Research coming out of Pennsylvania’s Muhlenburg College, conducted by Dr. Daniel Klem, estimates that over 1 billion birds are fatally injured every year in collisions with windows and paned glass. Beyond habitat destruction, this source of mortality is humanity’s largest impact on avian populations, and contrary to effects of predation, disease, or natural selection, window collisions affect the most-fit, as well as the least. Although bustling cities’ glassy high-rises are often viewed as the primary culprits, individual homes contribute more significantly to the problem; clear or reflective glass /plastic panes are essentially invisible to birds they are present everywhere birds are. Windows are not seen as barriers, but a continuation of habitat, as trees, clouds, indoor plants, or “approaching birds” are reflected. Sometimes birds defensively attack, the “competitor” they see, or use false images of a clear flight path, created by windows on two sides of the house, to access habitat beyond. When they impact the window for any reason, the outcome is often dire, and it is believed that one of every two collisions eventually leads to mortality. Check out the further reading section below and Dr. Klem’s website to see what interesting information has been gathered by researchers on the subject.