Determining the spacing of acoustic call count stations for monitoring a widespread forest owl

Nocturnal species are challenging to monitor, but with advances in bioacoustic technology, acoustic monitoring is becoming a more affordable, efficient technique for monitoring cryptic species. We tested the suitability of acoustic monitoring as a potential national monitoring method for morepork/rūrū (Ninox novaeseelandiae), in beech forest within the Eglinton Valley, Fiordland, during spring 2009–2010. We used radio telemetry and an acoustic call study to address two questions to help managers make evidence-based decisions on the spacing of acoustic call count stations: (1) What are the sex-specific and seasonal home-range sizes of rūrū? (2) How does acoustic detection decrease with increasing distance? Home ranges were the largest recorded to date for rūrū in New Zealand (mean 100% MCP = 307 ha, mean 75% kernel = 43.5 ha) with an average range spread of 270 m (75% kernel). Significant attenuation of recorded calls occurred after 150 m in southern beech (Nothofagaceae) forest and no calls could be detected by the recorders beyond 250 m. Acoustic monitoring is a promising technique to monitor rūrū nationally, but the spacing of stations needs to vary depending on home-range, habitat and the microphones used in the acoustic detectors.