How To Make Your Own Tortoise Or Turtle Egg Incubator
- tortoisetrust
- 6 days ago
- 8 min read
Updated: 6 days ago
While you can buy commercial models, the "low cost" designs tend not to be very precise or reliable, while the "professional" designs are incredibly expensive. The good news is that you can make an incubator that will outperform all but the most expensive professional models at very reasonable cost and which is, in addition, very easy to build.
by Andy C. Highfield
This article covers building and setting up an incubator, but for more on nesting, nest site selection and potential problems related to eggs and nesting see our separate article.
Incubators for tortoise eggs (and reptile eggs generally) fall into two main groups, “dry” incubators and “wet” incubators.
There are four main components to a good incubator.
1) A suitable box or enclosure. This is very basic and easy to construct.
2) A reliable pulse-proportional electronic thermostat
3) A separate (tested and precise) electronic thermometer with a remote probe to enable easy monitoring of the temperature next to the eggs from outside the unit
4) A suitable and above all reliable heat source.
The basic design is very simple, easy to construct, and is based upon easily available components as shown in this video:
Two main types of heat source can be recommended.
Heating pads
These are widely available from exotic animal and aquarium suppliers in a range of sizes and wattage ratings. For use in a well-insulated incubator a small 35 - 50 W unit is generally more than adequate. The better quality brands are extremely reliable but some cheaper brands are liable to failure so should be avoided.
Miniature industrial heating elements and compact thermo-tubes
These are generally only available through industrial electronics suppliers and are intended for use in process control, drying cabinets and commercial installations. They may not be easily obtainable through ordinary retail channels although electronic hobbyist suppliers can sometimes help. Most consist of a low wattage (typically 60 - 100 W) ceramic element contained within a metal shielding. The thermo-tube variety are often sold as window demisters and as greenhouse heaters. This type of heater is typically sold by length rather than by wattage. For incubator use a 300 to 400 mm model is generally adequate. The advantage of such units is their low cost and extremely high reliability. I have had one installed in an incubator of my own for over 15 years which has seen almost constant service and which looks like carrying on for at least as long again. For moderate humidity static air incubator use they are difficult to better and are definitely my own preference.
In fact, I have never had a single equipment failure ever with these designs.
Type I “dry” static air incubator design
A highly effective incubator which was designed by the author especially for incubating tortoise eggs which do not require a high incubation humidity.
Although simple to construct this incubator offers very precise temperature regulation and an easy inspection facility. The incubator is constructed from 15 mm chipboard, a material with excellent insulating properties. A transparent secondary lid is fitted to allow examination without heat loss; for this, polycarbonate sheet rather than glass is suggested. In the author’s own incubators a 60 watt industrial heating element is fixed to the base but a heating pad would be equally suitable. The eggs are placed in plastic ice-cream or margarine cartons within the incubator and rest on a lattice-work of wooden bars suspended above the heater. A water tray provides some degree of ambient humidity. This is usually adjusted to around 70%.
Temperature control presents more of a problem. Two main types of temperature switch or thermostat are generally available. The first type relies upon a simple bi-metalic strip and electro-mechanical action. This sort is widely available in the form of both aquarium thermostats or central heating air-temperature thermostats. Provided one is selected which encompasses the temperature range required these may be perfectly satisfactory for general use. They do however have their disadvantages. The first is that they are rarely very accurate and temperature swings or deviations of several degrees are quite possible. The other disadvantage is that should they ever fail they can jam either fully open or closed thereby causing a catastrophe.
The author prefers entirely electronic non-mechanical thermostats. These are widely available at reasonable cost and offer much increased precision and reliability over mechanical types. Such devices should be available from specialist aquatic and exotic animal suppliers or alternatively from electronic component sources.
Using an advanced proportional electronic thermostat, a temperature tolerance of +/- 0.25 C (measured directly at the egg container) was maintained over a 3 month period using the incubator illustrated. Whilst this sort of precision will not be required for general purpose incubation, where experiments into embryonic development or environmental sex determination (ESD) are concerned, extreme accuracy will be vital.
As a method of accurate temperature control the proportional method has few equals. Unlike on-off controllers (whether mechanical or electronic) there is no time-lag whilst heating elements warm up from cold and consequently much less chance of thermal overshoot. A time period, generally 10 seconds or so, is defined during which power is applied to the heating load for a variable percentage of the proportional band. This percentage is determined by reference to an integrated circuit which measures deviation from the set point and either increases or decreases the percentage of power on time accordingly. The heating element itself remains warm, varying in temperature according to the percentage of time power is applied throughout the proportional band. There is no sudden surge of heat which has the additional benefit of reducing the likelihood of thermal shock damage to the element - a primary cause of failure in on-off type systems. This also results in highly stable temperatures throughout the incubation period.
Type II high humidity incubator
Because of the humidity levels attained internally this unit must be constructed from moisture resistant materials; plastic, glass and marine grade plywood are all suitable. If plywood is used, be sure to seal with a thick coat of varnish - but ensure that this is thoroughly dry and well aired before use to allow potentially toxic fumes to dissipate. I would recommend leaving the unit for at least 8 weeks before use.
A 60 watt heat-pad rests beneath plastic plant propagators containing a vermiculite and sphagnum moss substrate which is hydrated 1:1 with water. A large water tray containing several sponges is also positioned within the incubator to raise the overall relative humidity. To further sustain local humidity, the plastic lids these units are normally supplied with are also utilised. Temperature control is provided by means of a proportional-type controller and is monitored by means of an electronic digital thermometer fitted with a remote sensing probe. The use of an electronic relative humidity meter is also highly recommended in conjunction with this type of incubator.
This type of incubator has proved highly successful with a wide range of aquatic and semiaquatic species which produce soft-shelled eggs and is used routinely for such at the Tortoise Trust.
Stabilising the incubator
Most incubators will require 24 hours or so to stabilise, so it is worth ensuring that an incubator is running satisfactorily well before it is actually required. Temperature adjustments take time to make and do not register instantly. One important point to note is that the thermal mass present within the incubator plays a critical role in temperature stabilisation. The greater the mass present the more stable the incubator will tend to become. In practical terms, a fully loaded incubator will, therefore, tend to behave with greater thermal stability than an almost empty one. Even if only a single clutch of eggs is to be incubated, it is well worth placing substrate in the unused egg trays as this will impart a greater thermal mass and consequently better overall stability. Similarly, if you wish to measure the actual or true temperature of the incubating eggs, this is best achieved by placing the thermometer probe right next to the eggs, and in contact with the substrate. The air temperature inside the incubator will fluctuate much more rapidly and may give a misleading impression, so do not rely upon internal air temperature readings. It is also important to be aware of the fact that the upper reaches of the incubator will be warmer than the bottom. To incubate a large number of eggs at the same temperature an incubator with a large internal horizontal surface area will be required. Stacking egg trays can certainly work, but they will not all be at the same temperature (this can prove useful, however, when seeking to influence sex by temperature and only one incubator is available). A few minutes experimentation with a fast reacting digital thermometer will prove both instructive and fruitful.
Humidity control and measurement
The easiest way to control incident humidity within the incubator is to position a tray of water in the base and to remember to re-fill it from time to time. Very accurate laboratory quality electronic relative humidity meters and controllers are available but are at present comparatively expensive. Whilst this may be justified in the case of research activities for day-to-day incubation purposes they are hardly essential. New, low cost designs which are almost (but not quite) as accurate are now available, however. These operate in much the same way as the digital thermometers mentioned earlier; indeed, some models combine the functions of a humidity meter and thermometer. These are ideal for zoological use and in tests conducted by the author have proved more than accurate enough for incubation monitoring purposes.
Incubation substrates
It is recommended that the eggs be placed in an open-topped plastic lunch box type container within the incubator and that vermiculite or a similar insulating particle medium should be used instead of sand. For high humidity incubation of turtle eggs, both damp vermiculite and a mixture of peat or moss have proved consistently successful.
Egg position
It is not generally advisable to completely bury the eggs. In a stable incubator half-burying or even resting them on the surface should be perfectly adequate. With soft-shelled eggs I generally half-bury them; with hard-shelled eggs I find surface incubation consistently satisfactory. However, if it is suspected that soil pH may be a factor then the eggs should be covered to allow all-round contact with the incubation medium.
As the time for hatching approaches the open top of the incubating box can be carefully covered with coarse linen gauze or netting. Otherwise unexpected hatchlings might escape within the incubator and injure themselves.
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