Eggs are getting scarcer and pricier ahead of the holidays. Here's why.

Americans planning to do some holiday baking this year may have to scramble to track down a key ingredient. 

Some stores around the U.S. are running short of eggs, especially those operating in states that require eggs from cage-free hens, as cases of Highly Pathogenic Avian Influenza (HPAI) flare and the virus spreads from wild birds to commercial flocks. More than 40% of the nation's roughly 300 million egg-laying hens are raised in cage-free facilities, but roughly 60% of "bird flu" cases recently detected involved cage-free farms.

"After two months of no outbreaks, we had them recently in Utah, Oregon, California and Washington, and three of those states are exclusively cage-free," Emily Metz, chief executive and president of the American Egg Board, told CBS MoneyWatch. "Where we are hearing reports of shortages it's at stores like a Whole Foods or a Trader Joe's."