A growing number of restaurants are adding "egg surcharges" as avian flu outbreaks cause nationwide egg shortages and higher prices. The American diner chain Denny's, based in South Carolina, announced Tuesday that some of its roughly 1,500 U.S. restaurants will be adding an egg surcharge to offset rising costs. Earlier this month, the Georgia-based Waffle House chain, a popular restaurant for breakfast food, said it would add a 50-cent surcharge for each egg. Avian flu outbreaks have forced egg farms to cull millions of chickens per month, leading to shortages that have led some retailers to ration sales. The average price of a dozen Grade A eggs in U.S. cities hit $4.95 in January, and the USDA predicts it will soar another 20% this year. Mac's Deli and Cafe in Santa Rosa, California recently added a $2 surcharge for dishes containing eggs. Manager Tatum Soltani said a case of eggs that used to cost $46 now costs $146. She said she hasn't heard any complaints because most customers understand that egg prices are rising.