Having trouble finding a 20-pound turkey? Blame bird flu.

frozen turkeys wrapped and on display in a grocery store freezer

Bird flu has devastated U.S. turkey farms this year. (Image credit: Spencer Platt / Staff via Getty Images)

If you're looking for a large turkey for your Thanksgiving table this year, you may be out of luck. Devastating outbreaks of bird flu have hit farms in 46 states since February, limiting the nation's supply of bigger birds.

Although there's been a recent downturn in the rate of outbreaks and farmers have been able to raise the supply of small turkeys in time for the holiday, there hasn't been enough time to increase the supply of 20-pounders (9 kilograms), U.S. Secretary of Agriculture Tom Vilsack said in a call with reporters on Nov. 1, according to Axios.

The strain of bird flu driving the big-bird shortage is known as "highly pathogenic avian influenza (HPAI) H5N1." The virus primarily infects domestic and wild birds, although it's occasionally been found in mammals, including pigs, cats and, rarely, humans, according to the Centers for Disease Control and Prevention (CDC). The rarity of human cases and lack of evidence for human-to-human spread of the virus makes H5N1 a very low risk to the general public, the CDC stresses.

Since February, H5N1 has been detected in 266 commercial flocks and 360 backyard flocks in 46 states, according to the U.S. Department of Agriculture. As of Nov. 3, more than 49 million affected birds had either died of bird flu or been culled after exposure to infected birds, per the CDC. This death toll included more than 8 million turkeys, Axios reported.

The rate of new outbreaks recently slowed as migratory waterfowl, H5N1-carriers who shed the virus in their saliva, nasal secretions and feces, wrapped up their fall migrations, CNET reported.

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Typically, commercially raised turkey hens take about 14 weeks to reach maturity and weigh about 15.5 pounds (7 kg) after processing, while toms take 18 weeks to reach 38 pounds (17 kg), the National Turkey Federation says; the hens are most often sold as whole birds, and toms are processed into smaller cuts and other products, like sausage. With the recent downturn in H5N1 outbreaks, farmers have had time to shore up the whole-turkey supply for Thanksgiving — but the birds may be on the small side.

"Turkeys being raised now for Thanksgiving may not have the full amount of time to get to 20 pounds," Vilsack said during the Nov. 1 news conference. "I don't think you're going to have to worry about whether or not you can carve your turkey on Thanksgiving. … It's going to be there, maybe smaller, but it'll be there."

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.