To listen to some keepers talk, you would think that humidity was some sort of mystical potion that was difficult to make but that works magic. While it may be tough to provide the high humidity we aim for if the air in your tortoise room is dry, the overall idea is simple. There are three basic rules to humidity:
Why is humidity important?
Forest Tortoises tend to come from areas of high humidity and generally do best in captivity at the right levels of humidity, at least in some places. Some species, such as Yellow-foot and some Hinge-back Tortoises, prefer very high humidity – 95% or more. Others do perfectly well at 80% or more, but can often tolerate lower levels as long as there is someplace they can hide that is more humid.
How Much Humidity?
We normally aim for roughly 70% to 100% humidity, often settling for 70% overall with some higher ratios in certain parts of the habitat. As mentioned, some species require more humidity (some Hinge-backed Tortoises seem to prefer almost 100% humidity), and baby Forest Tortoises seem to prefer the higher levels as well.
For Red-footed Tortoises and most other common pet species, 50-70% overall humidity is probably enough, especially if there are hides or other areas with higher humidity available.
We can raise the humidity in our habitat by…
The method that works best for me in the rather cold and dry Great Plains region is the one described in “Housing“: a waterproof heat rope in the substrate that heats the water to generate warmth and humidity. My habitat is about 60% covered and still stays very humid with very little attention including daily watering and checking water levels, and a thermostatic controller for the heat ropes so they are at the temp I want them at.
Too much humidity, especially combined with heat and low air flow, can lead to issues like mold and mildew, a smelly habitat, and plastron rot. A good airflow will help, as will elements such as live plants, a good substrate (like cypress), and regular monitoring.If you can, consider an airflow that lets a relatively small amount of air out at the top by drilling small holes around the edges of the lid, and creating more and/or larger air holes around the base. The warm humid air will leave slowly through the high holes, and new, fresh air will come in easily in the low holes.
What is Humidity?
Absolute humidity (AH) is how much water vapor there is in a given amount of air. (AH) is determined by dividing the mass of the water vapor (Mw) in a given volume (V), or AH = Mw/V. This is not as helpful to us as “relative humidity” is.Relative humidity (RH) is determined by a rather complicated formula, but the idea is simply how much vapor is really in a space compared to what it could hold total. This changes as the air gets warmer, and pressures change.A cubic meter of air at 30C/86F can generally hold 30 grams of water vapor (shortened to 30gr/C^3), making it 100% relative humidity. If the absolute humidity was half that, 15gr/C^3, and the temperature was the same, the relative humidity would be 50%.
As the temperature of our cubic meter of air cooled, it could not hold as much water vapor. The excess vapor becomes condensation, dew, or fog, but the relative humidity could still be nearly 100% because it is still holding as much vapor as it could at that temp. This relates to the “dew point”: as the temperatures drop, the relative humidity is rising. When it hits 100% and the temperatures keep dropping, the vapor it can no longer hold becomes dew.
Homemade Humidity Devices
(These are mostly just brainstorms and ideas, not finished thoughts.)
Add an inch or two of dampened sphagnum moss or similar product, and park the box in a warm zone to make a nice, humid chamber. A better alternative is to sew some absorbent material (like the same kind of moss) into a thin cloth bag and hang it on a side so there will be less moisture on the hide floor.
A small heating element (water-proof hot rock?) can be used in or under it to keep the temps comfy.
This is a plan for providing warm, humidified air for a large semi-enclosed space, like a big tortoise table. It is only an idea, and this is not meant to be a blueprint!
The idea is that a ceramic element space heater (with thermostatic controls, an intake filter, and a fan speed control set to low) blows into metal ducting that leads into a large plastic tub.
Inside the tub is a powered humidifier. (The device shown is a fogger unit on a brick in a pool of water.) The inside is also divided by baffles to slow the warm air so it absorbs more humidity. A second duct takes the filtered, warm, humid air into the habitat.
Take a plastic bottle with a large-mouthed lid, and install two tubes: a small one hooked up to an air pump on one end with an airstone on the other, and a larger tube to carry the humidified air to the habitat.
This is not a very powerful humidifier, but it is improved by adding a bigger pump, or a wick/sponge inside to help move water to vapor faster, or heating the water. It also helps to direct the output into a small, semi-enclosed space such as inside a hiding log.
(Do you like how it is working even though the air pump is not plugged in? Gotta love that Acme brand!)
Start with an automatic pet waterer. Use 4 sponges to build a little “castle” in the bowl area with a space in the middle.
Take a plastic tub that fits over the sponges nicely and cut a hole in each side and the top. Attach a small sealed fan at the top, blowing downwards. (Radio Shack sells small computer fans that will work. Get help if needed to wire it safely!)
Fill the waterer and set the tub down over the sponges. Trim sponges to allow a good fit.
The air will be pushed past the wet sponges and blow humidified air out the holes in the sides of the tub.
The large reservoir lets this run for a long time between services, and a drop or two of vinegar in the water will help prevent mildew.
Mount a piece of a substance like terrarium moss, indoor-outdoor carpet, or similar material to a wall of the habitat. At the base of the material, park a pan or tray to catch excess water. A “drip vine” along the top of some “reptile moss”, for example, would work nicely.
Position a dripper so it drips on the carpet. Drippers can be bought or made. Any jar with a spigot on the side will work if you can open the spigot just enough to let it drip out. A plastic milk jug with a pin hole in the side will work as well. With any dripper the tightness of the lid helps control the flow.
Edited 8-15-2012 (C) Mark Adkins