Understanding how to tell if a tortoise is male or female is important for a variety of reasons.
In breeding programs, sex determination ensures the formation of suitable pairs. Regarding health management, knowing the sex is needed for diagnosing and treating sex-specific conditions. Socially, recognizing sex helps in managing group dynamics to ensure a harmonious environment.
This article will provide you with all the information you need to identify and understand the sex of your tortoise.
Physical Differences Between Male and Female Tortoises
There are various physical characteristics you can use to help identify the sex of your tortoise.
A lot of these differences have evolved to aid sexual reproduction, and while they are typical, they can vary slightly between species.
Shell Shape and Structure
One way you can figure out the sex of your tortoise is through the shape and size of the shell. Typically, females are larger than males and have bigger shells and a wide body. This sexual dimorphism is to ensure there is enough room for the eggs to grow and develop inside the female.
A tortoiseshell is made of two parts that are sandwiched together to encase the body. The top part of the shell is called the ‘carapace’, and the bottom part of the shell is called the ‘plastron’.
Females tend to have a more highly domed carapace so they can hold large clutches of eggs. In males, the plastron is concave as this allows them to more easily mount females during mating.
Females tend to have a flatter plastron to provide the space needed for egg-laying.
Tail Characteristics
Male tortoises tend to have longer and thicker tails with a more pronounced tip. Conversely, females have shorter and thinner tails with a less pronounced tip.
All tortoises have a cloaca. This is a single opening which allows the expulsion of waste and reproductive products.
The cloacal opening is located towards the end of the tail in males to facilitate the mating process. In females, the cloaca is found closer towards the base of the tail to accommodate egg-laying.
Secondary Sexual Characteristics
As a tortoise begins to reach sexual maturity, from sub-adulthood onward, they begin to develop secondary sexual characteristics. These are characteristics that can be used to distinguish the sexes but are not directly involved in reproduction.
Males begin to sexually mature between the ages of 2 and 4 years old, whereas females sexually develop between 5 and 7 years of age.
Anal Scute Shape
Scutes are keratinous, armor-like plates that overlay a tortoise’s bony shell to create a protective layer. These scutes cover the carapace and plastron and are anatomically named according to their placement.
The two scutes located at the tail end of the plastron are known as anal scutes. Male tortoise’s anal scutes resemble an upside down ‘U’ while a female’s anal scutes resemble an upside down ‘V’.
Size and Weight Variations
In many tortoise species, males are smaller and more compact compared to females. This size difference is the result of evolutionary pressures related to mating and survival strategies. Females are usually larger and bulkier, which provides them with the additional space needed for carrying eggs.
Due to their smaller size, male tortoises tend to weigh less than their female counterparts.
Females are typically heavier as a result of their larger size and can weigh more when they are gravid. This increased weight supports their reproductive role.
Behavioral Indicators
During the breeding season, male tortoises exhibit specific courtship behaviors that tend to be quite aggressive. A common trait in many species is a display of head-bobbing and is used to attract the attention of a female.
They also chase and encircle females, usually pushing them into a corner in an attempt to trap and mount her. Additionally, males will nip and bite at the female’s legs and carapace edges.
Mating is typically a noisy affair, and males can often be heard producing hissing and grunting sounds.
Aggressive behavior can also be directed at rival males. Individuals combat with one another in an attempt to establish dominance and win over females.
Conversely, female tortoises take a more passive role in the courtship process. They will choose males based on their displays and persistence rather than actively engaging in courtship behaviors.
During mating, females remain stationary, allowing the male to mount and achieve the correct position.
Challenges in Sexing Young Tortoises
Determining the sex of younger tortoises can be challenging due to several factors, including their physical development and the subtlety of sexual dimorphism at an early age.
Juveniles will have undeveloped carapace, plastron and tail shapes. Young males do not exhibit courtship behaviors like mating displays or territorial behavior.
Additionally, juveniles can exhibit considerable individual variation in growth rate and physical development, making sex determination challenging.
Typically, a tortoise must be at least 4 years old before you can sex it, based on morphological factors. However, this age can vary between species and individuals.
Sexing becomes more reliable once a tortoise has reached sexual maturity. This is because the sexually dimorphic characteristics will be fully developed and easier to identify.
When to Consult a Professional
Certain situations may require the help of a veterinarian or reptile expert when attempting to sex your tortoise, especially in younger or less distinct cases. For example, juvenile tortoises have undeveloped features, making it hard to identify their sex.
Experienced professionals can use advanced techniques to provide a more accurate sex determination, even when physical differences are subtle. This often involves performing an endoscopy.
During this procedure, a veterinarian will insert an endoscope through the tortoise’s cloaca to view the gonads and determine its sex via the presence of testes or ovaries.
Genetic Testing Options
In most animals, the sex of an individual is determined during fertilization. However, in the case of reptiles, including tortoises, the sex of an individual is heavily influenced by the temperature of the eggs during the incubation period. This is referred to as temperature-dependent sex determination (TSD).
Generally, if eggs are incubated below 82.4oC the hatchings will be male. Temperatures above 87.8oF result in female hatchlings. This means that chromosomal sex determination cannot be performed.
When physical sexing methods are inconclusive, cystoscopy and cloacoscopy are used to visualize the gonads to determine the sex.
Common Misconceptions
There are several myths and misunderstandings surrounding tortoise sex determination:
- You can sex a tortoise by its shell color
While some species exhibit different shell colors or patterns between males and females, these differences are not consistent across all species and are generally not distinct enough for accurate sexing.
- Physical characteristics are reliable for all species
While the physical characteristics I have mentioned in this article are commonly used to identify the sex of tortoises, bear in mind these traits are not consistent for every species. For example, some males lack a concave plastron, and some females may have longer tails.
- Sex can be determined by behavior alone
Relying solely on behavior can be misleading, especially if the tortoise is not yet sexually mature or displaying breeding behaviors.
- Sexing is the same across all life stages.
Sexing methods that work for adults may not be applicable to juveniles. Many sexual dimorphic traits become more pronounced as tortoises reach sexual maturity, making sexing more accurate at this later stage.
If you enjoyed this article, here’s another that may be of interest: Tortoise Anatomy.
Citations
- Bvajournals.onlinelibrary.wiley.com – Endoscopic sexing in turtles and tortoises
- The Tortoise Group.Org ale Courtship – Male Tortoise Courtship
- Rero Doc – Sexual Dimorphism of Body Size and Shell Shape in Tortoises
- The British Chelonia Group – Temperature and Sex Determination in Reptiles
