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First, more than 1,000 dead birds fell out of the sky in Arkansas. Then, an estimated 100,000 fish washed up dead on the shore of the Arkansas River.

We don't know what exactly caused the bird and fish die-offs. But we do know that usually, these seemingly mysterious animal die-offs can be explained after science, zoology and environmental experts take a closer look.

Surge Desk found five other examples of similar die-offs.
  1. The disappearance of the honeybee.

    When an estimated 20 percent to 40 percent of the U.S. honeybee colonies began disappearing in 2006, environmentalists were alarmed. After all, the honeybee is a pivotal part of the North American ecosystem, pollinating many of our agricultural products.

    Status: Solved -- maybe.
    In late 2010, a team of military scientists and bee experts announced that they had identified the possible culprit behind the bee disappearance: a fungus combining with a virus. But not everybody accepts this explanation. Other proposed causes include pesticides, climate change, weakened immune systems and malnutrition.

  2. Bat deaths in upstate New York.

    Around 2007, an epidemic dubbed "white nose syndrome" began to kill off hibernating bats across upstate New York and into New England. Experts think that more than 1 million of the night critters died while hibernating. The infection appeared to spread from cave to cave.

    Status: Unsolved, but getting there.
    It turns out that "white nose syndrome" is caused by a fungus called Geomyces that thrives in the cold winter air. An estimated 75 percent of bats that get infected end up dying. In December, a group of experts proposed that the reason the Geomyces infection is so deadly in North American bats is that it damages the bats' wings.
  3. Frog deaths in the United Kingdom.

    Some frog populations in the U.K. declined by as much as 80 percent over a 12-year period.

    Status: Solved.
    The Zoological Society of London found that the frog deaths were caused by internal hemorrhaging, which in turn was caused by ranavirus.
  4. Pelican deaths in North America.

    In late 2008 and early 2009, more than 400 endangered pelicans were found dead or dying along the West Coast.

    Status: Solved.
    The U.S. Fish and Wildlife Service believes that the deaths were due to abnormally cold weather.
  5. Dolphin deaths in the Gulf.

    Before the BP oil spill wrecked havoc on the ecology of the Gulf, bottlenose dolphins were mysteriously dying at about three times their normal rate.

    Status: Unsolved.
    No cause for the deaths was announced. A similar dolphin die-off in Florida's Indian River Lagoon in 2008 also remains unsolved.