Chicago, Houston, and Dallas. These cities aren’t just hubs for human air travel. They are also on the paths of migrating birds–which, with the rise of urbanization, has made them the three deadliest cities for our winged friends in the U.S.
An estimated 600 million birds are killed by buildings every year. Especially during spring and fall migrations, birds are attracted to the glow of residential homes and skyscrapers alike. Sometimes the birds crash directly into their windows. Other times, it seems to throw off their internal compass, causing them to circle until exhausted.
A new study from the Cornell Lab of Ornithology has worked to quantify the brightest cities on the paths of migrating birds worldwide. After using advanced image analysis algorithms to study 20 years of migratory satellite data, cross-referenced against global brightness data collected by an NOAA satellite, the team built a map that demonstrates the areas where artificial light poses the greatest risk to birds.
What the researchers concluded was sad but fascinating. For one, they found that the 125 top urban cities in the United States accounted for only 2.1% of the landmass, but 35.4% of all light radiance. They also learned that all birds passing over these urban areas while migrating did so quite quickly–in just a few peak days each year–meaning the short-term behavioral habits of people could make a big difference on passing flocks. They built much of that information into a site that’s called Birdcast, which you can check for yourself to know when migrating birds are flying overhead.
“These forecasts can instruct building managers or household residents where and when birds will be migrating (and when to turn off lights),” lead researcher Kyle Horton, a postdoc at Cornell, tells Co.Design.
But just who should turn off the lights? In other words, do high-rises or domestic homes injure more birds? To answer that, I reached out to Scott Loss, assistant professor of global change ecology and management at Oklahoma State University and lead author on the 2014 research that brought us the harrowing stat that 600 million birds are dying because of buildings each year.
“We found that skyscrapers (12 stories and taller) caused the most bird deaths on a per building basis (average of 24 birds per building per year) and this equated to about 500,000 total birds per year across all U.S. skyscrapers,” Loss tells Co.Design. “Residences had much lower collision rates (about one to three birds per building per year), but there are far more residences than skyscrapers, so the total for all U.S. residences was estimated at about 250 million birds per year.”
In other words, skyscrapers in our big cities are the greatest danger by footprint, but there are many more single family homes in the United States. It’s urban-suburban sprawl, not density, that is most adversely affecting birds.
Architects can make all sorts of changes to buildings to make them safer for birds, too. Here’s a superb resource that walks through different structural interventions, which can be as simple as covering exposed glass windows with mesh facades. But one of the most actionable and inexpensive is simply to turn off the lights of your building when birds are likely to be migrating.
That’s good news for anyone who’d like to do their part to protect birds. But at the same time, it means that protecting avian flocks will necessitate a massive behavioral shift for many people. “It really does require a widespread change in action, especially at resident homes,” says Horton.