Natural Hydrograph of the Missouri River near Sioux City and the Least Tern and Piping Plover

The least tern and piping plover are threatened and endangered species that are indigenous to at least part of the natural Missouri River. However, would the river’s natural hydrograph near Sioux City, Iowa, including the spring rise, have historically been harmful to the birds? Three methods of hydrograph analysis, which were based on 1938–1939 stream-flow measurements at the Sioux City gauge site and based on new information of the time needed for mating, nesting, and rearing of the birds, were made. The results of the analyses are consistent with historical biologic observations of June rise flooding and suggest that the natural hydrograph of the Missouri River near Sioux City was not “friendly” to the two bird species as the hydrograph likely did not result in long-term recruitment.