In 2007 I was working in a university building that was just begging for bird feeders. It was a one-story square building, four sides enclosing a courtyard–two sides holding offices and classrooms, one side a brick-faced entrance hall, the fourth  a glass-walled corridor that allowed views of the underused, full of green stuff courtyard. This was where I set up my bird feeders, just one at first, then expanding as everyone expressed delight in seeing the Carolina Chickadees, Dark-eyed Juncos, and Downy Woodpeckers. Well, if you’ve ever had bird feeders near large glass windows near vegetation, you know what comes next.

I was shocked when I found the first body, a female Towhee. I hoped it was an anomaly.  Over the next few days, I found increasing numbers, goldfinches, juncos, white-throated sparrows. Were they always there and I just never noticed? There seemed to be a correlation between the number of birds coming to the feeders and the number of dead birds I was finding. I bought hawk silhouettes and cut out even more and taped them to the walls of the glass corridor and that appeared to make a difference (though apparently that practice is now frowned upon). There were no dead birds for weeks. Every day I made the rounds of the building, making sure the silhouettes had not fallen down, explaining what they were to our staff, checking the grounds. I had started slacking off, thinking the problem was solved, when I tripped over a bird body while filling the feeders. I picked up a Downy Woodpecker, an every-day visitor. The window silhouettes were gone. They were removed by a zealous member of the janitorial staff, I discovered later, but no one would give me the name and contacting the department was apparently the equivalent of contacting the University president, actually trickier because no one wanted to get on their bad side. I decided it was time to stop feeding the birds.

This Tufted Titmouse was found stunned in the glass corridor several years after the feeders were taken down, showing that clear glass and vegetation are not a good combination any time. I put it in a small box for several hours, where it appeared to recover, but studies have shown that internal injuries from a strike usually kill the bird.  ©2012 Donna L. Schulman

An estimated one billion birds collide with glass each year in the United States* and most of them die; window collisions are considered the second highest cause of death of birds after cats (putting aside the big overall causes, like habitat loss and climate change).* Many cities, including my home, New York City, have lights-out programs (the lights confuse birds, who fly down and often collide with glass buildings), building codes that require bird-friendly glass, and groups of volunteers, usually supported by a local Audubon or other birding group, who pick up dead birds every morning, contributing the data to one of several dead-bird databases. Many people who have bird feeders now use patterns or screens or paint to keep their windows from looking like the entryway to greenery, some even install bird-friendly glass, chosen from a list of products evaluated by the American Bird Conservancy. It’s not enough.

It’s not enough because we keep finding dead birds, or sometimes stunned birds who will, studies show, eventually die. And buildings without thought for birdlife, significant buildings like the Minnesota Vikings shiny “death trap” for birds, are still being built.** Dr. Daniel Klem, Jr., Sarkis Acopian Professor of Ornithology and Conservation Biology at Muhlenberg College in Allentown, Pennsylvania, is concerned. More than concerned, he is dismayed and alarmed and has been since January 1974, when he first witnessed a Mourning Dove fly into a window and fall to the ground dead on the Southern Illinois University campus. This was his trigger moment, when he decided to find out why birds fly into glass windows and die. Dr. Klem wrote his doctoral thesis on the subject, Biology of collisions between birds and windows, the first scientific study of bird and glass collisions, and has not let go, though it has taken decades for the topic to be taken seriously by others, especially the scientific community. Solid Air: Invisible Killer- Saving Billions of Birds from Windows is the summation of Dr. Klem’s expertise, experience, and professional life–what we scientifically know about bird and glass collisions, a handbook on how to prevent them, and, not insignificantly, the story of a remarkable career.

Solid Air is divided into 12 chapters, presented as if Klem was on an auditorium podium giving a logical argument on why people need to take window strikes seriously. Don’t misunderstand me, it’s not consciously presented this way, but as I read the book, I really did feel that Klem was writing as he talks, putting into text the many presentations he has done over the years. The first half describes the problem (why birds hit windows, the scale of the deaths, scientific research, what happens when birds strike windows) and the second half discusses what to do about it (community and worldwide education, window deterrent solutions, legal mandates and building codes, citizen science–what individuals can do). Interestingly, the two middle chapters talk about the value of dead birds and the value of live birds, a transition from how the dark to the light, from crying to hoping. Material before the main text introduces us to Klem’s mission and how he found it (Preface and Prologue); extensive material in the back of the book provides lists of resources, data, a comprehensive bibliography, and acknowledgements.

Photographs, charts, and a few cartoons illustrate every chapter, a total of 78 though it seems like less since many of the illustrations combine two or more photographs. There are far fewer photographs of dead birds than I expected. Most of the images are of houses and buildings where window collisions occurred, the flight cages and framed windows used in Klem’s field experiments, and the many products and structural solutions that can be employed to eliminate window collisions. But, yes, there are photographs of dead birds and x-ray images of the damage done to individual birds and photographs of the annual FLAP display, as shown below. FLAP is the Fatal Light Awareness Program, located in Toronto, Ontario, Canada, and this is how they raise awareness. (The photographs are actually in color in my Kindle edition but reproduced in black-and-white on the book’s Amazon page. I’m not sure which format is the most affecting, probably both equally.) It occurred to me that maybe I should post a trigger warning at the beginning of this review. But I think the title says it all and will warn away anyone who gets upset by descriptions or images of dead or injured birds. And I don’t think that will be many people. Dead birds are a part of the life of a birder, a feeder of birds, and of bird science.

Photographs of window-killed birds from Fatal Light Awareness Program (FLAP) Copyright © 2021 Daniel Klem, Jr.

I was particularly interested in the research chapter–“Scientific Evidence–Making the Case”- and was surprised not to find the classic scientific literature review, but rather Klem’s detailed account of how he did the research for his dissertation, from surveying museum bird collections on records of window kills to collecting window strike data from locations in Illinois and New York State, to controlled field experiments. The latter account even includes Klem’s first foray into fund raising, when he finds that his attempt to obtain reimbursement from a corporate foundation for personal monies spent on materials for his field experiments, $695.64 (which he could ill afford), violates every rule in the Southern Illinois University grant application playbook. Ah, yes, university bureaucracy, always an innovation killer.

My surprise at reading such a detailed account (I don’t have Klem’s dissertation in front of me, but I’m imagining this is a more personal retelling) was tempered by the thought that Klem wasn’t describing any old research, this was the FIRST research project investigating why birds fly into glass. He collected the first data set, invented the experimental equipment, came up with the first conclusions, the theories and findings upon which subsequent studies have been based.  Klem cites these studies towards the end of the chapter as he tells us what is known and not known.

Basically, wherever there are birds and glass and vegetation, birds are apt to fly into glass, just as they did in my university courtyard. Window strikes take place during the day, usually in the morning, and generally at large windows at heights over 10 feet, where vegetation is reflected in the windows and the birds think they are flying to another tree or green habitat. As Klem emphasizes in the beginning of the book, we really don’t know what a bird sees, we can only make educated assumptions based on what we know about their biology and behavior. Vegetation is a key ingredient, and Klem cites a 2013 study that found “bird strikes were correlated positively to window area and negatively to development. The more glass, the more bird kills. A greater number of buildings in a concentrated area without intervening green space results in fewer birds and fewer killed.” Density of birds is also a factor–the more birds near windows, the more likelihood of window strikes, and the fact that chickadees, titmice, juncos, woodpeckers, nuthatches, and hummingbirds are frequently reported as window strike victims is less about the features of the individual species and more about the fact that they love bird feeders.

There’s a lot more, of course, and it all makes you wonder if we should have bird feeders or urban green spaces or fountains or windows. Thankfully, there are alternatives to what I ended up doing, taking down the feeders, and they are detailed in the second part of the book, where we learn about the development of bird-safe sheet glass and the use of patterns or films on already installed glass windows. Klem’s research comes into play here too, as he describes testing a theory that angled windows would protect birds from fatal strikes (disappointedly, no), his work with glass manufacturers, and his efforts to obtain a patent for his own invention, a UV pattern that prevents bird-window collisions (a bad news, good news, bad news story that serves as a cautionary tale for any scientist seeking success in the business world). Connecting this all together is the’ discovery of best practices and effective deterrents, the former detailed at the end of the chapter, the latter listed in one of the book’s appendixes. (Would Acopian Bird Savers have worked in my glass corridor? Or maybe ABC BirdTape?)

Klem’s overall tone is one of scientific curiosity and measured patience, but there is also an undercurrent of melancholy, rooted in the 45-years plus he has endeavored to bring bird glass collisions to the public eye and prompt change. It has taken an incredibly long time. His seminal article, “Bird-Window Collisions,” based on dissertation research finished in 1979, was not published in a peer-reviewed journal until 1989.*** And it would be another 12 years before the topic had enough credibility to attract a body of scientific research. (I consulted Google Scholar to see how many scientific articles cited Klem’s article, which was published in The Wilson Bulletin, now the Wilson Journal of Ornithology. Of the 169 books and articles listed, 120, 70%, were published between 2011 and 2022.) Throughout the book, Klem tells story after story of talking to colleagues, professionals, businessmen,  even Senator Bill Bradley, about the bird collision issue–seeking publication, invitations to speak at conferences, ways to make his message heard–consequently receiving expressions of interest and then being rejected or simply hearing nothing. He describes the change model he was using as follows:

From my orientation, background, and bias, scholarly work must come first to document and establish a need for change. At the same time, or ideally shortly thereafter, the science will convince and stimulate popular writings to reach a broad audience, one that eventually enlist the general public to demand reasonable, justifiable changes that will benefit human society, which is part and interdependent with nature. (p. 111)

Did the model work? I don’t think so, and though Klem writes that “over time, scholarship did attract the attention of popular writers, and they in turn have educated a far broader audience than the scientific community” (p. 119), it’s clear from his comments that the scientific community still tends to put bird collisions on the sidelines. But we, birders and nature enthusiasts, do not. There are now multiple sites where people can contribute data on window strikes and bird deaths, including NYC Audubon’s dBird, FLAP’s Global Collision Bird Mapper, iNaturalist, and, on a social media level, the Facebook group Dead Birds 4 Science, run by the indefatigable Heidi Trudell. The American Bird Conservancy offers a Glass Collisions Products & Solutions Database, where products are evaluated and rated. Seven cities and one state have enacted legislation and ordinances mandating bird-friendly construction (not a lot, but it’s a start, and NYC and Toronto are on the top of that list). Although the Minnesota Vikings stadium (officially the U.S. Bank Stadium) continues to kill over 500 birds a year, the uproar over its design did a lot to publicize the problems of glass buildings. “Bird-friendly design” is becoming a common term in architectural and city planning circles and proponents can point to a successful initiative, the retrofitting of New York City’s Javits Center which reduced bird deaths by 90%. And, then there are the pick-up-dead-birds initiatives in major cities in North America–New York City’s Project Safe Flight, Chicago’s Chicago Bird Collision Monitors, Toronto’s Bird Collision Monitoring Patrols, Washington, D.C.’s Lights Out DC, to name a few. These programs provide the hard data (and bodies) that help convince politicians, administrators, and architects to create buildings and communities that are safe for birds, as well as save the few birds that are stunned, not dead.

These initiatives are mostly listed in Solid Air (not the Facebook group or iNaturalist, social media is clearly not Dr. Klem’s forte), but not in the detail or with the delight that I would expect. Maybe it’s because he’s still focusing on the research that still needs to be done–a long list that he would like to see encompassing areas of economics, law, architecture, psychology, sociology, and recreation as well as biology, zoology, and ecology. It’s not a bad idea. This is a concrete problem that is solvable, he points out, much more solvable than climate change. “We have the ability to fix it, but we still need the collective will” (p. 207). Perhaps if I had thought more about bird collisions from this perspective all those years ago, I would have enjoyed my courtyard bird feeders for a much longer time.

Solid Air: Invisible Killer- Saving Billions of Birds from Windows is a book about bird deaths, science, simple and complex solutions, and how one man’s passion and persistence really can make a change. It is worth reading for the facts and solutions concerning bird glass collisions (and the related city lights issues and even feral cat issues), for insight into how change based on science is made, and for an appreciation of Dr. Daniel Klem’s work.


*  American Bird Conservancy (ABC) scientists Christine Sheppard and Bryan Lenz expand on the reasoning behind the 1 billion number, which is cited everywhere, on the ABC birds and glass collisions FAQ. A 2014 Smithsonian study concluded that collisions likely kill 365 million to 1 billion birds annually in the U.S., with a median estimate of 599 million. They believe the number is closer to one billion because since 2014 there has been a steady increase in buildings of glass and because they think bird carcasses are undercounted.

** https://www.theguardian.com/sport/2017/feb/28/minnesota-vikings-stadium-deadly-birds-glass

*** Klem, Jr., Daniel, Bird-Window Collisions, Wilson Bull., 101(4), 1989, pp. 606-620.

Note: If you would like to hear Dr. Klem discuss the book, he was interviewed on the “Hannah and Eric Go Birding Podcast,” April 21, 2022. There is also a video of Dr. Klem talking about his work on the website of the Acopian Center for Ornithology, Muhlenberg College. Heidi Trudell talks about bird collisions with Nate Swick on the ABA Podcast, June 27, 2019.


Solid Air: Invisible Killer Saving Billions of Birds from Windows
by Daniel Klem, Jr., PhD
Hancock House, Oct. 2021
224p., illustrations, $24.95; available in eBook, Kindle & PDF format, $4.95
ISBN: 978-0-88839-646-4 [Trade Paperback] ISBN: 978-0-88839-640-2 [Trade Hardcover] ISBN: 978-0-88839-665-5 [eBook] Kindle Version

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Written by Donna
Having been attached to books all her life, Donna Lynn Schulman is thrilled to be engaged in a passion that requires fealty to an information artifact called a “field guide.” Donna divides her birding time between Queens, New York, where she grew up, and central New Jersey, where she is on the adjunct faculty of a very large public university. Donna was a Library Journal book reviewer for 15 years, reviewing over 100 titles, and has also reviewed labor relations books and contributed articles on labor relations research to specialized journals and monographs. She wrote her first birding book reviews for the Queens County Bird Club’s News & Notes, which she formerly edited, and has also reviewed for the American Birding Associations' Birding magazine. Donna was recently pleased to talk about the top birding books of 2017 with Nate Swick for the ABA December podcast. When she is not birding or working on her nature photography, Donna travels to Florida, where she attempts to turn her young nephews into birders (so far, they are fisherman who send her photos of birds), to Los Angeles to visit her writer daughter and son-in-law, or somewhere wonderfully new and birdy. She also contemplates someday writing an article for her blog, Queensgirl.