Polarisation signals

Humans are fascinated by the colour vision, colour signals and ‘dress codes’ of other animals as we can see colour. This property of light may be useful for increasing the contrast of objects during foraging, defence, camouflage and sexual communication. New research, largely from the last decade, now suggests that polarisation is a quality of light also used in signalling and may contain information at least as rich as colour. As many of the chapters in this book detail, polarisation in animals is often associated with navigation, habitat choice and other tasks that require large-field processing. That is, a wide area of the light field, such as the celestial hemisphere, is sampled from. Polarisation vision that recognises and extracts information from objects is most likely confined to processing through small numbers of receptors. This chapter examines the latest evidence on polarised signals from animals and their environments, including both linear and circular polarisations. Both aquatic and terrestrial examples are detailed, but with emphasis on life underwater as it is here that many recent discoveries have been made. Behaviour relative to signals is described where known, and suggestions are given as to how these signals are received and processed by the visual system. Camouflage as well as signalling in this light domain is also considered, with the inevitable conclusion for this new field that we need to know more before solid conclusions can be drawn