News  Using the past to learn about the future of a species

Wood turtles fit their name—they live in the woods and their carapace (upper shell) has a pattern and color resembling wood. This medium-sized turtle grows to roughly 8 inches in length. However, that wasn’t always the case. MassWildlife’s State Herpetologist, Dr. Mike Jones, discovered historic records of wood turtles in Massachusetts and compared them to the species today, and found some drastic differences.

Louis Agassiz and Sanborn Tenney were prominent turtle scientists who studied wood turtles in the Nashua River watershed during the early 1850s. Within his four-volume Contributions to the Natural History of the United States, Agassiz reported collecting over one hundred wood turtles in a single afternoon in the town of Lancaster. This number of wood turtles found in a single area over the course of a few hours is inconceivable today.

These historic observations represent the earliest quantitative reports of wood turtles in Massachusetts, providing a unique glimpse of past landscape conditions and population status of an animal that is today protected as a species of special concern under the Massachusetts Endangered Species Act. Dr. Jones, together with colleagues from UMass Amherst and Antioch University, visited Harvard University’s Museum of Natural History to measure and evaluate Agassiz’s remaining wood turtle specimens. The team also returned to Lancaster and found that although still present, the wood turtle population there is much smaller than in the 1850s.

Comparing the current surveys to those of the 1850s, it is clear to see that the wood turtle population has drastically decreased. While Agassiz had reported over 100 specimens in a single afternoon, Dr. Jones and his colleagues found only 2–3 turtles per survey. The team also compared shell dimensions, growth rates, and sexual dimorphism in modern turtles to those of Agassiz’s collection from Lancaster. Results from this comparison show that modern juveniles grow faster than their 1850s counterparts, and they also grow to larger sizes. Adult wood turtles living today are 20% larger than those in the 1850s! Dr. Jones’ team used a recent, statewide sample to evaluate whether the significant increase in adult body size is due as a partial response to a warmer climate, or as a density-dependent response to population decline. The results of their study, which were published earlier this year in Herpetological Conservation and Biology, reveal that modern wood turtle body size across Massachusetts is positively associated with warmer temperatures, and adult male body size is negatively correlated with population density. This suggests that the 1850s growth rate may have been reduced due to cooler temperatures, and that 1850s adult body size may have been constrained by density-dependent factors.

Learn more about wood turtles.