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Distance-dependent defensive coloration

17 December 2014

A new study by Bristol University's CamoLab shows that animal camouflage and warning colours can be combined to send different information to predators at different distances.

The various functions of animal coloration have largely been considered in isolation.  However, in nature, multiple selection pressures for different, and sometimes incompatible, colour patterns are likely to be present.  For example warning coloration and camouflage, the former promoting conspicuous communicative signals, the latter inconspicuousness. However, the eye can resolve different amounts of detail at different distances, so it has been proposed that an animal could combine fine-grain warning patterns that are only visible close-up, with course-grained camouflage seen (or not seen!) from a distance.

A new paper in Current Biology, by PhD student Jim Barnett and Professor Innes Cuthill, provides the first evidence that such distance-dependent colour patterns can provide survival benefits against natural predators in the wild.  They did so by the innovative adaptation of an image processing technique used in perceptual psychology: spatial frequency blending to produce hybrid images. Artificial moth-like prey were created with patterns that incorporated highly conspicuousness aversive components while maintaining effective background matching camouflage at a distance.  Hundreds of these prey were pinned to trees in natural woodland, with a dead mealworm attached as bait, and the rate at which birds attacked them was measured. The dual-colour patterns survived better than either camouflage alone or warning colours alone.

Understanding how these two conceptually distinct and seemingly mutually exclusive defensive colour patterns interact can give us new insight into how animal coloration evolves.  The experiments show that distance-dependent dual signalling has the potential to function in real-world predator-prey systems, and may explain situations where animal coloration does not fulfil the divergent predictions of traditional camouflage or signalling theory.  These principles could also be exploited to allow camouflage to be combined with other types of signals (e.g. sexually selected), wherever the audience is likely to detect the pattern at different ranges.

Find out more about camouflage research at Bristol at CamoLab

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