Criteria to infer local species residency in standardized adult dragonfly surveys

For dragonflies, the final exuviae are the most identifiable nymphal stage, can substitute for lethal processing of live animals, and definitively indicate life-cycle completion or reproductive success. However, dragonfly exuviae are difficult to find and identify relative to adults, and species richness in exuvial surveys is generally biased low. We tested readily acquired information in adult surveys as indicators of exuviae presence and, therefore, species residency. Repeated concurrent surveys of adults and exuviae were completed at 32 wetlands in New York and 30 wetlands in Oklahoma, USA. We modeled the occurrence of exuviae as logit-linear functions of adult abundance, detection frequency (across surveys), teneral frequency, and frequency of breeding behavior while controlling for imperfect detectability. Exuviae occupancy probabilities suggested several reliable indicators of species residency: 1) finding adults on >4 surveys, 2) finding tenerals on >2 surveys, and 3) counting >20 adults on >1 surveys (with caveats). The odds of exuviae occurrence when these conditions were met were 9 to 18× greater than when no adults were detected. Species residency may be accurately inferred during adult surveys, potentially improving freshwater applications and conservation via dragonflies.