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2. Under certain flow regimes, the Platte River generally provides whooping cranes <br />with the required open expanse for nightly roosting. The availability of shallow, <br />submerged sand and gravel bars in rivers and lakes appears to be one of the major <br />factors determining whooping crane use of these habitats as roosting sites. Cranes <br />observed during migration are most often found within short flight distances of <br />these wetland areas. <br />3. The Platte River provides needed isolation. Whooping cranes do not readily <br />tolerate human disturbances. A human on foot, at distances of over 0.25 -mile, can <br />quickly put a crane to flight. <br />Roost Habitat <br />The one common feature of the vast majority of whooping cranes sightings in migration <br />is undisturbed roosting sites. Whooping crane roost sites in the study area include river <br />channels that have a wide expanse of water and shallow, submerged sandbars. Water <br />characteristics apparently contribute to site security. <br />An evaluation of ten known whooping crane riverine roosting sites identified the <br />following characteristics (Johnson and Temple 1980; FWS 1981; Johnson 1982): <br />1. Wide channel, nine of ten roost sites measured were between 510 and 1,200 feet <br />wide <br />2. Unvegetated <br />3. Fine substrate, usually sand <br />4. Good horizontal visibility unobstructed from riverbank to riverbank and at least a <br />few hundred yards upstream and downstream (or to a bend in the river) at all sites <br />5. Good overhead visibility, absence of tall trees, tall and dense shrubbage, or high <br />banks near the roost <br />6. Shallow water except in the main channel (all sites evaluated were less than 12 <br />inches deep and six of nine sites were 2 to 6 inches deep); water in the main <br />channel may be considerably deeper <br />7. Slow flow, approximately 1 to 4 miles per hour (1.5 - 5.9 feet per second), <br />although water in the main channel may be flowing faster <br />8. Proximity (usually 1 mile) to suitable feeding sites <br />9. The presence of unvegetated sandbar with very low elevation above water and <br />near the middle of the river <br />10. A distance of at least 0.25 -mile from roads, houses, and railroad tracks <br />2 <br />