Reindeer are fascinating animals that live in some of the harshest environments on Earth. They have adapted to survive the long and dark winters of the Arctic, where finding food and avoiding predators can be challenging.
One of their most remarkable adaptations is their ability to see ultraviolet (UV) light, which is invisible to humans and most other mammals.
Reindeer's Favorite Food: Lichen
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Reindeer mainly feed on lichen, a type of organism that is composed of algae and fungi living together in a symbiotic relationship.
Lichen can grow on rocks, trees, and soil, and can survive in extreme conditions. Reindeer prefer a specific kind of lichen called reindeer moss, or Cladonia rangiferina, which grows in thick, white carpets across the Arctic tundra.
Reindeer moss is rich in carbohydrates and provides energy for reindeer during the winter, when other plants are scarce or buried under snow.
However, finding reindeer moss in the snow can be difficult, especially in the low light of winter. To the human eye, the white lichen blends in with the white snow, making it hard to distinguish.
But to reindeer, the snow and the lichen look very different, thanks to their ability to see UV light.
Reindeer's Secret Weapon: UV Vision
UV light is a type of electromagnetic radiation that has a shorter wavelength and higher energy than visible light. UV light can cause sunburns and skin cancer in humans, and can damage the eyes of most animals.
That is why most mammals, including humans, have a protective layer in their eyes called the lens, which filters out most of the UV light and prevents it from reaching the retina, the light-sensitive tissue at the back of the eye.
However, reindeer have a different eye structure that allows them to see UV light. Their lens is more transparent to UV light, and their retina has more cells that are sensitive to UV light. This means that they can see a wider range of colors than humans, from violet to ultraviolet.
But why would reindeer need to see UV light? What advantage does it give them in their environment?
Researchers from Dartmouth College and the University of St. Andrews in Scotland have found some possible answers.
They discovered that reindeer moss and some other lichen species that reindeer eat absorb UV light, while snow reflects it. This means that to reindeer, the lichen appears as dark patches against a bright background, making it easier to locate.
The researchers also found that the fur and urine of wolves, one of the main predators of reindeer, also absorb UV light, while the fur of reindeer reflects it. This could help reindeer detect and avoid wolves in the snow.
The researchers used spectral data from the lichen and light filters calibrated to mimic reindeer vision to get a visual approximation of how reindeer might see the world.
They also observed the behavior of reindeer in the Cairngorms mountains in the Scottish Highlands, where Britain's only reindeer herd lives.
They found that reindeer were more likely to choose lichen that absorbed UV light over lichen that reflected it, and that they were more alert and vigilant when exposed to UV light.
Reindeer vision is an example of how animals can evolve to adapt to their environment. Evolution is the process of change in the inherited characteristics of populations of organisms over time.
Evolution occurs through natural selection, which is the differential survival and reproduction of individuals with certain traits that make them better suited to their environment.
Reindeer vision may have evolved in response to the unique challenges of living in the Arctic, where UV light is more abundant and where food and predators are hard to see in the snow.
It may have given them an edge over their competitors and enemies, and helped them survive and thrive in their habitat.
Their vision also shows us how diverse and wonderful life on Earth is, and how different animals perceive the world in different ways.
Reindeer are not the only animals that can see UV light. Some birds, insects, fish, and reptiles can also see UV light, and use it for various purposes, such as finding food, mates, or predators.
Humans can only see a small fraction of the electromagnetic spectrum, and we may never fully understand how other animals see the world.
But by studying their vision, we can learn more about their biology, ecology, and evolution, and appreciate the beauty and complexity of nature.
