[jkaufman]

I listened to an explanation of this earlier (I will see if I can find documentation) -- the blackbirds travel in extremely large flocks and follow a leader very tightly (much closer in proximity to each other than most birds). The birds travel at night and can be disoriented by things such as fireworks, lightning, or other flashing lights. If the leading bird is disoriented, it could cause the bird to fly directly into the ground, a building, or any other large bird-killing object. This leads to an almost lemming-like mass suicide of the flock.

I also believe that it has been documented to have happened fairly regularly. The numbers I heard today were 16 times in the past 30 years there has been a mass death of over 1000 birds.

Found this regarding mass animal deaths -- http://www.nwhc.usgs.gov/mortality_events/ongoing.jsp