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TROPICAL RAINFOREST TORTOISES AND TURTLES: Practical techniques for the provision of adequate ambient humidity in captivity

By Andy Highfield

     The word "rainforest" was coined in 1898 by a German botanist to describe forests that grow in constantly wet conditions, with an average annual rainfall of 80 inches a year or more. Tropical rainforests represent the oldest major vegetation type still present on the terrestrial Earth. Like all vegetation, however, that of the rainforest continues to evolve and change, so that modern tropical rainforests are not identical with rainforests of the geologic past.

     Tropical rainforests grow mainly in three regions: the Malesian botanical subkingdom, which extends from Myanmar (Burma) to Fiji and includes the whole of Thailand, Malaysia, Indonesia, the Philippines, Papua New Guinea, the Solomon Islands, and Vanuatu and parts of Indochina and tropical Australia; tropical South and Central America, especially the Amazon basin and West and Central Africa. Smaller areas of tropical rainforest occur elsewhere in the tropics wherever climate is suitable. The principal areas of tropical deciduous forest are in India, the Myanmar-Vietnam-southern coastal China region, and eastern Brazil.

     A vertical stratification of three layers of vegetation is apparent in the typical tropical rainforest environment. These layers have been identified as A, B, and C layers:

'A' layer, or 'Emergent' layer:
     This layer is comprised of widely spaced trees 100 to 120 feet tall and with umbrella-shaped canopies extending above the general canopy of the forest. Since they must contend with drying winds, these trees tend to have small leaves. Some species are deciduous during the brief dry season. Birds and monkeys are typical inhabitants of this Emergent layer, which receives by far the most direct sunlight. Emergent level trees are very top heavy and have almost no side branches below the canopy.

'B' layer, or 'Canopy' layer:
     This layer is mainly comprised of a closed canopy of 80 foot-high trees. Light is readily available at the top of this layer, but is greatly reduced below it. Many of these trees have their branches intertwined and they are also tied together by various species of creepers.

'C' layer, or 'Understory' layer:
     The Understory layer occurs at around 60 feet, and is home to thousands of plants, insects and birds. Epiphytes are plants that perch on or adhere to other plants. They collect water in a variety of ways from rain and get nutrients from organic matter. Mosses, lichens, orchids, and ferns, are typical Epiphytes that grow in the Understory layer.

     Less than 3 percent of the light intercepted at the top of the forest canopy passes to the middle layer of ground cover plants, and less than 1 percent of the light that strikes the top of the forest penetrates to the forest floor. In such darkness few green plants grow, instead, typical vegetation includes a high density of fungi. The canopy above also reduces rainfall, and approximately one third of total precipitation is intercepted before it reaches the ground. On the forest floor, the air is very still and the ambient humidity is almost always above 75%, often extending to 90%, and the temperature is relatively constant year-round at 80-85° F.

     One hectare of pristine tropical rainforest (2.47 acres) might contain over 750 types of trees and 1500 species of higher plants. At least 80% of the developed world's diet originated in the tropical rainforest, including fruits such as avocados, coconuts, figs, oranges, lemons, grapefruit, bananas, guavas, pineapples, mangos and tomatoes; vegetables including corn, potatoes, rice, winter squash and yams; spices including black pepper, cayenne, chocolate, cinnamon, cloves, ginger, sugar cane, turmeric, coffee and vanilla and nuts including Brazil nuts and cashews.

     Tortoises and turtles that live on the rainforest floor (or at the edges of rainforest clearings) tend to feed upon a wide variety of fallen fruits, are often omnivorous, and enjoy regular access to rainforest pools and streams. Typical examples of these species might include Geochelone denticulata (the Yellowfoot tortoise) and Rhinoclemmys funerea (the Black pond turtle) from tropical Central America, or Kinixys homeana (Home's Hingeback tortoise) from the tropical African rainforest. It is typical that such species are not great baskers, tend to have soft, rather than scaly skin and limbs, and possess large eyes - all features well suited to a cryptic lifestyle in the dark, humid rainforest floor.

Practical considerations

     In captivity, the provision of appropriate high humidity environments for tropical species can prove problematic. The failure to provide such environments, however, can be catastrophic, as these species are typically very susceptible to environmentally induced dehydration. Some consequences of this include renal failure, skin problems, and eye problems. Despite the challenging nature of the exercise, then, every effort must be made to meet the biological needs of these animals in captivity. Typical centrally heated houses reveal relative humidity levels as low as 20% in winter: far too low for the maintenance of tropical species. Some books recommend "adding a dish of water in the terrarium" to solve the problem, but the reality is that such measures are almost totally inadequate, as is readily proven if a few accurate measurements are taken.

     A number of effective approaches do exist, however, and some of these were discussed in a previous publication (Highfield, 1998). The use of suitable substrates and a high density of genuine, live vegetation, for example. Although desirable, these methods may not be feasible in every situation. As an alternative, therefore, this present article discusses the installation and use of humidifiers and high pressure misting systems as a means of boosting local ambient humidity to create 'tropical' environments for rainforest reptiles.


     A wide range of humidity generating devices is available, from small domestic appliances to larger industrial models. Domestic models typically have a water reservoir in the one to five gallon range, while industrial versions may contain between fifteen to thirty gallons. The practical differences between models are mainly in the amount of humidity generated and the length of time the humidifier runs before its tank needs refilling with fresh water. By way of comparison, even a small, 4 gallon domestic model is usually capable of generating sufficient humidity to turn an 8 X 10 room into a fair imitation of a tropical rainforest - but in very dry environments, will require refilling twice or more daily. Larger models are far less demanding of attention in this respect. Several factors affect choice of model:

  • Size of area to be humidified
  • Existing ambient humidity
  • Rate of airflow or exchange through the area
  • Temperature

         A small vivarium tank may be humidified very effectively by means of even a one-gallon domestic humidifier, with the output of the unit fed into the vivarium by means of standard PVC pipes. Control of humidity level in this instance is best accomplished by means of a time switch. True humidity operated switches are available, but tend to be quite expensive. These are ideal for large, professional installations, but are rarely necessary for more basic set-ups.

         Humidifers come in two basic designs. Ultrasonic, or 'cool mist' and 'warm-air'. There are important functional differences between these designs that it is important to understand before making any purchase.

         The 'cool mist' humidifiers emit, as their name implies, a cold mist of water particles. It's rather like a layer of fog… ..hence, these are sometimes also known as "Ultrasonic Foggers". There are two problems, in my experience, with this design. The first is the immediate adverse impact upon temperature. The second is that the mist falls to lie at the bottom of any enclosure. The point of introduction must therefore always be at the top of the terrarium. In practice this is easily accomplished by using a system of large bore PVC plumbing pipes to direct the output to the desired point of entry.

         The 'warm air ' type humidifiers operate on a completely different principle. In essence, these devices include a water reservoir, a 'wick', a heating element and a fan. They produce a fairly high temperature 'steam type' output. In this respect, they overcome two of the main objections to ultrasonic design - there is no adverse impact upon temperature, which can chill sensitive species, and the output naturally rises and disperses evenly. One potential danger inherent in this design, however, is that close to the point of exit, the rising steam is very hot - and would be capable of inflicting quite serious burns. Fortunately, this is not a problem in chelonian applications, but it does mean that this type of humidifier must be used with extreme caution where other, arboreal species of reptile, such as snakes or iguanas are concerned. Under no circumstances must any animal be able to approach the steam exit vent. As with ultrasonic foggers, 50 mm (2") PVC plumbing fixtures can be used to direct the output into enclosures - but do bear in mind the need to ensure that no animal can come into immediate contact with the hot steam as it leaves the pipe.

         Overall, for most chelonian applications, I believe that the 'warm-air' design is to be preferred. Units of this type produce a genuine "warm, tropical forest" effect when used in any enclosed space. It can quickly become quite uncomfortable for humans, but for tropical Central American and Asian species, it is absolutely ideal. I have found that one or two 5-gallon units running in a 12 X 12 foot square terrarium are more than capable of sustaining ambient humidity levels in excess of 80%, if desired, for periods of up to 36 hours without the need to re-fill their fresh water reservoirs. One point to bear in mind is that when run at 70%+ humidity, units of this type will cause severe damage to household furnishings, books, papers and possibly even the structure of your property! Fungus does not grow in rainforests without reason! Therefore, use only in appropriate locations - a greenhouse, insulated and protected room, or custom terrarium.


         Although often confused with humidifiers, misters are very different in both design and function. They produce a droplet size that is many times larger than that obtained from humidifiers, and the net effect is close to that produced by a fine shower. Misters are excellent for providing periodic 'rainfall' in tropical terraria. Although introduction of regular fine 'rain' does boost local humidity considerably, and evaporation of this precipitation continues for some time after the unit has ceased active delivery, they are rarely a total solution to the humidity problem. Generally, they are best employed in combination with ultrasonic or evaporative humidifiers then, and not as an alternative to them.

    Two types of mister are typically available:

  • Low pressure

         This type of mister system is basically the same as that fitted into many agricultural greenhouses - those used by orchid growers, for example. Most connect direct to a domestic tap (faucet). This is turned permanently on, and actual flow is regulated by insertion of an electronically controlled timer. Various models of timer are available, providing from one on-cycle per day, to multiple on-cycles. One feature to check is that the on-cycle period can be adjusted - in most tortoise applications, a relatively short 'shower' is called for. Ideally, look for a timer that can provide an 'on-period' from one to 5 minutes duration. A system that provides for two on-cycles per day, one in the morning and another mid-afternoon is recommended for most tropical tortoise and turtle installation. Water is delivered to a series of very small (usually plastic) mist-heads that are simply screwed straight into a micro-bore tube that is, in turn, connected back to the timer module. Several different types of mist-head are often available, providing different grades of 'rain', spray or mist. Installation is usually very straightforward, and this type of system is both flexible and relatively low in cost. Beware, however, that in order to work properly a reasonable level of water pressure is required at the tap/faucet. If you have low water pressure you may find that this type of system is not especially effective. Most manufacturers will provide, on request, the minimum water pressure required by their systems.

  • High pressure

         High-pressure systems typically rely upon a separate reservoir and a very high-pressure pump rather than upon a direct feed from a domestic water supply. The quality of the line feed and all fittings and mist heads must be of a very high quality indeed, as the pressures attained would rapidly burst standard tubing. As a consequence, this type of system is considerably more expensive to install than those that rely upon ambient water pressure. In all other respects, they are very similar, also requiring use of an electronic timer to regulate flow. Typical reservoir sizes suitable for reptile use range from 5 to 15 gallons - more than sufficient in most cases to provide several days worth of tropical downpours at the recommended intervals. One advantage of high-pressure systems is that the water temperature in the reservoir can be allowed to adjust to room temperature before use. Low-pressure systems, fed by mains water, have a tendency to deliver water at far too low a temperature for tropical species. High-pressure systems are also, in general, capable of generating finer mist particles than lower pressure models.

         In conclusion, a combination of a warm-air humidifier, a misting system, and an area where soaking can occur are all likely to be required if an ideal habitat and environment for tropical species is to be attained. This combination of facilities suits many species, from Asiatic box turtles of the genus Cuora, to the larger Redfoot and Yellowfoot tortoises of South America. If you are thinking of accommodating such species, you may find that a visit to your nearest tropical butterfly exhibit is well worth while, as such places are excellent sources of ideas for designing and decorating artificial tropical environments.


    Highfield, A. C. Tropical vivaria for tortoises and turtles. Tortoise Trust Newsletter, Winter 1988 issue.