“…For methods relying on visual tracking, marking the animals to make them stand out from the background and also distinguishable from each other, can improve performance (Ohayon et al, 2013;Lorbach et al, 2017). However, this comes at the cost of increased human intervention and the possibility of changing animal behavior (Walker et al, 2013;Burn et al, 2008;Hurst and West, 2010;Hershey et al, 2018). Markerless techniques rely on inherent differences in animal appearance (Dell et al, 2014;Branson et al, 2009;Hong et al, 2015;Burgos-Artizzu et al, 2012;Brose et al, 2006;Unger et al, 2017;Pérez-Escudero et al, 2014;Kühl and Burghardt, 2013;Berman et al, 2014;Matsumoto et al, 2013).…”