Individual study: Evaluating the effectiveness of aerial baiting operations for rodent eradications on cliffs on Gough Island, Tristan da Cunha
Cuthbert R.J., Broome K., Bradley J. & Ryan P.G. (2014) Evaluating the effectiveness of aerial baiting operations for rodent eradications on cliffs on Gough Island, Tristan da Cunha. Conservation Evidence, 11, 25-28
The use of helicopters for spreading bait pellets in rodent eradication operations for conservation programmes is increasing. While aerial applications generally have a high success rate at eradicating rodents, operations that tackle extensive areas of steep terrain (slopes >50°) are more challenging, as the effectiveness of spreading bait pellets at the targeted density in these areas is unknown. We undertook an aerial baiting trial on Gough Island, where predation by the non-native house mouse Mus musculus is devastating the globally important seabird populations. It is therefore critical to deliver bait to the island’s large areas of vegetated cliffs that contain burrowing petrels and mice. Using a helicopter and bait hopper we spread non-toxic bait pellets on two areas of coastal cliffs and the adjoining flat ground, and measured the resulting density of pellets using teams of roped climbers and distance sampling. Compared with adjacent flat areas, the vegetated cliff areas retained an average 66-76% of pellets (lower 95% confidence interval 45-60%). While baiting rates on cliffs were lower than adjoining flat areas, the recommended best practice for aerial eradications prescribes applying two additional drops on steep areas. Consequently, current best practice would be sufficient to ensure coverage at densities at or above the targeted baiting rate. While these trials were focused on Gough Island, the results should be useful for eradication operations on other islands with cliffs with similar terrain and vegetation cover.