Animal Information

Two Tortoises from One Egg!

Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ('fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.

Administration at Crazy Critters Inc. recently experienced an amazing and rare joy. Ken Purvee, the founder of a turtle breeding and conservation group located in Eustis, Florida, was waiting for a clutch of Sulcata tortoise eggs to hatch this week. Ken noticed one of the hatchlings was having trouble getting out of its egg. While Ken doesn’t usually assist in the hatching process, something urged him to step in.

Inside were two teeny tiny perfectly formed and healthy tortoise twins, who were both attached to the same yolk.  Twins are a natural occurrence in the wild. Scientists do not know the percentages but it is thought that many pass away during the hatching process. Any that successfully hatch and dig themselves out of the ground are often smaller than siblings.

One single tortoise mating results in up to 30 eggs being fertilized, although does not mean they are all laid together in one clutch. Tortoise gestation is in fact quite remarkable with regards to the time ranges involved. This is because the female can vary the length of the gestation period depending on the environmental and nesting conditions. It is believed that tortoises can lay fertile eggs up to four years after mating, although fertility reduces significantly after each season.

Tortoises are very particular when it comes to choosing a suitable nest site. After the clutch has been laid, she covers the eggs with soil, refills the nest and flattens it with her plastron. The whole nesting procedure can take up to four hours to achieve!

The best incubation methods incorporate specialist shop-bought reptile incubators or adapted bird-egg incubators. A constant steady temperature of 86 degrees Fahrenheit is the “safest”. However, you could specifically hatch a group of tortoises of the same sex by incubating at either a couple of degrees above or below 86 degrees.

Eggs typically hatch in 100 to 120 days. Often most eggs hatch together over the course of a few days, but sometimes hatching takes place over weeks with nearly a month’s time between the first and last emerging hatchling.

Tortoise hatchlings use a temporary egg tooth called a caruncle to break open the leathery shell of the egg. The caruncle is pushed against the inner surface of the eggshell, breaking it. The hatchling then tears a larger opening and climbs out of the shell. After a pause to uncurl its body and shell from the cramped conditions within the egg, the hatchling begins to dig upward. 

This may be an individual effort, but usually, several hatchlings dig together, helping one another. It is possible twins hatch in the wild easier than in captivity because they have the siblings moving around in the ground which aids the escape. 

Assuming you’re human, the likelihood of having twins is quite little. But, depending on where you’re from, there’s a surprising amount of variation. In Central Africa, the twinning rate is almost 30 in every 1,000 births; in much of Asia and Latin America, the average is as low as eight per 1,000 births.

So that’s humans covered, but what about twins in the animal kingdom? Whenever an animal gives birth to multiple young, the offspring are fraternal twins. Well, if not twins then fraternal triplets, quadruplets or quintuplets. You get my point!

Different animals have different size litters. Primates, like humans, rarely have more than one baby at a time. Rabbits tend to have litters of three or four, whereas foxes have a maximum of 10 or 11. In this clutch of 21, we hatched 18. 17 eggs but 18 babies. The other eggs were infertile and fed to monitor lizards.

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