According to the American Bird Conservancy, an estimated 300 million to 1 billion birds die each year from collisions with glass on everything, from skyscrapers to homes.

An imprint left by a pigeon that flew into a window.
An imprint left by a pigeon that flew into a window. (Wikimedia Commons)

“Birds can’t see glass [and] they don’t understand the same cues [humans do]. They treat the world very literally,” says Christine Sheppard, bird collisions campaign manager for the American Bird Conservancy (ABC). “If they see trees on the other side of a glass wall, they don’t know there’s an obstacle and if they see the reflection of a tree in glass, they don’t know that they can’t fly to it. They slam into the glass and many of them die right away.”

In response to the concern, manufacturers such as Quebec-based Walker Glass have developed “bird-friendly” alternatives, such as fritted glass. According to Walker’s website, a “2-by-4 Rule” is used when addressing the issue.

“Glass surface treatments that reduce significantly the risk of bird collision have been researched by many experts, such as Dr. Martin Rössler, Dr. Daniel Klem and Dr. Christine Sheppard,” the website reads. “Their conclusions have consistently shown that most birds will not fly into surfaces that have two inches or less of untreated horizontal space or four inches or less of untreated vertical space. This criteria is commonly referred to as the ‘2-by-4’ rule.”

Walker Glass business development manager Marc Deschamps stresses the importance of the problem.

“The phenomenon is observed year-round across most areas in the USA and Canada, but is predominant in migration flyways, along coast lines, in the Midwest and Great Lakes area,” he told™. “The problem is getting very serious and the level of awareness is increasing significantly. Many states, counties, cities and provinces have instituted voluntary or mandatory bird-friendly standards or guidelines.”

In 2011, the San Francisco Planning Department passed the “Bird-Friendly Monitoring and Certification Program,” which provides buildings with a pathway to become a “Certified Bird-Friendly Building.” For buildings built prior to 2011, the standards are voluntary, but buildings constructed after 2011 will have to meet the regulations.

In Toronto, similar measures have been passed. In fact, because many of the birds dying due to collisions with windows were on the Canadian endangered species list, the province of Ontario now regulates buildings reflecting light that leads to bird fatalities, according to ABC.

The bird safety issue has been a hot topic of late, with a battle going on in Minnesota between conservatory organizations and the builders of the new Minnesota Vikings’ stadium. To read more about it, click here. assistant editor Casey Flores contributed to this story.