Frogs in sight and sound: Passive acoustics and visual surveys reveal complementary species detection in tropical rainforest anurans

Amphibian surveys in remote tropical rainforests are often constrained by rugged terrain, dense vegetation, limited accessibility, and high logistical demands associated with observer-based methods. Passive acoustic monitoring (PAM) using autonomous recording units (ARUs) has emerged as a promising, non-invasive tool for biodiversity assessments, however, its effectiveness can vary across taxa and landscapes. We conducted a comparative evaluation of PAM with traditional Visual Encounter Surveys (VES) to document the anuran community of a tropical wet evergreen forest within the Indo-Burma biodiversity hotspot. Our results show that PAM effectively detected most of the visually observed species, as well as many vocally active cryptic, arboreal, and fossorial species that were missed by VES. Its suitability for deployment in inaccessible areas underscores its potential for large-scale assessments. However, VES detected non-calling and conspicuous species, highlighting the limitation of a single-method approach. A mixed method—integrating PAM with VES yielded a more comprehensive inventory. These findings provide crucial insights into optimising amphibian monitoring protocols and support the adoption of integrated survey methodologies for long-term assessments, particularly in landscapes where conventional methods are constrained by terrain and effort.