Status of the Interior Least Tern and Piping Plover in Nebraska

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the next. Nesting habitat associated with off -river sandpits (e.g., along the Platte and Loup rivers) is also transient. With the passage of time, sandpit spoil piles become overgrown with vegetation or are leveled to develop housing or recreation areas. Consequently, a given site may be suitable for nesting one year but absent or unsuitable the next. Such changes do.not necessarily represent permanent losses of habitat inasmuch as suitable habitat may be forming elsewhere. As Erwin (1984) pointed out, the propensity of least terns to relocate their colonies within and between years makes breeding populations appear unstable, but it may be this tendency that enables the species to persist despite the hazards of flooding and other disturbances. This remark is equally applicable to piping plovers. If suitable habitat is not available at a previously used nesting site when breeding birds arrive, they may select alternate sites (Wycoff 1960) or delay nesting until sandbars or beach areas become exposed (Hardy 1957). Some researchers (e.g., Renaud et al. 1979) have also noted that piping plovers may shift their nesting locations from year to year for unknown reasons apparently not related to changing habitat 'conditions. If selected sites become unsuitable during the nesting season (due to flooding, human disturbance, or other factors), nest relocation or renesting may occur. Late nesting and /or renesting, however, may have a lower likelihood of success because of the time budget required (Schulenberg et al. 1980, Wingfield 1982). The inherent ability of least terns and piping plovers to adjust to temporal differences in local habitat availability is further exemplified by shifts in the utilization of riverine sandbar and off -river sandpit habitat along the Platte River. During recent years (1985 and 1986), sandpit spoil piles near the Platte have provided habitat for nearly half the breeding birds of both species that nest along this river. When flood conditions reduce the amount of mid - stream sandbar habitat, sandpits near the river assume even greater importance to the extent that during years of extreme and prolonged high flows (as in 1983 and 1984) they provide the only nesting habitat available. These findings document the fact that sand and gravel mining along the Platte River has created important supplemental nesting habitat for least terns and piping plovers. Least terns that nest at sandpits adjacent to the Platte River forage primarily in shallow areas of the river to obtain food (i.e., small fish). Foraging is apparently more limited on sandpits themselves because the steeper side - slopes and general lack of shallow water areas characteristic of these sites are less conducive to the capture of fish prey items. Thus, even during years when mid - stream sandbars are inundated during the breeding season, the river continues to play an important role as a foraging area for nearby least tern colonies. In contrast, piping plovers feed mainly on aquatic invertebrates and can presumably satisfy their dietary requirements by foraging along shoreline margins associated with either riverine or sandpit habitat. COLONY SPATIAL CHARACTERISTICS Available data (though limited) do not indicate greater crowding at colonies during years when high flows in the Platte River restricted nesting activity to off -river sandpits. Measurements of area per colony, area per nest, and inter -nest distances recorded at one river colony in 1985, when moderate flows prevailed during the breeding season, fell within the range of values measured iv