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Fig. 6. The effect of motion on visibility. (A) An optimal static camouflage
pattern where the pattern matches the background, and the orientation
minimises the number of lines obscured. Unfortunately, if the animal moves,
this pattern is far from optimal: the relative motion between the stripes on
the animals back and the background is highly visible, and there is a strong
relative motion signal together with occlusions along the side (marked by the
arrows). (B) A pattern without stripes minimises motion signals. Further,
orientating the body orthogonally to the substrate, the area of high relative
motion and occlusion is minimised. (C) Sand ripples in the natural environment
are oriented at 90° to the water flow
(Ayrton, 1910). Thus an
orientated substrate provides important information about the current. Similar
principles apply to shadows cast by waves. Orientating the body in the
direction shown by the arrow, as was observed, minimises drag, and maximises
the efficiency with which the animals can compensate for involuntary
movements.
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