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Why Do Birds Attack Windows?

By Environmental Management System (EMS)

November, 2014

Editor's note: This article was prompted by concern over a bird observed attacking a set of windows in Keystone in October.

It's Not Just "Pane-ful," It Can Be Deadly

Reflective windows of the Keystone building
At the Keystone Building, the windows are highly reflective and objects appear very life-like, so it is not uncommon to see birds hit windows.

Did you know that almost a billion birds are killed by window plate glass yearly? Most window pane collisions end up fatal for birds; even though birds sometimes may appear stunned and able to fly away, they are likely to die later of head hemorrhages or other internal injuries. Songbirds, as a group, are more likely to be killed by hitting windows. For these birds, window collisions are second only to habitat loss, in terms of reducing population numbers.

Collisions occur both during the day and night. During the day, birds may see reflected images of trees and plants, or even plants and objects through a second set of windows across a room. Incidents at night primarily affect migrating night fliers that navigate by the stars and become disoriented by the light from high-rise structures. Thousands of birds such as tanagers, orioles, catbirds, and warblers may die during a single migration.

But why do some birds seem to viciously attack windows, as the case recently for birds outside Keystone windows? It is likely that the birds, primarily males, are attempting to attack their own reflection. This behavior is most noticeable in the spring when birds are breeding and defending their territories, but may occur during any month. Northern Cardinals, American Robins, Titmice, and California Towhees all will spar with reflections, and while less harmful to the bird, these "fights" can still cause injury. A Titmouse was seen in October outside the Keystone Building sparing with his reflection, attempting to defend his territory from an "intruder."

How can collisions be minimized?

Over time, bird watchers have developed a variety of strategies to help minimize bird collisions:

  • Make window glass less reflective or transparent
  • Put up mesh or netting several inches from the glass
  • Use tape stripes or decals of snakes or owls to break up the glass reflection
  • Draw blinds
  • Place feeders away from windows.

For additional suggestions or more information, please visit Bird Watcher's Digest.

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