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<br />llllUb.:h1 <br /> <br />10 <br /> <br />Prairie Naturalist 24(1): March 1992 <br /> <br />elevation at the systematic sample of sites fanged from 0.0 m (no sandbar ex- <br />posed at 113 cms) to 0.7 m, with a mean of 0.21 m. These means were not sig- <br />nificantly different (t=1.51, P=0.14). <br /> <br />Table 3. Elevation' measurements from ground surveys of 402-m (1/4 mile) <br />systematic river segments (n=34) on the Lower Platte River (river mile 1-101, <br />Nebraska, 1 988. <br /> <br /> Site Site Nests Nests <br /> Mean Max. # Mean Max, <br /> Elev. Elev. Nests Elev. Elev. <br /> Nesting Sites <br />Min. 0.09 0.15 1 0.12 0.18 <br />Mean 0.30 0.67 9.3 0.52 0.64 <br />Max. 0.82 1.68 31 1.01 1.25 <br />SI. Dev. 0.18 0.37 7.8 0.24 0.30 <br /> <br />Systematic Sample of River Segments <br /> <br />Min. 0.00 0,00 <br />Mean 0.21 0.61 <br />Max. 0.70 1.65 <br />51. Dev. 0.18 0.43 <br /> <br />1 m above stage of 113 ems <br /> <br />The maximum elevation above the stage of 113 cms at nest sites ranged <br />from 0.15 m to 1.68 m with a mean of 0.67 m (Table 3). The maximum eleva- <br />tion at the systematic sample of sites ranged from 0.0 m to 1.65 m, with a mean <br />of 0.61 m. These means were not significantly different (t=0.71, P=0.48). <br />Nests were located usually on the highest sparsely vegetated ground avail- <br />able at a site. The mean elevation of nests above the stage of 113 cms was 0.52 <br />m (n=224, Table 3), which was significantly higher than the mean elevation of <br />the nest sites (x=0.30, t=6.77, P<O.OOI) (paired sample t-test). The mean maxi- <br />mum elevation by site (x=O.64 m) was not significantly different from the mean <br />maximum elevation of the nest sites (x=0.67 m) (t=-O.75, P=0.46). <br />We estimated the nest initiation date and computed the elevation above <br />water on the nest initiation date for 188 nests of 224 surveyed (x=0.49 m, range <br />0.03 to U8 m). Of these, 163 nests (86.7%) were initiated between the last two <br />dates of videography analyzed, 24 May and 15 June. Figures Sa and 5b show <br />the computed river stages associated with nests and the average daily river stage <br />measured between April-July 1988. <br /> <br />Central Platte. - The mean elevation above the stage of 11.3 cms (400 cfs) at <br />nest sites ranged from 0.06 m to 0.61 m, with a mean of 0.30 m (Table 4). The <br />mean elevation at the systematic sample of sites ranged fromO.04 m to 0.54 m, <br />with a mean of 0.13 m. These means were not significantly different (t=I.72, <br />P=0.14). <br />The maximum elevation above the stage of 11.3 cms at nest sites ranged <br />from 0.12 m to 1.34 m, with a m~an of 0.81 m (Table 4). The maximum eleva- <br />tion at the systematic sample of sites ranged from 0.09 m to U3 m, with a <br />mean of 0.42 m. These means were not significantly different (t=1.66, P=0.15). <br />