Monitoring populations of bioluminescent organisms using digital night photography and image analysis: a case study of the fireflies of the Selangor River, Malaysia

.  1. The ability of bioluminescent organisms to produce light provides opportunities for remote, non‐destructive sampling through imaging. A case study of its use in monitoring populations is described for fireflies that congregate on riverbank trees in an ecotourism destination in Kuala Selangor, Malaysia. 2. Digital images were captured from set locations at a standardised moon phase and time of night, at distances of 60–270 m across the riverbank. 3. Counts of bright spots by trained, cross‐calibrated operators were used as an index of abundance, and could often be predicted by regression equations for a subsample of particle analysis counts generated by image analysis software. 4. In tests of the sustainability of the technique, prediction of counts from an upgrade camera could be achieved by multiple linear regressions incorporating camera‐subject distance, particle size, and particle intensity characteristics. Multiple linear regressions could also be used to refine prediction of manual counts from particle analysis counts in this camera. 5. Sampling light emissions enabled a much larger area of habitat to be monitored than would have been possible with other methods. In total, 1.6 km of the river margin could be imaged in just three nights from 20:30 to 23:30 hours. The technique can also be adapted to monitor populations of other aggregating, light producing organisms and to study group display behaviour.