It might now be a distant memory, but by the end of last winter, the average cost of a dozen eggs soared to a record high of $6.23. (It’s now at $3.49.)

The cause was H5N1, a highly pathogenic strain of avian influenza — or bird flu — that wild birds shed near farms as they migrate for the winter. It’s now surging again in US poultry operations and could result in another winter of high egg prices — and tens of millions of dead birds.

Over the last two months, the virus was detected on nearly 50 commercial poultry farms, leading to the mass culling of 7.3 million farmed birds — more than during the same period in previous years. Three-quarters of those birds were egg-laying hens from just three egg factory farms.

Although that culling involves an enormous amount of animal suffering, the deaths represent less than 2 percent of US egg-laying hens, which, for now, isn’t enough to meaningfully affect egg prices.

But given the early wave of mortality across a range of species compared to the last couple years, the sheer number of farms that have reported outbreaks, and the fact that a newer bird flu variant has become dominant, it “doesn’t bode well for a quiet year” for the virus, Krysten Schuler — an associate research professor of public and ecosystem health at Cornell University — told me in an email.

For nearly four years, bird flu has wreaked havoc on the US poultry industry and the birds themselves. Federal policy requires that as soon as the virus is detected on a farm, the entire flock must be killed to slow the spread of the disease. So far, poultry farms have killed more than 180 million birds since the start of the outbreak in early 2022. And the prevailing method of killing is grim: Producers close barn vents and pump in heat to raise the temperature, which slowly — and painfully — kills the birds via heat stroke over several hours.

The virus has also spilled over to infect hundreds of other bird species and mammals, including dairy cows, foxes, bears, seals, and pet cats. Seventy human cases have been reported in the US, including one death. Scientists are increasingly worried that the virus could

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