Threats to Wildlife and the Platte River

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p. 22 WILDLIFE Bald Eagles on the Platte, as in most of their range, prey primarily on fish. The availability of fish is greatly influenced by the extent of ice cover. Estimating the percent of fish in their diet is problematical because the remains of fish are digested and often do not appear in egested pellets, the usual source of data for diet analysis in raptors. Of non -fish items in pellets, waterfowl (mostly pirated from other raptors), make up perhaps 40 percent, and mammals are eaten to a lesser degree (Lingle and Krapu 1986). Bald Eagles inhabit woodlands along the river and preferentially roost in large cottonwoods, which offer some shelter from the weather (Currier et al. 1985, p 31). They tend to congregate where ice -free conditions are most stable, as at surfacing groundwater springs and power plant discharge areas. During the winter when Bald Eagles inhabit the river, low flow conditions can enhance their capture of fish (USFWS 1981, p 79). However, very low flows are insufficient to maintain ice -free conditions essential for capturing fish. In moderate winter temperatures, flows of 1100 to 1300 cfs have been enough to maintain adequate open water for eagles (NGPC 1985a, p 36). The needs of Bald Eagles have been artificially enhanced in some areas along the Platte, resulting in an expansion of their traditional habitat. Prior to development, perching trees were more scattered and ice -free open water was primarily maintained throughout the winter in isolated spots where groundwater springs surfaced. Overall, lower flows, return flows from power plants, and an increase in the number of trees appear to have benefitted the eagles. In some areas, however, the effects of water depletion have been deleterious to the eagle. In certain areas, "populations of wintering waterfowl and fish have declined, severely impacting the food source of the eagles" (Currier et al. 1985, p 33). Least Terns and Piping Plovers The Least Tern, a small, graceful, fragile - looking bird which makes a living plunging for tiny fish, is fairly widely distributed in small numbers along coasts and major rivers in the United S tates. The Interior Least Tern, which nests inland of the salt coasts, is federally listed as endangered. Piping Plovers are small shorebirds that feed on invertebrates, often near the water's edge. They have nest site requirements similar to Least Terns in many respects, and they often nest in association with tern colonies. Least Terns nest on the ground in a scrape in sand or gravel, usually in close association with other breeding pairs in colonies (NGPC 1985a, p 42). Eggs are laid from May to June along