Researchers know that high-voltage power lines have some strange influence on animals. Creatures from reindeer to elephants to birds tend to avoid the areas around power lines. This was mysterious because the structures seem passive and simple to walk or fly past. However, scientists now say this may be because power lines emit ultraviolet light, invisible to human eyes, that appears as frightening flashes to animals that can perceive ultraviolet light. This paper is the first to offer a simple explanation for the power line-avoidance behavior. If true, the theory could explain fragmentation of wild habitats. Seeing the Light Humans, in the scheme of things, only see a very small percentage of what’s happening in the environment. Of the entire electromagnetic spectrum, only about 0.0035 percent of it is visible to humans. Many mammals, on the other hand, can perceive ultraviolet (UV) light—including cattle, cats, dogs, rats, red pandas and hedgehogs. In fact, humans and monkeys are among a small minority of mammals that can’t see UV. We also know that high-voltage power cables cause a build-up of ionized gases around the outside of the cable, which causes random flashes of UV light as the gases, or corona, dissipate. Power companies do what they can to prevent corona emissions because it wastes energy, but they can’t insulate the wires enough to prevent every emission. Wild Reindeer Both these facts are known, but the new paper from a team of researchers in Norway tied the two pieces together to explain habitat fragmentation. They focused on wild reindeer in southern Norway, where there are now 23 distinct populations of the species as a result of habitat fragmentation. Reindeer have reflective surfaces in the back of their eyes that help them see UV light, which is an adaptation especially important in long and dark Norwegian winters. Drawing on this and other anatomical evidence, scientists deduced that reindeer likely strongly perceive power lines and become conditioned by this fear to avoid them, even during the daytime. The findings were published last week in the journal Conservation Biology

. Study co-author Glen Jeffery told The Independent:

“Reindeer see deep into the UV range because the Arctic is especially rich in UV light. Insulators on power lines give off flashes of UV light…The animals potentially see not just a few flashes but a line of flashes extending right across the horizon. This is the first bit of evidence that explains why we think they are avoiding power lines.”

The scientists’ findings cast new light on the impact of human development, and could explain why habitats are fragmenting for many other species around the world.

Image by BMJ / Shutterstock