Bird flu has never done this before

At bird breeding grounds this spring and summer, the skies have been clearer and quieter, the flocks drastically thinned.

For months, experts worried most about the outbreak’s magnitude—it struck so swiftly and lethally that it’s become the most deadly H5N1 epidemic recorded in North America.

Now the looming concern is length: when, and if, the virus will withdraw.

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