Many animals, large and small, are known to avoid overhead power lines in remote regions. It’s not just that they avoid climbing on them or running along the conduit; it’s that they avoid them altogether.

And it’s not just new overhead power lines. Animals avoid these miles and miles of aerial cable even when those cables have been in the same place for more than 30 years. It’s as though the power lines are serving as some sort of invisible fence.

Over the years, researchers have advanced several possible hypothesis for this unusual observation. Is it that the lanes of open land created for these power lines (i.e. power line “lanes” in forests) makes the animals feel exposed to predators? Is it because of some sort of sound generated by the structures? Is it some combination of factors?

The mystery persists to this day, but a team of researchers from University College London (UCL), Moorfields Eye Hospital, London, UIT, The Arctic University of Norway, and the University of Oslo in Norway who conducted a study back in 2014 believe that UV emissions may be a major factor.

Reindeer and many other mammals have the ability to perceive at least some portion of the ultraviolet light spectrum. As a side note, this ability to visually detect UV radiation is actually believed to be the ancestral “default” of the vertebrate eye, but many mammals (including humans) have lost that ability over time. For those vertebrates that have retained the ability (like birds), UV sensitivity is believed to play a role in mate selection, foraging, predator avoidance, and detection of markers like urine.

In reindeer, it may also have the undesirable effect of making overhead power lines appear like distressing, chaotic sources of visual noise. As researcher Glen Jeffrey puts it, in the eyes of reindeer, lanes of power lines become “horrendous structures sending massive flashes across the sky.”

Overhead power lines can generate frequent irregular pulses (corona discharge) around components like insulators. From the human perspective, the ionization of the surrounding air can appear as nothing more than flashes of light similar to tiny bursts of blue or green colored lightning.

To reindeer, however, who are able to perceive both visible and UV light, the power lines probably appear much more distressing.

The video below provides some examples of what those discharges look like through a specialized UV+Visible light corona camera:

To reindeer, the leaky power lines may very well look like bright, almost blinding highways of bursting light stretching across the frontier. Couple that with the fact that snow reflects around 80% of the UV radiation that hits it and it’s easy to see how even though the power lines are overhead, their visual effects can reach well beyond their immediate surroundings; particularly at night or during dark arctic winter days.

This has major implications from a conservation and infrastructure planning perspective. When one thinks of the disruption to habitat caused by infrastructure, much of popular focus is on roads or dams, but this research seems to provide more support for that fact that power lines should be added to that consciousness.

In Norway, for instance, overhead power lines have been shown (PDF) to dramatically disrupt the movement of reindeer herds and create uneven impacts to the local ecology; despite the fact that they don’t technically create a physical, impenetrable barrier to the herds’ movement. The effects of that phenomenon ripple through not just the local ecology, but also into the agricultural arena (e.g. commercial herd management, grazing available for other domestic animals, pressures on local economies, etc.)

So what’s the solution? An obvious possibility is the conversion of overhead power lines to buried cables, but that would likely come with an enormous financial expense (not to mention environmental disruption). Another possibility, is improving insulation and conduit technologies to minimize unwanted discharges in overhead lines.

Regardless, addressing this phenomenon will only have long term net positive impacts for the involved animals and humans. Power companies, for instance, lose money each and every time electricity is discharged in any way other than through the our devices, so preventing these bursts of energy out into the environment has obvious benefits.

In the meantime, engineers and infrastructure planners should understand that walls can come in many forms and our narrow sensory perspective of the environment shouldn’t also limit our appreciation of the impact we have our vulnerable planet.

References and Further Reading

Douglas, R. H., & Jeffery, G. (2014). The spectral transmission of ocular media suggests ultraviolet sensitivity is widespread among mammals. (Open Access) Proceedings of the Royal Society of London B: Biological Sciences, 281(1780), 20132995.

Holdo, R. M., Fryxell, J. M., Sinclair, A. R., Dobson, A., & Holt, R. D. (2011). Predicted impact of barriers to migration on the Serengeti wildebeest population. (Open Access) PloS one, 6(1), e16370.

Tyler, N., Stokkan, K. A., Hogg, C., Nellemann, C., Vistnes, A. I., & Jeffery, G. (2014). Ultraviolet vision and avoidance of power lines in birds and mammals. (Open Access) Conservation Biology, 28(3), 630-631.

Vistnes, I., Nellemann, C., Jordhøy, P., & Strand, O. (2004). Effects of infrastructure on migration and range use of wild reindeer (PDF). Journal of wildlife management, 68(1), 101-108.

UCL News: “Invisible light bursts are keeping animals away from power lines”