Threats to Wildlife and the Platte River

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WILDLIFE P. 11 the channel at the confluence of the North and South Platte was more than a mile wide. The river has now shrunk to less than 10 percent of its former width in much of the reach of the North and mainstem Platte between Kingsley Dam and Overton ( Krapu et al. 1982). In addition, the distribution of roosting cranes in the river has shifted to the east. In response to habitat alteration, the western limit of roosting cranes is shifting east more rapidly than is the eastern edge; thus, the birds are becoming more densely concentrated (C. Frith 1988, pers. comm.). Accompanying the channel shrinkage has been the dramatic expansion of woody vegetation (shrubs and trees) into the former channel and onto sandbars and islands. Some reaches of the river now consist of several distinct channels through mature woodland. For wildlife such as waterfowl, wading birds, and sandbar nesters, which require open bars and wide unobstructed channels, vegetative encroachment has been deleterious and has led to the birds' abandonment of many areas that formerly provided prime habitat ( Krapu et al. 1982, Lingle 1982 in Iverson et al. 1987). Krapu et al. (1987) state: "cranes have been prevented from using a substantial part of the river channel in recent years because of a shrinking channel width and associated woodland expansion" (p 365). The marked reduction of flows caused by upstream diversion, irrigation, and groundwater pumping also has affected the once - extensive native wet meadows and grasslands bordering the river. The meadows are heavily used by foraging cranes and waterfowl, and their maintenance is intimately linked to the hydrology of the river (Hurr 1981, Nagel and Harding 1987), but the complex hydrologic interactions and the relationship between fluctuating water levels and vegetation are at present poorly understood. Large -scale removal of water has lowered the water table in some reaches, and large areas of wet meadows near the river are now dry enough to grow cash crops. More than 75 percent of the extensive original wet meadow habitat has been lost through development or conversion to cropland ( Krapu et al. 1982). The Nebraska Game and Parks Commission has described the importance of these meadows for Whooping Cranes (and much of this is applicable to Sandhill Cranes and waterfowl): The loss of this habitat poses the threat of shortage of the invertebrate foods that provide much of the calcium and protein in the diet of the whooping crane that is important to the maintenance of physiological condition required for successful reproduction. Maintenance of wet meadows close to the river would provide a readily available source of these nutrients near the roost. Availability of wet meadows could also lessen the impact of any future modifications to the present corn- livestock economy that might diminish the birds' access to various foods. (USFWS 1981 in NGPC 1985a, p 17).