Due to the acute shortage of females in many stocks, we now only breed with high-temperature incubation schemes in order to produce as many females as possible. Experimental approaches with long, high temperatures led to increased drying out and death of the embryos in the eggs. The question arose, how does a balanced sex distribution actually arise in nature, and how can we change the model in favor of a high proportion of females? Constant, high temperatures as in incubators of over 33°C for 24 hours do not occur near the ground and nesting pits in nature and yet the sexes always hatch relatively reliably equilibrium in the wild, how can this be? Females are known to be timed at high temperatures, which in nature can only occur over midday, when the sun is at its peak. In fact, the temperature in egg pits is often well above 34°C during midday, but only for a short time. In nature, therefore, the primary conditions for the timing of female embryos are high temperatures. Temperature peaks of +34°C over a period of about 3 hours is necessary to already allow a relatively balanced sex distribution in a clutch. If the high temperature peaks of +34°C are extended to 5-6 hours per day, the sex distribution automatically shifts in favor of female emryons. As in nature, the following longer temperature drops during the night obviously have no decisive influence on the sex determination. Only the reaching of relatively high and short temperature peaks during the day are responsible for this. Sexual development is already completed in the first third of the breeding cycle. A strong temperature reduction during the night to 24°C is even desired to initiate embryonic development at all and to avoid a diapause. In nature, however, other decisive factors are responsible for the sex-determining breeding temperature in nesting pits: cloudy days, the depth of the nesting pit and the position of the eggs in the nest, but also the shadows cast by neighboring vegetation or objects (e.g. trees, bushes, stones, roots, mounds, etc.), depending on the position of the sun, can have a decisive influence on the climate in turtle nests.
We recommend the following incubation schemes for the timing of the sexes:
We suspect the apex of sexual incubation in Radiated Tortoises to be 32.8°C. If incubation temperatures are long and high, the small tortoises often hatch too early, so that the yolk sac is not yet completely depleted. If incubation temperatures are too high and prolonged, embryos die halfway through development in the egg due to desiccation. Carapace abnormalities seem to be more common with unnatural, constant, and high temperatures often used in incubators.