An invisible assassin
For the past half century, Klem has been one of the leading scientists in the field of bird-glass collisions.
“99% of all windows in the world are reflective,” says Klem, also the author of Solid Air: Invisible Killer-Saving Billions of Birds from Windows. “Even perfectly clear glass covering a dark interior space acts like a mirror on the outside.”
This leads to collisions when the surface reflects trees or the sky: the birds simply think they are flying towards another habitat, not towards solid material.
The species affected are also diverse: in Klem’s study in Pennsylvania, over a dozen different bird species hit the experimental windows, such as mourning dove, downy woodpecker, red-winged jaundice, red cardinal, dark-eyed junco and Cooper’s sparrowhawk.
“It’s worth highlighting how dangerous windows are,” says Luke DeGroote, who wasn’t involved in the research but reviewed an early version of the study. DeGroote also praised the finding that half of collisions leave no marks, something he has seen firsthand anecdotally but has never seen acknowledged in the scientific literature.
However, DeGroote, who is the principal coordinator of avian research at the Powdermill Nature Reserve of the Carnegie Museum of Natural History in Rector, Pennsylvania, warns about the reliability of the study’s calculations.
For example, statistics from wildlife rehabilitation facilities have not been peer-reviewed. That doesn’t mean the data is incorrect, but DeGroote knows from his own research that rehabilitation success rates can vary greatly.
“I know that one of my rehabbers has a phenomenal success rate of over 90%,” DeGroote says. “So 70% mortality seems high to me.”
