Hide and Seek?

It’s no game.  Hiding successfully is an effective way to avoid predators.  It’s also pretty useful for predators as it allows them to surprise their prey.  The cheetah is the fastest animal on land with a maximum speed of around 60mph over level ground.  However, it can only run at top speed in straight lines and is exhausted after just 400 metres.  Without the element of surprise, its prey can usually outmanoeuvre the most determined cheetah long enough to munch grass for another day.

You’re probably familiar with the mottled green and brown patterning often used on soldiers’ uniforms to help them hide in bushes, but guess what?  There’s more to these games of hide and seek than sticking a branch in your hat.

Perhaps the easiest way to see how camouflage actually works, is to first look at why humans are often so good at seeing through it.

It’s all an illusion

People are fascinated by optical illusions; pictures that appear to be one thing, yet transform into something else when stared at.

Although they’re a lot of fun, such illusions aren’t just pieces of clever art, they reveal how our brains make sense of the world.  Have a look at the picture below.  See the circle?

There is no circle, just a series of stripes out of sequence.  See the triangles?

Once again, there are no triangles, just circles with bits missing.

When you looked at the illustrations your brain tried to find a recognizable pattern that matched the signals your eyes were producing.  This is an essential survival skill that allows us to decode camouflage and spot the hidden shape beneath.

Camouflage only works if it successfully disguises the shape of the animal (or tank) underneath.

Work by researchers in Germany has shown that barn owls, trained to recognize black squares and other geometric shapes against a white background can spot the unreal shapes hidden in optical illusions like the ones above.

Now you’ve had a bit of practice, look at the photograph and find the fish.

Not quite as easy, but I bet you managed it eventually.

Something tells me that seagulls are pretty good at optical puzzles too.

Optical Traps

Many animals set optical traps that try to fool us into thinking they’re not real.  The most common is counter-shading.

Naturally, light comes from above.  This means that the underside of an animal will always appear darker than the upper side.  Many animals have evolved a pattern that goes against this by having paler or even white undersides.  Look at a deer or a cheetah, they both do it.  Because their pattern goes against what our brains are expecting to see, they appear two dimensional, less real, and our brains fail to recognise them.

In the sea, this trick works in a different way.  Penguins and many fish, with their white or silver bellies, blend into the bright sky when viewed from beneath.  When viewed from above they present a darker side, blending in with the dim ocean depths.

Camouflaged with Confusion

It’s all very well talking about blending in with your surroundings, but what about zebra?  Their striking black and white stripes make them stand out a mile in the dry brown grass of the African savannah, don’t they?

Well, yes, but to see how the pattern works you’ve got to make them jump!  When a group of zebra panic, they all start running about as a group.  The effect of all the different stripy patterns, moving past each other in different directions, is incredibly confusing.  It becomes difficult to see where one zebra stops and the next one begins.  For a hunting lion, trying to pick an individual zebra, leap at its throat and get a good hold, this is a big problem.

To be (seen) or not to be (seen)

Here’s a problem…  if you want to avoid being eaten it’s good to hide and blend in to the background.  But how do you attract attention when you need it: to get a mate or warn others of danger?

One solution is to have brightly coloured bits, but keep them hidden.  After working in a zoo, looking after parrots, I was excited when I finally got the chance to visit a real rainforest and see them in the wild.  When I got there, I was shocked to find that, in their natural habitat, they are very hard to spot.

From a distance, a parrot’s bright colours can help them blend in by breaking up their outline.  In addition, when sitting on a branch or feeding, parrots often manage to keep their brightest colours hidden from view under their wings.  Only when they flap their wings in warning or take to the air do the colours show.  This sudden colour burst may well help startle predators and certainly works as a warning and recognition signal for any other parrots near by.

Another clever solution, is to have brightly coloured bits that your predators can’t see.  When you look at the brightly coloured fish of a coral reef, it’s difficult to imagine them blending in to the background, but they do.

Our eyes are designed to see through air, not water and are particularly good at spotting and differentiating reds and greens (possibly an adaption to help us and other primates spot ripe fruit and leaves).

Not all animals have eyesight that is so effective in these regions of the visible spectrum.

Take a look at the picture.  Did you see a number hidden in the dots?  Did you see the number 29 or the number 70?  If you saw the number 70, you may be one of the 20% of the population who have red-green colour blindness to some degree or another.  This is nothing to worry about, in fact, recent research suggests that this “disability” might be an important adaptation for a hunter/gatherer as it makes your low-light vision more effective.  If you are at all worried, it might be a good idea to ask for a colour test next time you visit your optician.