SCW Tortoise Database

Schildpadden Advies Oosterbeek has researched the effects of environmental parameters on fertilization and the development of embryos and hatchlings of T. hermanni boettgeri and T. marginata. Bert Eendebak has conducted this study.

A number of variables were recorded, such as characteristics of the male and female, nest location, time of nesting, order of laying within a clutch, egg weight and incubation parameters. The research focussed on the possible correlation and the relationship between these variables. The influence of these variables on fertilization, development of embryos and sex ratio has been analysed in more detail. The study involved a total of more than 2500 eggs laid from 1980-2010 by a group of T.hermanni and T.marginata and the follow up of more than 1000 hatchlings.

Housing of the tortoises
The tortoises are kept in outdoor terrariums that provide different areas to separate different species or individuals. Most of these areas contain a greenhouse or shelter to protect the tortoises from the Dutch climate during the early spring and autumn periods. The total area available to the group was approximately  400 m². Half of it is covered with grasses, clover and low herbs with a variety of ground flora. The other part is covered with low bushes and shrubs, like brooms and brambles. Nesting takes place on the various sunny, sandy slopes that are available, or in the greenhouse. Hibernation takes place in the outdoor shelters from October up to April for the adults. For hatchlings the first hibernation is limited to 3 months.

All tortoises are free to move in the open field and in greenhouses, except for the hatchlings in their first and second year. These are kept in indoor terrariums or in a greenhouse for most of the year, mainly to protect them from birds, rats, hedgehogs etc. Thereafter, the juveniles are kept in the same outdoor terrarium as the colony of full-grown tortoises.

Egg handling
All eggs are removed from the nests, marked with a pencil, weighed, inspected and placed in incubators, usually within 1 to 3 hours after nesting. Immediately after laying, the eggs are candled for the possible development of blood vessels, although these are normally visible only after 6-8 days of incubation. No sign of blood vessels has ever been detected on the first day, so a hypothetical onset of development within the female is unlikely and will not influence the results. Eggs that do not show any development or that have stopped developing are opened and visually examined for any sign of fertilization. If there was even the slightest sign of blood vessels or the presence of an embryo, the eggs were defined as "fertilized". Embryos with a length of 1 mm are already easily detected with the naked eye. Methods of incubation have been discussed in detail in the publication Incubation Period and Sex Ratio of Hermann’s Tortoise.

Juveniles were defined as male or female only when at least two different sex characteristics, usually the shape of the tail and anal scutes, were visible.
Most of the hatchlings produced have been distributed among members of the Nederlandse Schildpadden Vereniging.

Over the years all data has been recorded. Part of these records is made available in a spreadsheet file, which can be downloaded: SCW Tortoise Database.

Drawing firm conclusions from the information given in this database is not possible without more background information on the measurements.

For all questions on this background information and or permission to publish conclusions based on these data please contact Bert Eendebak.