Their thick coats, made of hollow hairs that trap heat close to their bodies, offer excellent protection against extreme cold. Their broad, concave hooves are designed to help them traipse through wintery terrain, and they are the only deer species in which both males and females sport antlers. Plus, a keen sense of smell helps caribou search out nutritious lichens buried beneath thick blankets of snow.
Arctic Eyes
In 2011, researchers at University College London set out to study how well caribou are adapted to another extreme factor in their habitats: Arctic light.
These mammals live through long, dark winters followed by long, bright summers. They’re also exposed to high levels of ultraviolet (UV) light, both because of the way light is scattered in the Arctic atmosphere and because snow- and ice-covered surfaces are highly reflective, bouncing back up to 80 percent of the UV light that hits them. Unlike humans, Arctic mammals show no evidence of snow blindness, a painful condition caused by overexposure to UV light that is actually a sunburn of the cornea.
Given these extreme conditions, the researchers wondered: do reindeer sense and process UV light? As it turned out, the study revealed that reindeer were able to see light wavelengths around 350-320 nanometers (nm), well outside of the so-called visible spectrum. And the ability to see the shorter wavelengths, researchers realized, gives caribou an important advantage in their harsh environment.
Lichens and Things
In springtime, caribou diets include grasses and leaves from willow and birch trees. But in winter, these mammals’ best bet for a meal is lichens, which they process with the help of a special bacteria in their gut.
And lichens, it turns out, absorb UV light, appearing black in a sea of highly reflective snow and giving these UV light-seers a big lead in their quest for a meal—an important part of surviving the Arctic.