Multi-surveyor detection-mark-redetection as a powerful tool for
butterfly population monitoring in the pre-imaginal stage
Abstract
1. For many elusive insect species, which are difficult to cover by
standard monitoring schemes, innovative monitoring methods are needed to
gain robust data on population trends. We suggest a monitoring of
overwintering larvae for the endangered nymphalid butterfly Limenitis
reducta. 2. We tested one removal and three detection-mark-redetection
(DMR) approaches in a field study in the “Alb-Donau” region, Germany.
We replaced movement of the study organisms by random movement of
multiple different surveyors, and we examined the model assumption of
equal detectability using simulations. 3. Our results indicate that
multi-surveyor removal/DMR techniques are suitable for estimating
abundance of overwintering L. reducta larvae. Detection probabilities
varied with surveyor experience and the uncertainty of population
estimates increased with a decrease in personnel expenditure. Estimated
larval densities on a spruce clear-cut ranged between one and three
individuals per 100 m². 4. We suggest a detection-mark-redetection (DMR)
approach with three trained surveyors for the monitoring of L. reducta
populations in the pre-imaginal stage. Besides L. reducta, the proposed
method is likely to be suitable for other insect taxa with specific
immobile life-stages and some sessile organisms, e.g. corals, elusive
plants, or fungi.