If you only need a rough estimate to answer questions about the tortoise’s diet, breeding capacity, or anticipated full-growth size or lifespan, then using general age-determination methods should be sufficient.
Don’t press on the shell to determine how soft it is! Just touch it gently, or you may injure the tortoise. A tortoise’s shell (more accurately called a carapace) is part of its bone structure. This means that a tortoise experiences pain if its carapace is damaged.
Tortoises are measured by straight-line carapace (shell) length. Hold a tape measure level above your tortoise’s shell—don’t follow the curve of the shell—and “eyeball” the length in either inches or centimeters. For example, female desert tortoises (native to the southwestern U. S. ) grow to an average length of 7–8 in (18–20 cm).
Different species of tortoise lay differing numbers of eggs, generally ranging from 1-30 at at time. The most common range is from 6-10.
Count each thicker ring (which develops during the tortoise’s main annual growth period) and the thinner ring beside it (which develops during the annual slow growth period) as a single ring. So, if you count 20 of these ring pairs, you might estimate the tortoise is 20 years old. Many experts view this as a very unreliable (or even useless) method for determining age, since rings develop during growth spurts, which don’t necessarily happen annually. A tortoise with 30 rings could easily be 20 or 40 years old (if not even 10 or 50), for instance. [6] X Research source
A blood sample can provide a metabolic profile that can help in making an age estimate, but it’s by no means a foolproof way to establish an animal’s age. Blood samples can be very helpful in identifying illnesses in tortoises and other animals, though.
Electronic tagging removes some of the leg-work from the “mark and recapture” process, but it still requires a long-term commitment to track individual tortoises for decades.
Skeletochronology testing typically involves cutting cross-sections of the scapula, humerus, femur, and ilium for examination.
As with captive tortoises, blood testing is more useful in identifying illnesses in wild tortoises.
In basic terms, more fungus equals an older tortoise. It’s a bit more complicated than that for the scientists doing the testing, though!
This method can only give a very broad estimate. Some tortoises naturally have smoother shells than others, and environmental conditions factor heavily into erosion rates.
Unless a wild tortoise has been tracked from near birth or has died and undergone skeletochronology, even tortoise experts are left having to make a “best guess” about its age.
