Acopian BirdSavers FAQ (Frequently Asked Questions)

The reason birds don’t fly into glass that has paracord in front of it is because the birds see the paracords and try to avoid them. Think about birds flying through the woods - there are many branches that they avoid flying into while they are flying through the trees. I think that birds ‘see’ the BirdSavers cords as branches and therefore don’t fly into them.

Birds sometimes do fly into solid objects. Think about people ¬- we have all bumped our heads on an object or walked into an object or even walked into a glass door by mistake. When this happened, you may not even have been walking very fast or maybe you were standing still or simply turning around. Just imagine, when that happened, if your whole body was moving at the speed that a bird moves when it is flying. Now think about that fast moving bird and what it sees as it’s flying. If the bird is looking down, it won’t see what is in front of it with 100% of its attention. It’s possible for the bird to fly into objects by mistake. And this does happen to birds. On rare occasions, they even fly into sides of windowless buildings! If a predator is chasing a bird, it is in grave danger and therefore giving all its attention to escaping the predator and not full attention to the direction it’s headed. So glass is especially dangerous to flying birds, because even if the bird has 100% of its attention on where it is flying and is looking directly at the window glass, the reflection of the surroundings on the glass could “tell” the bird that it’s OK to fly “into” the glass. This reflection appears like more trees or open sky, and they hit the window going full speed, head first, resulting in injury or death. BirdSavers cords in front of the glass have proven to reduce these types of collisions to almost zero.

2. We are having an issue with a bird that repeatedly flies into our window. We wake up every morning with this same bird flying into our window. I know BirdSavers don't work for that problem, but do you have any suggestions or advice to get this bird to stop this annoying behavior?

Acopian BirdSavers are extremely good at preventing birds from full speed flying into glass, but BirdSavers will not solve the problem you have. Your problem (called territorial aggression) is the bird seeing his own reflection and then “attacking” his reflection in the glass. One product I can suggest you try, to solve that problem, is called Collidescape. This product will eliminate the reflection in the glass and the bird will go away. Unfortunately, your view through the glass will be somewhat diminished, but some people don’t mind this aspect of Collidescape.

2a. There is a woodpecker that flies from one window to another and hangs from the BirdSavers cords - he doesn't peck the windows, just hangs from the cords. Do you know why?

I don’t have an explanation for why birds sometimes hang from BirdSavers cords. A few other people, over the years, have written me to say (sometimes with photos or videos) that birds sometimes perch on their cords, and that they really enjoy seeing birds that close! I’ve had BirdSavers on my house for over 30 years and have never seen any bird do that. I wish they would, because it certainly seems like a good way to see a bird close-up!

3. What is ‘paracord’?

The word ‘paracord’ is an abbreviation for ‘parachute cord’ and is the nylon cord used in the suspension lines of parachutes.

3a. When the cords are attached at both the top AND bottom, the cords sometimes become floppy on very tall BirdSavers. Is there any solution to this floppiness?

Depending on the atmospheric weather conditions, this can sometimes happen. This only becomes noticeable if the cords are attached at the bottom for cords that are over about 8 feet in height. The solution is to use polyester cord instead of nylon cord.

4. Can BirdSavers be mounted on the inside of the window?

BirdSavers should be mounted on the outside. The reason birds don’t fly into glass that has BirdSavers in front of it is because the birds see the paracords and try to avoid them.

If the BirdSavers are on the inside, the birds most of the time, depending on the outside light, won’t see the cords. Normally, the cords serve to break up the reflection of the outside surroundings that the birds see in the glass from the outside. When the reflection is clearly visible to the birds, if the cords are on the inside they will not be visible to the birds.

Here is a sad example of this:

A multi-million dollar building was recently built at Lafayette College in the BirdSavers hometown with a bird protective fritted design on many of that building's huge windows. Unfortunately, the bird protective fritted design was put on the INSIDE surface of the glass! We are not sure what the reasoning for this was, but it hasn't been as helpful for the birds as it should have been if the bird protective fritted design had been placed on the outside surface of the glass. Monitors at this building find dead birds under these windows much more often than should be found under windows that have a bird safe application on the windows.

5. Do BirdSavers work for small birds, like hummingbirds?

Yes. Many people use BirdSavers specifically to protect hummers. You can read some of their stories here. Recently, we have seen a few misleading posts on the internet that BirdSavers cords should follow a "2 inch spacing guideline". The American Bird Conservancy explains this misunderstanding best when they say, "the 2 inch spacing guideline refers to two dimensional patterns and does not apply to Acopian BirdSavers". With over 14 years of practical experience with Acopian BirdSavers at the 4 inch spacing, we can confirm that that spacing is very effective even for small birds. You can read more about 2” vs. 4” spacing in this BirdSavers FAQ.

6. Why don’t the bottom of the BirdSavers cords go all the way to the bottom of the glass?

When I make BirdSavers, I make them so that the cords do not go all the way to the bottom of the glass, because it looks more aesthetically pleasing when you can see an inch or two of space between the bottoms of the cords and the bottom of the glass. In other words, they look cool! But it makes little difference if the cords stop an inch or two above the bottom of the glass or if the cords go all the way to the bottom of the glass.

7. Why aren’t the paracord lines attached at the bottom? Don’t the lines get tangled when it’s windy?

Many people like the motion of the cords as they move in the wind, hence the alias name “Zen Wind Curtains” (others have come up with their own names such as "Acopian curtains", "paracord curtains", "cord curtains", "Acopian blinds", "bird deflectors", "string system"). BirdSavers cords DO NOT get tangled as much as one might think. A cord may get crossed over another cord sometimes. If that does happen, you can easily untangle the cords with your hand, or if it’s too far to be reached by hand a long stick or pole can be used to untangle them. At one of our Pennsylvania sites, where there is a lot of wind, the cords almost never get tangled. And when they do, it’s very easy to untangle them. It’s difficult to tell if a windy site will have a ‘tangling’ problem to the point of annoyance. ‘Tangling to the point of annoyance’ does not happen often, but it does happen at certain sites. On about 5% of windows with BirdSavers installed, the tangling problem was an issue. On certain windows in certain situations the wind tangles the cords (or a cord or cords may get blown to the side of the glass and then get caught on something that sticks out from the side of the building next to the window). The “Monofilament Snaring Technique” works very well to eliminate that annoyance! Or if you have purchased BirdSavers, you can always purchase a Bottom Tie-down Cord later if wind becomes an issue.

“Monofilament Snaring Technique”: To keep the cords from ‘blowing in the wind’ take some light weight fishing line and about three inches or so from the bottom of the BirdSavers cords, attach one end of the fishing line to the window frame. Then simply wrap the fishing line around the first cord, then move to the next BirdSavers cord and wrap it around that cord, then wrap it around the next BirdSavers cord until all the BirdSavers cords are ‘ensnared’. Then attach the other end of the fishing line to the window frame on the other side. It sounds complicated, but it’s rather simple. And it does work.

For especially inaccessible locations, we can make BirdSavers with a Bottom Tie-down Cord which can be ordered here:

8. I’m going to make my own BirdSavers and I’m wondering if it is okay to attach the cords at the bottom? Does it matter to the birds?

The cords can be attached at the bottom. The reason the birds don’t fly into the glass is because they see the cords and try to avoid them. So it really doesn’t matter whether they are attached at the bottom or not. It’s up to your personal preference and ease of installation.

9. How far apart should I space the BirdSavers paracords?

We space the Acopian BirdSavers paracords four and one quarter inches (4-1/4˝) apart. 4-1/4˝ spacing seems to be a very good balance between the visual aesthetics of the paracords on the window and the protection of the birds. Many people think Acopian BirdSavers look so cool that we’ve actually given them the alias name of “Zen Wind Curtains”. One young person told us that she can’t wait to own a house so she can put “Zen Wind Curtains” on the windows because they have such a calming effect on her! Because some people worry about the possibility of smaller birds trying to fly between the cords, although this very rarely happens, the paracords can be spaced closer together than 4-1/4” if you prefer (see DIY tables for 4-1/4, 4”, and 3.5” spacing). Please keep in mind that birds sometimes even fly into solid objects with no windows! (See FAQ – “Why do BirdSavers prevent birds from flying into windows?”)

10. Is it better to have 2” x 2” spacing or 2” x 4” spacing between visual indicators on a window to prevent birds from flying into the glass?

We can’t speak for other methods, such as dots, decals, or lines on the glass, but we have plenty of experience with BirdSavers.

The effective spacing for BirdSavers is about 4” between the vertical cords. Dr. Dan Klem’s research has proven that birds will avoid flying through spaces that are 2” high or less and 4” wide or less (this is known as the 2” x 4” Rule’). We space the BirdSavers cords 4-1/4” apart. Because the cords themselves are 1/8” thick, the BirdSavers we custom make are actually spaced at 4-1/8” apart. Because BirdSavers are extremely effective, even with that extra 1/8” spacing in the width, perhaps the name should be changed to the 2” x 4-1/8” Rule.

When asked about the suggestion that someone made to change the 2” x 4” Rule to a 2” x 2” Rule, Dr. Klem responded:
“None of my experimental results have changed since I published them in the 1970s. The 2” x 4” Rule has only been reinforced by further actual field testing. Perhaps, and I am perhaps-ing, to speculate that some are being conservative in reducing the distance between pattern elements to ensure the overall pattern is a “more” distinct barrier for birds to avoid. But the “more” part is an error in my view; if anyone asks me, I would offer the same answer: the 2” x 4″ Rule is valid and has not been changed to a 2” x 2″ Rule. If in practice anyone followed a 2” x 2″ Rule it would offer the same effectiveness as a 2 x 4″ Rule.”
-Dan Klem, Jr.

Although the idea of reducing the recommended horizontal spacing from 4” to 2” may sound logical, it is misleading! There is no scientific research, or any other evidence, to support the idea that just because a bird is smaller, that the cords need to be 2″ apart to deter bird-window collisions. On the contrary, after ten years with Acopian BirdSavers used in many places throughout the world, we have seen that the BirdSavers work as well or better than the 90-100% reduction of bird window collisions that were the results from Dr. Klem’s field tests.

Keep in mind that nothing is always 100% effective in eliminating bird-window collisions; birds sometimes even fly into solid objects that have no windows!

The supposed rational to use 2” vertical spacing (instead of the proven 4” spacing) is that ‘maybe’ small birds, such as hummingbirds, may try to ‘fly through the cords’. This hypothetical scenario made me think of a couple in May 2014 who were beside themselves because many hummers had hit their windows and died. They had four 103″ tall sliding glass doors next to each other (a total glass area over 12′ wide). I sent them BirdSavers to cover all that glass and hadn’t heard from them since. I called them two years later to see “how the BirdSavers were working out for them”. They said they hadn’t had any strikes since they put up the BirdSavers. You can read more about hummingbirds and BirdSavers here.

To get some idea of how well BirdSavers spaced at 4-1/4″ work, please read 140 users comments about BirdSavers here.

Recently I was at the Williams Visual Arts Center at Lafayette College here in Easton, PA., where I had installed BirdSavers three years ago. The Bushkill Creek runs right next to the facility and there are many species of birds in the immediate vicinity. On my recent visit I met a professor who has been there for 16 years. I was introduced to him as the ‘fellow who put up the BirdSavers a few years ago’. He said “thank you very much. It was horrible before when you’d hear a thud so often and then find a beautiful dead bird under the window.” He said that since the BirdSavers had been installed, there have been no more “thuds”.

11. What does a window look like with cords hanging in front of it?

The idea of “strings dangling in front of a window” does sound a bit odd. But once people actually see BirdSavers on a window, they are amazed. They look very good. Many people think Acopian BirdSavers look so cool that we’ve actually given them the alias name of “Zen Wind Curtains”. One young person told us that she can’t wait to own a house so she can put “Zen Wind Curtains” on the windows because they have such a calming effect on her! And we hear this type of comment regularly.

Acopian BirdSavers are elegant looking, easy to install, inexpensive to make yourself, long lasting, and they work. And a vast majority of people who actually see them on a window think they look cool. What more could you ask for?

12. I don’t want to drill holes into my window frame. Is there another way to mount the BirdSavers?

I understand your reluctance to put holes in the window frame. I was the same way once, many years ago! But we have been using Screws and Clamps to mount BirdSavers at many places and have had no bad effects. We use very small screws (#6 x 3/8” stainless steel sheet metal screws). The holes for the Screws and Clamps Mounting that we use are very small. (You can use a 7/64” size drill bit to make a pilot hole if necessary in frames that are not wood) and the holes are 'filled in' with the screw so the big thing that people always seem to worry about -leaking - is not an issue.

An alternative to using Screws and Clamps is to use Velcro, but the Velcro will eventually fail. Depending on many variables, Velcro can last anywhere from one month up to four or more years.

Another option is to mount the BirdSavers using 3M Command Outdoor Light Clips (Model #17017CLR-AWES). Many people who have made their own BirdSavers have had great success with these.

13. I made my own BirdSavers, but the white inner strands of the cord show where the cord is cut…

This can happen when the center strands of some supposed “nylon” paracord is actually made of a material other than nylon. If the center strands are made of nylon, then simply briefly burning the end with a match will seal it very nicely. If the center strands are still exposed after burning the end with a match, then the center strands are definitely made of a material that is not nylon. So a different approach is needed: Cut the paracord to the length you want. Then slide the outer nylon sheath back about an inch, so that all the center strands are exposed. Then cut about a half an inch or so off of the center strands. Then slide the outer nylon sheath back to it’s ‘original’ position and take a match to it briefly so it melts. Now you should have a very nice, clean looking end! Watch the I made my own BirdSavers but even after melting, the white inner strands of the cord show video of this procedure.

14. Can I make BirdSavers using paracord with a color other than dark olive green?

We have been using dark olive green colored parachute cord for many years and it has proven very effective, as well as aesthetically pleasing. The results of scientific tests conducted by Dr. Daniel Klem, Jr., confirm our own conclusions that Acopian BirdSavers with dark olive green colored parachute cord are very effective in preventing bird-window collisions. (The results were also published in The Wilson Journal of Ornithology.) We are fairly certain though, that any dark color, or for that matter probably any color or any type of cord, will be just as effective as the dark olive green color paracord.

15. My window glass is quite a few inches away from where I intended to hang my BirdSavers. Does the BirdSavers paracord need to be right next to the glass?

The paracord does not need to be right next to the glass. The paracord can be touching the glass or it can be much farther away from the glass. As long as the paracord is between the bird’s possible flight path and the glass, the bird will see the paracord and therefore not fly into it or the glass behind it.

16. Is it necessary to hang the BirdSavers on the screened part of the window?

Screens in front of glass is a good deterrent to birds. You shouldn’t need to put BirdSavers cords there.

17. We have casement windows that open outward, like a door. How do you attach the BirdSavers so they don't get tangled when opening or closing the window?

The BirdSavers should be attached to the frame immediately above the glass of the casement window, so that when the window is cranked out (or the door is opened), the BirdSavers cords move with the window (or door). See a photo here.

18. How do BirdSavers and Bird Screens compare?

Patrick Coy, who has experience with both, will answer that question:

We live in the Cuyahoga Valley National Park in a home with many windows, and many feeders. We had far too many strikes far too often. But when an annually reliable Yellow-bellied Sapsucker was killed when he flew into my study window, I finally dealt with the window strike problem by installing Bird Screens on the outside of the windows.

Hung about two inches away from the window glass on the outside of the window, bird screens are nearly 100% effective due to the double effect of the screens breaking up or eliminating the reflection from the glass, and, if a bird were still to make a mistake, the screens act as a sort of trampoline and dramatically reduce the force of the impact.

But over many years, we found there are three other problems with bird screens:

They dramatically reduce the clarity of your view from the inside of the house.
They get dirty and must be cleaned/vacuumed.
Critters like squirrels and raccoons will try to climb up them to get to the feeder hanging in front of the window, sometimes ripping them.

Last year I took all of our bird screens down and installed Acopian BirdSavers. These are quite simple; a single dark-colored nylon cord is hung vertically in front of the outside of the window glass, from top to bottom. These single nylon cords are spaced about every 4 inches apart across the horizontal width of the window.

The idea is that birds are used to flying through the woods, avoiding branches and the presumption is that they recognize these dark nylon cords, perhaps because they look similar to dark branches and they are used to recognizing branches.

Jeff Acopian developed and continues to refine the Acopian BirdSavers tactic. In addition, the Acopian Center for Ornithology at Muhlenberg College and Dr. Daniel Klem, Jr. conducted field tests in a wooded opening in a Pennsylvania forest with bare windows and windows with BirdSavers, with the cords hung at various distances apart from each other, all set up in front of a feeder station. All window strikes were recorded and compared. It is good science. (You can read the test results here and here.) The result was the nylon-corded windows with the cords hung at 4.25 inches apart fared quite well, reducing window strikes by upwards of 90% compared to unprotected windows.

My experience is about the same. We do occasionally get a window strike, but they are very far and few between and when they happen they tend to be quite “soft,” as the birds must try to pull away at last second due to the cords. The only exception are the rare panic strikes when our resident Cooper’s Hawk hunts our feeder station.

You can easily make your own BirdSavers and the Acopian BirdSavers web site shows you how. You can also send in window dimensions to them and they will make them for you. The latter approach is more pricey; the former approach is cheap, easy, and personally satisfying. I made all of ours except for four on our third floor casement crank-out windows; I ordered those pre-made.

There are other benefits to hanging BirdSavers cords on your home. All of your guests will inquire about them and it creates an opportunity to educate about window strikes and to promote responsible bird feeding, and responsible home management. Moreover, the cords actually look kind of cool from the inside; I was worried it might give our home a “prison-like” feel, but on the contrary, the cords actually lend a kind of elegance.

Let’s save the birds from our windows.

-Patrick Coy
Peninsula, OH

19. Do the BirdSavers need to be on ALL the windows?

Not necessarily. I’ve found that even though there are lots of windows on a wall, sometimes the birds only fly into a particular section. I don’t know why that is, but it is something I have observed. So it would be a good idea to put BirdSavers on the particular panes of glass that the birds are hitting.

20. Birds Crashing into windows – Is this really a problem?

When people think of bird mortality they usually think of cats, wind turbines, and pesticide poisoning, among other causes. In fact, in North America the largest number of birds are killed each year by glass! Windows in our homes and other buildings can be deadly to birds. Many people do not realize that birds are killed at the windows they look through unless they happen to be there when the bird hits the window. Birds that die directly under the offending window are often taken by scavengers – cats, raccoons, skunks, chipmunks, other birds, etc. If it is a window where many birds die from collisions, even though you do not realize that birds are dying there, scavengers know and routinely check the area for fresh food. Many times, the bird that just hit the window dies immediately. Other times, the bird may fly away only to die later. Sometimes birds recover if the strike is not too severe.

Although the “incidental, accidental, or unintentional take of migratory birds” is a criminal violation of the Migratory Bird Treaty Act, the U.S. Fish and Wildlife Service does not arrest anyone when birds are killed at windows! This is a good thing, as windows kill lots of birds. Because this problem is so overwhelming and there are no easy solutions, the USFWS doesn’t even attempt to deal with the problem!

One window manufacturer in the USA has developed a clear film that can be applied to existing windows that does reduce the likelihood of birds colliding with them. The film works remarkably well, but the manufacturer has not yet decided to market this product.

Until glass manufacturers design and manufacture window glass that deters birds from flying into it, and until people begin to use it, you might think there is little you can do to effectively eliminate this problem. But in fact, Acopian BirdSavers can significantly decrease or eliminate the incidence of birds killed at your windows. A vast majority of people who have Acopian BirdSavers on their windows or have seen Acopian BirdSavers on windows, if they even notice them, admire their elegant appearance and are happy to be killing few, if any, birds.

21. What is “Acopian” and how did Acopian BirdSavers come to be?

The first Acopian BirdSavers were made in the mid-1980s. Being a family of engineers and naturalists, we (the Acopian family) were upset when we realized that the windows of our home were killing birds as they flew into them, and we decided to try to figure out a way to stop the killing. The first Acopian BirdSavers were made from those “stylish hanging curtain beads” that were fashionable years ago. We took the individual bead strings apart and rehung them about every 4 inches in front of the offending windows. We had remarkable success on the first try. It worked! But our rooms faintly resembled those of a hippie pad with those beads hanging on the outside of the windows. But it was better than killing birds. And for some reason, the birds that previously were hitting the windows seemed always to be “rare” birds – species that we hardly ever saw. It was exciting to see them, but not exciting to see them dead.

In the early 1990s our family started the Birds of Armenia Project, with the goal of publishing a field guide for all the birds that occur in the country of Armenia. It took six years to complete the project, with the eventual publication of three books and one map;

Collaborating on the project were an Armenian ornithologist, Dr. Martin S. Adamian, and an American ornithologist, Dr. Daniel Klem, Jr. As we found out during the six years we worked together on the project, Dan Klem had done and was still doing pioneering research regarding glass and avian mortality. He was the world’s foremost authority on bird-window collisions!

He impressed upon me that birds flying into windows can happen anywhere. I thought the problem we had with birds flying into our windows was unique to us because of our house’s situation. I had no idea that glass anywhere could cause (and was causing) bird deaths. For many years Dan lamented to me that birds were being killed by windows everywhere and no one, not even those in the ornithological community, was doing anything to solve the problem. He also stressed that there was no good solution to this problem. Well, WE had a solution; our hippie beaded curtains!

Our ‘beaded’ BirdSavers lasted many years. As far as we knew, we had zero bird kills on the windows with these first-generation BirdSavers. The beads eventually began to deteriorate, and we couldn’t find more to replace them (this was before the internet). Our second-generation BirdSavers used very thin bamboo poles. These also worked, but they didn’t look as nice as the “beaded” ones.

Eventually we started experimenting with parachute cord. It turns out that this worked beautifully to stop birds from hitting the windows, and as an added bonus the paracord looked good on windows; BirdSavers have been variously described as “elegant” and “Zen-like”. The current design is easy to install and can be easily removed, although as far as we know, no one who has put up Acopian BirdSavers has taken them down. People like the way they look and think they look cool!

Because of Dr. Klem’s passion about this topic and after many years of him lamenting to me that there were no good solutions to prevent birds from crashing into windows, in 2010 I decided to create a website to tell people about the Acopian solution; effective, good looking, and easy to make. We decided to call this solution Acopian BirdSavers with the funny spelling of ‘BirdSavers’ as one word, with a capital B and a capital S. We also came up with the alias name of ‘Zen Wind Curtains’ because the BirdSavers move in the wind and they really DO have a calming effect on people when seen from inside a house or building. Because some people don’t want to make BirdSavers, and yet they have a desire to protect birds from being killed at their windows, we make custom BirdSavers for ANY SIZE window and they can be ordered online. But I also feel that a vast majority of people will want to make Acopian BirdSavers themselves, so we show how to make BirdSavers as well. We get many people emailing us to say they made BirdSavers, the killing has stopped because of the BirdSavers, and thanking us for making this simple solution available.

22. A Plea to Use BirdSavers

Acopian BirdSavers are a very simple, elegant, aesthetically pleasing solution to the major problem of bird window strike kills. I feel that once anyone uses this design, they will be convinced that it should be at the top of anyone’s arsenal of techniques who desires to easily prevent bird-window collisions. A vast majority of people who have Acopian BirdSavers on their windows or have seen Acopian BirdSavers on windows, if they even notice them, admire the aesthetic look of them. And people who have them on their windows are happy to not be killing birds anymore.

I feel great satisfaction when BirdSavers are used because house or building aesthetics are not compromised, birds are being saved, and people are happy with the results.

Where are BirdSavers?

Advances in Window Safety Come to the Cornell Lab and Cornell Campus

Q&A: How Jeff Acopian Invented BirdSavers And Made Windows Safer for Birds

- Jeff Acopian
Easton, Pennsylvania