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UU0625 Ziewitz, Sidle & Dinan: Nesting Least Terns and Piping Plovers 5 vegetation (area of total channel minus area of permanent vegetation). We test- ed the hypothesis that the means of IIleasurements at nest sites and systematic sample sites were equal using independent-sample t-tests. Ground Surveys We surveyed the systematic sample sites 13 June-lI July and the nest sites 1-12 August. We measured vegetative characteristics and vertical habitat di- mensions at each site on two transects crossing the river. Transects were located approximately 100 m (330 ft) upstream of the lower end of each river segment and 100 m downstream of the upper end. At nest sites, at least one of the tran- sects passed through the nesting area. We selected points for measurements along a transect that best depicted the contours and vegetation of the river bed, i.e., major inflection points in the river cross-section and changes in vegetation along the transect. We measured horizontal and vertical dimensions using a sur- veyor's level and stadia rod. We visually estimated the average height of vege- tation and percentage cover in a I-m' area centered over each point. Currier (1982) previously described the plant species occurring on sandbars along the Platte. We measured the characteristics of points selected along two transects with- in the 402-m river segments, rather than random points, to simplify the process of relating elevation measurements to the water surface elevation at the time of the survey. We believed transect sampling would better capture the range of variability in elevation and vegetation characteristics at a site than a random sampling design. We adjusted the water-surface-elevation datum of each transect to a com- mon elevation datum to compare the transects measured at different sites and river discharges. We selected the stages corresponding to 113 cubic meters per second (cms) (4000 cubic feet per second (cfs)) for the Lower Platte and 11.3 cms (400 cfs) for the Central Platte. Our adjustments yielded elevation meas- urements as if all Lower Platte data were collected at a discharge of 113 cms and all Central Platte data were collected at a discharge of 11.3 cms. We computed the adjustments using river stages and other data collected by the Nebraska Department of Water Resources and U.S. Geological Survey at gages near Overton, Odessa, Kearney, Grand Island (Central Platte), North Bend, and Louisville (Lower Platte). Given the distance of a study site from the nearest gage and an estimate of the average velocity of flows at the time of our survey, we computed a travel time for water between the site and the gage and determined the gage height at the time of our measurements plus or minus the computed travel time, depending on whether the gage was upstream or down- stream of the site. The datum adjustment computed for the site was the differ- ence between this gage height and the gage height corresponding to 113 cms (Lower Platte) or 11.3 cms (Central Platte). The above method of adjusting elevation measurements introduced error into these data. The adjustments were accurate only to the extent that the rela- tionships between river stage and discharge at our study sites were similar to those at the nearest gages. The accuracy of the adjustments was also dependent upon the estimates of water travel time. Establishing stage-discharge relation-