Automated Recording Unit Detection Probabilities: Applications for Montane Nesting Seabirds

Autonomous Recording Units (ARU) are a passive acoustic monitoring technology that are useful for detecting the presence and distribution of cryptic and nocturnal animals in challenging, remote environments as they can be deployed for extended periods of time. However, ARUs vary in their detection ability, thus making it critical to evaluate them in real world environments. In American Samoa, three Procellariiform seabird species nest on the remote island of Ta'u in difficult to access summit scrub habitat, for which we have little knowledge about their presence. Given the lack of knowledge about the distribution of these three species, coupled with the need to test different ARUs, our goal was to investigate the differences in detection probability for Song Meter sensors (Song Meter SM2 and SM4) under different habitat and environmental conditions on the island of Ta'u. Detection ranges for seabird calls varied from <10 m in high wind conditions, up to 90 m in low wind conditions. Under ideal conditions detection range varied from 40 to 100 m for Song Meter SM4 sensors and 40 to 70 m for SM2 sensors. Knowing the detection capabilities of ARUs will allow better design of sensor spacing, and a combination of acoustic recording with in situ weather data will allow for calculations of detectable areas and facilitation of determining animal densities.