…even the most optimistic could never have predicted the resiliency of the birds and the ferocity of their comeback. In Iowa, hopeful environmentalists set a goal of 10 or 20 nests by 2010. But exponential population growth took the Department of Wildlife by surprise. Last year, federal staffers lost count at 254 nests, nearly as many as once existed in the entire continental U.S. The birds left the Endangered Species List in 2007.