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(199 1) reported that least terns nesting in a sandpit complex in central Nebraska nested in <br />sites with less than 10% vegetation. Nests occurred from 0 to 56 in (mean = 19 m) from <br />vegetation, objects such as logs, or surface contours that provided a visual barrier to <br />nesting birds (Wilson et al. 1993). Least terns and piping plovers can nest in areas with <br />greater than 25 percent vegetative cover if some open areas still occur, especially if the <br />site has been used in previous years (Gochfeld 1983, Burger and Gochfeld 1990 in Sidle <br />and Kirsch 1993). Sidle and Kirsch (1993) observed a few single nests in areas with <br />greater than 25 percent vegetative cover late in the season on sandbars near existing <br />colonies, and at one sandpit in 1990 when the site was covered with fill material and <br />seeded that spring. <br />Elevation <br />On the central Platte River, mean elevation above the 400 cfs stage at nest sites ranged <br />from 0.2 to 2.0 feet, with a mean of 1.0 foot. Mean elevation at systematic sample sites <br />ranged from 0.1 to 1.8 feet, with a mean of 0.4 foot. These means were not significantly <br />different. Maximum elevation above the 400 cfs stage at nest sites ranged from 0.4 to 4.4 <br />feet, with a mean of 2.7 feet. Maximum elevation at systematic sample sites ranged from <br />0.3 to 3.7 feet, with a mean of 1.4 feet. These means were not significantly different <br />(Ziewitz et al. 1992). <br />Comparisons of sandbar area, channel width, mean elevation, and maximum elevation of <br />nest sites versus systematic sample sites in the Platte River suggest that least terns use <br />wide channels with a large area of dry, sparsely vegetated sand. By these measures, <br />habitat availability was greater on the lower Platte River than the central Platte River. <br />Although nest sites also had higher mean and maximum elevation than systematic sample <br />sites, these differences were not statistically significant in either river reach. On the <br />central Platte River, the mean elevation of nests was less than the mean site elevation at <br />half the nest sites (FWS 1997). <br />Low flows followed by sudden peaks generally results in inundated nests. Naturally <br />occurring riverine nesting areas on the central Platte are typically low in elevation above <br />water level and occur in the few existing wide channels (Sidle and Kirsch 1993). If nests <br />and /or chicks occur on these low sandbars, small flow increases can cause them to be lost <br />(Kirsch and Lingle 1993, Sidle and Kirsch 1993). An example of this occurred in 1988 <br />when low flows followed by sudden peaks in early and late July resulted in the <br />inundation of eight of thirteen nests surveyed at central Platte River sites. The median <br />elevation of these nests equates to a flow of about 2,895 cfs at the Grand Island gage. <br />Flows higher than 2,895 cfs during June 16 to August 31, the latter half of the nesting <br />season, occurred in 18 of the 30 years from 1959 to 1988 (Ziewitz et al. 1992). <br />Flow /Discharge, relative to sandbar areas <br />River discharge at Grand Island ranged from 25 to 2,570 cfs on the eight sampling dates <br />of aerial videography. With one exception, sandbar areas greater than 2 acres were <br />measured only on the two lowest flow dates (June 15 and 24). Mean sandbar area at <br />Draft Baseline Report, July 2002 <br />4 -13 <br />