Humidity in the Amphibian Enclosure

The humidity in an amphibian enclosure should match that of the species’s natural microhabitat. Humidity is generally controlled by adjusting the amount of ventilation, and by varying the amount of water that is added to the cage and released into the air.

A pump spray bottle can be used several times daily to increase humidity, but the effect each time is temporary. Reducing the amount of ventilation in an enclosure, by draping a sheet of plastic over the top, for example, will increase the humidity. But it may also create a stagnant atmosphere, reducing thermal and moisture gradients, and increasing the amphibian’s susceptibility to disease (Baetjer, 1968). Also, many species of plants fail to thrive in poorly ventilated environments.

An effective way to raise the humidity without reducing ventilation is to create areas of moving water - install a waterfall or stream, or put an airstone in a pool or bowl of water. Live plants will also help to increase the humidity.

Tall vivariums are especially prone to the accumulation of stagnant air near the bottom. Such enclosures often have very poor thermal and humidity gradients, due to a lack of air circulation. Small cooling fans, such as the ones used for cooling computers, can be put at the top of the tank to turn over the air. The fans should be directed downward, toward an inside wall of the enclosure, with the goal of minimizing any strong air flow onto the amphibians themselves. Alternatively, ventilation holes can be drilled in a lower wall of the tank to create a cross current (see Figure 5.9). The strength of the air current can be increased by installing a small fan facing upward at the top of the enclosure, so that it pulls air up through the vivarium.

Most species of nonaquatic amphibians spend large portions of their time in sheltered microhabitats where the relative humidity is high. Even species found in xeric macrohabitats may spend much of their time in burrows or under rocks where humidity levels are high. Activity patterns can be affected by humidity levels. For example, rain forest dendrobatid frogs will exhibit high levels of activity on a wet substrate in high humidity, but will seek refugia as humidity levels drop. A relative humidity above 70% suits most species of amphibians. However, it is best to provide a humidity gradient within the enclosure, so an amphibian can seek its preferred microenvironment. Some amphibians (e.g., the waxy treefrog, Pbyllomedusa sauvagii, the giant monkey frog, Phyllomedusa bicolor) will develop skin problems if continuously exposed to high humidity and are, in fact, adapted to spending at least part of their daily cycle in a low humidity environment. An area of lower humidity can be established using low wattage spotlights over part of the enclosure during the daytime. Refuges should be available throughout the humidity gradient in an enclosure, so an amphibian is not forced to select between security and meeting physiological needs.

If a room can be dedicated for housing amphibians, an area humidifier can be installed. Care must be taken to clean and disinfect the unit weekly, since it can harbor and spread potentially pathogenic bacteria and fungi (Hunter, 1989). A solution of 120 ml (4 fl oz) of white vinegar and 946 ml (1 qt) of water can be used to dissolve any mineral deposits and clean the humidifier (Pinkham & Higgenbotham, 1976).

This should be followed by a disinfecting bath or spray of sodium hypochlorite (bleach) at a dilution of 30 ml (1 fl oz) of bleach to each quart (946 ml) of water. The solution should be left on the humidifier parts for at least 15 minutes, then rinsed well with fresh water (Wright, 1993).

With regard to ventilation in the room, 1-2 air changes per hour should provide a satisfactory level of ventilation while still maintaining adequate humidity levels for amphibians (Pough, 1992).