Thursday, November 15, 2007

A Potential Simple Method for "Bird-Proofing" Windows

Update 16 November - There are a couple of points I think I should clarify. First - and I guess this may be clear already - I'm still not convinced this will work, or how well it will work, and it will probably work in some situations better than others, and never be 100% effective since the hard glass surface is still exposed. If you try it please let me know how it works, good or bad.

I should have mentioned the Bird Screen, which apparently does offer nearly 100% protection, and might be the best solution for a lot of situations. I suggest the potential of the highlighter as an easy, cheap, and possibly effective solution, but if you're really interested you should check out the Bird Screen as a proven, reliable method of preventing window strikes.

Update 17 November - It's definitely not 100% effective; I've had two bird strikes in the last few hours, but that's still only two in a total of about 16 hours, which at the previous rate would have resulted in about 20 strikes.

Update 19 November - A potentially serious flaw in the "highlighter method" of preventing window strikes has come up - the UV color fades quickly.
Here (left) is a window just 20 minutes after applying the highlighter and (right) another window after the highlighter has been on for six days. (Both photographed at night with 1 sec exposure, same distance and position of black light). The six-day-old highlighter is not as bright and obvious as the fresh ink, especially to the right in the less intense UV light, so effectiveness for preventing bird strikes presumably decreases. In order to maintain the effectiveness one would have to reapply the highlighter frequently, maybe weekly.

I'm investigating some sunlight-stable UV pigment, but it's said to be less bright, and it's much more expensive and can't be delivered by pen. More on that, hopefully, later.

In the meantime, if you need immediate bird collision prevention try the
Wisconsin Humane Society online store.

Estimates of the number of birds killed in window collisions each year in North America run as high as nearly a billion birds. It's the biggest source of direct human-caused mortality in wild birds. But a simple means to prevent birds from hitting windows on your house or office could be in your desk drawer, or at least as close as your local office supply store, costing only a couple of dollars and a few minutes of your time. This needs further testing, but it appears that an ordinary yellow highlighter can be used to draw lines on the window, and those lines may be visible to birds, warning them away from the window, but are almost invisible to people.

Windows like the one below can be deadly for birds. This is my window with a bird feeder I recently set up. Placing the feeder within one meter of the window prevents the birds from picking up much speed before they hit it, so any bird collisions are supposedly non-lethal, but this reflection was so deceptive that an average of nearly two birds every hour were hitting it in early November - incredible and distressing! I left the feeder empty after a couple of days but kept thinking it would make a good opportunity to study bird-window 'interactions'.

American Goldfinches and a Tufted Titmouse
photo taken automatically by a Wingscapes Birdcam

I live in a house with lots of windows, and I like to keep lots of bird feeders. This is good for me as a birder, but often bad for the birds. Over the years I have tried various methods of making the windows either more visible or less harmful, but sometimes it just doesn't help. Birds fly very fast and at times (for example, when startled by a predator) will try to fly through things they would normally avoid. Occasionally, Cooper's and Red-tailed hawks seem to learn that they can pop around the corner of the house, cause a panic at the bird feeder, and then have easy pickings from under the window.

I found lots of helpful info on the web. Groups like FLAP have good suggestions about how to minimize the danger of window strikes here, and New York City Audubon has a detailed guide to Bird-safe building. Some of that worked for me, but some of it was either impractical or unsatisfactory for my situation. For several years I had pretty good success with simple lengths of white string hanging in front of the worst windows. This cut down on collisions, but did not eliminate them, and the string was unsightly and distracting, tricky to install, and required some tedious maintenance. I wanted a better solution.

Experiment 12 Nov 2007
Hypothesis: Since birds can see ultraviolet wavelengths of light and we can't, it must be possible to add a UV-reflective coating to windows that would make them more or less opaque to birds but still transparent to humans.

Methods: In the darkened kitchen with a black light and piece of plexiglass, my kids and I tested various household products to see what, if anything, might meet the twin requirements of being visible to birds and invisible to humans.

Results: Various juices and cleaning supplies all proved to be non-UV-reflective: Pledge, Simple-Green, Windex, Rain-X, Dawn, Orange Juice, Apples, Shampoo, Conditioner,... all no.
Olive oil, yes! Drops of it look like red curry sauce under the black light, but once it's spread thin the color is so faint it would presumably not be obvious to birds (plus it's messy and hard to see through).
Thinking beyond "fluids" we wondered about dry-erase markers, but no, they don't glow under the black light either.
Then I noticed the brilliant orange light from a supermarket price tag reflecting the UV. I thought of fluorescent colors (duh) and wondered about a thin wash of diluted day-glo paint, then I thought of highlighters. My son found one in the desk drawer, and... Bingo! Under the black light we could draw a pattern of brilliant yellow lines on the plexiglass, but under normal light the lines were almost invisible. Now we needed to test it on an actual window with real birds....

13 November 2007
Here (above) is the window and new bird feeder that had been combining for an average of nearly 2 bird strikes per hour until I left it empty. I've already drawn on the window with a highlighter, but the lines are invisible in this photo. Below is the same window illuminated with the black light to show the grid of highlighter lines (window shades inside are glowing blue). Presumably the birds see something like this. I filled the bird feeder and went inside to observe.

14-15 November results:
As I write this on 15 November, I have spent 11 hours monitoring steady bird activity at the feeder. After nine hours with NO window-collisions, a light rain started. The highlighter markings were getting washed away and a goldfinch hit the window. So I wiped off the outside of the glass and drew new lines on the inside. That's working so far, with no strikes in about two more hours of bird activity. Not enough data to really say anything conclusive, but testing continues....

Markings inside vs outside the glass: The first test was done with highlighter drawn on the outside of the window. That seems to work very well to deter birds but the ink I used washes right off with water. I tested the highlighter on the inside of another window and the markings appear to be equally visible from the outside. So I assume that marking the inside - where the glass is generally easier to reach and the marks will be protected from weather - would be just as effective at stopping bird collisions. Testing that now, and so far so good.

Grid size and pattern: In this first trial I've drawn a rough grid with squares about 2.5 to 3" across. I'll try to test some other designs to see if less marking or different designs give the same benefit. You could be really creative and draw architectural patterns or write 'secret' messages on the glass, as long as you don't leave big parts of the window unmarked. From other research it seems that the "openings" should be no larger than 4 inches high by 2 inches wide, so maybe my grid is about right.

Other inks: It would also be interesting to test other colors of highlighters or other kinds of fluorescent ink or paint. I notice that there are commercially available "invisible" fluorescent inks, the kind that are used for admission stamps at concerts, etc. Those could be even better than the highlighter, being clear in normal light, and there's probably a formulation that would be water-resistant for outdoor use. I'll try to check that out too. But there's almost no disadvantage to the highlighter, and it's so simple and readily available.

Disclaimers: These are preliminary results, and it's possible that further trials won't be quite as successful, but these early results are so promising (and it's so easy and low-risk) I wanted to get this information out there so that other people could try it and hopefully save some birds. The highlighter that I used seems to wash off easily with water, and does not stain the window frames here, but I make no warranty against staining or other damage to windows or adjacent materials that might be caused by following the above instructions.

Let me know how it works for you.


Patrick B. said...

Fantastic! I'm going to give this a try.

Bird Guy said...

Great timing! We recently moved and installed a feeder at our new apartment. Although we had many strikes, we went a couple months before the first casualty: 3 days ago a Dark-eyed Junco died.

I have spent every day since discussing the issue with local birders and trying to determine the best course of action, but this new method sounds very promising and I will be deploying it tomorrow. Let's keep up-to-date on how it goes!

brdpics said...

This is a great idea! I have one window that is particularly plunk-worthy and have put up a bird screen (no more plunks on that window), but this would be so easy to do. Thanks for sharing the tip- keep us updated if you find that the invisible UV inks work. -Bill

birdchaser said...

OK, if this really works, I'm going to quit my day job as there is no way I could come up with anything better to help save birds. Not in a million years. You are brilliant!

Carolyn H said...

Great idea! i'm going to try it tonight. Like you, I've always kept my bird feeders very close to the window in hopes they wouldn't strike with such force when they hit it. I don't have the 2 per hour strikes that you did, but I have some, and occasionally a bird will be hurt. I can hardly wait to give it a try!

Carolyn H.

cyberthrush said...

very, very clever and interesting in its simplicity; anxious to see if a longer trial and larger sample size bears out the success of the technique (I suspect the 'grid' may need smaller, tighter squares but maybe not); if so, it might also work for the problem of birds incessantly pecking at their reflection in car windows and mirrors and the like (although that's a slightly different phenomena)...

rmharvey said...

Not everyone has access to a black-light to test their highlighters. Perhaps you should mention the brand and color that you used in your test. Perhaps those who do have black lights could tell what they have found that also fluoresces.

Frederick said...

This is a fantastic idea, but I am not sure how well it will work when the lines are drawn on the inside of the glass; doesn't window glass block UV?

Hilke Breder said...

For the past year I have made all my windows and glass doors "strikeproof" by drawing patterns with white bar soap... grids, loops, circles ... on the outside glass; all seem to work. Eventually the soap washes off. My housekeeper renewed it by drawing on the inside of the windows, which I thought would not work, but so far for the past two months no strikes. Of course something that's invisible would be nicer. HTB

Anonymous said...

Great idea! I'm going to try this myself.

songbirdfeeder said...

Our original 1959 single pane, aluminum windows are being replaced next month with energy efficient, low-e windows. Will the highlighter show thru low-e??

Unknown said...

This is a great idea, unfortunately the three unscreened windows in our sitting area are for viewing the bird feeders. If the invisible UV ink will work, that would be the ultimate for us. -Pat

Unknown said...

This is a great idea, unfortunately the three unscreened windows in our sitting area are for viewing the bird feeders. If the invisible UV ink will work, that would be the ultimate for us. -Pat

David Sibley said...

Thanks for the comments,
As I just added to an update, I've had a couple of bird strikes now, so this is not 100% effective (as I suspected). I'll keep working on it and testing different variations and combinations.

just a quick reply to some comments
I used a "Post-it" brand yellow highlighter, but I assume they all use similar ink, if not exactly the same. Black lights cost about $25 at a hardware store, if you want to test what you're doing, and it's fun to have around anyway.

I don't know about the UV blocking of glass windows. In my brief "eyeball" test it looked like it showed through just fine to the outside, but now I've had a couple of window strikes with lines on the inside, so maybe it is more effective outside.

I'm fascinated by hbreder's comment that lines drawn with soap have the same benefit, even inside. I think someone else commented that it might be the pattern that is the key, just to show birds that there is a flat plane there.

The visibility of the highlighter markings is going to depend on a lot of things like background, lighting, size of the window, etc. I can definitely see mine, but they're also very easy to look past. I'm sure that even the invisible ink will still leave lines of residue that will be obvious at certain angles and lighting. So truly invisible markings might be impossible for anything added to the glass.

Just having this discussion is very good and we'll all learn something, Keep the reports and suggestions coming

Unknown said...

I have seen sparrows fly successfully right through a chain link fence when pursued by a Coopers Hawk. I wonder if making the grid tighter might be the ticket?

David Sibley said...

Great example Salthaven. I was thinking along the same lines - that birds fleeing a predator might just take any option that seems to be available. This makes the Bird Screen a better option, and other readers have mentioned that they made their own safety net with garden-supply bird netting suspended in front of the glass. These screens prevent impact even if birds attempt to fly through it.

Another reader pointed out a paper by Martin Rossler presented at the European Ornithological Society meeting this year. A couple of things jump out to me from the abstract. He says the coverage of markings on the glass was less important than the shape of markings, and vertical stripes were avoided more than horizontal stripes. UV was not tested, and he specifically says that UV coatings have not been effective, but doesn't say if patterns have been tested or just uniform coatings. It sounds like this study just gave birds a choice of two different windows to fly through, so a decision to avoid one only means that the other was "better" in some way. So again, given a real-world choice of flying into the open with a hawk, or trying to fly through a window with stripes on it, many birds would probably choose the window.

cyberthrush said...

Birds fly into windows of course because they see a reflection of foliage they assume they can reach, so soap or ANYthing that interferes with that image/reflection should work; the beauty of David's technique is that it doesn't smear the window's appearance to HUMAN eyes.
There are 'specialty' glasses that would block UV light, but I believe most window panes only have a slight filtering or diffusive effect on UV (open to correction?). The only real question in my mind is whether the birds actually perceive the UV grid in the same manner we do and therefore see it as interfering with the reflection enough to be obstructive; thus far, from their behavior it appears likely they do.

David Sibley said...

A reader from El Paso reports:
"We have two large plate glass windows that used to be covered on the inside with dark wooden blinds. We got strikes continually and nothing that I tried worked. Then I redecorated the room and replaced the dark wooden blinds with wooden blinds that have a much lighter stain. The strikes stopped 100%. As long as I keep the blinds down - whether the slats are opened or closed doesn't matter - the birds avoid the windows. The birds just couldn't see the dark blinds through the glass. Thought my experience might help somebody!"
Thanks for the report! I guess the dark blinds made a nice background so the reflection was more obvious. I've heard others say that blinds or curtains help to reduce strikes, but maybe it depends on the color of the blinds and the lighting outside and how those two interact to make the reflection less visible.

Going back to the Rossler paper, I wonder if those white vertical hanging slat blinds would be even more effective at reducing strikes. Of course, blinds would have to be open when we want to look through the window at our bird feeders, so we need another way to prevent strikes on those windows at those times, but it sounds like the right blinds could have potential for many windows.

We could also think about using more than one method on the same window - e.g. lines on the glass AND blinds.

Unknown said...

Check this web site for "permanent" ultraviolet ink. I'm sure there are competitors. A 15 sec Google search turned this one up.

Hamilton, NY
Hambirders Yahoo Group

David Sibley said...

Thanks Harvey,

On the same website I checked out the "sunlight stable" page which says this about ordinary fluorescent inks:
"The organic inks are much brighter and less expensive, but will fade in about 1 week if left to sit under the sun."
I don't know if this applies to highlighter ink, but it might, meaning that birds might start hitting the window after a week or less and the lines would have to be reapplied frequently. Something else to consider...

Martha Harris said...

Would the ink affect the solar gain for a passive solar house?

Martha Harris
Earthaven Ecovillage
Black Mountain NC

Unknown said...

Here's another source of ultraviolet marking pens. These pans have ink not suitable for skin, but are to be used for marking plastics and glass etc. Probably worth a try because they call the ink permanent.

Unknown said...

Solar gain would probably be only slightly affected. First, the area covered by a grid or other openwork design would likely be a small fraction of the total area of the window to be effective. Second, the ink/paint would be ideally transparent in the visible so we humans wouldn't see it, so that means about 1/2 the energy for sure would be transmitted. Third, it's also likely that the UV ink would be transparent in the near infrared where most of the remaining energy is coming from the sun.

Jason Rogers said...

I've got an even easier solution. Lose the bird feeders. This would solve not only the window strike problem but a host of other ones.

Jason Rogers
Banff, AB

David Sibley said...

Another reader writes:
a friend told me about your highlighter experiment. I had recently added spider decals to the other decals on my windows after an immature yellow bellied sapsucker crashed into one and died a few weeks ago. I was still having strikes with the decals. I washed all the windows this weekend and used yellow highlighter on three French doors that lead out to a deck. I had no strikes on Saturday. I watched chickadees and titmice veer off all day as they got close to the windows. I have two feeders right by the windows. I also have suet and 4 other feeders about 15 feet from the window. Today a junco hit one of these windows. It was stunned and flew off after a bit. It was early in the morning and I wondered if perhaps the low light was a factor. No other birds hit for the rest of the day. So far this is working better than the decals and the viewing is much better too. I want to feed and watch my yardbirds but always feel guilty about putting them in danger. Thanks for sharing the idea.
Thanks for this report! That sounds really promising and I'm glad to hear that it works somewhere other than my window. Yes, I suspect lighting does play a role, and the UV may be less visible in some conditions; but strikes also depend on the way the bird is flying (i.e. if startled I think a bird would be more likely to try to fly through, or be traveling at higher speed so unable to veer off successfully). I also think different species respond to windows differently, and there are other variables.

Also keep in mind that the highlighter color may fade after a week or so. If strikes begin to increase again after a few days, the first thing to try is reapplying the highlighter.

byrd said...

I had a couple feeders up at the windows of my old place and i didnt have any birds running into the windows but maybe thats be cause my cats sat there in the window watching the birds all day .

Unknown said...

I remember that my brother used Woolite (detergent used to wash wool and other delicates)to paint pitures on his walls as a teenager. The detergent was only visible under a black light. I have not tested this on windows for birds but I wonder if a wash on the inside of the window would work. If it works then the whole window would be solid instead of a grid.

Joanne said...

Hi, I just bought a small feeder for my window with suction cups. I put it up mainly for the chickadees who get kicked out of the large feeder by all the house sparrows. I hope I haven't made a mistake. I would hate to see something happen to these little guys.


chris said...

We live in a log home with lots of windows. We have at least four strikes an hour, some fatal. We have tried decals and silver ribbon, but to no avail. We will try the marker, but I am interested in knowing if the Woolite solution actually works. Thank you for the ideas to keep our birds safe. Chris

cyberthrush said...

Contrary to what I said earlier, according to what I read around the Web normal window glass actually DOES filter out most UV light (I believe birds see UV-A, but there is also UV-B and UV-C, all of which I think get filtered), so it again raises the issue of marking inside vs. outside the window. I assume most people reporting results are marking on the inside (might be good if folks stated explicitly where they draw their marks), and this may not be the most effective (though easier).
Also, in lieu of one of David's earlier comments has anyone tried vertical lines only vs. horizontal lines only?
(...and practically speaking maybe all this will become moot if indeed the marks have to be freshened very frequently.)

David Sibley said...

Michael left this comment:
Just pointing out a few issues:

UV light is high-energy, it is what ‘sun fades’ many materials. Thus any ink or dye that reflects it is likely to break down rather quickly unless it is notably stable.

Inks & dyes that reflect a lot of low-UV/upper visible light may not be actually all that strong UV reflectors in the frequencies birds see, they could just be just good at frequencies we see.

UV reflectors are the special ingredient for whiter-then-white / brighter-then-bright detergents. By adding extra UV reflectivity to clothing those goods seem more vivid next to untreated material.

Thus as by others Whisk & the like do ‘glow’ under UV, especially when painted on a dull white background. However since they’re combined with detergents they’re not particularly good for the surfaces they’re painted on or soaking into.

Iron glass aka window glass is a pretty good UV filter on it’s own. Thus anything UV bright seen from the other side will be duller then unfiltered.

Do not mess with the new ‘self cleaning glass’ types of glass as it would seriously degrade whatever special abilities they’re claimed to have (FWIW they seem to be much more effective ‘self-cleaning’ in the lab then out in the world.)

Low-emissivity (Low-E) glass refers to Infrared (IR) light, aka ‘radient heat’. The barrier is typically an invisibly thin film applied to the inside of glass. It’s bird-neutral and hasn’t anything to do with UV qualities. But I wouldn’t recommend applying the solvents in ink or detergents to it.

The only other effect of adding additional UV reflector to a window is your furnishings will fade that insignificant fraction slower.

Bird strikes are an ongoing problem in commercial buildings, mostly because they’re frightening to the inhabitants & unsightly to clean up. A typical strategy is to plant bushes below the windows to hide the carcasses until maintenance (or natural predators) get to them.

However there is a type of commercial glass now being popularized that contains reflective patterns embedded in the glass. Hopefully these patterns, which lower the heatload on the building while allowing only slightly degraded views, would appear ‘solid’ enough for birds. However I haven’t seen that mentioned as a sales feature.

My solution to bird strikes? Windows with aluminum screens seem nearly never hit. Presumably the aluminum is bright & sold looking enough, when both new & shiny or particularly later dull & grayish, that it is considered part of the wall.

Carolyn H said...

Thanks for the update on probably needing to repaint my windows with highlighter weekly. That's a small chore and still much cheaper than the bird net. Not to mention that the highlighter doesn't interfere with my own view to the outside.

Carolyn H.

sitta said...

I thought it might be useful to have the citation information for the grid spacing; Klem's research suggests that a uniform pattern that has spaces no larger than 5-10 cm reduce windowstrikes.

Klem, 1990. Collisions between birds and windows: mortality and prevention. J. Field Ornithol. 61(1):120-128

Unknown said...

Emory building draped in black to save birds
Many crash into environmentally friendly design with soaring glass windows

David Sibley said...

From a reader in CT first commenting Nov 19th: I wanted to update you on how the highlighter on my French doors was working. During the last week when it was cloudy or raining the number of strikes rose. I wasn't home but my husband heard some strikes and there were feathers on the windows. This past weekend it's been sunny both days. While I've been home, there have been no strikes. I've seen birds veering off as they did last weekend. How the highlighter works seems to depend on how the light is - at least at my house. I decided to order some bird screens.
Thanks for the update. I hope the bird screens work out!

bashman Jeff said...

My house has large expanses of picture windows assumably with a low "E" rating. My solution was to hang single, clear, plastic "icicles" in front of the windows which provide a visual obstruction as well as a reflection. Though not perfect, these cheap devices have significantly reduced birds hitting the windows. Anecdotally, I have noticed that bird hits seem to occur more frequently when the sun is low in the sky. This probably causes more reflection of the landscape and birds either chasing or being chased apparently are distracted enough they aren't aware. I'd like to know if there is any difference in sky conditions where the drawn UV-lines work best. (There seems to be the makings of a wonderful Science Fair project here!) Also, as an aside UV-reflective paint for aircraft was proposed to reduce birdstrikes; perhaps, the same could work for wind turbines to reduce bird strikes.

Norma said...

We have two large windows on either end of our living room. Both windows have vertical blinds which we mostly keep in the drawn but open position - meaning the blinds are in place across the window, but are cantilevered so that we can see between the slats. The few times that we have pulled the blinds back (so that they are grouped at either side of the glass), we have had bird strikes during the day or early evening. When we return the binds to the normal (described above) position, no more bird strikes. I think it helps that there is a heating duck below the blinds and that makes they sway ever so slightly. Not sure why, but it works.

Unknown said...

I was reading about the anti-collision film on the site that can be applied to the windows. It is somewhat costly, but I could "adopt a window" every couple of months until they are all covered if it was going to work. The virtues are that it has no negative impact on the homeowners view and is supposed to be 100% effective. The downside is that it erodes over time and has a "life" of 5 years. (Isn't the power of the sun wonderous?) Has anyone here had experience with this product?

David Sibley said...

Dear "Only Creekers",

I'm anxious to try that window film myself. I did hear from someone at an Audubon center in PA where they use it. He said it was 100% effective at stopping bird strikes, and had the added benefit of making activity inside the building invisible to the birds, so birds will feed close to the window without being disturbed. On the other hand it does cut down on the amount of light coming through the window, and (like a window screen) makes the view a little less clear (and it's fairly expensive). One option might be to cut the film into strips and mount those vertically about 3" apart on the glass. This may not work for your house aesthetically, but it should be effective at stopping collisions, while obstructing the view less and saving money.

Please report back here if you try it.

Anonymous said...

Well, discussion on this issue seems to have slowed with the changing position of the sun and decreased daylight. But now the number of daylight hours is increasing again. . . I'm sure we all experience window strikes at varying times that change with the seasons, and I was getting 2-3 strikes a day last fall--my house has many large windows, and I have birdfeeders. As soon as the highlighter idea came to my attention, I grabbed the only highlighter pen I had in the house (Skilcraft chartreuse) and made inside marks on all the most troublesome windows. On some I made grids with no attention whatsoever to grid size or design; on others I simply drew a series of "S" waves back and forth. The window strikes came to a complete standstill on all treated windows. I have not noticed any strikes all winter, either--in past winters we would see feather marks on the panes fairly frequently--BUT in winter the reflections shift somewhat, and hawk/shrike activity was practically non-existent in our yard this winter. I haven't applied fresh highlighter for about 6-8 weeks. Therefore I'm not sure if the highlighter was effective over the winter months. I suspect the true test for my home will be spring and fall of 2008.
I don't think it is a coincidence that the window strikes stopped last fall. Without analyzing the scientific basis of this experiment, I can only say that I'm glad it seemed to work.

David Sibley said...

Thanks for the report! I've been watching my windows over the winter and thinking of renewing this discussion. The really interesting (confusing) thing here is that window collisions have stopped, even though I don't have any preventive measures up right now. So I'm ready to start some new experiments but I can't really start the next experiment if birds aren't hitting the window. Weird.

Thanks for posting comments here to report on your results, I look forward to hearing more.

Anonymous said...

Barry McGurk

Here in South Africa we don't have birds flying into the windows but a wood pecker pecking at the mirrored glass bathroom windows. He sits there for long periods pecking away....driving us mad and waking us every morning.

I'll try the UV pen and Iv'e ordered some UV decals...will let you know the outcome

Barry McGurk