Research overview: relative abundance indices and their limitations

Relative abundance indices, typically detections per unit effort such as photos per 100 trap-nights, are the simplest and most widely used camera-trap metrics, but their reliability is hotly debated. This overview explains the appeal of indices, no need for individual identification or complex models, and their central weakness: they confound true abundance with detection probability, which varies by species, behavior, placement, and conditions. It surveys evidence on when indices track real density and when they mislead, the role of trail-versus-random placement, and methods to make indices more defensible. For monitoring programs lacking resources for full density estimation, indices remain practical, but the overview stresses interpreting them cautiously and standardizing effort and placement to limit bias when comparing felid abundance across sites and times.