If a bird calls, will we detect it? Factors that can influence the detectability of calls on automated recording units in field conditions

Abstract

ABSTRACT Automated recording units (ARUs) are an integral instrument in a broad range of applications such as invasive species management, behavioural studies, and environmental impact assessments. They have become particularly important in conservation programmes for a range of cryptic threatened bird species. While the fundamental issues of signal attenuation and degradation are well known, understanding how environmental factors influence detectability of calls on ARU recordings in particular circumstances is essential for the accurate interpretation of their results. Using five transects spaced at equal angles running from a central playback source we tested the detectability of Pezoporus flaviventris (Western Ground Parrot) and Atrichornis clamosus (Noisy Scrub-bird) calls on Wildlife Acoustics SM2 and SM4 devices. Both species call from on or near the ground in moderately dense heathlands. Detectability of calls was affected by wind direction: fewer calls were detected on an ARU that was up-wind of the broadcast source compared with another on a down-wind unit. More calls were detected on ARUs deployed at higher relative elevation, and detectability decreased with increased distance from the playback source. Calls were detected at a greater distance from the playback source when using SM4 ARUs, compared to SM2 ARUs. Inconsistency in the detection of bird calls through space and time could lead to errors in metrics calculated from acoustic data. Further investigation is required to determine how environmental factors such as wind direction can be accounted for in data analysis.