The Blue-Light Special

There is a bit of a territory dispute in the sky. Once the realm of only birds and bats (and pterodactyls once upon a time), the sky now hosts millions of humans as they shuttle themselves across the globe—constantly. Unfortunately, birds often find themselves in the way.

Since 1990, aircraft over the United States have collided with birds more than 127,000 times (and those are only the reported cases). Those meetings of metal and feathers caused 223 human injuries and 23 deaths between 1990 and 2011, and have cost the airline industry about $700 million a year.

Of course, that’s the issue from our perspective. From the bird’s-eye view, the death toll is much, much higher. After all, a seagull isn’t likely to fly away from an encounter with a fighter jet (see clip below).

According to a report from the U.S. Department of Agriculture, the number of collisions is going up, up, and away—likely a result of rising populations of large birds, more wildlife inhabited open spaces around airports, and quieter aircraft.

Aside from being whacked out of the air by, in the case of Dr. Jones, a gargantuan deus ex machina, birds also suffer from preemptive strikes. The USDA’s Wildlife Services killed around four million animals in 2013 alone, citing conflict with livestock, crops, and proximity to airports the most common reasons for execution. On a list of the 10 animals most often killed by the government, birds take up half the spots.

Now a team of scientists is working on a new way to warn birds away from our sky machines before it’s too late—a method so simple, implementation would cost very little. In fact, let’s call it the blue-light special.

Our feathered friends have four types of photoreceptors, while humans have just three. According to Esteban Fernandez-Juricic, an ecologist at Purdue University and coauthor of a paper in the April issue of The Condor: Ornithological Applications, the additional receptor allows birds to not only see more colors than we do but also colors we cannot even imagine. For birds, for instance, shades of blue come in way better.

White lights are the most commonly studied and used, which is why the Federal Aviation Administration regulates them. Studying how birds react to white light, however, is problematic, because white light isn’t actually white—it’s a combination of wavelengths across the visible spectrum.

So, when a bird responds to what we see as white light, it might actually be to taking its cue from any number of wavelengths. In other words, birds don’t see what we see. That’s why adorning aircraft with lights designed for bird vision—say, blue lights instead of white—might be able to make the skies a little safer.

To test this hypothesis, Fernandez-Juricic and his colleagues scoured the literature for an avian species with a well-studied visual system, and settled on the brown-headed cowbird. This North American songbird also happens to be on that Wildlife Services Most Wanted Dead or Gone list. (In 2013 the agency euthanized 850,505 cowbirds and dispersed another 200,000.)

Combining the research on the bird’s eyes with some fancy mathematical modeling, the Purdue team determined that the most conspicuous wavelength for cowbirds falls around 470 nanometers. For us, this wavelength appears blue. (A little further down the spectrum and we’d hit ultraviolet, which birds can also see.)

The researchers then slapped blue lights on the wings of a five-by-four-foot, remote-control airplane and conducted fly-by trials. Interestingly, these trials took place during the day, since more than 51,000 bird strikes have been recorded during the day over the last 22 years, about twice as many as at night. After seven months of buzzing the bird tower, the team was able to deduce some patterns.

According to their study, when the wing and taillights were off, the birds didn’t react to the aircraft when it was flying by at high speeds, something called speed effect. When the researchers switched the blue lights to a pulsing pattern, the speed effect was a little better but not by much.

“The surprise was that when the lights were steady, the speed effect went away,” says Fernandez-Juricic. “In other words, the birds no longer had difficulty detecting the aircraft at different speeds.”

Now, before you go advocating for a society lined in blue light, the scientists say there’s still more work to be done. For starters, one bird retina doesn’t fit all. Different species may require longer or shorter light wavelengths in order to notice a speeding plane. (Songbirds generally tend to have less-advanced vision than other kinds of birds, like waterfowl and raptors.)

Some lights, particularly those of the red variety, might actually attract birds. One study found that solid red lights on transmission towers are responsible for the deaths of seven million birds each year. So we will need to make sure we aren’t repelling one species from airplanes only to lure another to its—and possibly, the pilot’s—doom.

The Purdue team was also limited by what types of lights were commercially available and able to fit on a remote-controlled airplane. Ultraviolet lights, for instance, might be even more effective than blue ones.

Furthermore, once we’ve installed deterrent lights on airplanes and runways, there’s a chance the birds will become accustomed to them and no longer see them as harbingers of danger. (This is also a potential explanation as to why a plane’s noise is not enough to keep birds away. If you live near an airport where loud engines are ever-present, you eventually stop flinching when you hear one revving by.)

Still, we’ve got to try something. Airplanes aren’t our only ambassadors into the sky. Skyscrapers, wind turbines, cell phone towers, and sports stadiums can also be deadly obstacles for which birds and bats have not yet evolved to navigate around. Together, they are sending bird numbers into a down spin.

Humanity’s ascendance into the heavens is proof of our problem-solving skills. Now that we’re up there, let’s work on keeping those skies friendly—for all of us.