Determining the gender of young star tortoises is not that easy because most of the gender characteristics apply to subadult and adult tortoises only. Burmese star tortoises can be especially tricky to sex when young. A lot of young males resemble females for quite a while.
Young male star tortoises have flat plastrons and short tails, but the tail will grow and the plastron will concave as the male ages and matures. Many male youngsters start out looking more like females and then suddenly grow a big tail.
Some subadult individuals are easily sexed because one or more of the sex characteristics is quite obvious. With others, figuring out the gender is more difficult due to ambivalent sex traits. In those cases, you'll need to consider all the attributes as a whole.
Breeding age Burmese star tortoise pair. Females grow noticeable larger than males.
Same Burmese star pair as above. Notice the difference in the overall size, length of the tails, and the shape of the anal scutes (blue). In males, the tip of the tail (red line) extends past the anal scute.
1.) Overall size - Adult females are much larger than adult males.
2.) Shell shape - Females are typically more rounded in overall shape while males are more elongated. Male tortoises can also have more flattened shells.
3.) Plastron - Females have flat plastrons (bellies), but adult males' plastrons are curved inward. Males' concave plastrons allow a better fit during mating. As youngsters, both sexes have flat plastrons.
4.) Tail - Females have short, stubby tails. Males have bigger and longer tails. In addition to overall size, this is the most noticeable gender characteristic in adult tortoises. As youngsters, both sexes have short tails. Mature Burmese star tortoise males may have a terminal tail spur. Scroll down for a photo.
5.) Angle of anal scutes - In males, the angle of the anal scutes is wider. In females, the angle is narrower, and the opening more roundish to allow passage of eggs. In adult females, the tips of the anal scutes tend to point towards the back and in adult males more towards the sides. However, the shape of the anal scutes varies from individual to individual and can, and often will, change in the same tortoise as it matures.
Note: For reference, see the shell scute diagrams.
Adult star tortoise females have short, fat, stubby tails with a little tip. Angle of the anal scutes is narrower than in males, and the bony opening is often roundish to allow the passage of eggs. The supracaudal scute does not curve down as much as in males, but opens up for egg laying. The cloacal opening in the tail is roundish, looking kinda like a star.
Adult star tortoise males have long, thick, deep letter V shaped tails. Anal scutes can be shaped like a mustache with the tips pointing towards the sides. The supracaudal scute typically turns strongly inwards in adult males. The cloacal opening looks more like a slit towards the tail.
Note: The direction of the supracaudal scute varies among individual tortoises and different species. For example, in my golden Greeks, both males and females have supracaudal scutes that open up. On the other hand, in my angulate tortoises, both males and females have supracaudal scutes that turn under.
1.) Growth rate - Among siblings, or same age unrelated tortoises who are raised together, females can grow faster than males. However, faster growth alone is not a reliable gender indicator. Any tortoise can grow fast depending on circumstances.
2.) Flashing - Many star tortoise boys start to "flash," i.e., show their private parts, in a warm bath when they reach the weight of 200-300 g. This is often the first sign that you have a male.
Note: Occasionally females may "flash" a tiny bit, but it's not common at all. Scroll to the end of this page to "Flashing vs prolapse" for more info.
This Burmese star baby was easy to sex. As a hatchling, he already had a long, male shaped tail and wide anal scutes. Indeed, he turned out to be a boy.
Here's another little Burmese star hatchling. Eventhough the bony opening and tail look boyish at this point, it's a girl. One clue for girlness can be a rounded, less oval, shell shape like here.
Ok, how about this Burmese star tortoise youngster. Is this a boy or a girl? Tail is short and stubby looking and the bony opening is circular. Must be a girl, right? Nope. This tortoise is too young to sex accurately because it hasn't developed the male gender characteristics yet. He turned out to be a boy!
For comparison, here's a young Burmese star female. She doesn't look that different from the male above. Tail is short and stubby and the bony opening is roundish.
Here's a young male. Tail is big and long, but the bony opening is still roundish. It will change over time.
Mature Burmese star tortoises may have nail spurs or terminal nails on their tails. They are not present in young males, but grow with age. These "tail nails" can also drop or wear off. This boy also lost his later on.
Young, maturing male star tortoises often flash, i.e., show their private parts, in a warm bath. This is often the first sign that you have a male. The tortoise male part is sometimes described as looking like a purple flower, a cowboy hat, or the starship Enterprise. :O)
Many new tortoise owners become alarmed when they see their male tortoise flash for the first time. They worry something is terribly wrong with their tortoise. As long as the private part goes back in after a short while, everything is ok. If it prolapses and stays out, take your tortoise to the vet ASAP to have it treated. Otherwise, it may become necrotic and have to be amputated. Key point: If it stays out for a long period, visit a vet quickly!
On a rare occasion, you may catch a glimpse of your female's private parts as well. The female part looks similar to a male's, but it's smaller and doesn't have a long stem. More likely though, it's probably just a young, maturing male tortoise showing his immature bits. In boy tortoises, the bits start out small and then grow bigger as the tortoise matures.