Cryptic Declines in a Widespread Australian Frog Complex

ABSTRACT Amphibian populations in upland areas have experienced disproportionately high rates of decline worldwide, yet the status of many remains poorly understood due to limited systematic surveys and long‐term monitoring. In eastern Australia, the Pseudophryne bibronii complex ( P. bibronii and P. dendyi ) was once widespread and common, but its current population status is uncertain. We aimed to quantify contemporary occupancy, relative abundance, and disease prevalence in this group by surveying 70 historically occupied sites spanning an elevational gradient from near sea level to ~1700 m elevation. Sites were surveyed up to six times over two breeding seasons, and adult males were swabbed to determine infection rates with the fungal pathogen Batrachochytrium dendrobatidis (Bd). Occupancy declined sharply with elevation, from 71% at low elevations to 28% in upland areas, with counts of calling males showing a similar pattern. Bd prevalence increased from 6.7% at low elevations to 29.2% in upland sites, with the highest infection intensities also recorded at higher elevations. These findings implicate Bd as a potential contributor to upland declines, possibly alongside other environmental pressures. Our results demonstrate that common species can undergo substantial, unrecognized contractions in the absence of targeted monitoring and provide an example of time‐lagged declines potentially associated with chytrid fungus.