Can You Tell the Turtle by its Eggshell?

Posted on Nov 9, 2018


by Siow Yan Jennifer ANGOH, Lauren A. HOOTON, and Christina DAVY
CWBM 7 (2): 90-95

Correspondence: Christina Davy, Ontario Ministry of Natural Resources and Forestry, Wildlife Research and Monitoring Section, Trent University, Peterborough, Ontario, K9J 7B8, Canada.



Species at risk in Canada receive different levels of habitat protection depending on their status under the federal Species at Risk Act (e.g., Endangered or Threatened, vs. Special Concern). Accurate detection of species presence can facilitate appropriate habitat protection. For example, the Blanding’s turtle (Emydoidea blandingii; Threatened, COSEWIC 2016) receives legislated habitat protection for its nesting sites on federal lands throughout its Canadian range, and on Crown and private lands in Ontario under the provincial Endangered Species Act. Nesting sites of the sympatric northern map turtle (Graptemys geographica; Special Concern, COSEWIC 2012) do not receive the same legislative protection. The eggs of these 2 species look very similar, making nest identification challenging. In this study we tested whether external egg morphology can reliably identify these species’ eggs, using measurements from 13 Blanding’s turtle clutches (143 eggs) and 72 northern map turtle clutches (873 eggs). Although the mean length, width and volume of eggs differed significantly between the species, strong overlap in the ranges of these measurements prevent reliable identification to species. Alternative methods for egg identification include incubation and identification of the hatchlings, scanning electron microscopy of eggshell fragments, or eDNA analysis of swabs taken from the surface of recently laid eggs.

Key Words: Blanding’s turtle; Egg Morphology; Emydoidea blandingii; Habitat Protection; Graptemys geographica; Maternal Investment; Northern Map Turtle; Species at Risk.



View Full-Text    Download PDF