By Kathryn Stocks

In Canada, window collisions kill somewhere between 16 to 42 million birds a year. It’s an alarming number.

Most bird activity occurs between the ground and the treetops, so many collisions occur at houses and low-rise buildings. How dangerous a window is depends on how reflective or transparent it is. To determine if a window, deck railing or other clear structure made of glass is dangerous, look at it from outside at different times of day and from many angles. If it reflects trees and other vegetation, it’s dangerous.

Applying regularly spaced markers on the outside of the glass tells birds that there is a barrier to avoid and is one of the best ways to prevent collisions. In order to be effective, tape or marking must be applied at a spacing of 10 centimetres or less vertically and horizontally across the entire glass surface. The markers must be at least 5 mm in diameter and their colour should contrast well with the reflected vegetation and be easily seen.

Freely swaying cords evenly spaced and hung up at the top of the window on the outside are also an effective deterrent.

Decals can work, too, but must be applied densely, not more than 10 centimetres apart. One or two decals or large silhouettes on a big window won’t work. Birds may avoid the decal, but will fly into the unmarked area of the window. Also, UV decals are difficult for birds to see under low light conditions, will fade and need to be replaced regularly.

For those concerned that something on the windows will affect their view, a uniform pattern covering the whole window won’t do that. The eyes will look past the pattern and focus on what’s through the window rather than what’s on it. Occupants of buildings with bird-friendly markers report that they do not notice the pattern within a short time after installation.

Here are some other measures that can help to reduce collisions:

  • Keep houseplants away from windows.
  • Avoid cleaning windows during migration seasons.
  • Some migratory birds travel at night, so turn off lights and close curtains or blinds when rooms are not in use when it’s dark out.
  • Try moving your bird feeders to within three feet of your windows. Studies have shown that panicked birds are less likely to hit glass at high speeds if feeders are close to the window.