Estimating animal density using camera traps without the need for individual recognition

Rowcliffe and colleagues introduced the Random Encounter Model, a method to estimate density for species that cannot be individually identified, such as unmarked cats and many prey species. Borrowing from ideal-gas physics, the model relates the rate at which animals trigger cameras to their density, given knowledge of animal movement speed (day range) and the camera detection zone geometry (radius and angle). Validated against a known density of animals in a park, the estimates were encouragingly accurate. The REM opened density estimation to the majority of mammals lacking natural marks, freeing researchers from reliance on coat patterns. It spawned an entire family of recognition-free estimators and is a foundational reference for camera-trap density methodology beyond individually marked felids.