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Again, bird populations are declining in North America. According to the Bird Conservancy of the Rockies, bird populations have decreased by 29%, meaning almost 3 billion birds are gone. The most upsetting part: this decline happened in only 50 years.

North America isn’t the only place this is happening. In a 2018 report, 40% of the world’s bird species were found to be in decline, according to All About Birds. Birds are in major trouble. And you can probably guess why.


Putting habitat loss aside, U.S. Fish & Wildlife Service reports that predation by cats, collisions with windows, vehicles, electrical lines, electructions, oil pits, and poison are all top threats to bird populations. However, there are a couple of threats that stand out from the rest.

Cats annually kill 2,400,000,000 birds out of 3,324,184,012 human-related deaths. According to ABC Birds, approximately 63 extinctions among mammals, reptiles, and birds were partially because of cats. The second deadliest threat is collisions with building glass, which annually kill 599,000,000 birds. (Cats, by themselves, account for almost 70% of fatalities!)

Annual Bird Fatalies

Median Estimates in the US, 2017, by U.S. Fish & Wildlife Service

Why Are Cats A Problem?

You probably already know that cats like to hunt. Cats are known to bring all sorts of "presents" home, like mice, snakes, frogs, insects, other rodents, and birds. Their natural hunting instincts are strong, whether they’re a feral cat on the streets or live comfortably in a home.

Their effect on birds and other animals is disturbing. In a study conducted by the Mammal Society in England, according to American Bird Conservancy, 964 cats killed approximately 14,000 animals, 25% of which were birds. Another British study tracked 78 cats in Bedfordshire for a year. These cats killed a 1,100 animals, from birds to other small mammals, including bats, according to the book Where the Wild Things Were. A quick internet search turns up even more disturbing studies like this.

As mentioned previously, cats are the cause of almost 70% of human-related bird fatalities (2.4 million every year!). It's not that a couple of cats are killing hundreds of tiny creatures; it's that there are so many cats, when each cat kills a few animals very year, the numbers quickly add up. And some note that this number might not fully encompass the animals cats eat or bury.

Obviously, cats are the largest problem for birds (outside of habitat loss). If you have a cat or know someone who does, please visit our Cats page! There are quite a few misconceptions about how to protect birds from cats, like using bell collars.

Top: What does a human see, and what does a bird see?

Bottom: This may look like a picture of a tree, but it's a reflection from a window! @Anna Hartwick for both photos.

Why Are Windows A Problem?

Birds can’t see glass….and, actually, humans can’t either! We’re taught at a young age what glass is, and we can use contextual clues, such a window frame, to evaluate if glass is present. Birds cannot mentally comprehend contextual clues, and they take everything they see literally.

Oftentimes, a window reflects an object, such as the sky, a tree, or you! They also can reflect the ground or other surrounding vegetation like shrubs or flowers. These reflections are why birds fly into windows—let’s say that a window is reflecting the sky. Since birds take everything they see literally, they think that sky is actually there. And as they try to get to that sky, they collide into the window.

Additionally, birds sometimes collide with windows because of the “Dark Hole Effect.” This is where the window appears to be black due to shade. Birds also think this is a passageway they can fly "through."

More on Building Glass Collisons

If you look closer at which types of buildings birds are colliding with, you might find a surprise. First of all, buildings were classified in one of these three categories: High-Rise (more than three stories), Urban/Rural Residences, and Low-Rise (1-3 stories). Which one do you think causes the most bird fatalities?

According to U.S. Fish and Wildlife, 44% of collisions occur at urban/rural residences, 56% occurs at low-rise buildings, and less than 1% occurs at high-rise buildings (view report here). ABC Birds estimates that skyscrapers cause 508,000 birds fatalities per year. In comparison, low-rise buildings cause 339 million.

High-rise buildings are still an issue for birds—they cause more bird fatalities per building. However, there is not nearly as many high-rise buildings as there are low-rise buildings. The result? Low-rise buildings pose a greater risk to birds due to their sheer numbers. They have a bigger impact on birds cumulatively.

And so, it’s easy to understand that everyday people, such as you, need to take action to help birds. Your home may be contributing to these numbers.