Platte River Management Joint Study Final Report

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27 Although human disturbance at a nesting colony may be a problem one year and not the next, the frequency of disturbance at riverine sandbars may be greater at locations where bridge crossings or nearby roads provide access to the river channel. Least terns nested.successfully at river sandbars near the Two Rivers State Recreation Area in 1982 but not in 1981 (Ducey 1982). Human use such as wading, hiking, and vehicular disturbance were apparent'at this site in 1981. Least tern colonies at sandpits adjacent to the Platte River are also subject to human disturbance (NGPC 1982-1988) (Table 9). Predation = Least tern and piping plover nesting colonies in the Platte River are subject to predation. (NGPC 1982, 1983; Ducey 1982). Sandpit colonies are not typically surrounded by water and thus allow'easier access for terrestrial predators. Recent data suggest similar levels of known loss to predation at sandpit and sandbar nesting colonies (Table 9). Water barriers do not always protect nesting colonies from predators. Observed or suspected predators of least tern and piping plover eggs and young include snakes, turtles, great blue heron (Ardea herodias), great horned owls (Bubo virginianus), red-winged"blackbird (Agelaius phoenicus), American kestrel (Falco sparvarius),' , raccoon (Procyon lotor), skunks (Mephitis sp.), dogs, and coyotes (Canis latrans) (NGPC 1982 - .1988) . __. . ..'. '? 2 , Whoopinct Crane - ? . Water Fluctuations - Whooping cranes have:been recorded in the Platte River at, discharges ranging from 700 - 4000 cfs. Suitable sandbars are present in the river at varying discharges allowing whooping cranes to use the river for roosting. During flows of 6,240 to 7,920 cfs (X=7,051 cfs) in March 1984 (USGS 1984), some sandhill cranes in the Big Bend reach were observed roosting in flooded fields adjacent to the river as well as in the river channel. Some speculation exists as to whether there was increased availability of roosting habitat provided by flooded fields or whether portions of the river channel became unusable because of physical flow parameters. We do not know if whooping cranes would respond similarly. Human Disturbance - Most of the water-based recre.ational activities that pose disturbance problems for nesting least terns and piping plovers are not present during the period of whooping crane migration. Residential and commercial development, roads, bridges, and railroads are potential disturbance factors near roosting habitat (USFWS 1981, Johnson 1981, Currier et al. 1985). The presence of houses can also increase opportunities for human activity and domestic animal disturbance-near roosting areas. - Overhead lines and fences are known sources of mortality among