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The Understory: Window Pain

by Berks Nature

May 05, 2021

In the early hours of Friday, October 2, 2020, birds rained from the sky in Philadelphia. Over a roughly 3-block radius downtown, an estimated 1,000-1,500 birds crashed into buildings and subsequently perished in the largest single mass collision event recorded here in 70 years.

It’s not fully understood what made the night of October 2 so deadly for those ill-fated songbirds, who were migrating south seeking warmer wintering grounds. Most likely, a combination of poor weather and Philadelphia’s lights encouraged the nocturnal migrants to fly low into the disorienting cityscape where they succumbed while running the glass gauntlet.

As commonplace as they are, glass windows, while offering health advantages and aesthetic charm for the humans living and working indoors, are indiscriminate bird-killers.

In the United States alone, an estimated 365 million to 1 billion birds die each year from collisions with glass windows. As a conservative estimate, that’s 1 million bird deaths per day. Apart from domestic cats, there is no human-created threat in the United States that kills more birds than windows.

This problem isn’t unique to cities, although the publicity attracted by tragedies like Philadelphia’s mass collision event reinforce this popular misconception. In reality, most window collisions occur during the day and your average, one to three story building is responsible for almost half of these fatal window strikes, accounting for 253 million bird deaths annually.

Any window, anywhere, at any time of year can kill birds.

Birds collide with windows because glass is invisible to them; being transparent, birds perceive windows as open passages instead of solid barriers. But poor eyesight is hardly to blame. Birds are very visual creatures with a highly developed sense of sight. For example, while humans can only process about 20 pictures per second, a bird can process around 180. Plus, birds can see colors in the UV spectrum; humans are stuck with ROY-G-BV.

Despite their ocular advancements, birds cannot see glass. But then again, neither can you! That’s right, humans can’t see glass either. Instead, we’ve learned to interact with this solid but transparent material using physical cues; windowpanes, door handles, and our location relative to the building all signal the presence of glass. But birds are not afforded the same luxury in education; 1 in 2 bird strikes are thought to be fatal, meaning that most birds don’t get the chance to learn from their mistake.

The reflectivity of glass is just as dangerous as its transparency. Like a mirror, windows reflect the environment around them. A bird takes these reflections at face value, trusting the inviting images of blue sky and verdant branches before them. Trees and other plants growing as far as 50 meters (164 feet) from a window will still be reflected by the glass, concocting mirrored mirages with deadly consequences.

Bird lovers be wary, for if you build it, they will come! But the more birds in close proximity to windows (just 10 meters or 32 feet), the higher the likelihood of a fatal glass collision.

While landscaping with birdfeeders and native plants provides invaluable habitat for birds trying to survive in a human-dominated landscape, if these resources coincide with the “danger zone” of your home’s windows, you may be inadvertently inviting your feathered friends into a high-risk situation. Increased bird activity combined with the window’s reflective deception is a recipe for disaster.

Creating truly safe, bird-friendly habitats was of paramount importance for Berks Nature as they made plans to build The Nature Place at Angelica Creek Park.

Berks Nature always intended The Nature Place to serve as a community demonstration of what “green” architecture can achieve, not just in the construction of the building itself, but in the way the new building would come to exist in and interact with the surrounding environment.

Intentional landscaping to accommodate stormwater and support native communities of plants transformed The Nature Place campus into a kaleidoscope of wildlife habitat from teeming wetlands to jubilant meadows to sun-dappled woodlands. All year round, Angelica Creek Park hums with activity thanks to the abundance of resources afforded by these habitats.

To ensure the safety of these new park visitors and residents, Berks Nature has installed bird-strike reduction glass windows at The Nature Place. Part of Walking Glass Company’s AviProtek series, The Nature Place’s unique windows feature an acid-etched pattern of horizontal lines, spaced 2 inches apart, across the entirety of each glass pane. These windows are approved by the American Bird Conservancy and performed well in field tests assessing bird deterrence.

A close up view of The Nature Place’s bird-strike reduction glass windows. These windows, etched with a pattern of horizontal lines, are installed throughout The Nature Place and reduce the likelihood of birds accidentally colliding with the glass!

There are two features in particular that make these windows especially effective at preventing bird collisions.

First, the pattern of horizontal lines – each spaced 2 inches apart – abides by what the industry calls the “2-by-4” rule. Birds are acutely aware of their own body dimensions and therefore will not attempt to fly into spaces smaller than their height and wingspan. For songbirds, the most frequent victims of window strikes, an opening of 2 inches by 4 inches is considered too tight of a squeeze by most and therefore, window patterns designed with these dimensions will deter birds.

Second, the horizontal line pattern is etched on the exterior surface of the glass. Decals or similar patterns meant to alert flying birds of the barrier ahead are mostly ineffective if applied to the inside of windows. Reflections on the outside glass surface can mask these visual cues, rendering them useless. But the deterring pattern of The Nature Place’s windows have been applied to the glass’ exterior, dispelling any reflected illusion.

Berks Nature isn’t alone in their efforts to minimize window-collision risks for birds. Following the tragedy last October, several of Philadelphia’s most prominent skyscrapers have opted into a voluntary initiative called Lights Out Philly. Participating buildings have agreed to turn their lights off between midnight and 6:00 am during prime songbird migration periods in the spring and fall to reduce the city’s beacon effect.

Philadelphia joins 30 other cities including New York, Boston, Atlanta, and Washington D.C., that also run Lights Out programs of their own.

At the federal level, the United States House of Representatives passed the Bird-Safe Buildings Act in July 2020. The bipartisan bill mandates that all newly constructed or acquired public buildings managed by the General Services Administration – the agency charged with managing government buildings and real estate – be designed or altered with bird-safe materials to reduce fatal interactions.

You too can make your yard safe for birds by minimizing the risk associated with your home’s windows!

  • Relocate bird feeders and birdbaths within 3 ft of your home’s windows. It may seem counter-intuitive, but at close proximities, birds can’t reach top speed reducing the likelihood of a fatal collision!
  • If you have trees, shrubs, and other attractants within 150 ft of your windows, where misleading reflections occur, consider retrofitting them to be safer for birds! Windows can be retrofit with 2-by-4 patterns using non-toxic tempera paint, tape, or decals. Whatever you use, remember to follow the 2-by-4 rule and apply your pattern to the outside of the window where it won’t be masked by any reflections!
  • Retrofit solutions do not always need to be applied directly to your windows! External, lightweight screens virtually eliminate reflections and, if a collision still occurs, the screens will cushion the bird’s impact, hopefully reducing injury. These screens are easy to install on existing or new homes. If you’ve already got external insect screens, you’re all set! But several companies (like Easy Up Shades and Bird Screens) sell products that can be installed with suction cups or hooks.

Hanging rope or string in front of windows, spaced 2-4” apart, is another retrofit option that does not physically impact your windows. These hanging deterrents are very effective at preventing collisions! Acopian BirdSavers and Bird Crash Preventers are two string-based systems that you can buy but this solution is easy to make on your own as well!

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