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<br />UllUtil~ <br /> <br />Ziewitz, Sidle & Dinan: Nesting Least Terns and Piping Plovers <br /> <br />9 <br /> <br />Aerial Videography - Central Platte <br />In the videography of the Central Platte, we commonly observed moderately <br />vegetated sandbars and sandbars that were slightly exposed above water. We <br />rarely observed areas that could clearly be interpreted as potentially suitable <br />nesting substrate. The differences between the Central and Lower Platte are <br />readily apparent (Tables 1 and 2). <br />River discharge at Grand ,Island ranged from 0.7 cms (25 cfs) to 73 cms <br />(2570 cfs) on the eight dates of aerial videography. With one exception, we <br />measured sandbar areas greater than 0.8 ha only on the two lowest-flow dates <br />(15 and 24 June). <br />The mean sandbar area of nest sites was 0.48 ha for the eight dates exam- <br />ined. This was significantly greater than the mean of 0.24 ha for systematic <br />sample sites (t=2.26, P=0.028) (Table 2). The mean channel width of nest sites <br />was 295 m, significantly greater than the mean of 201m for the systematic sam- <br />ple sites (t=2.70, P=O.OIl) (Table 2). <br /> <br />Table 2. Measurements from aerial videography of 402-m (1/4 mile) systematic <br />river segments (n=29) and river segments centered on least tern and piping plover <br />nesting sites (n=6) on the Central platte River (river mile 167-251), Nebraska, <br />1988. <br /> <br /> Area of dry, sparsely \legelaled sandbar (ha) <br /> Mean Sandbar <br /> Channel Channel May 5 May 11 May 24 June 4 June 7 June 10 June 15 June 24 area for <br /> Area {hal Width(ml 64 emsl 73 48 35 32 19 8 0.7 all dates <br /> Systematic Sample of Ri\ler Sites <br />Min. 2.5944 64.5 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0025 0.0585 0.0000 <br />Mean 8.1050 201.5 0.0854 0.0911 0.0638 0.0725 0.0364 0.0945 0.5018 0.8944 0.2428 <br />Max. 14.2251 353.6 0.6558 0.5821 0.6922 0.8047 0.3365 0.6166 2.0709 2.6486 2.6486 <br />SI. Dev. 3.0857 76.7 0.1525 0.1567 0.1430 0.1596 0.0709 0.1543 0.4440 0.6242 0.4068 <br /> Nesting Siles <br />Min. 7.2927 181.3 0.0013 0.0025 0.0000 0.0000 0.0000 0.0009 0.0205 0.3301 0.0000 <br />Mean ] 1.8772 295.2 0.1667 0.1439 0.2460 0.2111 0.2295 0.3382 0.7786 1.8167 0.4856 <br />Max. 15.3585 381.8 0.3922 0.4695 0.7867 0.7336 0.7094 1.8095 1.9478 3.8120 3.8039 <br />SI. De\!. 3.27:18 81.4 0.1738 0.1962 0.3522 0.3117 0.2923 0.7217 0.7345 1.1871 0.7688 <br />'Average daily nows at Grand Island. <br /> <br />Ground Survey <br />Our measurements of vegetative cover and height at nest sites were not <br />comparable with those at systematic sample sites because we surveyed the two <br />at different times of the breeding season to avoid disturbance to the birds. Many <br />nests that were first observed in June as scrapes in barren sand had by August <br />acquired a thick cover of vegetation. However, most nests (90.3%) still had less <br />than 50% vegetative cover in the surrounding l-m2 area, and all had average <br />vegetation heights less than 0.76 m. We computed the mean and maximum ele- <br />vation at a site using only those points that shared these vegetative characteris- <br />tics, and did not use the vegetation data to compare nest sites and systematic <br />sample sites. <br /> <br />Lower Platte. - The mean elevation above the stage of 113 cms at nest sites <br />ranged from 0.09 m to 0.82 m, with a mean of 0.3 m (Table 3). The mean <br />