Acoustic Monitoring of Invasive Species: Continental Patterns in Calling Activity of the Invasive Cane Toad

Invasive populations are managed most effectively when surveillance targets periods and places of maximal activity or detectability. Understanding the factors influencing breeding of invasive species is also important for modelling population growth and spread. Despite their continued successful advances, the patterns and drivers of invasive cane toad (Rhinella marina) calling activity remain poorly resolved at broad scales in Australia. Using continent-wide passive acoustic recording data paired with a machine-learning acoustic classifier, we describe patterns in when, where, and under what conditions cane toad choruses begin and persist across most of their current range in Australia, spanning three states and climate zones (~15° latitude and 27° longitude). A total of 163,701 minutes of cane toad calls from 33,799 nights of recordings showed that they chorused near year-round, with seasonal peaks. Cane-toad calling probability and intensity increased on dark, calm, humid nights, and near lentic systems or temporary water, and with low- to medium canopy cover, and decreased with increasing wind and moonlight. Social cues were important: prior-week calling activity strongly elevated both probability and intensity of calling. Interestingly, temperature effects were context-dependent, without a prior chorus, calling probability and intensity peaked at moderate temperatures; following chorusing, both metrics remained high across a broader thermal range. However, variable importance differed among climate zones: atmospheric and lunar factors were more influential for initiating choruses in subtropical and semi-arid sites, whereas habitat and hydrology contributed more to sustaining choruses in the tropics. Together, these results reveal a detailed picture of cane toad calling ecology in Australia, identifying when, where, and under what conditions chorusing is favoured. This study not only demonstrates the use of ecoacoustics for effective monitoring and understanding of vocal invasive species, but also supplies a comprehensive, data-driven foundation for predictive models and future real-time monitoring that can allow targeted management for this global invader.