The specific case of the blackbirds actually could make sense that fireworks led to the deaths. The dead birds found were primarily blackbirds and few other species known to flock with blackbirds. So they suspect that it was a large flock that, when fireworks went off, became panicked and broke off the flocking pattern, causing multiple collisions and subsequent plummets to their death or flying head long into things due to this disorganization of the flock.
Overall, before you go and look for the mystical or miracle or anything related to an apocalypse, read this:
http://www.google.com/hostednews/ap/...14e0644cda18a6