To keep birds from striking aircraft, think like a bird

On the afternoon of January 15, 2009, US Airways Flight 1549 took off from New York’s La Guardia Airport bound for Charlotte, North Carolina. Several minutes after taking off, the aircraft’s engines met with a flock of Canada geese. In airplane parlance, it’s called a “bird strike,” and the Airbus A320 hit enough birds to take out both of its jet engines. After realizing that the plane was unable to land at LaGuardia or nearby Teterboro Airport in New Jersey, the plane’s crew decided that the safest thing would be to land in the Hudson River near midtown Manhattan. All 150 passengers and 5 crewmembers survived the crash, but the birds were (obviously) not so lucky.

More than 127,000 bird strikes have been reported in the US since 1990, and the number of unreported strikes is likely much higher. Economic losses due to bird strikes average some $700 million each year in the US, and the collisions pose safety risks to passengers and aircraft operators. From 1990 to 2011, they led to 23 deaths and 223 injuries. And, of course, bird strikes are an important source of mortality for birds. And when those birds are threatened or vulnerable – like the endangered Hawaiian duck or the Tasmanian wedge-tailed eagle – then bird strikes become a conservation concern as well. As the number of routes and flights increases, the threat to birds and passengers also increases.

To try to limit the occurrence of bird strikes, airports have implemented a variety of measures with mixed levels of success. The problem is that bird strikes can occur high in the air, far away from an airport, as was the case with US Airways Flight 1549. The best strategy would be to outfit the aircraft themselves with means of minimizing the likelihood of a bird strike. At the present, there are no good, specific ways of doing so.

As far back as the 1970s, researchers proposed that properly tuned lights could be useful deterrents for birds. All experiments ever conducted have used white light, and have had mixed results.

That could be because bird eyes and human eyes work differently, and what’s obvious to a human may not be obvious to a bird, and vice versa. And, even where white light is effective, it isn’t necessarily clear why, because white light is a mix of other wavelengths, and the birds could be sensitive to just one or a few of those wavelengths.

Birds typically have four types of cones in their eyes, compared to the three that humans possess, which allows them to perceive a wider range of colors. They have oil droplets that coat their photoreceptors, which filter incoming light to provide even greater color discrimination abilities. And they can perceive ultraviolet light. If researchers can tune a light beacon the birds’ own visual systems, then they might be able to minimize the chances of a strike. If effective, such a beacon could also be used on tall buildings or wind turbines, other important sources of mortality for birds.

To get a better sense of what lights might be good for keeping birds from getting sucked into and pulverized by jet engines, Purdue University biologist Megan S. Doppler turned to brown-headed cowbirds (Molothrus ater).

Cowbirds are among the types of birds implicated in bird strikes and are a good species to test because their visual system itself has been extensively studied. Doppler and her colleagues rounded up a bunch of the birds and flew remote-controlled airplanes at them with different types of LED lights on them, in different colors, which were either solid or flashing. She also tested their responses to stationary RC airplanes with the same variety of LED lights. All tests took place during the daytime since most bird strikes take place during the day, and all tests were conducted in an open grass field to approximate a more naturalistic environment than what could be done inside a laboratory.

They determined that of all the commercially available LED lights, the most effective color – that is, the most conspicuous given the cowbirds’ visual system – had a frequency of 470 nanometers (you’d see it as “blue”). They noticed a stationary aircraft more quickly if it had those lights on (whether static or flashing) than if it had its lights off.

Most animals, including humans, are slower to notice approaching objects when they’re moving faster. By the time that animal becomes alert, the approaching object might be too close to effectively avoid it. Doppler and her colleagues found that pulsing lights helped to mitigate that, allowing the birds to become aware of the rapidly approaching aircraft sooner than they would have otherwise. Continuous, static lights, however, were far more effective for fast-moving aircraft.

They also discovered that higher ambient noise levels delayed the cowbirds’ avoidance responses, suggesting that the sound of the aircraft (compared with the ambient acoustic environment) is also an important factor to consider.

One might see these results and immediately decide that aircraft, airports, skyscrapers, and wind turbines, should be outfitted with continuous, non-flashing blue lights. But this was just a first experiment, and more research, with a wider variety of species involved in bird strikes, must be carried out first. Do resident birds respond differently to lights than migratory ones? What about diurnal versus nocturnal species? How might birds’ perceptual preferences differ when approached by a fast-moving object like an airplane versus when they rapidly approach stationary objects like buildings or wind turbines?

Still, the researchers tentatively suggest that dual strategies will probably wind up being useful: airports might consider stationary lights alongside airport runways, timed to sync with taxiing, while the aircraft themselves might be outfitted with lights that can be altered depending on the plane’s location. For example, they might be most effective if flashing during taxiing but static during takeoff and while in flight.

As ever, the bottom line is that to deter birds from striking aircraft, one must learn to think like a bird. – Jason G. Goldman | 17 April 2015

Source: Doppler M.S., Bradley F. Blackwell, Travis L. DeVault & Esteban Fernández-Juricic (2015). Cowbird responses to aircraft with lights tuned to their eyes: Implications for bird–aircraft collisions, The Condor, 117 (2) 165-177. DOI: 10.1650/condor-14-157.1.

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