Protecting prey by deceiving predators: A field experiment testing chemical camouflage and conditioned food aversion

Complicated conservation problems may arise if predator numbers increase beyond their natural boundaries due to anthropogenic influence. For example, dramatic declines in ground-nesting birds are linked to increased nest predation by alien or human-subsidized mammals. While predator control can be temporarily effective, it is often laborious and carries ethical issues. Thus, we need alternative, non-lethal methods for reducing predator impact on their prey. We performed a landscape-scale experiment to study whether two non-lethal methods could protect ground-nesting waterfowl from nests predation. We spread either non-rewarding waterfowl odour (chemical camouflage) or eggs containing an aversive agent (conditioned food aversion) in the surroundings of study wetlands located in southern Finland. Predation of artificial waterfowl nests by red foxes decreased in sites with chemical camouflage, while there was no effect on predation by invasive raccoon dogs. Food aversion created less obvious effects than the chemical camouflage, but both methods indicated potential for reducing nest predation. Based on wildlife-camera data mesopredator observations did not, however, decrease near treatment wetlands. This suggests that treatments did not reduce predator activity, but affected foraging behaviour of predators and reduced their ability to find the nests. We conclude that managers considering non-lethal methods should carefully consider the effectiveness of different methods and potential species-specific responses. Nevertheless, our study support calls for wider use of non-lethal methods in reducing predator impacts on prey. These methods offer ethical and potentially effective approaches which keep native predator fauna intact, but create protection for vulnerable prey