Life Stage

Life Stage, # of Annuli, and Determination of Sex

Life Stage
Hatchling – has spots, size of half-dollar, and cannot withdraw into shell
Juvenile – if is not a hatchling (bigger than half-dollar) and < 60mm SCL
Adult – can determine if it is a male or female (usually cannot tell until it is ~60mm SCL)

# 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>

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

Annuli Diagram

Close-up of annuli

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”