Three novel methods to estimate abundance of unmarked animals using remote cameras

Moeller, Lukacs, and Horne introduced a family of estimators, the space-to-event, time-to-event, and instantaneous-sampling models, to estimate abundance of unmarked animals from camera-trap data without requiring movement-speed or detection-zone calibration. These methods reframe detections in terms of the space or time elapsed until an animal appears, drawing on encounter-rate theory to infer density. They relax some of the demanding assumptions of earlier recognition-free approaches and can be applied flexibly depending on available data. The paper broadened the menu of options for surveying species that cannot be individually identified, including many cats and their prey. It is an increasingly cited methodological contribution in the active research area of density estimation for unmarked populations.