Wherever the climate will allow monitor lizards should be housed outside, where they will greatly benefit from increased space available, the sunshine and the fresh air. The local range of temperature and air humidity are the factors that must be taken into consideration when deciding whether to try an outdoor enclosure. The tolerance of monitor lizards to cool northern climates is not well documented. A number of species (i.e. V.albigularis, V.niloticus. V.griseus. V.bengalensis. V.flavirufus. V.rosenbergi and V.varius) experience cold winters tn at least pan of their range. The lizards maintain a satisfactory body temperature by remaining in deep burrows which remain surprisingly warm. There is no reason why they should not be kept outside and provided with heated shelters. at least during the warmer parts of the year. Tropical species are unlikely to take kindly to temperate climates in any season.
Elaborate precautions need to be taken both to stop the animals escaping and to prevent the entry of cats and wild animals. Monitor lizards are excellent diggers and so the enclosure should have a very hard bottom, otherwise the walls need to extend underground for at least I m to prevent them escaping. The walls should be smooth to prevent the lizards from climbing over the top. If the lizards can climb a tree and leap to freedom they will certainly do it. Care must also be taken to ensure that the lizards do not consume any poisonous animals, including slugs and insects treated with pesticides. Sheets of corrugated metal designed for roofing provide an economical fence if they are riveted together and fixed firmly in the ground.
Insulated "kennels" are the easiest way to provide warmth and shelter in outdoor enclosures. Burrows are liable to flooding and forbid access to the lizards without excavation. The kennel is typically a wooden box covered with a thick layer of polystyrene and a waterproof coating (e.g. asphalt). It should have a single entrance via some sort of tunnel to reduce heat loss and be provided with a source of drinking water. It need only be large enough to allow the lizards to curl up inside and can be heated with an electric greenhouse heater or a soil warming cable to provide a temperature of about 18°C to which the animals can retire at any time. In cool weather the animals can be shut in the kennels. When the lizards are first housed outside only heated shelters should be available to them. This eliminates the danger of them being unable to locate a source of warmth in cold weather and becoming stupefied. Once the animals are acquainted with their kennels unheated retreats can be provided with impunity.
Plenty of shade from the sun and elevated basking platforms must also be provided. Supplementary basking heat can be provided with a waterproof spotlamp. Water should be plentiful and small pools, just large enough for the lizards to immerse themselves, can easily be constructed by lining a hole with several sheets of butyl rubber. Pools for large heavily clawed animals must be tougher; fibreglass moulds or concrete are more suitable. The more decadent enthusiast may consider installing a pool heater. The furnishings of the enclosure are limited only by the imagination. Rock piles, caves, trees and waterfalls are just some of the options that are not usually available in an indoor terrarium.
Sadly, in most parts of the world the summers are too short and mild to make outdoor enclosures worthwhile and the lizards must be kept inside in large heated boxes. Once constructed the box should be in place for over a decade, so careful planning at the outset is highly desirable. The shape of a monitor terrarium depends on the habits of the species to be housed, as well as any aesthetic or practical considerations. The most important factor is that it should be as spacious as possible. The importance of providing monitor lizards with adequate space has been mentioned before, but it needs to be reiterated. Many large snakes can be kept successfully in very small enclosures, but this is never true of the monitor lizards. They will not thrive in a cramped environment; they are unable to thermoregulate properly, become weak, lethargic and obese and their resistance to disease is lowered.
Attribution / Courtesy: Daniel Bennett. 1995. A Little Book of Monitor Lizards. Viper Press U.K.
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