From this story in the Washington Post:
It's death on a wide scale, biblical-type stuff: Millions of spot fish died last week in the Chesapeake Bay; red-winged blackbirds tumbled from the skies by the thousands in Arkansas and Kentucky over the holidays; and tens of thousands of pogies, drum fish, crab and shrimp went belly up in the summer in a Louisiana bayou. For an explanation of these mysterious events, some have turned to Scripture or to the Mayan calendar, which suggests the world will end in 2012. But wildlife experts say these massive wildlife kills were not the result of a man-made disaster or a spooky sign of the apocalypse. They happen in nature all the time.
_"...In Arkansas, "5,000 birds falling dead in people's yards is just weird," said Kevin McGowan, an ornithologist at the Cornell Lab of Ornithology. "But the question is, has this happened before?" The answer is yes, "but probably in a cornfield. And foxes ate them all," McGowan said. "All birds die," he continued. "You rarely see them for several reasons. They're usually alone. They're often eaten by the thing that killed them, or they go to some sheltered place to die. You rarely see dead birds until they whack into your window."