Drone Surveys Reveal Seasonal Sex Differences in Painted Turtle Basking Behaviour and Advance Freshwater Turtle Monitoring

Abstract

Basking is an essential thermoregulatory behaviour in freshwater turtles, but accurately quantifying basking behaviour is challenging. Traditional survey methods can lack temporal precision, be disruptive, and have low detection probability. To address these limitations, I developed a high-frequency drone-based monitoring method that records repeated, minimally invasive video surveys of individually marked painted turtles (Chrysemys picta). I then applied this method to test whether basking probability varies seasonally between sexes. I predicted that females would bask more than males early and late in the active season, when reproductive energetic demands are highest, with smaller differences between sexes during mid-summer. I conducted autonomous drone surveys every 20 minutes on 13 days from June to September 2025 at a wetland on the Kenauk property in Montebello, Québec, Canada, generating 423 surveys and 127 hours of video footage. Flight initiation distance trials confirmed that surveys at a 15 m altitude did not disturb turtles. Basking probability declined over the season and was influenced by environmental conditions, peaking at intermediate temperatures and around midday, and decreasing with wind speed and cloud cover. Females basked more than males early in the season, but this difference diminished by mid-summer and did not re-emerge later. This study demonstrates that drone-based surveys enable minimally invasive behavioural monitoring at high temporal frequencies and reveal fine-scale temporal, environmental, and sex-specific patterns in freshwater turtle basking behaviour.