It’s surprising that more animals don’t crash into power lines. The wires don’t look like much of a barrier, yet scientists have found that animals will avoid them even after they’ve been in place for 30 years. This suggests it is not the human presence, noise, or other construction-related disturbances that keep them away. Why aren’t birds and other creatures accidentally wreaking havoc on electric grids around the world?

Last week, researchers in Norway and the United Kingdom proposed an answer. In a report published in Conservation Biology, the scientists wrote that animals’ avoidance of power cables is likely linked with their ability to detect ultraviolet light. While the spectrum of light emitted from the lines is beyond what humans can see, it is visible to birds, rodents, and reindeer. These animals may see power cables as randomly flashing bands. The scientists write:

We suggest that in darkness these animals see power lines not as dim, passive structures but, rather, as lines of flickering light stretching across the terrain. This does not explain avoidance by daylight or when lines are not transmitting electricity … but it may be an example of classical conditioning in which the configuration of power lines is associated with events regarded as threatening.

The video below uses a UV-sensitive camera to approximate what the phenomenon looks like from the point of view of many animals. In fact, the flashing is probably even brighter to them.

It has been known since the 1970s that birds can see UV light, and more recent studies have shown that many (mostly small) mammals can, too. Reindeer, more so than many other large mammals, have retinas that are adapted to living in the dark, which helps them forage for food during long Arctic winters. That, combined with the fact that UV light is more visible in snowy landscapes due to reflection, means that reindeer are particularly sensitive to the apparent flashing of power cables.

The study implies that above-ground power cables could be having an effect on wildlife across the globe. Just as roads are known to break up habitats and interrupt migration routes, power lines might now be on “the list of offenders,” in the words of Norwegian team member Nicolas Tyler. The cables probably interfere with migration routes, breeding grounds, and grazing areas, which could fragment natural habitats and cause herds to shrink. The ramifications of such disruptions on local ecosystems have been studied in some areas, including the Serengeti.

The most immediate impact of the new research is likely to be in Norway, where a plan to construct a 186-mile-long power line through the northern part of the country has come under pressure from reindeer-herding locals. The new research gives herders more reason to care where the power lines go. More broadly, it lends additional support to environmentalists and others who seek to keep wild areas pristine and cable-free.