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I <br />29 <br />that the risk to whooping cranes may increase substantially <br />because they use much the same habitat in southcentral Nebraska. <br />A single case of avian tuberculosis was diagnosed with the <br />isolation of Mycobacterium'avium from the liver of a sandhill <br />crane found on the Platte River near Overton, Nebraska, in April <br />1978 (Windingstad 1988). A secondary pneumonic fungal infection <br />by Aspergillus fumigatus was also pr.esent in this sandhill crane. <br />Avian tuberculosis was diagnosed in one whooping crane in the <br />experimental Grays Lake flock (.J.C. Lewis, pers. comm). There <br />have been no known instances of avian•tuberculosis in the <br />Aransas-Wood Huffalo flock. . Predators - There are no known.instances of whooping crane loss <br />to terrestrial'predators (USFW5 1986) while on migration. Timber <br />wolves (Canis lupus) are known to prey on whooping cranes on the <br />breeding grounds in the Canadian Northwest Territories (USFWS <br />1986). " . <br />3. Bald Eaale <br />High water flows, human disturbance, and predation have not been <br />reported as a problem for bald eagles in the Platte River system. <br />Among these three factors, human-.disturbance poses the largest <br />potential threat to bald eagles. Potential problems include <br />private and commercial developments, and activities near winter <br />roost sites, gunshot wounds, and contact with overhead wires <br />(either collisions or electrocution). Bald eagles tend to <br />concentrate around areas of open water (USFWS 1981). Ice <br />formation on the Platte River influences the distribution of <br />wintering bald eagles-(NGPC, unpubl. data). The presence of ice <br />can influence the abundance and distribution of potential prey <br />items (USFWS 1981). <br />4. Fora e Fish <br />Habitat suitability index cur.ves for forage fish in the Platte <br />River show the river's.contemporary suitability for sand shiners. <br />These curves do not address whether the current conditions in the <br />river are optimal for sand shiners, but rather which habitats the <br />fish find most suitable to_day. The curves are useful in <br />addressing how habi.tat suitability in terms of depth,.velocity, <br />substrate, and cover could change. <br />Potential effects of temperature and water quality on forage fish <br />in the Platte-River have not been investigated"for present <br />conditions, past conditions,.or potential future conditions. <br />Chemicals used by agriculture-have increased over time to the <br />point that concerns have been raised about contamination of <br />municipal groundwater wells along :the. ,.Platte River (Snow and