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UUU622 2 Prairie Naturalist 24(1) March 1992 the same sites (Ducey 1981, 1982, 1989; Mayer and Dryer 1988; Schwalbach 1988; Kirsch 1990; Lingle 1988, 1989). The Platte River, a major tributary of the Missouri, supports a substantial fraction of the nesting populations of both species. About 600 least terns, comprising 13% of the population (Sidle et al. 1988, USFWS 1990c), and about 300 piping plovers, comprising 9% of the northern Great Plains population excluding Canada (USFWS 1988), nest along the Platte. Nesting occurs on sandbars in the river and on sand spoil piles asso- ciated with gravel mining operations (sand pits) near the river (Wilson 1991, Kirsch 1992, Sidle et al. 1991). Numerous dams and water diversion canals in the upper Platte River Basin have reduced water and sediment discharge in the Platte, resulting in the trans- formation of wide, open channels to multiple narrow channels separated by wooded islands (Williams 1978, Eschner et al. 1981). This vegetation encroach- ment has eliminated much habitat for several species of birds, including least terns and piping plovers (USFWS 1981, Currier et al. 1985, Sidle et al. 1989). The loss of open river channel has been greatest in the Upper Platte, from the confluence of the North Platte and South Platte Rivers to Lexington (Fig. I) (Sidle et al. 1989). Least terns and piping plovers no longer nest along this reach of the river except at a few sand pits. Extensive vegetation encroachment also has occurred in the Central Platte, from Lexington to the mouth of the Loup River, but some sites are still used for nesting. Most nesting in recent years has occurred on the Lower Platte, below the mouth of the Loup River, where vege- tation encroachment of the river channel is least advanced. The channel of the Lower Platte remains dynamic; the area of sandbars suitable for least tern and piping plover nesting has increased and decreased during 1949-1988 (Rodekohr and Engelbrecht 1988). High flows continue to periodically scour vegetation from sandbars along the Lower Platte (Sidle et al. in press). Several authors have described various sandbar and river channel dimen- sions as important nest site characteristics of least terns and piping plovers along the Central Platte (Faanes 1983, Armbruster 1986, Carlson 1987). They noted the need for high spring flows to scour vegetation and maintain sandbars suitable for nesting, lower but continuous summer flows to ensure the availabil- ity of food items and to isolate sandbars from mammalian predators and human disturbance, and the clearing of vegetation and artificial deposition of sandbars to sustain nesting on the Central Platte. Our objective was to assess whether the availability of suitable riverine habitat may be limiting nesting populations of least terns and piping plovers on the Central and Lower Platte River, and, if so, to formulate habitat restoration measures. We measured several habitat characteristics in a systematic sample of the Central and Lower Platte and in river segments used for nesting during 1988. We related these measurements to records of river discharge. STUDY AREA Our study area on the Central and Lower Platte during the 1988 breeding season (April-August) encompassed the extent of known least tern and piping plover nesting activity on the Platte in recent years. We worked in the Central -,