Reindeer can see in ultraviolet, say boffins
Very useful for not eating the yellow snow, apparently
Reindeer can see much further into the ultraviolet than humans can, according to new research. This is thought to offer the antler-sporting capreolines several important arctic survival abilities.
"We discovered that reindeer can not only see ultraviolet light but they can also make sense of the image to find food and stay safe," says top reindeer boffin Professor Glen Jeffery. "Humans and almost all other mammals could never do this as our lenses just don't let UV through into the eye."
According to pioneering research by Jeffery and his team, reindeer can see wavelengths as short as 350 or even 320 nanometres, well beyond the human limit of 400: such frequencies would be "black light" to us.
Apparently the ability to see in the ultraviolet is pretty handy up in the frozen north, where the sun seldom gets far above the horizon. This means that a lot of the light available has arrived by atmospheric scattering rather than directly, and as such it is blue or ultraviolet (the sky is blue rather than white or red for the same reason).
Nonetheless it might appear that UV vision would be of little use in northerly climes, as the prevalent snow cover reflects it and everything would tend to look white. Not so, according to Prof Jeffery:
"When we used cameras that could pick up UV, we noticed that there are some very important things that absorb UV light and therefore appear black, contrasting strongly with the snow," he explains. "This includes urine – a sign of predators or competitors; lichens – a major food source in winter; and fur, making predators such as wolves very easy to see despite being camouflaged to other animals that can't see UV."
The ability to avoid eating the yellow snow even in dim lighting certainly seems worthwhile on its own.
Apart from a greater understanding of reindeer, Jeffery thinks that the research might offer insights into human eyesight. Not only can humans not see in the ultraviolet, UV actually damages our eyes – for instance in the phenomenon of "snow blindness" where UV glare off snow can temporarily render the front parts of the eye cloudy or even opaque.
"The question remains as to why the reindeer's eyes don't seem to be damaged by UV," says Jeffery. "Perhaps it's not as bad for eyes as we first thought? Or maybe they have a unique way of protecting themselves, which we could learn from and perhaps develop new strategies to prevent or treat the damage the UV can cause to humans."
Jeffery and his team's research is published in the Journal of Experimental Biology. ®