Shedding light on predator detections: evaluating the impact of camera-trap flash type for feral cat monitoring through in-field observations

Abstract

White flash camera-traps are avoided in predator monitoring as they are assumed to lower redetection, despite infrared cameras producing lower-quality night images thus limiting the scope for individual identification and, consequently, the accuracy of density estimates. We sought to determine whether flash type impacts the behaviour of cats (Felis catus). We identified different behavioural responses exhibited by photographed cats, and quantitatively assessed relative activity, redetection rates, and the activity of specific individuals using 11,389 images of feral cats from 62 white flash and 62 infrared camera-traps across Tasmania. We found no difference in the relative activity of cats between flash types (odds ratio of 0.90, [null expectation = 1], CI = 0.55, 1.47), and there was no evidence of a reduction in redetection rate of feral cats following initial detection (odds ratio = 0.83, CI = 0.47, 1.46). The activity of individuals was similar between white flash (average = 0.026, CI = 0.021, 0.032), and infrared cameras (average = 0.028, CI = 0.022, 0.035). White flash cameras appear suitable for monitoring feral cats without resulting in a negative bias, highlighting the need for researchers to critically examine assumptions regarding best methodology.