Desert Tortoises: Male or Female?

During the years I have spent working with desert tortoises, the one thing that I am continuously asked is “How do you know if it is a female or a male?” Well, it’s not an easy answer because there’s more than one way to determine the sex of a desert tortoise, and it can take some practice to get it right.
Plastrons of female, left, and male desert tortoises

But first things first: it takes 15 to 20 years for a desert tortoise to reach sexual maturity, so it can also take that long before it starts showing physical characteristics that are typical of the two sexes, including plastron concavity, gular shape and size, tail size, and the presence or absence of chin glands. So we don’t know the sex of a young tortoise unless we hatched it ourselves at a particular temperature in the incubator (tortoise sex is based on the temperature of the nest, not on genetics).

But once a tortoise reaches adulthood, I find that the best way to identify the sex is to look at the plastron (the lower shell); but please do not flip a tortoise on its back, since that can be very stressful to the animal. If you lift the tortoise just slightly off the ground and get down there with him or her, you will see that a male desert tortoise has a concave plastron, or an indented curve, toward the tail end. Females, on the other hand, have a flat plastron, though on a rare occasion you will see slight curvature of the plastron, causing you to second guess yourself as to whether the tortoise is a male or female.

If you’re not sure about the plastron then check the gular (a long, extruding piece of the plastron under the neck). Males tend to have a large gular, which is used to fight and flip other males. However, a long gular may be damaged in a fight, broken off during an encounter with an off-road vehicle, or may even be bitten off by a predator, so it‘s important to check for other sex-specific characteristics as well.
Female, left, and male

Another way to determine the sex of a desert tortoise is by its tail, which is a great way to help determine if a tortoise is male or female without actually picking up the animal. Males tend to have longer tails than females, but the female’s tail is usually no longer than the end of a cotton swab, so the male’s tail is not exactly gigantic, making this another tricky technique that takes time and practice to use.
Tails of female, left, and male

So finally, the last method we use to identify the sex in desert tortoises is to look for chin glands. Sometimes, especially during the active mating season, male tortoises will have enlarged glands under the chin, and they may have a gooey liquid extruding from them, while females rarely, if ever, show these glands.
Female, left, and male

The moral of the story is that there are many ways to help determine the sex of a desert tortoise, but to avoid sexing your pet desert tortoise incorrectly, you should use all the techniques described. Or better yet, the best thing to do is just look and enjoy. Remember, the desert tortoise is a threatened species, so it is against the law to touch one in the wild, and you should never flip a desert tortoise over, even if it’s your backyard pet.

Daniel B. Essary is a research associate at the San Diego Zoo’s Desert Tortoise Conservation Center.

Read a previous post, Desert Tortoise: Twizzler.

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