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ULl06l8 8 Prairie Naturalist 24(1): March 1992 Aerial Videography - Lower Platte Nesting substrate (sandbar area) varied along the Lower Platte depending on the variable flow (Table 1 and Fig. 4). Vegetation growth during the nesting season also contributed to variation in sandbar area. Sandbar area was greatest in the reach below the mouth of the Elkhorn River. The mean sandbar area of nest sites was 1.9 ha for the six dates examined, although nesting occurred at sites with less than 0.2 ha available (Table 1). This was significantly greater than the mean of 0.76 ha for the systematic sample sites (t=4.75, P<O.OOI). The mean channel width of nest sites was 519 m, significantly greater than the mean of 430 m for the systematic sample sites (t=3.40, P=O.OOI). (Table I). Table 1. Measurements from aerial videography of 402-m (1/4 mile) systematic river segments (n=34) and river segments (n=25) centered on least tern and piping plover nesting sites on the Lower Platte River (river mile 1-101), Nebraska, 1988. Area of dry, sparsely vegetated sandbar (ha) May 5 May 11 May 19 May 24 Jun 15 255 211 1 Z3 196 58 187 256 157 280 96 Channel Area tha) Mean Channel Widlh(m) Apr25 108 ems!. 159 ems] . Sandbar area for all dales Systematic Sample of River Sites Min. 8.5209 211.8 0,0000 0.0000 0.0000 0,0000 0.0000 0.0000 0.0000 Mean 17.2908 429.8 0.9982 0.9492 0.6209 0.8932 0.5642 0.6318 0.7762 Max. 23.9383 595.0 4.8531 7.7050 3.3347 4.8898 4.1517 2.7846 7.7050 .," .A,,51. Dev. 4.1108 102.2 1.2506 1.5496 0.8284 1.2954 0.9498 0.8077 1.1331 Nesting Sites Min. 13.7742 342.4 0.2190 0.1120 0.1354 0.1397 0.1101 0.0913 0.0913 Mean 20.8786 519.0 2.4562 2.2130 1.4945 2.1612 1.4571 1.5189 1.9019 Max. 30.8530 766.9 13.1463 12.0723 12.7030 13.9372 10.5033 7.9761 13.9372 Sl. Dev. 3.8717 96.2 3.0572 2.9133 2.6644 3.0022 2.2902 2.0522 3.8849 1 Average daily flows at North Bend. 1Average daily flows at Louisville. 350.0 300.0 Louisville '; 250.0 E u -- 200.0 w <.:l '" -< 150.0 :r: U V1 Cl 100.0 -. North Bend 1'''./1 I I . J \ ~ II oJ I 'V1 I' I ,," ) I \, I ,\ :\^ ~ \\ \ \ \ ,I I '..j1\ l .' ,"" l.A~\..../' ...... Grand Island 50.0 . 0.0 .... Apr May Jun Jul Aug Figure 4. Flows at the U.s. Geological Survey's Grand Island, North Bend, and Louisville gages on the Platte River during April-August, 1988.