Estimating tiger populations from camera-trap data using capture-recapture models

Ullas Karanth pioneered the use of camera traps to count tigers as individually identifiable animals, recognizing that each tiger's stripe pattern is a natural, permanent mark. Working in Nagarahole, India, he photographed tigers at paired camera stations along trails and roads, then treated the resulting photo-captures as a closed-population mark-recapture problem analyzed with program CAPTURE. This reframed an intractable counting problem into a rigorous statistical estimation with confidence intervals, replacing unreliable pugmark censuses. The paper established that detection is imperfect and must be modeled, and that abundance can be estimated even when not every animal is seen. It became the founding methodological template for nearly all subsequent big-cat camera-trap density work worldwide and remains a cornerstone reference for the field.