A recent study found that nearly 600 million birds are killed each year when they fly into windows, leading scientists and bird activists to revisit how best to prevent these deaths.

According to Daniel Klem Jr., an ornithologist at Muhlenberg College in Allenton, Pennsylvania, these collisions kill more birds than oil spills or pesticides.  The problem is especially bad during the spring and fall migration periods, when many birds travel through cities and suburbs full of windows.

The US Fish and Wildlife Service explains, “Glass is invisible to birds, and if it reflects the images of trees, bushes, the sky, or other natural habitat[s], a bird may fly directly into it.”

Skyscrapers can also cause problems, especially for birds that migrate at night and use the stars to navigate.  They can be easily distracted by building lights in their flight path, leading to hundreds of dead birds littering the sidewalks after a particularly bad evening migration.

Bird died from flying into a window

The solution, according to experts, is in how we use window glass in buildings.  Though funding is limited, scientists like Klem Jr. are studying how birds see and what products can be used to help them avoid windows, particularly by using patterns in the glass.

Window screens, sunshades, and tempera paint can all create a good visual warning pattern for birds.  Klem Jr. says that the trick is to keep the pattern spaced effectively:  horizontal lines no more than two inches apart and vertical lines no more than four inches apart.  Otherwise the birds will try to fly right through it.  Patterns should be placed on the outside of the window so that lighting conditions will remain optimal, not reflecting sky, trees, or any other distracting natural element.

Of course, these lines can obstruct the view of people actually using the windows, so some manufacturers have begun experimenting with developing patterns that are only visible to birds.  For example, most birds can see ultraviolet light, but humans can’t, making this a potentially good way to develop safer glass.  The trick would be to develop UV patterns that broadcast over a wide range of frequencies, as different birds tend to see different frequencies.

Another solution for skyscrapers in particular is a requirement that building lights be turned off at night as much as possible.  Many cities have this sort of regulation in place already.

If you find a bird that has struck a window, experts advise you watch it for a while to make sure predators don’t approach it and that it’s able to fly away.  If not, call a licensed wildlife rehabilitation center in your area for advice.