One morning in early fall, I was shopping in downtown Keene, when I was stopped in my tracks by a yellow lightning bolt. As I crouched down, I found a beautiful palm-sized bird, olive above, with a belly as golden as the sun. It was a species I had never seen before, and it lay dead on the floor under a store window.
After consulting with several field guides and two friends who know the intricacies of identifying warblers much better than ever, I deduced that it was a grieving warbler – a secret songbird from the glades of boreal forest and high altitude, with a migratory route that follows to Central and South America. Imagine flying here – a marvel of beauty and color – only to be shot down by a collision with a window.
Unfortunately, the warbler is part of a much larger model. Migrating birds face many dangers, including storms, habitat loss and predation. But two threats working in concert proved particularly deadly: artificial light and windows.
Many birds refuel during the day and migrate at night, when temperatures are cooler and aerial predators are less active. Starlight can also help with navigation. Artificial lights can both attract and disorient migrating birds, luring them to cities – and, for many, to collision paths with windows.
One of the best-studied examples of the effects of bright lights on migrating birds is the Tribute in Light, the powerful twin beams that light up the New York City skyline each September in memory of those who have been lost. during the terrorist attacks of September 11. , 2001. September is the peak period for songbird migration, and when the weather conditions align well, thousands of birds can be “trapped” in these clusters, circling around until they fall from exhaustion or hit the sides of neighboring buildings. Studies have shown that bird densities in lower Manhattan are up to 150 times higher when Tribute lights are on. NYC Audubon is now coordinating volunteers to watch over the memorial; when too many birds are caught in the lights, Tribute operators turn them off for a brief period to allow the migrants to disperse.
New York is not alone. Intensive surveillance at a 40-story convention center in Chicago, for example, has documented 40,000 window strike deaths since 1978 – but also showed that the number of birds rose from thousands to hundreds a year when the building began turning off its lights at night in the early 2000s.
Birds can strike windows from any height at any time. However, during migration, window collisions usually occur in the early morning hours, when hungry migrants drawn to buildings by nighttime lights search for food and instead encounter glass – imperceptible to birds – which reflects the sky or vegetation nearby.
Between 365 and 988 million birds – from songbirds to raptors – fall victim to building collisions in the United States each year, just behind outdoor cats as the primary source of direct human-caused mortality for them. American birds. Despite the attention attracted by large-scale skyscrapers, a 2014 study in the journal Ornithological applications found that tall buildings were responsible for less than 1% of window strike deaths, with 56% attributed to low-rise buildings and 44% to residences. The researchers also determined that structures that kill only a small number of birds each year – like my local mall in Keene – account for a large portion of the total mortality from window impacts.
Fortunately, this is a problem with solutions. We can all help you by turning off exterior lights and unused interior lights at night, especially during peak bird migration season in spring (April 1 to May 15) and fall (September 1 to October 31) . When you need to use interior lights after dark, go for lamps that light up a small area instead of overhead lights that light up the whole room and keep your curtains or shades closed.
Also, if you live or work in a building with large windows, keep an eye out for victims of window hits, then apply screens, stickers, or decals to break up reflections from any problematic glass. For helpful tips on design considerations for buildings large and small, visit the American Bird Conservancy’s Bird-Friendly Building Project at abcbirds.org/glass-collisions.
Migration has always been fraught with dangers, but today’s glass-hardened landscape presents a new and extraordinary threat. With a little effort, we can soften this landscape and help the birds that honor us with their presence to move around safely.
Brett Amy Thelen is Scientific Director at the Harris Center for Conservation Education in Hancock, New Hampshire (harriscenter.org). Illustration by Adelaide Murphy Tyrol. The Outside Story is attributed and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation: www.nhcf.org.