The video above runs for three minutes. It’s repetitive and rather boring — there’s no need to watch most of it. It shows a cardinal — the bird, to avoid any confusion for you non-watchers — flying into a set of windows, over and over again. Five times in the first thirty seconds. Eight more before the first minute is up. As the uploader of the video notes, this happened “day after day, month after month.” And it’s not all that uncommon. Birds do this type of thing.
They just don’t understand glass.
Really, they don’t. And the death toll is significant. According to an “Ask a Scientist” article by American Museum of Natural History, there are an estimated 200 to 400 billion birds on the planet, total. A lot of them may fall prey to glass. An Audubon Society official quoted by the New York Post, states as many as 90,000 crash into glass buildings and die each year in the New York City region alone. The Boston Globe cites Daniel Klem, an ornithologist at Pennsylvania’s Muhlenberg College, who estimated that as many as a billion birds die each year from crashes into glass, most during migration. (That number, though, has been called into question by others, who call it “guesswork” at best.)
What’s going on? According to NPR, “birds don’t have good depth perception beyond their beaks — they have to get relatively close to an object to see much detail or distinguish it from background. Reflections in glass can make it seem as if there’s no building there — just more sky, clouds and trees.” Similarly, some believe that the birds see their own reflections but, not recognizing themselves, mistake the reflection for a predator, and take to battle. That’s probably what is happening above. You’ll note that the cardinal seems to lead with its feet, explaining in part why it can do this repetitively, without dying or harming its brain in the process.
Another theory — which is not necessarily in conflict with the previously-stated one — suggests that the birds see through the glass much like people do, but do not understand that there is something in the way. As many birds are attracted to light, they therefore fly into windows of tall office buildings at night. In another NPR article, an architect working on a special type of glass which aimed to limit bird accidents explained:
In the 1990s, they focused on getting big buildings to turn out the lights at night because they attract migrating birds. “I had to find out myself if this was really happening,” he says, “and sure enough, I got up bright and early one morning, went down into the city and was finding birds on the sidewalk.”
The difficulties in creating glass that birds can “detect” are significant, mostly because we humans don’t want our experiences interfered with. While putting up bars or some sort of translucent (but not transparent) coating would save the birds, it would defeat the purpose of having glass in the first place. Some are tinkering with using bands of light (such as ultraviolet) which are visible to birds but not people, although for now, that’s aspirational. For the time being, the best advice experts offer? Don’t have too many plants near windows and turn off your lights at night.
From the Archives: Going the Distance: The very long trip of a migratory bird.
Related: An intro guide to bird watching.