Using Environmental DNA to Detect Radio-Tagged King Rails: Initial Validation Results and Needed Advancements

Abstract Secretive avian species can be difficult to detect. For such species, environmental DNA (eDNA) monitoring could improve our ability to estimate occupancy and population trends. There are often challenges associated with efforts to establish eDNA as an effective monitoring tool for species of conservation concern because it is difficult to hold nonmodel organisms in captivity to complete validation tests. To address this issue, we tracked four king rails Rallus elegans in Ohio, USA, in 2020 with radio telemetry to determine whether our eDNA monitoring approach could indicate king rail presence where these individuals occurred. Also, we collected eDNA near locations surveyed by human observers within potential habitat where king rail status was unknown. The eDNA surveys indicated king rail presence at one of five locations where we knew that an individual king rail had occurred within 30 h and at one of four locations where king rail presence was unknown but feasible. At these latter locations, human observers detected no king rails, although in 2022 human observers using traditional survey methods detected a king rail near the same location where our eDNA detection occurred in 2020. This study provides a preliminary, although informative, king rail eDNA monitoring methodology that we validated with radio telemetry data. We suggest ways to improve our approach to increase king rail detection rates and to add confidence in results.