I held my breath as I lowered myself into the swift, cold waters of Central Oregon’s Metolius River. What had been a welcome relief from the heat of the day was now a frigid—and somewhat dangerous—task.
But what brought me to the Metolius wasn’t its chilly, spring-fed waters, but its darkness. I study how artificial light—largely from streetlights, sports fields, billboards and the like—affect animals that live in rivers. Sometimes my work focuses on fish like trout or salmon, but my current research is investigating how larval aquatic insects such as mayflies and stoneflies might change their behavior in response to exposure to light over several generations.
Not many people think much about the insects that live in water, but they play a key role in their ecosystem. They are an important source of food not only for fish, but for terrestrial animals like songbirds and bats as well—but it’s their interaction with fish I am most interested in. In order to avoid being eaten, these larval insects will move through the water, or “drift,” only when it is dark and the fish can’t see them. Even the light from a full moon is enough to prevent them from drifting. But larval mayflies and stoneflies in urban streams are exposed to light levels greater than a full moon every night, thanks to artificial light.
That’s why I’m here, at night, at this beautiful, wild and dark river: I’m sampling rivers across a light gradient to see if the insects in streams that have been exposed to light at night for many years are equally likely to drift during the day as during the night, while those in dark areas still wait until darkness falls.
After a moment, the initial shock of the icy water subsides and I turn my attention to setting up my drift net. The current is strong and the water hits me mid-thigh. It would be dangerous to slip and fall, so navigating the stream by my headlamp demands my full concentration. Once the net is set and I’m back on dry land, I’m able to turn off my headlamp and let my eyes adjust to the pervasive darkness.
Edward Abbey wrote in Desert Solitaire how using a flashlight isolates us from the natural world, and my experience on the Metolius supports that assertion: my eyes quickly adapted to the bright beam of my headlamp and made everything outside of its small beam even darker and more frightening. When I turn the light off, I feel a tingle of fear; everything looks black. But as I allow my eyes to adjust to the natural sky (I’m doing this research while there is no moonlight) I can actually make out quite a bit of the landscape, and it becomes less unnerving. Gradually, the Milky Way comes into focus, and I am instantly connected to the view my ancestors saw thousands of years before me.
Sadly, this view is one not many in the developed world get to experience any longer. Almost 80% of North Americans and 60% of Europeans live in areas where light pollution prevents them from seeing the Milky Way.
I have experienced the loss of the dark in a very visceral way. I grew up on a farm about 30 miles outside of Portland. When I was a small child, my mom used to take my brothers and me out at night to yip and howl at the full moon in chorus with the coyotes, or to admire the Milky Way. Now, just 25 years later, the dome of light emanating from Portland has completely overwhelmed the stars. The Milky Way is no longer visible, though the coyotes still yip and howl at the full moon. They are resilient animals.
It remains to be seen how resilient our river organisms are. My current research will help provide some insight into that question, though previous work by myself and others suggests that all of us would be better off with more darkness in our nights.
After completing her doctoral studies in river ecology in Germany, Liz Perkin returned to the Pacific Northwest to enjoy some of the darkest skies in the developed world. She will join the faculty of Maryland’s McDaniel College this fall as a visiting professor, and is looking forward to driving across the country and seeing the rivers and night skies of the United States.