Turtles and turnarounds: Small animal exclusion fencing effectively reduces turtle road mortality

Abstract

Mortality and habitat fragmentation associated with roadways are leading threats to the persistence of freshwater turtles. While roadway mitigation for wildlife is becoming more common, it is often expensive, and effectiveness for small animals remains understudied. Proven designs can maximize benefits and budget, and effective wildlife barriers have the added benefit of improving road safety. Here, we test and evaluate the efficacy of a design for small animal exclusion using off-the-shelf chain-link fencing. Design modifications to help prevent turtles from accessing roadways included wrap-around end treatments and burying the fence bottom. The goal of the fencing was to redirect turtles away from roadways and to existing under-road infrastructure where practicable. We implemented a Before-After-Control-Impact (BACI) study at 11 sites (4 Impact, 7 Control) from 2018 to 2021, with data collected during weekly walking surveys. Results for the first three years showed a strong reduction in mortality (62 %) for adult turtles after fence installation, with a significant interaction between Treatment and Period for Impact sites when compared to Controls (Z = −2.42, df ᵣₑₛ = 818, P = 0.015). However, the initial design did not decrease mortality of juvenile and hatchling turtles. After retrofitting fences with 1.27 cm wire mesh in 2021, we documented a substantial reduction in mortality across all age classes of turtles (up to 91 % over pre-treatment). This study demonstrates that barriers with wrap-around end treatments can be an effective way to reduce road mortality of turtles, while meeting economic objectives.