Blackbirds rest in large flocks.

Blackbirds do not normally fly at night.

It was new year's eve when many people celebrate with fireworks.

A large display of fireworks quite probably frightened the birds off their roosts.

There were large numbers of "aerial fireworks" confirmed in some of the areas where bird deaths were reported.

There were reliable reports of at least some of the flocks flying at unusual altitudes and following erratic paths while attempting to avoid the fireworks.

Blackbirds of this kind are nearly blind in the dark.

I have seen "bird collisions" in flocks of several kinds of flocking (I think I spelled that right) birds, resulting in two or more birds "falling out of the sky." These do happen even under "normal conditions." In a mass disoriented flight many more collisions are quite reasonably to be expected. Flying in a flock, if the birds on the "near side" of a disturbance turn away from it, they inevitably turn into the path of the other birds.

Minimal observation of how flocks turn will suggest that even a few "disoriented" individuals can be extremely destructive to the "flock structure." (If you don't have large flocks of birds, you can watch schools of fish for the same behavior.)

A collision between two birds flying at 30 or 40 mph can easily incapacitate, and possibly kill, both birds. Collision of a flying bird with a falling one would have similar consequences.

If the initial collision is insufficient to kill, the ground impact likely would, but would leave less physiological evidence of the secondary impact with the ground than would be evident from the bird/bird collision.

Similar "mass deaths" are actually fairly common, but are reported as newsworthy only when there's little else to report.

The "collision" explanation is quite reasonable and is supported by knowledge of behavior in this kind of birds and by the unusual and widespread occurrence of "fireworks" in the celebrations around the time of the incidents.

A flock disrupted in the ways expected may continue to exhibit "unusual" (sometimes bizarre) flocking for a significant time, until the flock reorganizes itself, so repeated - probably smaller - events likely will occur, even if the birds fly only under conditions when it is normal for them to do so. In normal times the smaller events would be ignored by the media, but since one big one was hyped, there will have to be reports on all subsequent ones until the "hysteria factor" loses its ability to "sell the news."

John