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? <br />31 <br />be quickly and adversely affected by minute changes in their <br />immediate environment. Migratory endangered species, such as <br />those occupying the Platte River, may be- affected more by the <br />cumulative effects of habitat change over their entzre range. <br />Habitat loss can also be incremental (occurring over time) making <br />it difficult to evaluate the effect of sma11 quantities of <br />habitat loss on the species. The bald eagle was listed endangered or threatened over inost of <br />its range in 1978 (43 Fed. Register: 6230-6233) , A primary cause <br />of endangerment was habitat modification and the accumulation of <br />pesticides derived from their food items. Populations of bald <br />eagles were reducecl seriously in many states in the 19th century. <br />Land development and increased human activity were considered the <br />key factors adversely affecting the suitability of both breeding <br />and wintering areas (USFWS 19$3). The Great Plains population of <br />piping plovers was determined to be threatened in 1986 (50 Fed. <br />Register 50726-50734). Reservoirs, river channelization, and <br />modification of river*flows that eliminated sandbar nesting <br />habitat along hundreds of kiloineters of the Missouri and Platte <br />rivers in the Dakotas, Iowa, and Nebraska, were identified'as <br />causes for threatened status (USFWS 1984,1988). The interior, <br />least tern was listed as endangered throughout its range because <br />the species' riverine habitats had been and were continuing to be <br />modified through sandbar..elimination and vegetation encroachment <br />(USFWS 1985). The whooping crane was listed as endangered in <br />response to severely reduced population levels. An important. <br />factor contributing to their endangerment was habitat Ioss (USFWS <br />1986). In none of the instances listed above was'enviranmental <br />change or habitat loss at any one location considered the only <br />reason for listing. Rather, the cumulative effects of change <br />over the species' ranges was identified. Recovery plans for the piping plover (USFWS 1988) and interior <br />least tern (USFWS, in press) call for increases in breeding <br />populations to remove each species from endangered or threatened <br />status. Actions to accomplish that objective will include <br />restoration of nesting habitat, improving nesting success where <br />nesting still occurs, and protection of nesting habitat to ensure <br />that the birds have a safe place to nest. The Piping Pl.over <br />Recovery Plan (USFWS 1988) specifically states that one of the <br />actions necessary to delist the piping plover in the northern <br />Great Plains is to "eliminate current or potential threats to <br />breeding habitat." The Recovery Plan also specifies that • <br />essential habitat including the Platte River from Lexington, <br />Nebraska, downstream to the confluence with the Missouri River <br />must be protected and enhanced to provide for species recovery. <br />The Recovery Team described essential habitat to include <br />unvegetated riverine sandbars in the Platte River.