Behavior & MigrationPreventing Window Strikes

Preventing Window Strikes

QUICK TIPS: To prevent bird strikes, do not place feeders near windows or move them closer (1-3 feet away) or farther away (25-30 feet.) Break up the reflection with fruit netting or CollidEscape window film.

Incoming. Bluebird striking window in territorial response. Photo by Barbara Burnham.Migrating birds, or birds startled at feeders or bird baths may crash into windows. Breeding adult birds, both male and females, and juveniles may peck or hit glass panes. The banging can start at dawn and last until dusk, for weeks on end. They may leave streaks of droppings on the glass. I had a female robin engage in this behavior, and if it weren’t the State bird, I think I would have hired a hit man.

This behavior is not just annoying or messy. Birds may be injured (fractured bones or bills, head trauma, internal bleeding, broken beak), killed, or eaten by a predator while stunned. According to David Malakoff (Audubon magazine, March 2004), window strikes kill between 100 million and 1 billion birds in North America each year, particularly migrating birds. 25% of North American and Canadian bird species have been documented striking windows. Window strikes are reportedly the most common cause of death associated with bird feeders.

Birds collide with glass for four reasons: either they:

  • cannot see the glass at all because it is transparent (especially a problem with two windows or a window and mirror opposite each other, creating a “corridor effect”)
  • see a reflection of the outdoors, and try to fly through what looks like unobstructed open space (the “mirror effect”), or
  • are attempting to defend their territory from a perceived intruder – their own reflection (“territorial strikes”). Bluebirds, cardinals, and robins typically do this. Territorial window strikes are more common in springtime, but may occur year round. During the fall, male birds often get a second flush of testosterone (called “gonadal recrudescence”).
  • some bluebirds are just “nosey,” and will cling to a window screen or will come to the window to beg for mealworms, but do not crash headlong into it. (See bluebirds apparently alerting hosts to problems.)

There are a number of options to prevent birds from striking windows. If the problem is the reflection on the exterior of the window, changes inside won’t help. Keeping blinds or shades drawn, or putting up a curtain inside rarely solves the problem, unless you are dealing with the corridor effect. In that case, light colored drapes or partially closed vertical blinds on sliding glass doors when the sun is shining direction on the window may help break up the reflection, or closing or covering the opposite window or moving a mirror may help. Otherwise, choose from the following methods – moving attractants ; dulling/breaking up the reflection, or putting up something that moves or is scary. Also see Plexiglas sides on bird feeders.

If you have a large house or lots of large windows/glass doors, you are may have a correspondingly large problem – especially if the bird has already developed the habit of going from window to window. Usually the bird will have a “favorite” window (e.g., facing east); deploy your countermeasures there first.

See below if bird is stunned. If you find seriously injured birds, contact a local wildlife rehabilitator.

Move attractants: feeders, bird baths, nestboxes and perches

  • Do not place feeders directly in front of windows.
  • Move bird feeders or bird baths farther away (25-30 feet from the window).
  • Put feeders or bird baths closer (within 1-3 feet of the window) so birds aren’t moving fast enough to get hurt. They are also more likely to see the windows.
  • Move nestboxes 100 feet or so from the building (to prevent territorial strikes).
  • If the bird is using a favorite perch or two while watching the window, try removing those perches, or temporarily blocking access to them (territorial strikes).
  • Don’t hang houseplants inside windows where strikes are common.

Dull, break up or otherwise eliminate the reflection on the exterior surface of the window. You’ll need to leave the material up for at least two or three weeks for territorial strikes. After a few weeks, the bird should get out of the habit. The sooner you eliminate the reflection, the easier it will be to break the habit. See Suppliers List to purchase commercially available items.

Remember to put the material on the outside of the window. For patterns/objects placed on windows, they should uniformly cover the entire glass surface, and be placed no more than 2-4″ apart.

Most effective:

  • Drape or tack thin netting (fruit or crop, small mesh like 1/2″, sold garden centers and home improvement stores, or volleyball net), a soft fabric screen, or shade cloth over the outside of the window. It can hang loose, stretched taut, or tacked onto a frame. It is unattractive, but supposedly 100% effective.
  • Suspend old window screens, storm window screens or screen do rs in front of the windows birds are hitting regularly.
  • Apply a material like CollidEscape, a window film with small perforations that reduces exterior reflectivity and transparency. Je
    collidescape photo by Jennifer Brown
    CollidEscape film on window, photo by Jennifer Brown. She says you don’t even notice it is on from the inside (see photo above.) Easy to self-install – just clean glass, spray with soaping water (dish detergent + water), peel sticky backing from film, apply to glass and smooth out any wrinkles using a squeegee/our hands. You can move it around a bit until the water dries underneath. It is supposed to last 3-5 years at least. Jennifer has had no strikes since installing it, and she used to get several per month.

    nn in NH said this worked when fishing line, hawk decals, and moving the feeder and birdbath didn’t. She has not had a single dead bird or strike since it was installed. Looking through a window with CollidEscape on it is similar to looking through a screen window. It also reduces the amount of UV infiltration (which can bleach hardwood floors.) She found that since birds can not see inside as well, so she is able to observe them better. See photo on a picture window.

  • Apply a material such as products used on greenhouses to make glass opaque, or plastic applications that make glass look frosted, or frost the window yourself.
  • If the bird is attacking car mirrors, cover them with socks, shower caps, or put bags over the mirrors.
  • One inch vertical white cloth strips, four inches apart OR one inch horizontal strips two inches apart. Strips of tape, or streaks of soap, no more than 10″ apart, may also work. Vertical stripes are most effective. You can buy cords called Acopian Bird Savers – I don’t know anyone who has tried them though.
  • Bird Crash Preventer – preassembled “curtain” of monofilament lines strung between two aluminum square tubes. This “curtain” is supported by brackets over the exterior of a window. Not for use on a moving sliding door.
  • Feather Guard (6 feet long strings with 5 colorful feathers, attached to glass with 2 suction cups) – Greg Robert Pet Supplies – my mother said these did not work for her.
  • Cloud the outside of the window with something that will leave a non-reflective, opaque or chalky surface on the glass. Brasso, glass-wax or fake snow, Epsom salts mixed with beer, a light smearing of toothpaste applied with a damp sponge, or other products that do not have abrasives that will scratch glass (check instructions to verify that they are okay to use on glass and can removed with a sponge and water.)

Other choices:

  • Tape newspaper, architects paper (opaque), cardboard, or sheets over the outside of the windows.
  • Cover windows with clear gift wrapping with a light colored patterns (available in 40″ roll) and replace when it loses its static cling (every few years),
  • Cover windows with plastic food wrap (e.g., Saran or Glad wrap). If needed, spray a light coating of vegetable oil like Pam on first to get the wrap to stick. Wax paper can also be used.
  • Plant shade trees planted outside the window to cut down on the reflection.
  • Install window dividers (snap on type)
  • Let your windows stay dirty.
  • Stick “post-it” notes or the little round, white reinforcements rings for three-holed notebook paper all over the window.
  • Put a hanging plant outside the window.
  • Suspend/drape tree branches in front of the most frequently struck windows. Get good coverage over the pane of glass without completely eliminating the view. This may slow birds down (as they plan to negotiate through branches) enough to allow time to swerve/land on the branches.
  • Consider installing awnings that can be lowered at night or raised when you want a view.
  • Tape 1 foot squares of aluminum foil to the outside of windows.
  • Place commercial decals (also called “window clings”) like dots, spider webs, or bird silhouettes or other shapes (e.g., leaves, snowflakes) or leaded glass on the glass. They work better on the outside; but will last longer, stay cleaner and are easier to put up on the inside. Space decals uniformly, two to four inches apart (which is about as far apart as a grown man’s stretched out hand). You can buy them at some hardware stores, Wild Birds Unlimited stores (pack of four for $8)or at Whispering Windows. Wash right over them. These may have limited effect – some say they must cover 80% of the glass surface to work. One person using a Hawk decal did see a reduction in the number of goldfinch strikes.
  • Dim or turn off night lights during migration season.
  • Put bright lights on during the day to eliminate the reflection and allow birds to see what’s inside — human stuff — rather than the reflection that results from darkness inside and bright sunlit objects outside. Turn the inside lights off as dusk approaches. (for territorial strikes)
  • Try yellow highlighter X’d on the inside window as one big X or several little X’s. Humans can’t see the yellow on the window but the birds can (untested – see Sibley’s blog.)

Put up something that moves or is scary (best for territorial strikes)

  • Build a “feather guard.” String bird feathers strung about 8 inches apart on fishing line, and then string them vertically (no more than 10″ apart) across regularly struck windows.
  • Hang something that moves in the breeze in front of the window: mylar (at least 3/4″ strips cut from a Happy Birthday sign hung a few inches apart, or in the form of a sparkling wind sock, or attached to a paper town cardboard roll that is suspended from a string in front of the window); old CDs, tin foil pie pans, colored balloons, short strips of plastic surveyor’s flagging (available in rolls), strips of a plastic garbage bag, or yarn.
  • Thumb tack string diagonally across the windows, in an “X” shape. Tie strips of cloth or surveyor’s tape (colored plastic strips) to the string so the ends flutter in the wind.
  • Hang kinetic sculptures like the long, twirling rainbow colored plastic ornaments (that look like icicles) that can be found in birding/gardening stores.
  • Hang CDs (shiny side out) on small suction cups with hooks.
  • Make a color copy of a photograph of a local barred owl, and tape it inside the window (territorial strikes).
  • Drape rubber snakes on top of the window frames, hanging down just a little (works best with pecking).
  • Try putting a stuffed animal in the window.

Plexiglas sides on bird feeders

  • If your bird feeder has Plexiglas sides, birds may panic when trying to exit and crash into the Plexiglas side(s). Most people put tape on it, or mark it (with a plaid design, stripes, crosshatching, or X’s) with a permanent black magic marker or black electrical tape so the birds don’t try to fly in/out that way.

What usually doesn’t work:

  • Hawk/owl/crow silhouettes (commercial or traced onto black paper or vinyl), owl decoys, blinking lights, eyeball patterns, wind chimes are typically NOT very effective. Several people even reported that a bluebird attacked a silhouette. Hawk silhouettes work better if they move (e.g., hanging from a chain/rope.)

What to do with a stunned bird:

If the bird does not recover in a few moments and is motionless, put an upside down box or colander over it, or place it in a small box with a lid, or a grocery bag that has been folded closed. Put the container in a warm, quiet location. Do not attempt to force the bird to eat or drink, but you can leave a small bowl of water in the box/bag. Avoid handling the bird. Release it outside as soon as it is alert and active (usually within an hour.) If the bird is seriously injured or doesn’t recover in a few hours, contact a local wildlife rehabilitator. More on what to do with injured birds.

References and More Information:

Sometimes they don’t stop for a long time and seem determined to brain themselves. I wonder if birds ever become self-destructively psychotic. Some of these head-bangers act as though they’ve really lost it. They slam themselves into the glass all day long and seem to find no time to eat or tend to their reproductive responsibilities.

Bruce Burdett, NH Bluebird Conspiracy, 2001


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