Why do birds fly into windows?
Sometimes a bird may be flying and not know that a window is there. They will keep flying and end up slamming into a window. This would seem to be a case of a simple misperception and accident. However there are widespread reports of birds compulsively knocking into the same window repeatedly over days or weeks. This would appear to be a different phenomenon whereby the bird is choosing to fly into the window for whatever odd reason. In this example, the bird sits on a nearby branch flies into the window, leaves or returns to the branch and repeats it again. This lasts hours, days and weeks to the point where the glass is completely smudged. There are various theories about this peculiar behavior, but nothing definitive and conclusive. The most commonly found opinion is that they are protecting their territory by attempting to thwart off the image of themselves in the glass, mistaking it as a threat.