Using commercial incubators for hatching tortoise eggs

Several designs of commercial incubators are available and suitable for incubating tortoise eggs, but they can be quite pricey and range from a very simple design to something much more complex. For the hobbyist and private breeder the small, still-air models (i.e. without a fan) are the cheapest and easiest. Makes/models used by breeders on the Tortoise Protection Group include the Hovabator, Brindsea Hatchmaker, Curfew, and Ecostat.

It should also be noted that 'Homemade' incubators can be very good, and many tortoise breeders including the breeders on the TPG breeders list are successfully using them.

The main feature in any incubator is that it should be able to maintain a suitable, stable temperature and the humidity required for successful egg incubation.

In a recent survey of members on the TPG approved breeders list, out of the 20 responses received, it was found that 12 commercial incubators and 14 home-made incubators are in use. Some breeders use both types.

What to look for when purchasing an incubator:

A basic incubator should include:
• Thermometer

If using a separate thermometer make sure it is sufficiently sensitive and accurate over the range 25°C-34°C. It is important to use one that has been made for use with an incubator (garden thermometers etc. are often inaccurate). Temperature stability can be more accurately maintained using a digital maximum/minimum thermometer.

• Heater
• Thermostat to enable maintenance of a constant temperature
• Ventilation grill to allow air flow
• Tray for easy cleaning or holding water for humidity
• Still-air type. Fan assisted incubators will dry out the albumin in the egg and should not be used.

More expensive models in addition may have:

• A Celsius/Fahrenheit interchangeable facility
• Humidity setting and control/hygrometer
• Alarm system for water addition
• Facility to add a rotation turner, but this is NOT required for hatching tortoise eggs. Unlike bird eggs, tortoise eggs must NOT be rotated during incubation and doing so could lead to the death of the developing embryo.

For the successful hatching of tortoise eggs the still-air type of incubator is recommended. This is where the heat is spread evenly throughout the incubator from a heating element by a process of radiation and convection. Still-air incubation is used by all 20 breeders who responded to our survey.

How to use the incubator

Ensure the incubator is placed on a level surface and will be in a permanent position whilst incubating the eggs. It is possible that damage may occur to the delicate membranes and organs of developing embryos caused by accidently bumping the incubator whilst moving it. The incubator should be positioned in an area which is not prone to vast fluctuations in temperature and humidity; so ensure it is not in a draughty environment or in direct sunlight and that it is positioned away from central-heating radiators. Most tortoise eggs will be incubated during the summer months, but sometimes tortoises surprise us and lay their eggs out of season. So remember that in winter, rooms do become very cold at night once the heating is off, and if there is too great a temperature drop, it is possible that the incubator will be unable to maintain a steady temperature. It is important to maintain a steady heat in the incubation room over the full 24-hour period.

Setting up the Incubator

1. The first task is to clean and disinfect the incubator with a proprietary reptile disinfectant such as F10. Set the incubator up at the first signs of the tortoise being gravid to enable the correct temperature and humidity to be established and to check on the normal functioning of the thermostat prior to introducing the eggs.

2. Follow the manufacturer's instructions about setting the temperature. In some still-air incubators, there is quite a large temperature gradient inside. An ideal temperature for tortoise eggs of Mediterranean species is between 30°C and 31.5°C, although a wider range of temperature can be utilised.

In some incubator models the thermometer is situated at the top where the air is warmer; so it is recommended that a separate thermometer, which is suitable for incubators, is placed at egg level to give an accurate reading of egg temperature.

3. After achieving the correct temperature, tape the wall plug over and/or make a small notice saying ‘LEAVE ON' so as to avoid accidental switching off.

4. You may wish to consider using an audible temperature alarm so that if there is an alteration in temperature you get an early warning.

5. Humidity assists in balancing out the natural evaporation of fluid from within the egg as the embryonic tortoise develops and the air space increases. To prevent the eggs from drying out too quickly or losing sufficient water, keep the water tray topped up with warm water. Too much humidity at the wrong time is just as bad for a developing egg as is too dry an environment. Approximate humidity levels should be around 70%.

(N.B. Please note that this article deals only with the incubation of tortoise eggs and not the eggs of aquatic species, which need a humidity level of around 90%).

It is interesting to note that of the 20 breeders that responded to the survey only 8 use a hygrometer to accurately measure humidity. Although not asked, breeders included in their responses a statement acknowledging that they either filled a tray or a bowl of water inside the incubator for humidity. Even though some the breeders on the TPG list do not use a hygrometer, the importance of getting a correct humidity level, by the use of one to ensure normal egg development, is to be recommended for the novice. Thus if the incubator does not have a hygrometer you should consider purchasing one separately. A Haar Synth hair hygrometer is one that is recommended by several of the TPG approved breeders.

6. If ventilation holes/grills aren’t provided the incubator lid must be opened daily to allow oxygen to circulate. Eggs require a suitable flow of air to supply enough oxygen for the embryos to develop and for the carbon dioxide which has been produced to be removed. The humidity and the temperature inside the incubator will be affected by opening it up, so this should be done quickly and left open for no more than 30 seconds to minimise temperature and humidity fluctuations.

7. Do check the incubator frequently to ensure that nothing has been placed on top of the incubator to interfere with airflow.

To summarise

The important factors to note for successful incubation are:

Sanitation of equipment
Appropriate still air incubator
Suitable environment
Stable temperature
Correct Humidity
Good air flow

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