Disruptive camouflage

The response of birds to a sparrowhawk alarm varies.  Most small birds flee into dense cover if they can, hoping that the hawk won't be able to follow them.  A great spotted woodpecker reacts differently - it freezes, not moving a feather. At first glance the woodpecker's reaction seems almost suicidal but it relies on the fact that a sparrowhawk's eyesight is tuned to detect movement with relatively poor colour vision.

Only when the danger has passed will the woodpecker dare to look around to check that all is clear.

Of course most alarms are false alarms but it pays to be cautious.

To our eyes its black, white and red colouring makes a woodpecker very easy to see but in fact it is taking advantage of its disruptive camouflage.  The bold patterns break up the outline and if the woodpecker doesn't move it is difficult for the sparrowhawk to see it, especially in dappled light in woodland.  A similar idea was used to protect Allied merchant ships in WW1.  Known as dazzle camouflage, ships were painted in bold confusing patterns which made them harder to see through a German periscope.  Even if they could be seen it was difficult to make out which was the bow, confusing assessment of the ship's course and making it hard to predict the aim of a torpedo.  Dazzle camouflage was invented by English artist Norman Wilkinson and this painting is by another English artist, Edward Wadsworth, who was also responsible for making the designs for the ships.

This is the SS West Mahomet in dazzle camouflage 100 years ago.

Of course it didn't always work in the war, just as it doesn't always work out for the woodpeckers.  Whether that's because they lose their nerve and move, or whether the sparrowhawk can sometimes see them anyway is hard to say.