Preliminary assessment of thermal imaging equipped aerial drones for secretive marsh bird detection

Rails are a highly secretive group of marshland obligate species that are difficult to consistently survey and detect. Current survey efforts utilize either call-playback or autonomous recording devices, but the low detection probabilities for rails create challenges for long-term systematic monitoring. Between 8 April and 16 May 2022, we flew a small aerial drone equipped with a thermal camera to survey for six species of rail (Black Rail (Laterallus jamaicensis), Yellow Rail (Coturnicops noveboracensis), Sora (Porzana carolina), Virginia Rail (Rallus limicola), Clapper Rail (Rallus crepitans), and King Rail (Rallus elegans)) along the Gulf Coast of Texas to assess the feasibility of long-term drone monitoring. We successfully conducted 33 flights at 15 m above ground level and detected rails on the first visit at 42% of known occupied points. We achieved 27 total rail detections, including 12 Black Rail/Yellow Rail detections. Of the birds detected, 81% exhibited no response to the drone's first approach. We intend for this preliminary data to shape future survey protocol for secretive species occupying difficult to navigate terrain.