Distribution, Productivity, and Habitat Use by Interior Least Terns and Piping Plovers on the Niobrara River in Northern Nebraska, 1996-1997

Interior least terns (Sterna antillarum athalassos) and piping plovers (Charadrius melodus) are endangered and threatened species, respectively, and have been protected under the Endangered Species Act since 1985. Dam building on the Missouri River has produced changes in the availability and suitability of nesting habitats while both species continue to experience population declines throughout their range. The Niobrara River in Nebraska is one of the least modified rivers in the northern Great Plains that currently supports breeding populations of least terns and piping plovers. Nesting sites were identified and various nest site parameters were measured. Distribution of the nesting birds, productivity, nest success and habitat use were also evaluated. Aerial videography was flown for the Niobrara River in early June of 1996 and 1997. Sandbar characteristics including total area and areas of high, low, wet sand, and heavy vegetation were obtained from the videography. Least terns and piping plovers were found along the entire portion of the Niobrara River monitored in 1996 and 1997 and equaled 30% to 40% of the total Nebraska population. Piping plovers usually initiated nests earlier than least terns with terns being more synchronous nesters than plovers. Piping plover known fate nest success ranged from 54% in 1996 to 73% in 1997 while least tern nest success was 80% during the 1996 and 1997 breeding seasons. In 1996 and 1997 respectively, the majority of sandbars used for nesting by least terns also supported nesting piping plovers. Other analyses, including the aerial videography analysis, also suggested that terns and piping plovers were selecting for the same types of habitat. Least terns may also be keying in on the presence of piping plovers and decreased amounts of vegetative cover in their selection of islands for nesting. Piping plovers, however, are selecting for high sand and the presence of heavy vegetative clumps on the sandbars. Using analysis of aerial videography, least terns were determined to need l.3% of an islands total area in high sand and \u3e 7% of low sand. Piping plovers also needed at least l.3% of an island to be in high sand and\u3e 9% of the total island area in low sand. Therefore, it is possible that one nesting habitat model based on piping plover selected characteristics could be developed and used to predict the use or non-use of a sandbar for nesting by both species