Each year hundreds of millions of birds die in the U.S. after colliding with windows. Skyscrapers are not the chief cause, but mostly mid-rise buildings.
My guide in trying to understand why birds are more likely to collide in three and four-story buildings is Heidi Trudell. She’s an avian collision specialist who works with groups such as Washtenaw Safe Passage.
We met at the Eastern Michigan University campus, where Washtenaw Safe Passage monitors for bird window collisions.
"So this campus combined absolute minimum kills well over 100 birds a year depending on the building," said Trudell. "So right now we're at the library. This one that we know of kills about 40 birds a year. But we can't monitor the entire thing so it's probably well upwards of that.”
There are buildings like this four-story building all over. Trudell told me about a District Courthouse in downtown Ypsilanti where they find dead birds all the time. They hit the windows on the backside and fall onto an apartment complex parking lot. I stopped by to see what she was talking about and immediately found the remains of eight birds.
They were in various states of decay. Cars run over them after they've died hitting the window, and they're flattened with the traffic coming in and out. Some of them were pretty old.
Washtenaw Safe Passage monitors buildings all over the county and try to keep track of how many birds die by colliding with building windows.
There are a couple of things about cities and buildings that cause the birds to crash into them.
Ben Winger is the Curator of Birds at the University of Michigan Museum of Zoology. He recently researched bird collisions and found that birds that chirp or make faint flight calls are more likely to hit buildings.
First, they are attracted to city lights.
“As birds are drawn to artificial light and disoriented by it, that if they're using flight calls they're probably attracting more and more members of their species or potentially other species to the lights. It's like a vicious cycle where they're calling and bringing each other in and getting further disoriented,” Winger explained.
If they manage to miss hitting skyscrapers, they end up confused and landing in the middle of a downtown.
“They may then get drawn to an area that is more dangerous and although they don't collide with the building or the lighted structure directly the next day they may collide with reflective glass based on the fact that they're trapped in this area," he said.
That’s because they don’t see the windows. They see the trees and sky reflected in the windows.
This kind of thing is so common, Heidi Trudell says it’s become a comedy trope.
“Even in Harry Potter the bird hits the window and you're like oh silly owl. No, this is actually a huge problem,” Heidi Trudell noted.
But, something can be done about it. There are decals that can be put on windows which signal to a bird: you can’t fly through this.
“So Solyx window film has pretty patterns that are very neutral to ... individual passersby," explained Trudell. "So you have architectural products like that you have retrofit things like Kaleidoscope film, Feather Friendly tape. These are pre-manufactured things that are designed by 3M. They're intended to be weatherproof.”
But, institutions and businesses can be reluctant to go to the expense of a retro-fit when they’re not sure there’s a problem.
“At this point there's enough data in the body of collision knowledge to look at a building and say this is going to be highest risk he should fix it but nobody wants to fix it without data. So collision monitoring is basically like, ‘Okay do we have enough bodies yet. How about now? How about now? How about now?’ And ultimately the problem is not going to get better and it's just going to keep going until we stop it,” said Trudell.
So, bird groups keep counting dead birds.
Architects and building owners have the information they need to reduce bird collisions. It’s simply a matter of whether they’ll add the cost into the budget.