Nature

20
Mar

Power Lines Look Like Terrifying Bursts of Light to Animals

What does a power line look like? To humans, they don’t look like much—just strands of metal draping from towering poles. But for many animals, they’re terrifying.

They see power lines as lines of bursting, popping lights. That’s because they can see ultraviolet light that’s outside the spectrum of human vision. According to recent studies from scientists in the United Kingdom and Norway, It suggests high-voltage lines have more potential to disrupt wildlife behavior than previously thought.

corona-discharge-power-lines
The corona discharge seen here is off a corona ring of a 500-kV high-tension line, which is mean to limit corona discharges. But they don't eliminate all of them.

These blazes of light are called corona discharge. They happen where the power lines aren’t well-shielded, and the concentration of electrons rushing through the line causes the nearby air particles to ionize. This forms a brief cascade of glowing plasma that sporadically triggers a burst of ultraviolet light.

Scientists have known for decades that birds can see UV light because their eyes have an extra type of cone cell specifically tuned to detect those wavelengths. But UV light—and corona discharge—is invisible to us. Each of the three types of cones in our eyes isn’t all that sensitive to UV light. There’s no evolutionary reason for them to be because our lenses filter most UV light before it even reaches our retinas. To get a sense for what the discharges might look like, we need special digital cameras.

Helicopter inspections of high-voltage power lines use special UV sensors to detect corona discharge.

With UV vision, birds see a much different world than we do. Feather patches that to us seem an unremarkable shade of blue scream brightly in UV. Birds can hunt their prey by following urine trails, which reflect UV light. But with the exception of some rodents and marsupials with a fourth type of cone, we didn’t see a way that mammals could access this extra dimension of color.

Or so we thought.

In a study published earlier this year in the Proceedings of the Royal Society B, scientists analyzed the eyeballs of 38 different mammalian species. What they found suggests that most mammals can, in fact, see UV light—including dogs, cats, ferrets, and reindeer. Unlike humans, these mammals have lenses that allow UV light though. Even though they lack the specialized UV-sensitive type of cone, the other three kinds of cones can combine to make up for it. (In fact, when people have the lens in their eyeballs removed—either through injury or surgery—they’re able to do the same trick, and report seeing UV light as something like a pale violet.)

Nathanael Boehm | Reindeer | Flickr | CC
Reindeers can see ultraviolet light.

This anatomical discovery could have major ecological impacts. Damian Carrington, writing for the Guardian:

“It was a big surprise but we now think the majority of animals can see UV light,” said Professor Glen Jeffery, a vision expert at University College London. “There is no reason why this phenomenon is not occurring around the world.”

[Dr Nicolas Tyler, an ecologist at UIT The Arctic University of Norway and another member of the research team] said the discovery has global significance: “The loss and fragmentation of habitat by infrastructure is the principle global threat to biodiversity – it is absolutely major. Roads have always got particular attention but this will push power lines right up the list of offenders.” The avoidance of power lines can interfere with migration routes, breeding grounds and grazing for both animals and birds.

One example is reindeer, whose habitat has become severely fragmented by growing infrastructure in the Arctic, including power lines. Up to now, though, exactly why reindeer avoided power lines was a mystery. But in the dark arctic winters, such light reflecting off the snow can be blinding.

Reindeer aren’t alone in their avoidance of power lines. We’ve long known that many animals avoid crossing high-voltage corridors, but blame was placed mostly on the change in habitat configuration—the mowed vegetation below the lines is often substantially different from the surroundings. That hypothesis is likely valid for some animals, but this new data on corona discharge suggests the problem is more complex than we originally thought.