The Department of Agriculture warned egg prices may increase more than 20% this year, after December saw a year-over-year increase of 36.8%.

The ongoing bird flu outbreak is driving up egg prices, which had led to a nationwide shortage. When buying eggs, choose only refrigerated eggs and refrigerate them immediately once they are brought home.

The humble egg, one of nature’s perfect foods, a self-packaged, relatively inexpensive source of protein that can serve as a lowly hangover remedy or help a souffle rise to heavenly heights, is also a great teacher. It’s helping Americans understand how a free-market economy works: When demand is high and supply is low, prices rise.