Testing the reliability of ring counts for age determination in the Egyptian tortoise (Testudo kleinmanni)

Counting shell growth rings is a common method of determining the ages of young tortoises, but the accuracy must be validated for each species. The objective of this study was to test if the age of Egyptian tortoises Testudo kleinmanni can be reliably determined by counting the growth rings on their shells. Our results suggest that as individuals become larger and older, age is more difficult to determine. Seventy-five percent of individuals below 90 mm carapace length (n=24) exhibited a one ring per year relationship, which was the case for only 6% of the 16 individuals with a carapace length above 90 mm. Ring counts were relatively reliable for determining ages of tortoises five years or younger, as 76.2% of these individuals exhibited a one ring per year relationship. The threshold age for the reduced reliability of ring counts is around six years of age, as only 16% of the tortoises six years or older exhibited a one ring per year relationship.