Sexual Dichromatism of Tomia in Blanding’s Turtles (Emydoidea blandingii) in Central Ontario

Kelsey Moxley^1,*, Scott Gillingwater², and Madelaine Kellett¹

¹Scales Nature Park, Saving Turtles at Risk Today (S.T.A.R.T.) Project, 82 Line 15 S, Oro-Medonte, ON L3V 8H9, Canada. ²Upper Thames River Conservation Authority, 1424 Clarke Road, London, ON N5V 5B9, Canada. *Corresponding author.

Northeastern Naturalist, Volume 31, Special Issue 12 (2024): E59–E67

First published early online: 30 May 2024

Abstract
Researchers have observed sexual dichromatism in chelonians, but it has not been formally documented in Emydoidea blandingii (Blanding’s Turtle). We tested if this characteristic can be detected in the upper tomium coloration and pattern of Blanding’s Turtles, and if so, how accurately sex can be determined using this characteristic. We sorted individuals based on non-color traits to confirm the presence of sexual dichromatism. We created the following sexual dichromatism guideline: males have dark upper tomia, and females have cream/yellow tomia with black banding. Thirteen observers categorized 179 tomium photographs to assess the guideline accuracy. Observers correctly identified the turtle’s sex 96.78% of the time. The guideline can be a useful tool for determining sex in the field and has beneficial conservation applications.

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