiles noted for basking such as fence lizards (Sceloporus spp.), bearded dragons, frilled lizards, etc. Others do not bask and prefer a more dappled shade method where an incandescent lamp is used at one end of the vivarium controlled by a dimming thermostat. This creates a suitable temperature gradient and a focal UVB source which then creates a UV gradient in the tank as well with a high point underneath the heat lamp. Shelter is then provided using vegetation and plenty of hides so that the reptile is not continuously exposed to UV light. This is most suitable for reptiles such as rat snakes, anoles, water/garter snakes. More information can be found in Baines and Brames (2010) and Ferguson et al. (2010).

Cage ‘furniture’ and environmental enrichment

Many reptiles are relatively poorly adapted to captivity, being wild animals in a confined space, and so it is important to ensure that their environment adequately caters for their requirements.

As previously mentioned, many arboreal species enjoy exploring vertical space. They should therefore be provided with branches and ramps up, which they may climb. It is often useful to provide an elevated basking spot which they can lie out on near to the focal heat source.

In the case of ground-dwelling species, the provision of some form of floor furniture is important. Tortoises are best kept singly, except when breeding of course, or in the case of small hatchlings which prefer to be in groups. In these cases, the provision of visual barricades which they can hide behind and so escape from one another is useful.

All reptiles should be provided with a hide. This is important particularly for many snakes which will often refuse to eat their prey in the open, but rather prefer to take it back into the hide area away from view. The size of these areas does not need to be that large, in the case of most species a space 2–2.5 times the size of the reptile housed is sufficient. The number of hides should ideally be equivalent to the number of reptiles housed plus one.

Flooring

The substrate of the vivarium, or floor covering, is important. It is vital that any substrate used is nontoxic to the reptiles housed and is easily cleaned. In many cases the provision of newspaper or unbleached household paper is perfectly sufficient, although possibly not so aesthetically pleasing, as more naturalistic substrates. Care should be taken with smaller reptiles with newspaper, as the ink from the newsprint may prove irritant.

Other substrates used commonly include bark chippings, calcite sand and peat. Bark chippings are a good choice for deep litter situations, particularly when providing enough substrate for a pregnant female to dig a nest in which to lay eggs. However, the chips should not be of cedar as the resins from this can be irritant. It is also more difficult to monitor the cleanliness of bark chippings as faeces and urine may fall into the substrate and so avoid detection.

Sand is useful for desert species such as leopard geckos, collared lizards, sand boas, etc., but care should be taken with any reptile on this substrate. If the diet contains mineral deficiencies or if there is intestinal parasitism present, many species will consume the sand and may suffer intestinal blockages.

Peat can be useful for species requiring damper conditions such as water dragons, red-footed tortoises, etc., but care again should be taken with the hygiene of this substrate, as waste materials may build up unnoticed.

Certain types of substrate are best avoided. Coral is not advised as a substrate for ecological reasons as well as the tendency for reptiles to eat the substrate and suffer gut impactions. Corn cobs should also be avoided as these are often inadvertently eaten, swell and cause intestinal blockages.

Aquatic species and amphibians

Some reptile species, such as the terrapins and turtles, require large areas of free water; some, such as frogs and toads, a small area but damp environmental conditions (Figure 18.3).

Figure 18.3 Example of hospital tank provision for an amphibian, in this case an Argentinian horned frog.

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