Detections of house mice on Gough Island approach zero within days of aerial baiting

Context. House mice (Mus musculus) on temperate Gough Island (6500 ha) are known for their large size, boldness, and tendency to kill large prey such as albatross chicks and even adults. To remove this threat, a mouse eradication operation was implemented in June-August 2021. How mice react to bait during eradications is not well understood, so we capitalised on this operation and conducted the first study with wild house mice during an actual eradication. Aim. To document how rapidly mouse activity declined after application of rodent bait, to improve eradication guidelines. Methods. We set up a monthly monitoring regime using 10 trail cameras without lures, active for three nights in various habitats around a research station, because this area supported the highest abundance of mice and was logistically feasible. Monitoring commenced before the mouse eradication operation (January-May 2021), and continued when rodent bait was spread (from June 2021), when mouse activity was monitored for 17 consecutive nights, starting the day before baiting. In addition, an increasing number of cameras (up to 15) associated with lures were set further afield in July-August to detect survivors. Key results. In the months before bait application, mean daily mouse activity was 3.2 detections/camera (range: 0-56 detections/camera). Immediately after the first bait application, detection rates declined dramatically, from 9.6 to zero detections/camera per day on Day 4 post-baiting. From 1 week post-baiting, mouse detections were extremely rare on both cameras with and without lures. Our last mouse record, 27 days after the first bait application, may be related to initial rapid bait disappearance. Opportunistic camera traps first detected surviving mice 6 months after the first bait drop. Conclusions. The rapid decline in detections suggests that most mice consumed bait as soon as it became available, which is faster than what laboratory trials suggest. Future similar operations can expect that mouse activity will decline sharply within 1 week, although some mice may survive longer. Implications. Documenting similar declines in mouse activity using cameras could inform operational decisions such as timing of a second bait application or non-target monitoring on future eradication projects. Cameras, particularly with attractive lures, are an effective addition to the mouse detection toolkit, and facilitated a timely confirmation of eradication outcome.