A mouse that rocks: camera trapping shows that mound assessment criteria do not reliably predict pebble mouse (Pseudomys chapmani) activity

Context The western pebble mound mouse (Pseudomys chapmani) is an understudied Australian rodent that tunnels in rocky substrate to excavate a complex subterranean burrow system that is topped with a ‘fortress style’ pebble mound. Most of the species’ current distribution occurs in the Pilbara region of Western Australia, which is a hub of anthropogenic disturbance, primarily because of iron-ore mining. In 1996, a scoring system based on external mound features was developed to allow for quick assessment of whether a mound was ‘active’ or not. However, we identified that the investigation that developed the scoring system had several shortcomings, including a lack of a test of repeatability across investigators and minimal trapping effort to validate the criteria. Because this scoring system has been applied to ‘determine’ presence or absence of this species in environmental surveys, there are concerns about the accuracy of population data that have informed the management of this species. Aims The aim of our investigation was to provide a rigorous assessment of the established western pebble mouse mound scoring system. Methods We obtained independent mound activity scores from three investigators and intensively camera trapped western pebble mouse mounds during their most active period of the year. Key results Our analyses produced four key results: (1) western pebble mouse activity is highly variable across mounds; (2) activity scores derived from using the mound assessment criteria were not reproducible among investigators; (3) there was a lack of congruency in mound status (active or not active) as determined by the mound activity scores (predicted activity) and camera detections (actual activity); and (4) mounds that had higher predicted activity scores tended to have a greater number of camera detections. Conclusions Our investigation demonstrates that the use of external mound structures to determine western pebble mouse activity is not reliable. We show that high variation in activity across mounds is likely to be a population trait and suggest that mounds with low or no activity are critical resources, either to be occupied by locally dispersing females or as temporary respites for males that move transiently across the landscape. Implications We provide recommendations on how to adequately assess western pebble mouse activity, the application of which will be important in defining the current and future conservation status of this important Pilbara ecoengineer.