RT Journal Article SR Electronic T1 TRex, a fast multi-animal tracking system with markerless identification, and 2D estimation of posture and visual fields JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.10.14.338996 DO 10.1101/2020.10.14.338996 A1 Walter, Tristan A1 Couzin, Iain D YR 2021 UL http://biorxiv.org/content/early/2021/02/23/2020.10.14.338996.abstract AB Automated visual tracking of animals is rapidly becoming an indispensable tool for the study of behavior. It offers a quantitative methodology by which organisms’ sensing and decision-making can be studied in a wide range of ecological contexts. Despite this, existing solutions tend to be challenging to deploy in practice, especially when considering long and/or high-resolution video-streams. Here, we present TRex, a fast and easy-to-use solution for tracking a large number of individuals simultaneously using background-subtraction with real-time (60Hz) tracking performance for up to approximately 256 individuals and estimates 2D visual-fields, outlines, and head/rear of bilateral animals, both in open and closed-loop contexts. Additionally, TRex offers highly-accurate, deep-learning-based visual identification of up to approximately 100 unmarked individuals, where it is between 2.5-46.7 times faster, and requires 2-10 times less memory, than comparable software (with relative performance increasing for more organisms/longer videos) and provides interactive data-exploration within an intuitive, platform-independent graphical user-interface.Competing Interest StatementThe authors have declared no competing interest.