First, the blackbirds fell out of the sky on New Year's Eve in Arkansas. In recent days, wildlife have mysteriously died in big numbers: 2 million fish in the Chesapeake Bay, 150 tons of red tilapia in Vietnam, 40,000 crabs in Britain and other places across the world. Blogs connected the deadly dots, joking about the "aflockalypse" while others saw real signs of something sinister, either biblical or environmental.

The reality, say biologists, is that these mass die-offs happen all the time and usually are unrelated. Federal records show they happen on average every other day somewhere in North America. Usually, we don't notice them and don't try to link them to each other.

Since the 1970s, the U.S. Geological Survey's National Wildlife Health Center in Wisconsin has tracked mass deaths among birds, fish and other critters, said wildlife disease specialist LeAnn White. At times the sky and the streams just turn deadly. Sometimes it's disease, sometimes pollution. Other times it's just a mystery.

In the past eight months, the USGS has logged 95 mass wildlife die-offs in North America and that's probably a dramatic undercount, White said. The list includes 900 some turkey vultures that seemed to drown and starve in the Florida Keys, 4,300 ducks killed by parasites in Minnesota, 1,500 salamanders done in by a virus in Idaho, 2,000 bats that died of rabies in Texas, and the still mysterious death of 2,750 sea birds in California.

On average, 163 such events are reported to the federal government each year, according to USGS records. And there have been much larger die-offs than the 3,000 blackbirds in Arkansas. Twice in the summer of 1996, more than 100,000 ducks died of botulism in Canada.

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