[Tweeters] Stop Window Strikes

Neil Johannsen neil.johannsen at gmail.com
Fri May 27 12:22:08 PDT 2016

Bird Lovers:

An estimated 100 million birds die each year from window strikes. Most of us have experienced the heart-breaking thud sound, or found dead birds below our windows.

The death of a beautiful Golden-crown Sparrow set me hunting for the best solution a week ago - to end the carnage.

For the sake of others in our group,I found this: windowalert.com <http://windowalert.com/>. It’s a product from Bend. Oregon. I have no financial relationship with this company; i simply want to save bird lives.

What I learned:

Birds can see certain light frequencies--including ultraviolet--that humans cannot see.

In fact, many songbirds have feathers that reflect ultraviolet light. This light is used to communicate species, gender, and perhaps even social standing. Birds can see this ultraviolet light under normal, daylight conditions. Humans require the assistance of a black light.


1) Both birds and humans have photoreceptive 'cones' in the retina located at the back of the eye. These cones allow us to see color light. The human eye contains 10,000 cones per square millimeter. Songbirds, for example, have up to 12 times this amount or 120,000 cones per square millimeter.

2) In humans, these photoreceptive cones consist of three types. Each cone is sensitive to red, green, or blue light. This is called trichromatic color vision. Birds have an extra cone for tetrachromatic color vision. This extra cone expands the visible light spectrum, allowing birds to see ultraviolet frequencies.

3) During low-light conditions, both humans and birds rely on photoreceptive ‘cell rods’ in the retina. The human eye has 200,000 cell rods per square millimeter. Some birds, such as owls, have up to 1,000,000 cell rods per square millimeter.

4) Bird eyes, on average, account for 15% of the mass of the bird’s entire head. Human eyes, by contrast, account for less than 2% of the head.

5) Bird retinas, in contrast to humans, contain no blood vessels. This prevents light scattering and thus provides birds with greater visual acuity than humans.

The decals are very non-conspicuous; after a while, you may not even notice them, but birds will!

Thank you all,

Neil C. Johannsen
Kitsap Audubon
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