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41 <br />19 <br />Midwinter survey efforts have demonstrated recent use of the <br />Platte River by bald eagles (Table 7). Wintering bald eagles are <br />found in the largest numbers near Lewellen and Overton along the <br />Platte and North Platte Rivers (USFWS 1981, NGPC unpubl. data). <br />Ice cover on the P.latte River begins to decline with warming <br />temperatures in lafie February and early March. Additional <br />migrant bald eagles begin to arrive on*the river during the <br />spring thaw, and then disburse according to the distribution of <br />open-water areas on the river. The bulk of the wintering <br />population has departed by mi.d-April; the latest date is 12 May <br />(Johnsgard 1980). The earliest arrival date in fall is 16 <br />September (Johnsgard 1980). Eleven bald eagle•nocturnal roost <br />sites were located'on the central Platte River in 1978 - 1979 <br />(USFWS 1981). Although the roosts wer.e scattered throughout the <br />stretch of the river from Lewellen to Kearney, three major roosts <br />occurred in the immediate vicinity of Overton. Censuses of bald <br />eagle use have been made annually at 12 roosts since 1980 (NGPC, <br />unpubl. dataj: . <br />Ground and aerial surveys of bald eagles were conducted during <br />January - April 1988 between Lake McConaughy and Overton, <br />Nebraska. The surveys included the Platte and North Platte • <br />Rivers as well as associated supply canals and storage <br />reservoirs. Areas supporting the highest number..of bald eagles <br />included the reach from Johnson Lake to 4 miles below the J-2 <br />river return including the supply canal and 2 power plants (105 <br />on 1 March), and near Sutherland Reservoir (154 on 15 February). <br />Along the Platte River, nocturnal roosts consist primarily of <br />large eastern cottonwoods which offer protection from the wind <br />and other weather factors. The same nocturnal roosts are <br />apparently used yearly, as was the case with 11 roosts monitored <br />during the winters of.1978-79 and 1979-80. Roost site tenacity, <br />however, diminishes as ice on the river.thaws in early spring and <br />additional migrating eagles begin"to arrive on the Platte River <br />(Lingle and Krapu 1986, NGPC, unpubl. data). <br />3. Chancres Over Time in Platte River Conditions. <br />Changes in the areaZ ext-ent of Platte R.zver system habitats since <br />pre-settlement times (pre 1840's) are quantified in Table 8. The <br />two habitat components that have been reduced the.most are 1) <br />open, unvegetated river channel, and 2) the grassland complex . <br />(Currier et al. 1985). • <br />A. AQUatic Habitat <br />On the average, 67% of the water-carrying channel area has been <br />lost in the Big Bend reach (Currier et*al. 1985). The abandoned <br />channel area has been converted to brushland and forest in many <br />areas. Channel losses along the Platte River range from 58% near