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REPTILES AND ENVIRONMENTAL TEMPERATURE

First broadcast on www.provet.co.uk on August 9th 2000.


This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Reptiles do not maintain their own body temperature within a narrow range like mammals and birds, so controlling their environmental temperature is critical for normal activity and good health

Reptiles are poikilothermic - which means that their body temperature alters with the surrounding environmental temperature. The reason for this is that they do not generate and maintain body heat internally, but rely on external heat sources - ie they are ectothermic creatures - hence the common description "cold-blooded". As a result, when environmental temperatures increase a reptiles' activity  increases, and vice versa, when environmental temperatures fall a reptiles' activity decreases.  This does not mean that reptiles can survive in any temperatures, their bodily functions still have to operate within an optimum range of body temperature and if the environment is too hot (certainly over 36 degrees C) or too low (below 4 degrees C) it can be fatal. 

Contrary to popular belief snakes and other reptiles do not necessarily have exactly the same body temperature as their environment - studies in some species of snake have shown that in cold weather it is often slightly higher, and this is due to heat generated within the body by muscle activity or physiological mechanisms; and if environmental temperatures are very high the body temperature may be slightly lower, so some reptiles do have slight control over their body temperature. 

Reptiles easily lose body heat across their skins because they do not have insulating layers of hair or feathers, and in the wild they are rarely protected by layers of subcutaneous fat - obese reptiles are usually only seen in captivity. On the other hand they are well adapted to absorbing heat from the environment through their skin - by radiation from the sun or by conduction from rock, stones or sandy surfaces. Species of reptiles living in cooler parts of the world are often darker or black compared to variants of the species which live in warmer climates, and this probably reflects the fact that black objects absorb heat better than light-coloured objects. During pregnancy some snakes (eg Madagascan Tree Boas)  change to a darker colour - probably reflecting their need to absorb more heat for energy. Also, black headed reptiles may have evolved because rapid heat absorption to the brain would ensure that early in the daytime cycle the individual is alert and local sense organs are functioning properly, before the creature exposes itself fully to the environment where predators may be waiting.

In their normal, wild habitat a reptiles daily routine is controlled by environmental temperatures, when it is cold they seek out warm places and bask in the sun, when it is hot they seek out shade, they hunt, feed and reproduce during periods of optimum temperature. When we attempt to keep them in an artificial environment (a vivarium) we need to control temperatures and reproduce as closely as possible their natural environmental conditions. This is one of the challenges of keeping reptiles as a hobby and knowing the optimum temperature range for a species is important. In snakes it has been found that most species prefer to maintain body heat at about 30 degrees C (86 degrees F) and their peak activity occurs within the temperature range of 10-40  degrees C (50-104 degrees F). 

If a reptile has not eaten for a while, is about to shed it's skin or is unwell it may not have the energy to move from a cold spot in the environment to a warmer one, and so it can become trapped in an unfavourable location. 

When there is a prolonged period of cold reptiles become dormant - which is not the same as true hibernation in mammals, but basically all activity slows down and stops. Reptiles will usually seek damp shelter (often underground) to hibernate and frequently  they congregate together. Some species of snake which are adapted to living in cold climates have been reported to survive being frozen ! This ability is not full understood but it  is achieved by two possible mechanisms :

  • Freezing tolerance - the body is able to survive freezing and ice formation in tissue cells followed by thawing
  • Supercooling - the body contains natural substances like glycerol which act like antifreeze and  prevent ice formation in tissue cells.

Nevertheless,  for many species of reptile freezing will kill them. 

Heating a Vivarium

Needless to say tanks or cages used to keep reptiles must be drought free and should be maintained at optimum temperatures for the species being kept.

It is important to set up the vivarium so that there is a temperature gradient across it - with areas that are warmer or cooler than others. The range across a vivarium that is usually recommended is about 10 degrees eg 75 - 85 degrees F . This gives the reptile a choice and encourages movement around it's environment. There are two main ways of heating a vivarium :

  • Using a light - placed over basking rocks (a 40 watt incandescent light in a conical reflector- or a "dark light" which only emits heat). Lights should be guarded  (eg by a metal grill) to prevent direct contact by the reptile - as they can cause serious burns.
  • Using a heater pad - placed under the substrate, away from a hide-box, and only across about half of the vivarium floor.

"Hot rock" heaters are also available - these are artificial rocks which are heated by a filament but problems have been reported with these because :

  • They may not be waterproof - especially if damaged
  • Reptiles have been burned by basking on them for too long

If the vivarium is intended to mimic the natural environment of the reptile, it may be necessary to provide a long period of cool temperature to mimic winter, and this is important for successful breeding of some species of snakes.

The temperature of the vivarium should be monitored continuously using one (or more) strategically placed thermometers. It is no good putting a thermometer right under a heater lamp - as this will only tell  the temperature of the basking area. It should be placed in a neutral area of the vivarium.

 

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