How to tell age of a box turtle

# of Annuli — involves counting the number of Annuli (growth rings). In the past, it was thought that annuli corresponded to age, but recent findings suggest that this is not the case. However, we still count the annuli because it may yield important life history information. See diagram and image below that illustrate the annuli on a box turtle’s shell.

What are Annuli?:
Rings represent growth on the scutes of the carapace and plastron.

How to count Annuli:
“0” is the natal scute (formed prior to hatching) – do not count it /p>

Caution:
If annuli are crowded at edges of scute or shell is smooth, count the number of annuli and add a “+” (e.g., “20+”).

Determination of Sex — On the Capture Datasheet, you must choose Male, Female, or Unknown. Do your best to determine whether it is a male or female, but if you’re uncertain, you should record “unknown.” See images below illustrating the typical difference in the plastron between males and females.

Adult males:
Concave plastron – main feature to look for (not obvious until about 60mm SCL)
Often have bright red eyes (but are exceptions)
More posterior placed anus and longer tail (not obvious until about 60mm SCL)
More colorful head and legs
Older males have flanged posterior marginal

Adult females:
Flat or slightly concaved plastron
Eye color brown, but also can be yellow or dull red
Have deeper, domed shells

Hatchlings/Young turtles:
Do not show characteristics, so record “Unknown”

Everybody knows that box turtles can live a very long time, and that they are long-time commitment pets. Some box turtles have even lived more than 100 years. But how do people manage to find out how much turtles live, how do they find their age?

How to tell how old a box turtle is? There are multiple ways of finding out how old a turtle is, the most known and used methods are:

• The Counting Method
• The Size Method
• Mark-Recapture
• Studying the Skeleton

So there are 4 methods that you can use. While two of them require special equipment, two of them can be used by anybody at home. So let’s take a look at each method.

The Counting Method

The age of many hard-shelled turtles, like box turtles, red-eared sliders, painted turtles, musk turtles and snapping turtles, and many other species, can be estimated with a margin of error of about 6 to 7 years by counting the number of growth annuli. Growth annuli are small groves on each of the scutes of the shell. This is very similar to the way you will count the rings of a tree to find out its age because each ring or growth annuli in the case of the turtle will indicate one year. During periods of inactivity, like the winter, the scutes of a turtle will grow slower, or they won’t grow at all in some cases, and during spring or summer, the scutes will grow faster, resulting in a ring-like pattern on the scutes.

The counting method still has some flows. One of them is that it can only be used on hard-shelled turtles, since the shell of soft-shelled turtles works in a different way, there won’t be any growth annuli to count. Another problem with this method is that it won’t work well with pet turtles, if you keep your pet turtle at a constant temperature year-round there won’t be any difference in the speed at which the shell grows so there will be no annuli to count. Rings can also be an inaccurate measure of the age in turtles in which the shell has become worn and smooth because the rings will be faint or they will disappear completely.

Some turtle species like the mud turtles from North America will reach maturity when they are around 6 or 7 years old, at which point their growth will slow down considerably. Mud turtles will still grow after that point but a lot slower, and during periods of slow activity, like the winter, they will grow even slower or they won’t grow at all. At this point, their growth annuli will become very compact and it can be easy to get them mixed up because they will be very compressed.

Another factor that can influence the ring counting method is the environment, more exactly the unusual environmental conditions. For example, if a certain area has a lot of food at the beginning of the year and then a drought happens out of nowhere and the food is gone this will make the turtle enter in a long period of inactivity that it normally wouldn’t. And after the drought is over food starts to reappear the turtle will enter a period of full activity in which the shell will once again start to develop at full speed. Events like those can create fake growth annuli that are almost indistinguishable from real ones.

So overall this method has its flaws and it’s not always the best for scientific research, but it’s a great way to get an estimate of the age of a turtle, after all, it will be very obvious if a turtle has over 50 years or under 20 no matter how many false growth annuli it has. So if you find a turtle in the wild you can easily get an estimate of how old it is using this method.

The Size Method

This method usually is not very precise and it requires a lot of prior knowledge, so it’s not the best option for most people, but it’s one possibility so I am going to tell you about it

Compared to other animals, turtles grow very slowly, some species will grow faster than others but in general, they will grow very slowly. The fact that they grow this slow will help a lot of people with knowledge and experience with turtles determine the age of a turtle. If you have experience working with turtles or if you have one yourself, you will be able to tell apart a 6 months turtle from a 2-year turtle from a 10-year-old turtle.

At first sight, this method will seem more like guessing, and that it’s true, but at long as it’s a person with good knowledge about turtles that guess will be pretty close. As you gain more experience the closer you will get to the actual age.

Like all methods, this one has its flaws. The most obvious one is that if you have little to no knowledge you will be way off with your guess. Another one is that even if two turtles belong to the same exact species they will grow at different rates based on their environment. This is why you can usually get good results with this method only if you apply it to well-researched species like slider turtles and painted turtles, and if you know the area where they live very well.

So overall this is not the best method and it can only give good estimates if you have good knowledge. This method is usually not used for scientific research, but researchers will occasionally take notes and they will estimate the age of a turtle using this method if they didn’t have the chance to get close enough.

Mark-Recapture

This method is mainly used by biologists to determine the age of a turtle, and not by normal people, so please don’t try this with any turtle, you could hurt them in the process if you don’t know what you are doing.

When using this method turtle biologists will use a file or a small drill to carefully place a mark on the shell of a wild-caught turtle. Those marks are usually small, so the turtle won’t be affected by it at all, but noticeable at the same time to make sure that the measurements will be accurate.

After the mark is placed the turtle will be released in the wild from where it came. After a period of time, these turtles will be caught back and their shells will be studied to see their evolution and how did the mark age compare to the anulli count method. After that turtles are free once again to go back into the wild.

Studies that use this method are usually long-term and can help determine the age a turtle can reach. For example, one study that used this method was conducted on multiple turtles that belonged to the following species: slider turtles, eastern mud turtles, and painted turtles. When they were first caught the turtles were estimated to be between 6 and 10 years old. The next part of the study took place 25 years later. A lot of the turtles were found, this proved that a lot of them can live more than 30 years. There are a lot of factors that can influence the lifespan of a turtle, especially in the wild, but a study like this definitely proves that a lot of those turtle species could live that long.

Studying the Skeleton

The last method that you can use is again better left for biologists and people that know what they are doing.

As the name implies this method requires the biologists to study the skeleton of a turtle to find out the age. Neither this method is 100% accurate but it can give good estimates, especially if there is no other way to find out.

This method is mainly used for fossils and on the skeletons of extinct species since there is no reason to use it for a turtle that is still living.

The exact process that the skeleton will go through can differ since there are a lot of methods to study the bones so i am not going to go into details any further for this method, the only thing that you have to know about this is that this is the way they determine the age of turtle fossils and extinct species of turtles in general.

Conclusion

In my opinion, the simplest way to estimate the age of your turtle is the counting method. While not 100% precise, it will still give you a good estimate.

I hope this article helped you in finding the age of your box turtle. But in case you still have questions or you would like some help, please let me know in the comment section and I will answer you as soon as possible.

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