Dark Skies for Birds

Columbus Downtown Night

With fall migration underway (see the migration forecast for Columbus here), Audubon’s Lights Out programs around the nation are raising awareness about the deadly effects of urban light pollution on migratory birds. Ohio is a leader in this important initiative, with programs operating in the state’s six largest cities, including Lights Out Columbus, a recipient of one of Columbus Audubon’s Conservation Grants this year. However, there is still much work to be done.

A growing body of evidence demonstrates that light pollution poses manifold hazards to birds and other wildlife. Fortunately, smart lighting decisions can protect birds during migration season and beyond without compromising human safety. During the present migration season, simply turning off unnecessary lights overnight could save the life of a southbound bird.

This warbler did not survive a building collision. It doesn't have to be like this.Birds that migrate at night, including most songbirds, are often drawn toward illuminated buildings, throwing them off course. Tragically, this often leads to collisions, many fatal. Although it is not known precisely what proportion can be attributed to artificial lights, hundreds of millions of birds perish in building collisions every year in the US. Other birds succumb to exhaustion after becoming entrapped by lights and wasting energy. This phenomenon can be observed perhaps most strikingly during New York City’s Tribute in Light, the installation of vertical spotlights displayed annually to commemorate the victims of the 9/11 terrorist attacks. Thousands of disoriented warblers, redstarts, and other migratory birds swirl around the towering beams of light, unable to extricate themselves until the lights are switched off. Their unintended participation in the tribute is no act of solidarity but fatiguing and life-threatening confusion.

Outside of the fatal risks of collision and exhaustion, city lights can threaten birds by drawing them into areas where there is less suitable habitat as well as other risks such as free-roaming domestic and feral cats. Seabirds can become so disordered by artificial lights that they become temporarily grounded, where they are vulnerable to predation, poaching, vehicular collisions, and other threats. Night lighting is a particular threat to birds that frequently vocalize during flight, such as warblers, thrushes, and sparrows; their calls lure other members of their species into danger.

The fact that artificial lights can disorient birds has been known for over a century (one study published in 1918, for example, examined bird collisions and exhaustion at lighthouses), but it assumes a much greater urgency in today’s world, in which outdoor illumination is increasing by over 2 percent each year and bird populations are plummeting.

While the Lights Out campaign is an important part of the solution, the dangers of light pollution to birds don’t end with migration. Artificial night lighting is becoming increasingly recognized as a threat to biological organisms and even entire ecosystems, with serious consequences for both resident and migrant birds throughout the year.

Window Collision Fatality in Cleveland - Photo Michelle Leighty JonesMany of us humans are already aware that nighttime exposure to bright lights, especially blue light, disrupts our circadian rhythms. This is why, for example, our computers and smartphones now come equipped with a “night shift” feature. Like us, birds are susceptible to disruptions of their circadian rhythms due to exposure to artificial light at night. One recently published study, for example, found that pigeons and magpies are prone to sleep deprivation when exposed to street and residential lighting, making them less effective at finding food and avoiding predators. Previously, independent studies of scrub jays, blackbirds, and tree sparrows have suggested that artificial night lighting lowers reproductive hormones in birds and sometimes even impedes the development of reproductive organs. And, unlike us, birds lack the option to install blackout curtains or set the lights around their habitat on night mode.

Although the full scale of the consequences aren’t yet known, artificial outdoor lighting is also impacting the timing of birds’ behavior. For many songbirds, for example, sunlight is an evolutionarily hardwired trigger to begin singing. Various studies have revealed that birds, including American robins and multiple species of European songbirds, begin to sing earlier in the night in areas with artificial night lighting. Light pollution also impacts feeding schedules. Like other predators, wading birds have been found to hunt for longer hours in areas with artificial night lighting. Whether these impacts are good or bad for particular birds, it is clear that outdoor lighting is significantly impacting the long established rhythms and timings in the natural world.

That raises the final point: in addition to its direct effects on birds, artificial light is affecting other animals and plants on which birds depend. As one notable example, light pollution has been implicated as a major driver of today’s “insect apocalypse”, with insectivorous birds already facing severe declines. Outdoor night lighting also reduces the activities of nocturnal pollinators, with damaging consequences for plant communities and the birds that depend on them. Here in Columbus, the Ohio State University’s Stream and River Ecology Lab is collaborating with the Ohio Department of Transportation to study the effects of light pollution on aquatic ecosystems like rivers, streams, and wetlands. The research team has already shown artificial light to be associated with reduced food chain length in invertebrate communities, a consequence likely to adversely impact the functioning of the ecosystems.

On the bright side — so to speak — light pollution is one of the easiest forms of pollution to clean up. After all, it takes only the flip of a switch to eliminate unnecessary outdoor lighting.

Of course, it would be impracticable and unreasonable to turn off all outdoor lights. However, some lighting choices are much better than others for birds and the environment. One of the most bird-friendly lighting strategies is to shield fixtures to keep illumination directed downward (where we need it) instead of upward (where we generally don’t). In addition to disorienting hundreds of millions of migratory birds each year, upward-directed light is scattered and amplified by clouds, increasing biologically disruptive light pollution over cities and beyond (a drastic effect that one can witness nearly every evening during a typical Columbus winter). 

Opting for dimmer lights is, of course, another way to mitigate light pollution. Moreover, despite the common conception that greater brightness equates to greater safety (for humans if not birds), dimmer lights can improve human safety by reducing glare. The color of light also plays a role. Just like setting your phone to night mode, choosing lighting with less blue light can lessen adverse effects on the biological rhythms of both people and birds (the International Dark-Sky Association recommends color temperatures of 3000K or less). That said, the best color for bird-friendly lighting is still a matter of investigation, with some evidence that red light disrupts migratory birds by interfering with their magnetic orientation. Thus, for now, the safest bets for birds are to turn off unnecessary nights (or use motion sensors or timers), choose lights that are less bright, and keep lights shielded and directed only where needed. 

Finally, it should be kept in mind that indoor lights also contribute to light pollution when used near uncovered windows. This too has a simple and safe solution: install blackout curtains or other opaque window coverings to keep indoor light indoors, and turn off unused interior lights.

If you’ve already done your own part to reduce light pollution and protect birds (cheers to you!), additional steps include talking to your neighbor and supporting municipal lighting ordinances

These measures come with an added bonus (besides lower utility bills): less light pollution makes it easier for us to see the same stars that guide our favorite feathered migrants.

Window Collision Victims in Cleveland 2017-10-26