Accuracy of the Missouri River Least Tern and Piping Plover Monitoring Program: considerations for the future

The upper Missouri River system provides nesting and foraging habitat for federally endangered least terns (Sternula antillarum; hereafter “terns”) and threatened piping plovers (Charadrius melodus; hereafter “plovers”). These species are the subject of substantial management interest on the Missouri River for several reasons. First, ecosystem recovery is a goal for management agencies that seek to maintain or restore natural functions and native biological communities for the Missouri River system. Terns and plovers are recognized as important ecosystem components that are linked with the river’s ecological functions. Second, although both species breed beyond the Missouri River system, the Missouri River is one of the principal breeding areas in the Northern Great Plains; thus, the river system is a focal area for recovery actions targeted at regional population goals. Third, a Biological Opinion for Missouri River operations established annual productivity goals for terns and plovers, and the recovery plan for each species established annual population goals. Meeting these goals is a key motivation in management decision making and implementation with regard to both species. A myriad of conservation and management interests necessitate understanding numbers, distribution, and productivity of terns and plovers on the Missouri River system. To this end, a Tern and Plover Monitoring Program (TPMP) was implemented by the U.S. Army Corps of Engineers (hereafter “Corps”) in 1986, and has since provided annual estimates of tern and plover numbers and productivity for five Missouri River reservoirs and four river reaches (U.S. Army Corps of Engineers, 1993). The TPMP has served as the primary source of information about the status of terns and plovers on the Missouri River, and TPMP data have been used for a wide variety of purposes. In 2005, the U.S. Geological Survey (USGS) Northern Prairie Wildlife Research Center (NPWRC) was tasked by the Corps to evaluate the accuracy of the TPMP and provide guidance on revising the program to assess tern and plover numbers and reproductive success. Accordingly, NPWRC studied terns and plovers on two river reaches and one reservoir (hereafter “the evaluation”), and used the results of those studies to help understand properties and potential limitations of TPMP data and to provide guidance for TPMP revisions. The purpose of this report is to present an overview and evaluation of the TPMP data, the results of our intensive monitoring, and propose an alternative idea that provides a framework for making decisions about how to monitor terns and plovers.