BatLog: Open-source Passive Integrated Transponder (PIT) Tag Logger For Wildlife Behavioral Studies.

Automated monitoring of individually marked animals enables the collection of high-resolution activity data, yet commercial systems capable of continuous individual organism tracking remain inaccessible to many research programs. BatLog is a modular, open-source passive integrated transponder (PIT) tag logging system built on Arduino-compatible hardware, costing ∼180 USD. BatLog is designed to extend the application of existing PIT tag infrastructure by incorporating individual identification data into continuous behavioral datasets, without requiring additional animal handling or marking. The system is well-suited for studies conducted in controlled or semicontrolled environments with defined movement points, such as nest boxes, roost entrances, burrows, or other confined passageways. BatLog is most effective in study systems where animal movement is constrained through a defined opening, and individuals reliably pass through the antenna. A dual-antenna configuration enables directional detection, allowing each tracking interaction to be classified as an animal entry or exit event. Deployed in a controlled laboratory setup at Bucknell University, USA, the BatLog system recorded 80,109 paired directional events across 27 individually identified bats. The Arduino-compatible architecture supports integration with additional sensors, including temperature, humidity, accelerometers, and acoustic monitors, making BatLog broadly applicable to behavioral and ecological studies across taxa.