Guest Essay by Kip Hansen — 7 February 2023
Hark! I hear birds singing. And I hear a study reaching out for attention.
The new study is about stickers that people apply to their windows hoping that they will prevent birds from flying into the window because they think that there is a clear route to some place of safety.
“A thump on the window, if you’re around to hear it. A dead songbird below. Many people seek to prevent this sorrowful scenario by warning birds away with decals or film applied to windows of homes and office buildings.” [ source ]
A 2014 study found:
“Building collisions, and particularly collisions with windows, are a major anthropogenic threat to birds, with rough estimates of between 100 million and 1 billion birds killed annually in the United States. However, no current U.S. estimates are based on systematic analysis of multiple data sources. We reviewed the published literature and acquired unpublished datasets to systematically quantify bird–building collision mortality and species-specific vulnerability. Based on 23 studies, we estimate that between 365 and 988 million birds (median = 599 million) are killed annually by building collisions in the U.S., with roughly 56% of mortality at low-rises, 44% at residences, and <1% at high-rises.”
National Audubon encourages homeowners to protect birds by applying anti-collision stickers to windows: “Those homeowners that want birds in their yard are probably killing most of them, unfortunately,” Kummer says. “The more birds that there are in the yard, and the more birds that are closer to a house and windows, the more likely that a collision is going to occur simply by sheer numbers.” “Use a Lot of Decals — Many forest birds readily dart between branches and leaves, so a single decal will not deter them.”
The New York Times covered the latest study, which only compared two commercial “invisible to the human eye” anti-bird-collision films, it did not study the effect of placing stickers with birds shapes on windows. (the most popular treatment). There have been other studies of various types that seem to show that stickers can help prevent bird-window collisions – but there are caveats.
1) The latest study with window films finds that films on the inside surface of windows are totally worthless – basically, did nothing. These types of films must be applied on the outside surface of the window. These films reflect frequencies of light easily seen by birds, but not by humans, all the while remaining fairly transparent. Pretty easy to apply to sliding glass doors leading to decks and patios and other first floor windows. Not so easy to apply to the windows of office buildings’ upper floors.
2) Other studies (not the new one) have found that adding lots of window stickers to the outside of windows helps prevent collisions. The most popular seem to be bird-shape stickers. Dr. John P. Swaddle, lead author of the latest study and author of many similar studies, is quoted saying: “People who are buying decals and putting them on the windows, they want to do good, they want to do right by the birds.” but if you are putting the sticker on the inside of the windows “Really all you’re doing is some interior decorating”… “You do have to take the extra step of putting it on the outside of the window.”
Additional recommendations from Cornell’s All About Birds for preventing bird window collisions are (excepted):
Treatments for Existing Windows:
To deter small birds, vertical markings on windows need to be spaced no more than 4 inches apart and horizontal markings no more than 2 inches apart across the entire window.
Tempera paint or soap. Mark the outside of the window with soap or tempera paint, which is inexpensive and long lasting. You can use either a grid pattern no more than 4 inches by 2 inches
Decals. Put decals, stickers, sun catchers, mylar strips, masking tape, or other objects (even sticky notes) on the outside surface of the window.
Dot Patterns and Tape. Long-lasting tape products offer an easier way to apply the correct spacing of dots across your window.
Acopian Bird Savers. Also known as “zen curtains,” these closely spaced ropes hang down over windows.
Screens. Installing mosquito screens over your windows is very effective
Netting. Cover the glass on the outside with netting at least 3 inches from the glass, taut enough to bounce birds off before they hit.
One-way transparent film. Products such as Collidescape permit people on the inside to see out, but makes the window appear opaque on the outside.
Other suggestions are to attach outside bird feeders directly to the windows or to locate bird feeders no more than three feet away from the windows (this is the solution we use at my home, along with exterior window screens on most windows).
The estimate of ~ 600 million birds being killed by colliding with windows in the United States annually is of course a WAG (wild guess) – but we should accept it as representing some significant number. If your home has frequent bird-window collisions, you should do something. I would suggest that frequent means more often than “it happened once”, your call.
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If you find yourself opening the plate glass slider with bird stickers on it to let the cat out – you have missed the real problem.
But we need to compare this to another study – even more shocking:
One of National Audubon’s repeating themes in its fund-raiser emails is to repeat Cornell Lab of Ornithology’s 2019 study’s finding that since 1970, bird populations in the United States have decreased by nearly 3 billion birds. Of course, this is an estimate made up of estimates. But there is probably no doubt that there are fewer birds today than 50 years ago, mostly due to changes in land use: conversion of forests to farms, tall grass prairie to rangeland and corn fields, etc. resulting in altered habitat availability. Some of this (very little) may be marked down to window collisions.
“We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals.”
Now, let me repeat that “free-ranging domestic cats kill 1.3–4.0 billion birds…annually.”
Compare that to “since 1970, bird populations have decreased by nearly 3 billion birds” – that’s 50 years.
But for free-ranging cats: in that same 50 year period — 50 times 2.65 (average of 1.3-4.0) comes to 132.5 billion birds killed by free-ranging domestic cats.
When we say “free-ranging domestic cats” we simply mean pet cats that are allowed outside of a home to roam free, at least part of the day and this obviously includes all feral cats.
Now, our first study today said that “between 100 million and 1 billion birds killed annually” “by building collisions in the U.S”. For building collisions read window collisions – very few birds collide with solid walls. Now that is a very wide estimate – the higher estimate is ten times the lower estimate.
But even the very highest estimate — 1 billion a year — is less than the lowest estimate for the number of birds killed by free-ranging cats: “free-ranging domestic cats kill 1.3–4.0 billion birds…annually.”
And there is a simple and sensible solution to this problem as well – keep your pet cats indoors and/or confined to your own property. Just like you do with your pet dogs (who will be picked up by Animal Control if they are found running loose). And this would apply to your pet cheeta, your pet tiger, your pet chickens, your pet pot-bellied pig, pet llama – in fact – like you do with all your other pets.
[ If I’m perfectly honest, there is one pet often intentionally allowed to roam free for a short time each day – pet pigeons. My father-in-law kept pigeons for years, in a coop that allowed them to fly free (when he raised a hatch) and was equipped with a one-way door for them when they returned, which they always did. ]
If you want to protect birds, keep your cat(s) indoors unless they have an outdoor cat run (such as these). And encourage your local community to pass local regulations requiring that cats be restricted to their owner’s property.
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Author’s Comment:
I like to write about interesting things – part of the purview of WUWT.
I like birds. Birds of all kinds. I like my backyard birds. I like raptors of all kinds. I don’t mind when the local raptors take a few of the song birds feeding at my backyard bird feeders. I even like our chickens – which are rather like little dinosaurs.
I like cats. Cats of all kinds. I like pet cats. Buy I don’t like free-roaming domestic cats or, worse, truly feral domestic cats. They are simply little killing machines – it is their nature and I don’t really hold it against them.
Every time I have mentioned cats as a problem, a battle breaks out in the comments. There are those who consider cats (and dogs) to be persons and think that they deserve all the rights to which homeless people are entitled. There are others who feel that truly feral cats should be rounded up and euthanized en masse. And yet others demand that the Trap Neuter Vaccinate Return (TNVR) approach is the best to deal with the large feral cat population problem.
Readers may comment on cats if they chose (WUWT has a very liberal commenting policy) but this essay is really about birds – and windows.
Address comments to “Kip” if speaking to me.
Thanks for reading.
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At our house in Utah, about two years ago a bird flew into one of four picture windows offering a panoramic view of the Wasatch Mountains, hard enough to crack the window, but not hard enough to kill the bird. Although we never found the bird, we suspected a bird impact because the window was too far away (and also uphill) from the back fence for someone to throw a rock at it from a neighboring yard.
Back in the 1970’s, the library at the college I attended had large picture windows, and the intake ducts for the ventilation system were below, covered by metal grates, and there were usually several small dead birds on the metal grates. Apparently the birds flew toward the library, got caught in the downdraft, and crashed on the grates. Students tried to remedy the problem by taping pictures of hawks or other predatory birds to the window (particularly on the ground floor) to scare away the small birds.
My parents also owned a cat when I was growing up in New Jersey, which would usually kill about three or four birds per year (as well as far more mice, chipmunks, and squirrels). If cats kill 4 billion birds a year, it would require about a billion pet cats similar in hunting skills to my parents’ cat, which seems to be a bit of a stretch for a country with 330 million people. How many American families really own three cats allowed to hunt outdoors?
Somehow, it seems like the most efficient bird-killer is wind turbines, far beyond the casualties inflicted by pet cats and windows.
Stevez ==> Well, there are about 90 million pet cats in the USA and an unknown number of feral cats. The stats on cats killing birds come from “kitty cam” experiments (quite a few of them now) that place a miniature video cam on pet cats for a week at a time and then count the kills. These studies have been repeated in many countries with the same shocking results. The worst damage is from cats killing hatchlings and nestlings of ground and low-nesting birds — not just adult birds, though some cats become quite skilled at what I believe the cats view as “sport”.
There are estimates from surveys on cats allowed to roam at will, at least part of each day, don’t have the data readily to hand.
As I have mentioned above, wind turbines kill mosty big birds, not songbirds (because they are harder to hit?)
Your bird strike must have been large bird moving at speed to crack a modern plate glass slider.
Your library windows with stickers may have been effective if the birds could see the pictures though it matters little what images were of — cats, dogs, spots, triangles, or raptors….it only needs to clue the birds that SOMETHING is there. They would be more effective on the outside.
Note: Even people walk into plate glass doors if distracted. Safety regulations had to be changed when I was a kid because way too many kids (and adults) would run through plate glass windows and be cut up by the falling glass. Now safety glass is required.
The only True and Humane solution is to immediately ban all windows… And windmills too!
GreatGrey ==> yes, there are draconian and nutty solutions of all kinds to all problems. In this case though, in your home, you only need a solution if window strikes are a problem — too many strikes on the same window means you maybe need to do something.
Wind turbines do need solution to the killing of big raptors.
The estimates seem high but I don’t see any way of confirming or denying it. However …
In 2020, there were approximately 518.3 million chickens in the United States.
https://www.statista.com/statistics/196085/top-us-states-by-number-of-chickens/
Compare that number with the median estimated annual bird vs window deaths at 599 million (above). I have a lot of glass and a lot of birds around my house but I know that the number of chickens I eat in a year is far above the number of dead birds I find.
And before you ask, there are no cats around to walk off with the carcasses.
roving ==> I doubt that cats make off with dead birds. Cats like moving interesting targets — its in their genes. (Think cat toys) — even laser pointers). Estimates are very wide…uncertainty is high.
Not all windows are subject to bird strikes.
If the bird death stats included chickens and turkeys, the numbers would be much higher.
I strongly suggest that anyone at risk for finding this ariticle persuasive look up “fear factor” in relation to biodiversity. A good start is to be found at:
https://academic.oup.com/bioscience/article/66/8/625/2464152
I confess to having window stickers both outside and inside some of my windows. They’re ugly, overpriced, not very effective, and outside they fall off and blow away easily.
OTOH, I’m a keen armchair bird watcher and photographer. I have several bird feeders, and go to consicerable lengths to make them inaccessible to the neighbourhood cats. But I find the birds unappreciative of the security measures provided. Many prefer to feed on the ground .
I spend a lot of time sitting by the windows overlooking my backyard, and I often have a dozen or more birds on the feeders. And when I hear a window collision, I’m quick to look for bodies, but can’t say I’ve found any dead ones in many years in this location. They appear to bounce off and keep flying.
I have a single cat adopted from life in the street. He’s neutered, but can’t be cured of his urge to be out and about and to hunt, no matter how amply jhe’s nourished at home. He insisted on going out a -22C last week, when no birds had been around for quite a while.
I guess he’s a bit of a maverick, seemingly preferring non-native species (sparrows) to native ones. But mostly he goes for mice.
I bother to comment on this because I feel it’s the same sort of hate-mongering “research” that would disarm all lawful firearms owners, except our big brothers, of course, on the pretext of stopping violent crime. Only in this case, the target is feline pets, whereas the real problem is unneutered feral cats.
otropogo ==> The studies are not meant to add to the “fear factor” however, advocacy groups use the studies, with exaggeration and without caveats, to scare people into donating money to them.
There are better window appliques for outdoor use that don’t fall off or blow away.
Like all types of collisions, the results depend on speed and mass and direction.
Your cat is not a maverick, about 50% of domestic cats are natural hunters — can’t help themselves. Some cats are not interested in active hunting.
The solutions are simple for cats, keep them indoors.
I’ve got low E glass at http://theviews.org/ and it’s pretty much opaque to UV, which birds can see. So, in spite of all that glass, we never get a bird strike. Some of the gold and bald eagles have found out that the vertical wall of glass produces a really good updraft, so I’ve had them get 8-10 feet out from the glass. That is quite a site!
mcsandberg007 ==> How big are those windows that give an updraft? Great story, thanks for sharing. Oh, found the website — fabulous home! I see that the updraft is also created by the site itself.
My knowledge is very limited but the few people I know who claim window success believe it to be because their window sticker (single) has the silhouette of a hawk.
Andy ==> It is questionable that the shape matters — but, anything that works, works.
This most supportable idea is that anything that the birds can see that allows them to identify the window as something (and not nothing, not just open space) does the trick.
Seems people are missing the obvious solution:
Get a wind turbine in your back yard.
/snark
“Tempera paint or soap. Mark the outside of the window with soap or tempera paint, which is inexpensive and long lasting. ”
How is tempera paint or soap long lasting? Not everyone lives in the desert that is California.
I live in a rural area.
My house has a sun room that I use as a greenhouse.
We have sliding glass doors.
Birds hit our windows frequently. Starting early spring and continuing through to mid summer (July).
Most hit a window because they believe they are being taunted by another bird and they hit the window trying to attack their opponent.
All of the windows have near branches on which they can perch and study their opponent.
Some of the bluebird males repeatedly attack the window from shortly after dawn till the sun passes behind the local treeline.
I have watched pigeons attack windows exactly the same way, only from inside a tall office building. Only they mostly flare their feathers and peck at their reflection while standing on a window ledge
Over thirty years we’ve had a few fatalities; a grackle, a hummingbird and a Carolina wren.
The hummingbird was chasing an opponent and didn’t turn as fast as the hummingbird he was chasing. That bird made a solid hit on the window and was dead when we opened the sliding door. We had been watching hummingbird antics from our dining room table just inside of the window.
We also have had red shouldered hawks eating an occasional songbird and non-songbirds in our backyard. The red shouldered hawks nest in our woods and we hear their whistle shriek most of the year, but especially when their ravenous young are out and about.
One morning, I watched the hawk finish devouring a dove on top of my bird feeder, then later ate a goldfinch.
What I’m trying to say, I suspect the grackle and the wren were possibly trying to escape the hawk. Red shouldered hawks are amazing woodland flyers.
When urbanites start estimating from rough estimates from unscientific surveys and abjectly sparse real data. Along with their imagination regarding possible means of bird extermination gives real meaning towards GIGO..
Their estimates ain’t worth using, for any purpose.
As far as I know, all of the large bird watching/conservation organizations bemoan wind turbine bird slaughterhouses as they make irrational claims about cats, birds and windows.
The trouble with hawks, dogs or cats eating wild birds is that they do not eat feathers. Which always leaves a pile of feathers.
Once while fishing I spotted a pile of feathers and two wings from an owl as I walked the path. From the prints, I think a fisher caught an owl that was snacking on a mouse.
The scene contained a pile of feathers and feathers don’t degrade rapidly.
My cat has brought me many mice and voles, a couple of rabbits, a squirrel and the Carolina wren already mentioned. He apparently collected it from the window where we had already seen the dead bird.
Unlike the rabbit and squirrel body parts, our cat wanted nothing more of the wren.
Several times while hiking or hunting, I’ve come across fox dens. Easy to spot because there are usually lots of bones and feathers near the den entrance.
We also have black snakes (a type of rat snake) and they do eat birds feathers and all. No feathers left behind. Owls also eat a fair amount of feathers and fur. The owl pellets found below their vantage spots show bits of feathers, fur and bones.
If food is abundant, birds will be abundant.
Our woods, hills and mountains used to have many very effective and efficient hunters, wild cats; the lynx, bobcat and puma.
Other areas of North America has other species of wild cats.
Prey populations boom, predators boom; prey populations collapse, predator populations collapse. It is a very natural order.
I’ll tell you what.
Every fall, grackle and blackbirds flock together in enormous numbers all along the East Coast of America. Flocks that spend significant time wheeling, landing, flying, circling heavily windowed high rises and office buildings in the urban areas.
These flocks swirl around very close to the windows frequently.
When the bird organizations can actually tell us definitively how many birds are in the flocks; how many chicks were hatched, raised and joined that year’s flock; exactly how many birds died at each and every building from every flock all demonstrated by hard evidence; then I will consider their evidence seriously.
Let’s see.
A couple of small birds will have up to three clutches a year contrainng 3-4 nestlings. They will do this for perhaps 3 years.
So each breeding pair will produce at least 25 nestlings.
Of whom 23 will have to die to maintain a stable bird population.
That is a 92% death rate. Of which some may fly into windows, and some may get found by cats, but the majority will starve. Or have heart attacks. Or freeze. And then be found by cats.
Birds will expand to fill the food supply. It’s that simple. Only top tier predators are in danger of hilltop bird mincers.
Ah, estimates… Going by the numbers in this study (the median kill rate, actually) – my house should be killing an average of a bit more than 3 birds every year. No window treatments, and the wife has feeders and bird baths scattered around the yards, both back and front, so probably we should have more than “our share” of kills.
Data.. In the 25+ years we have lived here, I have picked up a TOTAL of four dead birds after they thumped into one of our windows. ZERO in the last year (a pigeon did whack into the living room window – but when I was called out to dispose of it, it was already waking up from its unplanned nap, and flew off after a couple of minutes wobbling around).
Kills of feral birds by feral cats – yep, lots of those. Also a lot of kills of feral (and domestic) cats by feral canines. It’s called something like “the circle of life.”
As far as windows: would the regular old 8 x 11 residential-type window frames do some good? If so, seems it could be adapted to both plate glass on residences and not-so-high office-style buildings.
In ten years I have not found a single dead bird from window collision. One pretty little thing did hit the window and fell to a table below. Before I could take a picture it shook itself awake and happily flew away.
Perhaps the double glazing that is usual in this part of the world is a factor, Perhaps an abundance of trees for cover is a factor. There is certainly no lack of birds.
The birds seem to be pretty adept at avoiding cat predation and even seem to tease a cat by staying at a barely safe distance. The poor cats have much better luck catching mice. They earn my gratitude and a piece of dry loose dirt in my yard for their exclusive use.
Birds, as well as thieving deer, are encouraged by well stocked feeders at my neighbors and the many fruit trees and berry bushes at my place.
Only the most careless birds are occasionally caught. An example are the cedar waxwings which seem exceptionally careless, but are far from being endangered. They show up by the thousands at different times of the year to strip leftover fruit from the trees. They also seem to know when their favorites are ripening. They beat me to most of them. Cats will wait beneath the berry bushes and snag an occasional victim.
From my experience at least, the birds face very little threat from either cats or windows.