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I I I I I I I I I I I I I I I I I I I 000005 In comparing the summary of changes the Platte River has undergone since pre- settlement times with the requirements for an ideal whooping crane roost site, it is apparent that significant aspects of the required conditions have been reduced or nearly eliminated. The loss of grasslands within 3.5 miles of the River has directly affected the wet meadows used by the whooping crane for foraging. Whooping cranes feed in a variety of habitats in the Platte River valley including cropland, wet meadows, palustrine wetlands and native grassland (U.S. FWS 1981). Foraging sites are generally associated with sites near nocturnal roosts (U.S.FWS 1987), Although only around 2% of the migrating whooping cranes use the Platte River as a stopover point during their migration (E.A. Eng. Sci. and Tech. 1983), the wet meadows provide a reliable and abundant invertabrate food source (U.S.FWS 1987). The hydrology of the Platte River directly affects the critical habitat area in the Big Bend reach. The Platte River flows in response to surface water inputs from numerous tributaries, surrounding groundwater fluctuations, and human storage and withdrawals. Natural flow in the North Platte River and South Platte River originates primarily from melting snowpacks in the highest elevations of Wyoming and Colorado during the spring. This snow melt, together with spring rainfall, recharges the alluvial aquifers, causing the flow rates to peak in May and June. Following this springtime peak, streamflow decreases significantly during the summer. In the fall, streamflow again increases to a relatively uniform level until the following spring (Bentall and Others 1975). Present day streamflows, however, have been significantly modified by water development projects within the basin. Most of the large-scale irrigation systems were completed by the 1940's (U.S. FWS 1990), In many instances, declines in peak and mean annual discharge correspond to the development of the following reservoirs in Wyoming (see Figure 1): Pathfinder, 1909; Guernsey, 1927; Alcova, 1938; Seminoe,1939; Glendo, 1957; and Lake McConaughy in Nebraska, 1941 (Williams 1978). These changes have also caused a significant decrease in the channel cross-sectional area of the Platte River over the past 40 7.