Birds fly into windows because glass reflects sky and trees, or shows a clear path straight through, and the treatment that reliably stops it is a pattern of markers on the outside of the glass with gaps no wider than 5 cm (2 inches). Which product fits depends on the window: dot markers suit large panes, removable clings fill in when it is too cold to apply markers, and UV decals work only as a backup.
Why Do Birds Fly Into Windows?
Birds do not recognize clean glass as a solid surface. A window that reflects branches or open sky looks like more habitat to fly into, and two windows lined up across a room, a glass corner, or a clear railing can look like an open passage through the house.
Any pane that shows a convincing reflection is a risk, whatever its size. Large picture windows facing a garden, patio doors, and glass near feeders or shrubs see the most strikes because birds are already flying close to them.
What Spacing Actually Stops Window Strikes?
Markers stop strikes only when they cover the whole pane with gaps no wider than 5 cm (2 inches) in any direction, which leaves no open space a bird will try to fly through. Each marker needs to be at least 6 mm across, and every marker belongs on the outside surface of the glass.
One or two bird shaped stickers on a large window do almost nothing, since birds simply aim for the untreated glass around them. The number of decals in a package matters far less than whether the finished pattern meets that 5 cm spacing.
What Works on a Large Picture Window or Patio Door?
Where a large pane reflects the yard, a grid of small dots applied to the exterior meets the spacing standard while leaving the view mostly clear. The Feather Friendly Decal, 1 Roll lays down 6 mm (1/4 inch) squares at 2 inch spacing, is rated to last eight years or more, and must go on the outside of the glass.
These markers need a glass temperature of at least 10°C to stick, so in most of Canada they are a spring, summer, or early fall job rather than a winter one.
How Much Treatment Does a Window Need?
One roll of Feather Friendly markers treats 16 square feet of glass, the size of a 4 by 4 foot window, so measuring every pane before buying avoids running short halfway across a door. A 6 by 8 foot patio door covers 48 square feet, which works out to three rolls, the amount packed in the Feather Friendly Decal, 3 Roll set.
Treating the windows that cause strikes first, then the other reflective glass around the house, spreads the cost without leaving the worst pane unprotected.
What Can Go on a Window When It Is Too Cold for Dot Markers?
Static clings can be applied in cold weather, which makes them a practical stopgap between a fall strike and a spring installation. Through a cold snap, the prismatic Birds Window Gems can be dipped in hot water and pressed onto the outside of the glass, and a pack holds seven bird designs from 5 to 7 inches across.
One pack of decorative clings will not reach 5 cm spacing on a large window, so they work best on small panes, as a temporary measure, or alongside dot markers once the weather allows.
Where Do UV Decals Fit?
UV decals are the least reliable option for a window that birds keep hitting. Their ultraviolet coating is harder for birds to see in shade or overcast weather, owls and some other raptors have little or no ultraviolet vision, and the coatings wear off relatively quickly outdoors.
Spaced every few feet and replaced every 9 to 12 months, as its own instructions direct, the Window Alert Transparent Bird Strike Deterrent leaves gaps far wider than the 5 cm standard. That makes it a backup for low risk glass rather than the main treatment for a problem window.
Frequently Asked Questions
Can markers go on the inside of the glass if the outside cannot be reached?
Rarely to much effect. Reflections on the outer surface hide markers placed indoors, so an upper window that cannot be reached safely is better handled with an exterior screen or professional installation.
How close should a bird feeder be to a window?
Very close, half a metre or less. A bird leaving a feeder that near the glass cannot build up enough speed to be seriously hurt if it does hit the window.
When are window strikes most common?
During migration. In southern Ontario that means roughly mid March to early June and mid August to early November, when large numbers of birds unfamiliar with the area pass through.
What should be done if a bird hits a window and is stunned?
Contain it and call a wildlife rehabilitator. Place the bird in an unwaxed paper bag or a small cardboard box with a few air holes, keep it somewhere dark, warm, and quiet away from pets, and give it no food or water, since birds that look only stunned often have internal injuries.
