Bird-Window Collisions Increase Avian Mortality

Dr. Daniel Klem, Jr., the world's leading expert on birds killed by collisions with windows, gave a presentation on October 18, 2013. Photo Credit / Rebecca Jasulevicz
Dr. Daniel Klem, Jr., the world's leading expert on birds killed by collisions with windows, gave a presentation on October 18, 2013. Photo Credit / Rebecca Jasulevicz
Dr. Daniel Klem, Jr., the world’s leading expert on birds killed by collisions with windows, gave a presentation on October 18, 2013.
Photo Credit / Rebecca Jasulevicz


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On October 18, 2013, East Stroudsburg University’s Biology Department hosted Dr. Daniel Klem, Jr., of Muhlenberg University. As the second bio-colloquium of the semester, Dr. Klem gave a presentation entitled “Bird-Window Collisions: Overview of Current Knowledge and Prevention.”

Dr. Klem is a Sarkis Acopian Professor of Ornithology and Conservation Biology who has received a number of awards throughout his lifetime, such as the Hawk Migration Humana Service Award.

The main interests of Dr. Klem’s studies are ethology (the study of animal behavior), ecology (the study of interactions among organisms and their environments), conservation, ornithology (the study of birds), and wildlife mortality resulting from the actions of man.

Dr. Klem is considered to be the world’s leading expert on birds killed by collisions with windows.

An estimated one billion birds are subject to human-associated mortality every year. According to Dr. Klem, this could be a conservative estimate.

“The avian toll exacted by glass is indiscriminate, an additive rather than a compensatory population mortality factor,” said Dr. Klem.

Birds only have to take off from about a meter away from the window in order to build up a sufficient amount of momentum to receive serious, life-threatening injuries upon impact.

The problems are not due to the physical or mental fitness of the bird.

“If we believe they act as though the glass is invisible to them, they are all subject to the fatality,” said Dr. Klem.

Glass causes so many casualties to birds because they do not believe there is a barrier between themselves and the habitat that resides on the other side. This is known as the see-through effect.

Another property of glass is known as the reflective effect. This is when the glass reflects the image of the habitat opposite of it. Instead of it appearing as though there is no barrier present, it will seem like the habitat they are already in is continuing.

As long as the conditions exist for these effects to take place, according to Dr. Klem, “Birds are vulnerable to sheet glass of all sizes and colors.”

Glass casualties are responsible for the deaths of eight percent of the world’s bird species and 28 percent of North America’s bird populations.

The most common casualties of North American birds include species such as the American Robin, Dark-eyed Junco, Cedar Waxwing and the Ovenbird.

The Swift Parrot is an endangered species, yet, according to Dr. Klem, “1.5 percent of the world population of 1,000 breeding pairs is killed annually colliding with windows.”

Being able to estimate the number of birds subjected to window collisions is a matter of examining population density. Dr. Klem said, “The best predictor of the number of bird strikes at any site is the density of birds in the vicinity.”

If an area has a large population of birds, there will be a proportionally higher number of bird strikes annually than if fewer birds lived in the area.

Many forms of prevention exist, including increasing the use of screens, making glass more visible to birds with either creative awnings or novel panes, the angling of panes, using frosted glass and altering the placement of attractions.

Novel panes are also known as “Klem Glass,” and they utilize nanoparticle coatings and interior films within laminated glass.

Angling the pane of glass to face downward instead of being perpendicular to the ground not only helps the glass to be more visible, but it also allows birds that fly into it to have a greater survival rate.

Utilizing glass that is non-reflective is also an option, as is using glass from manufacturers that will impose an ultraviolet signal into the glass.

Many birds have a wider range of site than humans. This is in part because some species have about a million cones per square millimeter in each of their eyes, and also because they have double cones, while humans only have single cones. Cones are the retinal structures responsible for color, sharpness, and acuity.

While we cannot see ultraviolet light, many species of birds can. If the glass has patterns or images in the ultraviolet wavelength, this may aid in the bird’s ability to see the glass and avoid it.

The location of bird feeders and trees in relation to buildings also affects the mortality rate of birds. When bird feeders and other similar attractions are placed closer to buildings, there is a drastic decrease in the number of casualties.

Dr. Klem encourages people to educate others about the severity of bird strikes. Preventing the installation of harmful windows can be done in a number of ways, including encouraging architects to adhere by greener building codes.

Additionally, Dr. Klem recommends to encourage governments, whether they are local, state or federal, to enforce existing legislation in order to ensure bird-safe human structures. The Migratory Bird Treaty Act of 1918 and the Ecological Society of America work to protect wildlife and diversity.

“We have the solution. We just have to convince people that we have the power to take some action. I need people to take it seriously,” said Dr. Klem.

As human construction continues to expand, prevention of avian mortality is becoming an increasingly prevalent issue. Buildings littered with windows have the opportunity to inhibit the creation of unnecessary victims.

Taking simple precautions can prevent the deaths of, quite literally, billions of lives. Taking Dr. Klem’s advice, individuals can act as catalysts for a safer future for avian populations worldwide.

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