Are Tiger stripes camouflage?

I can’t explain it (or maybe I can—news to come!) but I’m seeing orange everywhere.

Orange mushrooms on my forest walks. Mandarin oranges that make the trip to and from school in my children’s lunch boxes. Traffic cones around the construction site near my home. The world seems filled with orange. And now that you’ve read this, I bet you’ll see a world of orange too.

Orange gets attention. It’s why traffic cones and road worker’s vests are orange. Life preservers are orange, and astronauts wear highly-visible orange suits to make them easier to locate in case of an emergency landing in water.

But what if you couldn’t see orange?

Many animals can’t. Most mammals have dichromatic colour vision, which means they only have two types of colour receptors in their eyes. (The name comes from the Greek words di- meaning two and chromo meaning colour.) Most humans, apes, and monkeys have trichromatic vision (tri meaning three) which means they have three types of colour receptors in their eyes. These three colour receptors allow humans and other primates with normal colour vision to see millions of colours, including orange.

Dichromatic colour vision, on the other hand, means that an animal's retina only contains colour receptors for blue and green, which means they aren’t able to see red or oranges at all. Many colourblind humans (including my father and son) also have dichromatic vision and have difficulty distinguishing between reds and greens, blues and purples, and greens and browns. I knew my son was colourblind when he almost ate a blob of wasabi, thinking it was peanut butter.

Dogs, cats, and most ungulates like deer, moose, horses, pigs, and cows have dichromatic vision. Which isn’t a particularly interesting fact unless you’re thinking about tigers. Which, of course, I am.

As you probably know, tigers are orange. Very orange. And you probably also know that orange is particularly visible amongst the greenery of a forest or jungle, where most tigers live. I think it’s fair to say that orange and black tiger stripes are among the most eye-catching patterning in the animal kingdom, right?

Well, it depends on what type of colour vision you have. If you have trichromatic vision, tigers are very, very visible. But if you have dichromatic vision, you can’t see orange, which means those bold orange and black stripes actually sort of look like leaves and shadows.

Check out the two images below. The image on the left is what dichromatic eyes see (no orange). The image on the right is what trichromatic eyes see. (Just a note: if you can’t see any difference between the two images, you might be colour blind.)

Tigers hunt many animals such deer that can’t see orange. For a deer, tiger stripes just disappear into the background. In other words, a tiger’s bold orange and black stripes are actually evolutionary camouflage. Wild!

However, here’s a funny thing: tigers are also dichromatic, which means they can’t see their own orange fur or any other tiger’s fur! Tigers are camouflaged from each other! Double wild! This also means that tigers struggle to see the difference between a deer’s brown fur and the surrounding greenery—just like my son’s inability to distinguish green wasabi from brown peanut butter.

Luckily most primates (including us humans) have pretty good colour vision. (But most certainly not the best colour vision. Maybe I’ll write more on that later.) Scientists think primate developed colour vision for spotting ripe fruit and hungry predators like big cats and snakes. But most cats and snakes can’t see orange. In other words, this golden lion tamarin’s stunning orange fur looks greeny-brown to a tiger (good camouflage!) while the bright orange monkey has no problem spotting the tiger’s bold stripes through the jungle.

Colour is most definitely in the eye of the beholder.

I’ve always been fascinated by how we all see colour differently, especially since I was told that people who carry the colourblind gene might have extra colour perception. That’s me! I’m a gene carrier! My dad is colourblind; I carry the gene, but I can see colour. Maybe it’s all in my imagination, but I have always had the sense that I see colours differently. I’m really good at spotting animals on forest walks. If you lose a green marble in the green grass, I’ll find it. Do I see subtleties between shades differently? Is this all in my imagination? Maybe. Perhaps. Probably not. Who knows? I’ve never actually spoken to an eyeball expert. But it’s fun to think about.

In any case, if you want to test your vision, here’s an online colourblind test:

https://enchroma.com/pages/test

And here’s a so-called Ultra-Difficult Colour Test for distinguishing between subtleties of hues:

https://www.lenstore.co.uk/vc/colour-is-in-the-eye-of-the-beholder/#/

Obviously, these tests depend on the colour and quality of your computer or tablet monitor, so take it all with a grain of salt. But yes, I did get a perfect score on the Ultra-Difficult Colour Test. Ha! No tigers are ever going to sneak up on me!