Birds, Light, and Night

By David Cronenwett

Each time I open my laptop to put this column together, I am greeted by a bright, glowing screen. The technology of the blue, light emitting diode (LED) makes all cell phone, computer and flatscreen television displays as well as the newer and highly efficient LED “lightbulbs” possible. Three scientists were recently awarded the Nobel Prize in physics for this achievement, which paved the way for the now ubiquitous screen and household-lighting technology. In nearly every way LEDs are superior over conventional incandescent and fluorescent lighting using a fraction of the energy of other means and now, very inexpensive to manufacture and purchase.

However, as we generally find, there is often a flip side to every new and promising technology. It turns out that the “blue spectrum” of visible light produced by our many screens and devices cause our brains to inhibit the production of melatonin, a hormone that strongly regulates the body’s 24-hour circadian clock. When this biological rhythm is disrupted, it affects mental health, the immune system, and the ability for the human body to heal. Sleep researchers suggest that our penchant for reading on tablets and smartphones prior to bedtime is about the worst thing one could do to ensure the many benefits of a sound night’s sleep.

Of course, a profusion of artificial light can be found across large swaths of the United States as NASA satellite images in recent years have plainly revealed. The human health concerns related to light pollution are becoming better understood and so are the effects of over-illuminated landscapes on wildlife, particularly birds. Scotobiology is a relatively new discipline that examines how wildlife and natural systems respond to anthropogenic light pollution.

Many bird species have evolved to migrate during the night, mostly to avoid detection by raptors. During this time, they are extremely vulnerable to the powerful effects of glowing lights from large urban areas, which can effectively turn night into day along some flyways. National Audubon estimates that roughly 100 million birds (probably a conservative estimate in my view) are killed annually from direct collisions with illuminated buildings, broadcast towers and other structures around the country. The hypnotic draw of artificial light can pull birds from miles away. When shark researchers on the Gulf coast began finding large numbers of songbirds like tanagers and meadowlarks in the stomachs of their specimens, they suspected something was up. Further investigation found that thousands of brightly lit offshore drilling platforms in the Gulf were causing neotropical migrants to be pulled far off course, toward the glow. The birds would then circle the platforms until exhausted and then fall from the sky, becoming shark food.

I witnessed similarly disturbing behavior one November night during the autumn snow geese migration in Montana; heading south from their stopover at Freezout Lake, several thousand birds became disoriented by a combination of an unusually low cloud cover and sky glow from Helena. The geese became obviously transfixed and confused, squawking and circling the city lights for hours. This is an enormous waste of energy that long distance migrators like snow geese can ill afford and some may have ultimately perished on their long journey because of the incident.

Besides outright collision and disruption during migration, excess lighting from the roadways and buildings of human communities can cause more subtle problems for birds. For example, the behavior of night hunting species like owls can be severely impeded by artificial light and give advantages to other, normally diurnal raptors, whose hunting niche is expanded by greater visibility at night. Another example comes from a 2014 Austrian study of five songbird species investigating the link between excessive, artificial light and reproduction. Because female songbirds tend to select mates who are the first to begin singing and displaying in the morning (a sign of vigor and dominance) and because artificial light causes more males to begin singing hours earlier and therefore longer than they would naturally, some females inevitably end up accepting mates with lower quality genes. This could have longer term impacts for the survival of the species. Also, since male birds exposed to the “endless daylight” of a modern city tend to engage in much more active mating behavior than normal (singing, displaying, defending territory), they tend to get less sleep and expend much more energy, which can ultimately produce greater mortality. We are now finding that light pollution has many profound and unintended effects on ecological systems.

Our impulse to illuminate the natural nightscape probably stems from many things, including a fear of both nature and other humans, but it appears that the cost to this fear is exacted from our health and quality of life. A growing body of evidence supports the view that living creatures are most healthy when their experience of the natural 24-hour cycle of light and dark is most intact. There are other reasons to turn down the lights too such as energy conservation and lest we forget, preserving our collective inheritance of the universe in its evening glory.

Of all the overwhelming, depressing conservation problems of our age (climate change, habitat loss, etc.) the restoration of the natural nightscape is a refreshingly easy fix; lights can be shut off, put on motion sensors, directed downward where needed and changed out to produce light that is not in the harmful blue-white spectrum. From improving human health to the conservation of night for wildlife and wild places, reducing light pollution is an issue that is win-win for all involved.