Window-killed Yellow-throated Vireo below the patio door it hit in Henningsville, Berks County, Pennsylvania. Photograph by Peter G. Saenger.

My purpose is to update my review of bird-window collisions that was published in Bird Observer in 2006 (Klem 2006). Although that article is now dated, almost all of its content is still accurate and relevant. That work was my first review article, and since then I and others have offered updated versions (Klem 2009, 2010, 2014, 2021, Loss and O’Connell 2018, Basilio et al. 2020, de Wilde and Bleil de Souza 2022, Rossler et al. 2023). What follows is a short summary of the field’s history, our current knowledge, and work yet to be done.

My doctoral dissertation research on birds and windows was conducted from 1974 to 1979 (Klem 1979). Thus 2025 marks my 51st year of studying, writing, and teaching about the lethal threat posed to birds by clear and reflective sheet glass and plastic in the form of windows. Except for the results of the most current research, I comprehensively document the details of my studies and those of others in my 2021 book: Solid Air, Invisible Killer: Saving Billions of Birds from Windows (Klem 2021). The topic has gained legitimacy since the late 1970s, when I began a decade-long struggle to convince scientific journal editors that this conservation issue was important for birds and people. Since then well over 200 articles have been published on the topic in popular and scientific literature (Klem 2021, American Bird Conservancy 2024). Especially rewarding to me are the number of young scientists, prominent among them the research team at Oklahoma State University (Loss and O’Connell 2018), who have dedicated their talents to studying the details and dynamics of bird-window collisions.