Dual aerial 1080 baiting operation removes predators at a large spatial scale

As New Zealand attempts to become predator free by 2050, transitioning aerial 1080 (sodium fluoroacetate) operations from predator control to complete predator removal has become an important research objective. Aerial 1080 operations may not remove every last target animal, but they may be able to remove a very high proportion (> 0.99). We trialled a modified [dual] aerial 1080 operation for the removal of brushtail possums (Trichosurus vulpecula), ship rats (Rattus rattus), and stoats (Mustela erminea) at large spatial scale. Our trial involved two toxin applications (TA#1 & TA#2), each preceded by two applications of non-toxic pre-feed bait. Different types of cereal baits and lures were used for each toxin application. Camera traps (n = 142; 200–1431 m asl) were used to detect the target species and to incidentally observe house mouse (Mus musculus), birds, and ungulates across the study area. The operation had no significant impact on the number of cameras detecting most birds and ungulate species; however, house mouse, blackbird (Turdus merula), and red deer (Cervus elaphus) were detected on significantly fewer cameras after TA#1 than before. Numbers of cameras that detected target species were significantly reduced for all three target species after TA#1, and significantly reduced again for possums after TA#2, when no stoats were detected on cameras and a small number of cameras detected rats. Mean relative abundance estimates based on camera trap indices (proportion of camera trap days that target species were detected) showed the operation appears to have removed over 99% of ship rats, stoats, and possums.