The polar bear (Ursus maritimus). If asked to describe one I think I could take a good guess that we would all state the obvious, in that that it is a very cute, very large, white bear. So what if I told you that this icy predator technically isn’t as white as you may have first thought….
As the planets largest terrestrial carnivore in such an open landscape, they face the challenge of discretion when hunting its scarce prey. To aid its success the polar bear maintains its white coat appearance all year round, unlike some other artic mammals who have darker coats during the summer months, to provide camouflage against the icy background. However, their coat actually contains no white pigment. Polar bears have both an under-coat layer and a guard coat layer to their fur. Believe it or not, these layers of fur consist of transparent hairs. The guard hairs are made up of keratin, the hollow medulla of which are filled with air and light scattering particles.
Each time a sunbeam contacts the transparent guard hair, some of the light energy gets trapped within the hair, and collides with the light scattering particles that disrupt and disperse the beams of light into different directions towards other light scattering particles. This creates a continual emission of whitish light from the fur giving the polar bear its white appearance to help conceal itself against its environment. This reaction is known as luminescence and is further increased by the salt particles caught between their hairs when swimming. The salt particles also act as light scattering particles thus increasing the amount of light being dispersed and therefore increasing the amount of whitish light being emitted.
The fluorescence reaction that occurs when the UV light from the sun’s rays contacts the bears dark skin at the base of the guard hairs, also produces a whitish pigment. Furthermore, the keratin molecules within the hair are slightly off white in colour, which when combined with the fluorescence and luminescence, additionally contributes to the polar bears overall white appearance.
So, there you have it. The science behind the coat of a polar bear. I hope you guys found it as interesting as I did when I studied it! If you like these ‘fun fact’ kind of posts, please let me know in the comments below as I am more than happy to cover more species! Our natural world is full of fascination after all!