'Odours of mass deception' - Understanding and manipulating the foraging behaviour of alien predators using chemical camouflage

Abstract

Alien predators pose a pervasive threat to native species globally, yet our understanding of the behaviours that allow them to forage so effectively in novel environments is relatively limited. Many alien predators are mammals, relying upon olfaction to acquire information on prey location and hone their foraging effort. Understanding how predators occupy the landscape and use the spatial context of prey odour cues to decide where to devote foraging effort may explain the vulnerability of prey, and offers opportunities to alter odour environments in order to disrupt predator success.

In this thesis I examine movement patterns of predators at increasing ecological and spatial scales to gain insight into factors that motivate foraging decisions and influence prey vulnerability. Using a combination of semi-wild and field-based experiments I investigated how spatial variation in olfactory cues (or ‘chemical camouflage’) influences the foraging behaviours of three alien predators. Firstly, using wild house mice, Mus musculus, I found that when prey are camouflaged, predators can show rapid temporal improvements in foraging success, although the degree of improvement depends upon prey quality. Secondly, using stoats, Mustela erminea, I found that increased search costs influenced a predator’s decision to switch to alternate prey, but that its foraging motivation was sensitive to the ease with which alternate prey were found. Thirdly, using free-living populations of black rats, Rattus rattus, I found that egg survival could be significantly enhanced by priming rats with birds nest odour cues. I was able to induce perceptual filters such that rats ignored formerly conspicuous prey odour cues even when eggs were present. Finally, using a multi-predator (red fox, Vulpes vulpes, and dingo, Canis lupus dingo) landscape, I show that unpredictability in predator behaviour is another layer of risk for prey to negotiate. My results indicate temporal variability of predator movements may serve to enhance prey vulnerability. In combination, my thesis demonstrates that the behaviour of alien predators influences the vulnerability of prey at multiple scales, from an individual within a patch to a species within a larger community. The olfactory conspicuousness of prey is a primary element motivating foraging decisions of alien predators, with prey vulnerability curtailed when the spatial variability within odour backgrounds is reduced.