How many eggs do you see?

An important aspect of studying populations is understanding the reproductive potential of females in those populations. One method of doing this when turtles are the study animal is to take radiographs (a.k.a. x-rays) of gravid (“pregnant”) females. Turtles incorporate calcium into their egg shells, so any present eggs in the female will show up in a radiograph. This can provide information on turtle clutch size, which is the number of eggs that are produced in a reproductive event.

Two Alabama map turtle females sitting politely for their radiographs.

In our study, we have been able to get clutch size data on a number of our target species, especially the Alabama Map Turtle (Graptemys pulchra). Previously, the average clutch size was reported to be 4-6 eggs, but this observation came from detected nests. However, from our radiograph data we routinely find AL Map Turtle females with 8-12 eggs. The discrepancy from our observations to previously reported could result from females depositing their clutch in more than one nest.

This Alabama Map Turtle female from 2018 contained 13 eggs in this radiograph.

It is important to note that the radiographs do not seem harm the females or their eggs. Another cool thing you can notice from the radiograph is how far the turtles can pull in their head into their shells.