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Scientists Struggle to Make Windows Safer for Birds

Safer Windows for Birds

Story at-a-glance -

  • Millions of birds are killed each year in collisions with windows. Birds don’t see glass as an obstacle and fly right into it.
  • For the last four decades, one U.S. ornithologist has been working on solutions to the problem of window crashes, but creating no-crash glass is a more difficult challenge than you might think.
  • Obstacles include translating what we know about bird vision into safer window designs, and getting safer windows approved and accepted for use. The growing popularity of “green” buildings has also posed a challenge – more natural light means more windows birds can fly into.
  • Another challenge to designing safer windows is that birds’ eyes are positioned on the sides of their heads, making their forward vision less acute.
  • While the experts continue to struggle to make windows safer for birds, there are immediate steps home and building owners can take to reduce the likelihood of bird collisions.

By Dr. Becker

Many people aren’t even aware of this sad fact, but estimates are that up to a billion birds die from crashing into windows each year in the U.S. alone. They simply don’t see the glass and fly right into it.

Fortunately, there are three avian research facilities in the country testing methods to prevent window crashes. But as it turns out, creating no-crash glass is more complicated than you might think. The first U.S. researcher to tackle the problem, ornithologist Daniel Klem Jr., has been working on solutions for 40 years. And while much has been learned about what birds can and can’t see, applying that knowledge to safer window designs – and getting those windows accepted for use by public and commercial interests – has proved difficult.

One problem, oddly enough, has been the growing popularity of “green” buildings. More natural light means more windows, which means more glass for birds to fly into. According to ornithologist Christine Sheppard of the Powdermill Avian Research Center in Rector, PA, tests show that opaque stripes or dots on windows can reduce bird collisions… if people are willing to use them.

Klem, Sheppard and others in the field have been searching for an ideal solution, which is a window with patterns that birds can see but humans cannot.

Birds Didn’t Evolve to Recognize Glass as an Obstacle

Daniel Klem’s interest in the subject of birds and windows began in the mid-1970s when he witnessed a mourning dove crash into a high-rise window so hard that feathers scattered and the bird dropped to the ground to die. At the time, no one really knew why birds fly into glass, but the general thought was that the birds were at fault.

So Klem began conducting experiments, using panes of glass propped against tree trunks, and a 12-foot tunnel he constructed. He quickly learned that birds fly toward glass as though it isn’t there. Clearly, the problem wasn’t the birds, but the glass. Birds don’t see glass as an obstacle.

Next, Klem began testing bird-deterrence markings on glass. After some trial and error, he discovered what is now known as the two-by-four rule. Most birds won’t fly through a space less than four inches wide or two inches high between horizontal stripes.

Sadly, for the most part, Klem’s findings have not been used to make windows and other glass structures safer for birds. As Klem explained to Science News in an interview:

“People told me time and time again, ‘You know, Dan, you go mucking around with the way people look through their windows, and you’re going to lose.”

It seems the only place humans are willing to accept patterned glass is in bathrooms.

Another Challenge: Birds’ Eyes Are on the Sides of Their Heads

Another big challenge in creating bird-safe windows is that most birds’ eyes are on the sides of their heads, which means their best vision is sideways rather than directly ahead of them.

Some big birds (eagles and vultures, for example) actually have a gap between the right and left visual fields that creates a blind spot to what’s ahead. As soon as they look down, they are essentially “flying blind.” Not only do these birds not see obstacles ahead, they also would not see warning patterns in windows. They fly assuming nothing will be in their way, which, of course, was the case for millions of years.

Smaller birds more often collide with windows than larger birds of prey, and while they don’t have a frontal blind spot like the big guys, their forward vision is also not great. In addition, birds don’t pick up contrast as well as humans do. In order to be an effective deterrent for birds, a grayscale pattern in glass would need to have 10 times the contrast required for human eyes.

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How You Can Help

While Daniel Klem, Christine Sheppard and others like them continue to work to perfect crash-safe windows and raise public awareness, Sheppard offers the following recommendations for home and building owners interested in preventing or reducing bird collisions:

  • Install window screens to reduce bird collisions and provide a softer crash surface.
  • Use washable tempera paints to provide a simple, colorful warning to birds.
  • Close shutters or exterior shades when windows aren’t in use and during spring and fall migrations, which are peak seasons for collisions.
  • Place stripes or dots on the outside of glass to break up reflections. If possible, space vertical lines no more than four inches apart, and horizontal lines no more than two inches apart.
  • Consider using fritted glass (glass that is finely porous), with fritting on the outside surface, to reduce reflections and collisions.

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