Using acoustic recorders and accounting for imperfect detection to understand spatial and temporal breeding patterns of a cryptic burrowing amphibian

Understanding the determinants of detection and occupancy at breeding habitats is crucial in the management of threatened amphibian species. This study investigates the spatial and temporal breeding patterns of the giant burrowing frog, Heleioporus australiacus australiacus , a cryptic and threatened amphibian species, through acoustic monitoring. We aimed to quantify the detectability of this species and identify environmental factors that influences its breeding behaviour. Passive acoustic recorders were deployed between May 2018 and November 2021 across eastern NSW. From 5,030 survey nights, the giant burrowing frog was only detected calling on 44 occasions. The estimated probability of detecting a giant burrowing frog during a single survey was p̂ = 0.01, confirming the cryptic nature of its breeding behaviour. Our analysis revealed that calling behaviour in the giant burrowing frog is correlated with climatic variables, with increased detection probabilities associated to higher nightly temperatures and impending rainfall. Conversely, higher daily rainfall and solar radiation levels were associated with a decrease in detection probability. Temperature, precipitation, seasonality and habitat aspect were identified as key factors influencing breeding site occupancy. Overall, our study highlights the importance of accounting for imperfect detection in monitoring programs and provides valuable insight into the breeding behaviour of a difficult to detect species. These findings have implications for the management and conservation of giant burrowing frog populations, particularly in the face of changing environmental conditions. Continued monitoring efforts, focusing on tadpole surveys and passive acoustic monitoring, are recommended to improve our understanding of their ecology.