Threats to Wildlife and the Platte River

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p. 25 WILDLIFE channels would be minimally suitable at 50 feet and maximally suitable at 500 feet, water depth surrounding nesting sand islands would be maximally suitable (as predator/human disturbance barriers) if more than two feet deep, and the elevation of nest sites would be minimally suitable at six inches and maximally suitable at heights of two feet or more (USFWS 1987d). Significant changes in nesting habitat, primarily associated with the encroachment of woody vegetation, have meant that conditions suitable to least tern nesting have seriously deteriorated" (NGPC 1985a, p 43). "Much tern nesting habitat has been lost or adversely modified on the Platte and South Platte rivers because of vegetation encroachment caused by modifications in the flow regime, primarily a reduction in flows responsible for scouring the channel bed" (NGPC 1986, p 13). Over the evolution of this species on inland rivers, the timing of nesting coincided with pre- dictable relatively low summer flows. Ironically, under the present regime of regulated flows on the Platte, high -water periods during summer can inundate low sandbars, while the higher sandbars are covered with trees and shrubs, making nesting in the channel impossible (Currier et al. 1985, p 38). High flows during certain years have inundated all potential river nest sites in major stretches of the river (NGPC 1986, p 13). Attempts to nest outside the river channel in sand and gravel quarry sites adjacent to the river, due to loss of preferred habitat, resulted in very poor productivity and high abandonment rates associated with human disturbance and predation (NGPC 1985a, p 44). Earlier in this century, Least Terns nested in Nebraska from North Platte to Grand Island (150 miles) (Currier et al. 1985, p 37). But loss of habitat has proceeded so rapidly that, for the most part, by 1979 they were confined primarily to an eight -mile stretch adjacent to Mormon and Shoemaker islands near Grand Island, Nebraska10 (Currier et al. 1985). In 1979, approximately 30 pairs nested in three colonies along a two -mile stretch between Wood River and Grand Island (Faanes 1983). All these sites were unsuitable and abandoned by 1982 because vegetation had encroached upon the channel. Following restoration through mechanical clearing by the Platte River Trust and the Nebraska Game and Parks Commission in the fall of 1982, three pairs recolonized one of the sites in 1984 (NGPC 1985a, p 43), and recolonization occurred in other sites, including Audubon's Rowe Sanctuary near Gibbon, Nebraska (K. Strom 1988, pers. obser.). 10 The Platte River Trust (see chapter IV) has acquired land or easements on these islands (Krapu 1981).