Camouflage and the light environment

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Being spotted by a predator can spell the end for an animal. Camouflage is therefore critical to the survival of many species and is one of the most common anti-predator strategies in nature. An animal's camouflage often depends on matching the colours and patterns of its surroundings, but how can it achieve this when the lighting conditions continually alter the background's appearance? The vegetation and textures in a scene create complex shadows and patterns that rapidly disappear when a cloud passes over and diffuses the lighting. Likewise the colours in a scene depend on atmospheric conditions; on a clear day shadows are blue-tinted, and when overcast the lighting colour becomes uniform. Interactions between lighting conditions and three-dimensional habitat structure could therefore be essential for the success of an animal's camouflage and affect its very survival.A number of camouflage strategies have been identified that help animals stay unseen, and they often depend on specific lighting conditions. For example, counter-shading is a strategy found in many species that have dark backs and pale underbellies. This coloration helps to cancel out the shadows on the animal's underside, making its tell-tale shape less easily recognised. Coloration that creates false textures and depth cues is also found in many species; tactics that mimic illumination by direct sunlight. Background pattern matching can protect animals from predators, but the background patterns will shift and change throughout the day. It is therefore possible that these strategies become ineffective or even counterproductive under diffuse, overcast conditions. Beyond basic colour differences it remains unknown how these camouflage strategies perform in different light environments and habitat structures; understanding this interaction - which could affect the survival of any visually hunted species - will be the focus of my proposed research.I plan to use an innovative range of experiments to investigate the importance of three-dimensional habitat structure, colour and lighting conditions on camouflage. First, I will determine whether reed warblers can select nest sites with lighting conditions that optimise the camouflage of their eggs, and test whether a mismatch between egg coloration and lighting increases their likelihood of being spotted by predators. Next, I will create artificial nests in the wild, testing how different camouflage strategies perform given the habitat structure and lighting conditions at the time of predation. Finally, I will use an online evolution game that allows computer-generated 'eggs' to evolve under different lighting conditions and against different backgrounds. I predict that the optimal camouflage strategy should switch depending on how light interacts with the three-dimensional structure of a scene. Flat habitats should favour strategies that create false textures and depth cues, and direct lighting should promote counter-shading and red-green colour matching over blue-yellow.My research will provide fundamental insights into the importance of lighting conditions and the shape of a habitat on the survival of individual animals. These findings would be of immediate value to conservation projects to develop land-use strategies and farming practices that help protect vulnerable species from predation. Humans are changing the lighting conditions of habitats across the world as a consequence of climate change, potentially altering the efficacy of camouflage strategies that had evolved under different lighting regimes. My research therefore has the potential to open up new areas of research in camouflage, environmental change and conservation.