[MHGinTN]

The Earth’s magnetic field is preparing to flip. During this phase the magnetic lines are all screwed up, causing confusion in animlas which use the magnetic data. Exhaustion may be the major cause of these ‘bird falls’ and possibly even fish die-offs.

[txhurl]

The Earth’s magnetic field is preparing to flip. During this phase the magnetic lines are all screwed up, causing confusion in animlas which use the magnetic data. Exhaustion may be the major cause of these ‘bird falls’ and possibly even fish die-offs.

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This easily explains bird exhaustion, freezing and dropping, but it does not explain the fish and crab dieoffs.
Crabs and fish don’t migrate, well, most fish don’t. They hug the shore.