For the Birds Radio Program: Window Strikes, Part I
Thud! That sickening sound resonating in our ears can stop our hearts, as yet another bird hits the window. We run to see what it is this time. Sometimes the victim has already flown away, apparently good as new. But sometimes it’s injured, or even killed.
The first documented record of a bird killed at a window that I could find was from 1832, when Thomas Nuttall wrote in A Manual of the Ornithology of the United States and of Canada, an account of a Sharp-shinned Hawk crashing through two panes of greenhouse glass before being killed at a third. Back then, large windows were not at all common. It wasn’t until the post-World War II building boom that picture windows became popular on houses. As the sheet glass industry boomed and steel-framed architecture soared, more and more skyscrapers and other large office buildings became encased in glass.
Nowadays, windows represent a significant cause of mortality for birds. Windows of lighted, tall buildings kill huge numbers of nocturnal migrants. The windows on our own houses kill our backyard residents as well as birds passing through the neighborhood.
In a major survey of window-killed birds, Dr. Daniel Klem, Jr., of the Department of Zoology at Southern Illinois University at Carbondale found records of window strikes in 225 species, belonging to 42 families. That is at least 25 percent of all species of North American birds. Some species are more vulnerable than others. Robins, juncoes, cardinals, Cedar Waxwings, Ovenbirds, catbirds, flickers, sapsuckers, and several species of thrushes are among the most commonly killed, in part because they’re common species in suburban habitats, and in part because they fly at window height. Considering that they’re so much less conspicuous than other birds, cuckoos are killed by windows surprisingly often. I’ve received many calls and notes from people who’d never even seen a cuckoo in their lives until one crashed into their window.
The injuries and cause of death in window strike cases are generally skull, neck [UPDATE–bird necks are seldom injured], or wing fractures, and internal hemorrhaging. Based on several studies, Dr. Klem estimated that one out of every two birds that collides with a window will die of its injuries. Even birds that seem to recover can suffer serious injuries. In one study by Dr. Klem, two birds that had struck windows but were alert and active a few hours after the collision, appearing completely recovered, were euthanized and examined. Both had sustained severe inter-cranial hemorrhaging.
In his charming book, The Golden-crowned Kinglet, Robert Gallati recounts the tragic story of a young kinglet he studied in captivity. That little bird had a collision with a shelf in a grocery store, but seemed to completely recover. Some time later, he keeled over, dead. Examining the body, Gallati found a massive blood clot in the front portion of the head.
Sadly, when birds do survive a window collision, they don’t seem to learn from the experience. One Indigo Bunting that was banded after surviving a window collision in Canada killed itself striking the exact same window a year later.
How big is the problem? Dr. Klem estimates a minimum of 98 million birds die at windows each year, and thinks it quite possible that even 980 million birds a year is a conservative estimate. With such a huge problem, isn’t there anything we can do? Next time I’ll talk about what to do if a bird hits your window, and how to prevent most strikes from happening in the first place.