Status of the Interior Least Tern and Piping Plover in Nebraska

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SYSTEMATIC SURVEYS Recent systematic surveys conducted along Nebraska's rivers have 1) documented substantially larger least tern breeding populations than were observed or estimated during the initial census in 1975 (Downing .1980); and 2) established the fact that Nebraska is a major stronghold for this species. In 1986, 438 adult least terns were censused along the Platte River and 181 adults were censused along the Missouri River from Gavins Point Dam to Ponca, Nebraska. Although the Niobrara River was not surveyed in 1986, 174 birds were censused along this river in 1985. Assuming stable abundance along the Niobrara from 1985 to 1986, these census results reflect a total of 793 adult least terns as of the 1986 breeding season. This compares with a total of 200 adults observed (and 400 adults estimated) by Downing based on his 1975 survey of these same three river areas. Other least tern breeding populations have also been discovered in recent years in areas not surveyed by Downing. For example, an aerial inventory of the Loup rivers in 1985 yielded 56 adult terns which, considering that aerial surveys typically census only about half of the birds present, suggests a population of twice that size. In addition, 25 adult least terns were censused in 1986 along the Missouri River between Fort Randall Dam and Lewis and Clark Lake upstream of the Gavins Point Dam to Ponca reach. Thus, systematic survey results through 1986 indicate a total statewide population of approximately 900 birds. Because these surveys did not include all potential or known nesting habitat within the state, this statewide estimate should be considered conservative. In view of the fact that Downing's 1975 inventory served as a primary basis for the Service's proposed rule to list the interior least tern as endangered (reference 49FR 22444 - 22447), the results of recent systematic surveys in Nebraska are particularly noteworthy. Although Downing (1980) believed the 80 least terns observed along the Platte River in 1975 were more birds than the habitat seemed capable of supporting, census results recorded in 1986 (438 birds) represent more than a five -fold increase. Similarly, given that the population observed along the Missouri River below Gavins Point Dam was more than five times larger in 1986 than in 1975 (181 versus 35 birds), it is also apparent that Downing substantially underestimated the habitat potential of this river segment. It deserves particular emphasis that the 619 least terns censused only along the Platte River and the Missouri River below Gavins Point Dam in 1986 represents more birds than the total number (616) actually seen by Downing during his entire survey of the greater part of the species' breeding range (which included 11 rivers of the Mississippi /Missouri River drainage, plus national wildlife refuges in three U.S. Fish and Wildlife Service regions). As in 1975 (Downing 1980), flood conditions following the nest initiation period were also observed on the Platte and Missouri rivers in 1986 (NGPC 1986, Schwalbach et al. 1986) when least tern breeding populations censused on both rivers were substantially larger. Fewer birds have been inventoried during other survey years when lower flow conditions have prevailed and habitat was apparently more abundant. It may be that abnormally wet conditions in 1986 broadly reduced the amount of habitat throughout the species' breeding range, resulting in greater utilization of those nesting areas that were available. In any case, the more than five -fold increase in the size of least tern breeding populations censused along the Platte and Missouri rivers in 1986 ii