Assessment and Mitigation of Road Mortality of Turtles at Colonial National Historical Park

Seigel, Richard; Scarangella, Kai; Murasaki, Ryo

doi:10.36967/2316981

We studied seasonal and spatial patterns of road mortality of turtles at Colonial National Historical Park from March–October of 2024. The study area was the Jamestown Island Loop Drive (hereafter Loop Drive), a 7.7 km paved road that was open to cyclists during the entire study period and motor vehicles from mid-June onwards. The road is divided into two segments; a shorter “Small Loop” and a longer “Big Loop.” Turtle species found included Box Turtles, Snapping Turtles, Spotted Turtles, Painted Turtles, Red-Bellied Cooters, and two species of Mud Turtles (Eastern and Striped), that were classified together due to morphological similarity. We conducted a total of 281 road surveys from 26 March until 29 October 2024 during which we found a total of 330 turtles. Mud Turtles and Box Turtles were the most common species and Red-Bellied Cooters and Painted Turtles were the least common. Turtle activity reached a maximum in mid-May, declining gradually through the end of August and early September. Of the 330 turtles encountered, 80.3% were found alive and 19.7% were found either dead or badly injured. For turtle species with at least 10 observations, Mud Turtles had the highest probability of being found dead (24.6% dead), whereas Snapping Turtles had the lowest probability of being found dead (7.0% dead). This is attributed to the much larger body size of Snapping Turtles, which made them more visible and more easily avoided. Although some dead turtles were found in April and May (before the road was opened to vehicular traffic), the largest number of dead turtles was found in July (21 dead, representing 32.3% of all dead turtles). Mortality events in April and May were the apparent result of collisions with bicycles, rather than motor vehicles. Although more turtles were found on the Big Loop, we did not find any differences in patterns of road mortality between these road segments. For Mud Turtles, frequency of deaths was significantly higher for immature turtles than for adult females or adult males. Conversely, we did not find any significant differences in frequency of deaths among age classes for Box Turtles. Our management recommendations are to (1) continue current public outreach campaigns and (2) close the Loop Drive to motor vehicles from 15 March to at least 15 June each year, with the understanding that these dates can be modified as more information on turtle activity and population viability becomes available.

Assessment and Mitigation of Road Mortality of Turtles at Colonial National Historical Park

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