Acoustic surveys improve landscape-scale detection of a critically endangered Australian bird, the plains-wanderer (Pedionomus torquatus)

Abstract

Context Monitoring the population dynamics of threatened species requires a landscape-scale understanding of their distribution over time. However, detectability is inherently low for rare, widely dispersed, and cryptic species. For animals that vocalise, passive acoustic recorders allow for efficient and repeated surveys over a large geographic area, increasing inference in relation to detectability and occupancy. Aims Our aim was to determine how well acoustic surveys, combined with automated species detection, identified the presence of the critically endangered plains-wanderer (Pedionomus torquatus) relative to a traditional method of nocturnal spotlighting surveys at sites across the Northern Plains of Victoria, Australia. Methods Using Hidden Markov Models, we created 17 different plains-wanderer call recognisers by varying input parameters and assessed their performance on the same training and testing audio dataset. We then applied our best-performing recogniser to a field audio dataset to estimate detectability and compared the presence of plains-wanderers at sites paired with nocturnal surveys. Key results Recognisers varied in their overall performance in detecting individual plains-wanderer calls but were equally effective at determining whether any plains-wanderer calls were detected at a site within our training and testing datasets. Although survey effort was not standardised across field survey methods, we found audio surveys and nocturnal spotlight surveys were equally successful at establishing site-level occupancy; however, acoustic surveys provide the potential to survey more sites over a given time period. Conclusions We suggest acoustic surveys can be an effective and efficient means to document occupancy at the landscape scale, facilitating prioritisation of nocturnal surveys to assess population demographic parameters including abundance and breeding status. Implications Acoustic surveys can provide a complementary method to establish occupancy for cryptic, vocally active, threatened species. We provide recommendations on ways to develop an effective acoustic monitoring program workflow, from data collection to acoustic analysis, that can be used by different user groups.