What Does ’Bird-Safe Glass’ Even Mean?

From football stadiums to your own kitchen window, here's your guide to bird-safe glass.

Birders across the country are up in arms about the Minnesota Vikings’ new stadium, which is likely to be a death trap for migratory birds that can’t see glass and fly into it. The stadium design includes 200,000 square feet of glass, and the Minnesota Sports Facilities Authority (MSFA) has said they won’t spend the extra $1.1 million to use bird-safe glass. 

But what exactly is bird safe glass? And if not having it is such a big problem, how can you keep birds from flying into your windows at home? You have questions, we have answers.

Why do birds fly into glass?

Birds can’t see glass.  Instead, they see whatever happens to be reflected in its mirror-like surface. Often, this is open sky or trees, which, if you’re a bird, are appealing (and perfectly safe) things to fly towards. It’s estimated that between one hundred million and one billion birds die every year in collisions with manmade structures—one of the biggest killers of migratory birds. 

What is bird-safe glass?

Bird-safe glass is specially designed to make glass a visible obstacle to birds. Luckily, it’s possible to make glass visible to birds while still keeping it transparent enough for humans. 

A variety of approaches, such as fritting, silk-screening, or ultraviolet coating, create a pattern that breaks up the reflectivity of the glass and alerts birds to its presence. More important than the technique used to create the pattern is its spacing: Testing has shown that the “2x4 rule” is most effective—meaning that the silk, coating or markings are added across the pane, spaced two inches apart horizontally, and four inches apart vertically. Research has shown that birds will not fly through spaces less than two inches high or 4 inches wide. 

What does bird-safe glass look like? 

Because the spacing is what counts, bird-safe glass can be designed to feature many different types of patterns and etchings.

For example, the Minneapolis Central Library used bird-safe glass that they designed to look like a forest. The glass was purchased from Viracon, a Minnesota-based company that's providing the glass for the Vikings Stadium.

As the library demonstrates, the Vikings could customize a bird-safe glass, perhaps using their logo. 

Another company, German-based Arnold Glas, patterns its Ornilux bird protection glass with an ultraviolet-reflective coating. Birds can see the coating, but it is virtually invisible to humans.

Where can I buy bird-safe glass?

Many companies offer bird-safe glass, and the price is often just 5 percent higher than standard glass. Another option for limiting bird collisions is to construct buildings so that the glass is angled slightly downwards, and therefore won’t reflect the skyline in the same manner.

What about glass in your home? 

If you’re not going to make the switch to bird-safe glass, there are other steps you can take to ensure that birds don’t chart a collision course for your windows at home:

1. Paradoxical as it may feel, try placing your bird feeders close (1.5 feet or less) to your windows—it will make birds slow down as they approach.

2. Apply a thin film to the outside of your windows. The glass will become visible to birds, but remain transparent for you. As an added bonus for being so eco-savvy, the film will cut down on incoming infrared radiation, so it will also lower summer cooling costs.

3. Keep curtains or shades drawn during the day to reduce reflection.

4. Place window decals, sun catchers, tape strips, ribbons, or anything of your choosing (get creative!) in a dense pattern in the “2x4” format (a single decal will not work).

5. Move houseplants back from your windows, as they may attract birds.

6. Install a screen or net a few inches outside of your windows, to lessen the impact.