Preventing Bird Strikes

July 1, 2023

A review by Heidi Trudell 

Solid Air: Invisible Killer. Saving Billions of Birds from Windows by Daniel Klem Jr.

Hancock House Publishers, 2021

224 pages, paperback

ABA Sales–Buteo Books 15241

First off, let me be entirely clear: I am biased. I am extremely biased. In 2005, I attended a conference in Chicago where Dr. Klem gave a presentation to architects about bird mortality caused by windows. He was the frustrated voice of an ornithologist surrounded by architecture professionals who didn’t understand the extent of the problem, nor did they rush to fix it because at that time the solutions were limited and expensive. I, on the other hand, was a college undergrad with a freezer full of dead birds I’d collected underneath windows on campus. I had driven four hours just so I could attend his lecture. Dr. Klem was very confused as to why anyone would make that much effort to attend, nor why they would ask for his autograph, but he kindly obliged.

For an idea of why I was so compelled to meet Dr. Klem in person, nearly my entire college experience revolved around my daily check of four “bad” buildings on my campus. On a good day, I’d come up empty handed. On a bad day in fall, I’d have half a dozen dead birds bagged, plus a few injured ones awaiting transport to the local bird rehabber. The mental and emotional toll of the school’s dismissive attitude ultimately led to my leaving that school.

It may come as a surprise that window collisions were not particularly understood until Dr. Klem pushed forward with his research in the 1970s. Indeed, his pioneering work brought the entire field of bird window collision research into existence. Solid Air: Invisible Killer has brought that wealth of knowledge to the world in an accessible way. His early journal publications provide the foundation for our understanding of collisions today, and Solid Air pieces together the most complete history of bird window collisions that currently exists. In that regard, Solid Air is a wealth of meticulously documented information that reflects on who the people were who have picked up the torch on researching bird collisions and when they began their studies. We are also offered a thorough review of physiological effects of collisions on the birds themselves, something that few people seem to take into account when encountering stunned birds.

While we do get an understanding of the setbacks from the early days, it’s hard to overstate just what a challenging position Dr. Klem was in. Many people working to prevent window collisions today face the same pushback: “It’s not a problem.” Just because we don’t see it doesn’t mean it’s not happening. What we do see is just the tip of the iceberg. A very, very small tip of an extremely large iceberg. And hawk stickers are not the answer.

In Chapter 4 we are introduced to an observation that is truly harrowing. A residence had been experiencing chickadee collisions every year during migration in ever decreasing numbers, until finally there were none. It wasn’t that the windows got safer or the birds somehow learned to avoid collisions. It was a result of there being fewer birds alive from that migrating chickadee population that passed through the area. How many times has this scenario quietly played out elsewhere, undocumented? With bird populations plummeting, how can environmental protection laws and building codes be so far behind?

If you want to skip ahead to resources for window collision prevention, there is a thorough list of residential collision prevention products towards the end of the book. Each product includes a discussion of applications and prices broken down to the cost per square foot. Those costs have undoubtedly gone up by now, given that Solid Air was published in 2021. Between the products listed in the book and those supported by the American Bird Conservancy, there is a product for every budget, every aesthetic, and every level of DIY experience, though of course there are professional installation options as well.

Solid Air, taken to heart, will end up full of post-it notes, highlights, and within arm’s reach for questions we have, and to answer questions from friends and family. You might not end up reading it in a linear manner (it took a lot of self-restraint on my part), but this is a must-read first step in moving toward safer windows for birds.

Suggested resources to accompany Solid Air on your nightstand:

  • Animal Help Now is a nonprofit dedicated to connecting people with wildlife emergencies to nearby rehabbers and provides references to those experiencing wildlife conflicts.
  • Rosemary Mosco’s collaboration with FLAP Canada, featured on the site bird and moon, is the single best bird collision prevention infographic for residential purposes to date.
  • American Bird Conservancy’s glass collisions page includes resources for bird collision prevention products, sample letters, and legislation for grassroots movements, along with a wealth of information for new construction and retrofits.
  • An American Bird Conservancy and Cornell study showed that bird populations have plummeted since the 1970s, and takes a look at the most significant ways that we can turn the tide.
  • 101 Ways to Help Birds by Laura Erickson - A compelling look at the often unexpected ways that we can help birds through everyday decisions and actions in all aspects of our lives.
  • Why Birds Matter: Avian Ecological Function and Ecosystem Services edited by Çağan Hakkı Şekercioğlu, Christopher J. Whelan, and Daniel G. Wenny - An in-depth exploration of the agricultural importance of birds and beyond.
  • 100 Plants to Feed the Birds by Laura Erickson - This book offers a thorough breakdown of native plants ideal for creating backyard habitats that can help birds survive.
  • Bird-by-Bird Gardening by Sally Roth - Plants and their seeds, berries, and associated insect life are critical for bird survival. This book provides easy ideas of what to plant to attract different types of birds.


With two decades of experience with bird collisions, Heidi Trudell is an architectural and campus consultant, researcher, and advocate. She is tired of picking up dead birds and wants to make the world a safer place for them. Learn more about her work at She lives in Michigan with her partner and their houseplants.