Millions of birds die each year in collisions with planes, and airports have used everything from fireworks to herding dogs to scare them away. While some ground-level methods have been successful, they’re ultimately useless in the air. Now, with brown-headed cowbirds as their test subjects, researchers at Purdue University are using lights to measure key properties of the bird’s visual system in hopes of finding a solution to this very serious problem.
In collaboration with the USDA Animal and Plant Health Inspection Service, the researchers have discovered that red and blue LED lights lead some birds in the opposite direction, creating an avoidance behavior.
“The way we figure this out is to give the animal a choice,” said Esteban Fernandez-Juricic, a professor of biological sciences at Purdue who led the study at the Ross Biological Reserve.
Here’s how it works: Researchers release a bird (in this case, a brown-headed cowbird) and it flies away from them. A few inches away, the flight path is divided — one side has a light on and the other doesn’t. A single-choice test, in which the bird decides between the light on or off, rather than between two colors, is ideal for measuring avoidance behavior, Fernandez-Juricic said. If the bird goes to the side without a light, that light might be a good candidate for warning birds of danger.
The test was repeated with five different commercially available lights with similar viewing angles from Super Bright LEDS Inc. — 5-mm through-hole format LEDs with peaks at 380-nm UV (RL5-UV0230-380), 470-nm blue (RL5-B2430), 525-nm green (RL5-G7532), 630-nm red (RL5-R8030), and cool white (RL5-W18030).
Fernandez-Juricic told Photonics Media that the birds consistently avoided the LED lights with peaks at 470 and 630 nm.
Giving birds a choice test helps researchers determine what kinds of light the animals tend to avoid. Courtesy of Gabriela Sincich, Purdue University.
“We were expecting cowbirds to avoid some lights, particularly the UV ones because some people have said UV lights could be good candidates to use in aircraft given that the human eye is not sensitive to deep portions of the UV spectrum,” he said. “Interestingly, we found that cowbirds were indifferent to the UV lights. However, we found a significant effect of the blue and red lights, which led to avoidance behavior.”
This finding directly contradicts previous experiments in which people have tried using UV lights to shoo birds away, based on the idea that they have better vision in the UV range.
The types of lights birds avoided in this Purdue study had high levels of chromatic contrast, or differences in color, but lower levels of achromatic contrast, where differences occur only in gray level. Whether the findings are a result of light peaks or levels of contrast, Fernandez-Juricic isn’t sure. He hopes to answer this question, along with how other bird species respond to different types of light, by modifying the test and performing more experiments.
“We now have a behavioral assay we can use to test these attraction and avoidance behaviors in a systematic, standardized matter, and we can do it on various species,” he said. “We’re able to test not just whether a light may be highly visible to a bird or not, but whether that light leads to the behaviors we’re trying to generate.”
Fernandez-Juricic and fellow researchers intend to explore other properties of the LED lights — including intensity, rate of pulsing, and rate of looming — to see if these would further enhance the avoidance behavior of birds. They also plan to use the same approach on other bird species with a high frequency of bird strikes. The Purdue researchers would like to partner with industries to implement the biological findings into real-life situations, ultimately reducing the frequency and severity of bird strikes.