Dec. 19 - Scientists have discovered that the colour of Arctic reindeers' eyes change dramatically between summer and winter, as they adapt to extreme changes of light intensity. The researchers say it's part of the animals' defence strategy, although for Santa's reindeer, they say it could also pose problems during next week's round-the-world present delivery marathon. Jim Drury has more.
The Arctic reindeer is best known for helping Santa Claus deliver Christmas presents to the world's children. But it also possesses an evolutionary pecularity, according to scientists from University College London and the University of Tromso. The reindeer's eyes change colour to cope with the extremes of Arctic light conditions - from gold in summer to a deep blue in winter. The findings surprised lead researcher Professor Glen Jeffery. SOUNDBITE (English) GLEN JEFFERY, LEAD RESEARCHER, SAYING: "There was a clear distinction between summer and winter eyes and we were completely shocked by that. We'd never expected it, it was the last thing we were looking for, but it was the most obvious thing that you saw when you opened the eyes. Big colour change." Jeffrey's team make annual winter trips to the Arctic to examine reindeer eyes bought from slaughterhouses. But this year they travelled earlier than usual and by accident, discovered the colour change - the first ever spotted in a mammal. A layer of tissue called the tapetum lucidum lies behind the retina and reflects light back through the eye to enhance night vision. By changing its colour the tapetum can cope with either extreme darkness or extreme light. The team also placed gold electrodes underneath the eyelids of live, sedated reindeer in order to see their visual threshold. The findings suggested the colour change may be caused by pressure within the eyes. In winter, seasonal pupil dilation compresses the tapetum, allowing the shorter wavelengths of the blue light common in Arctic winters to be reflected. Jeffery says the reindeers' winter eye allows it to detect predators moving in the darkness. SOUNDBITE (English) GLEN JEFFERY, LEAD RESEARCHER, SAYING: "That is the primary problem for the reindeer. 'Can I see something moving? That is a potential threat. I've got to run, I've got to move.' So he needs to be sensitive to low light levels and he needs to be sensitive to movement at low light levels." But for Santa's reindeer, that seasonal sensitivity could pose problems on Christmas eve. SOUNDBITE (English) GLEN JEFFERY, LEAD RESEARCHER, SAYING: "When Rudolf comes down from the Arctic he's going to be very very dark adapted and he's going to have a blue eye and the one thing we don't want Rudolf to do is to come up against a whole load of street lights and a whole load of front room lights, so a good thing if you want Rudolf to call in at your place might be draw the curtains, so he doesn't get glared by all the light." ...although it's also possible that Santa himself has adapted, and equipped his sleigh with sunglasses.