Do Birds Commit Suicide?

The other day, I was in the office when I heard a heavy thud against the glass door. I was startled to see a flock of birds, one of which flew at great speed and smashed against the door and dropped dead. Was it suicide? Was the bird sick or injured, or disoriented? Judging by its physical appearance, it was not injured in any way. We have heard stories of animals including birds commit suicide. The most famous of course are the lemmings which reportedly committed mass suicide due to some deep rooted impulses. One story has it that it was Walt Disney that perpetrated this myth in its movie "Wild Wilderness" released in 1958 that depicted lemmings jumping off the cliff. One theory has it that sick or injured animals including birds do commit suicide to bring a quicker end to their existence. I wonder if this bird was suffering from some kind of sickness. Or was it merely an accident? It was a sad thing.

Note the globule of blood near the beak