Every Bit Hurts: Quantifiable Effects of Low-Level Anthropogenic Disturbance on Movement, Habitat Selection, and Energetics of Blanding’s Turtles (Emydoidea blandingii)

Abstract:

Anthropogenic development negatively affects biodiversity worldwide, particularly wildlife with low fecundity, long lifespans, and extensive habitat requirements such as freshwater turtles. While large-scale habitat degradation's effects on freshwater tur- tles are well-documented, the impact of low-level disturbances remains understudied, even though these subtler disturbances may alter movement patterns, increase energetic demands, and reduce reproductive success, threatening population viability. Understanding the impacts of all disturbance levels, including those considered minimal, is critical for effective conservation of sensitive species. In this study, we examined the response of the federally endangered Blanding's Turtle (Emydoidea blandingii) to a narrow range of low-level human disturbances in Northern Mnidoo Gamii (Georgian Bay), Ontario, Canada that included a reference site with no visible disturbance (REF), a site experiencing moderately low disturbances (DIS1; with roads), and a site experiencing higher levels of anthropogenic disturbances (DIS2; roads, industrial development). Using radio telemetry, we tracked 14 individuals (501 relocations) in REF during 2021 and 2022, as well as seven individuals (199 relocations) in DIS1 and 13 individuals (367 relocations) in DIS2 during 2023 and 2024. Turtles in DIS2 exhibited significantly larger home-range size, longer home-range length, and greater daily distance traveled than those in REF. Significant habitat selection was observed only in DIS2 at the landscape scale, whereas turtles in DIS1 and REF showed no significant selection at either the landscape or home- range scale. The increased movement in DIS2 was estimated to cost females the energetic equivalent of producing 1.85 more eggs per active season (18.5% of a full clutch). These findings highlight that even moderate habitat disturbances can impose substan- tial energetic burdens on freshwater turtles, and that there may be a disturbance threshold above which the long-term population viability is compromised. Conservation strategies should prioritize minimizing even low levels of habitat degradation to support the viability of at-risk freshwater turtle populations.