Why are Trader Joe's stores short on eggs?

(NEXSTAR) – The hottest commodity at Trader Joe's these days isn't a seasonal holiday treat or a miniature tote bag. Shoppers around the country are finding stores wiped out of a staple ingredient: eggs.

"Chickens on strike!" reads a sign posted to an empty refrigerator case where you'd normally find cartons of eggs. "We are experiencing an egg shortage and apologize for the inconvenience," reads another.

A third sign, posted at a store in Chicago, provides one possible explanation: "Where are the eggs? We're transitioning to cage-free only, which may temporarily reduce our supply."

Trader Joe's made the commitment to switch to all cage-free eggs eight years ago following pressure from an online petition, according to AllRecipes. It promised to make the change at all locations by 2025, and the deadline is fast approaching.

But here's where things get even more complicated. The massive bird flu outbreak, which began in February 2022, has led to the slaughter of more than 111 million birds, mostly egg-laying chickens. Anytime the virus is found, every bird on a farm is killed to limit the spread of the disease.

The flu is spread through the droppings of wild birds as they migrate past farms, so allowing chickens to roam freely actually puts them at greater risk of catching the virus, said Chad Hart, a professor and agricultural economist at Iowa State University.

California, Nevada, Washington and Oregon already require all eggs sold in their states to be cage-free, so supply is especially tight there.

“We’re having to move eggs from other areas of the country that are producing cage-free to cover that low supply in those states, because those states only allow for cage-free eggs to be sold,” Emily Metz, president and CEO of the American Egg Board, told the Associated Press last month.

We've also entered peak holiday baking season, where demand for eggs typically rises. Reduced supply and increased demand is the perfect recipe for not just shortages, but also high prices.

The average price for a dozen eggs in U.S. cities was $3.65 in November, according to the Bureau of Labor Statistics. That's up substantially from this time last year, when a dozen eggs cost $2.14.

Nexstar reached out to Trader Joe's for comment but didn't hear back.

The Associated Press contributed to this report.