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<br />0009111 <br /> <br />, <br /> <br />was the first sighting confirmed since 1960, the point when <br />changes in sediment transport is said to have reached quasi- <br />eqUilibrium. A confirmed sighting is defined as one where the <br />identity of the bird(s) is determined by visual observation by a <br />conservation officer or biologist. For the purpose of this <br />review these sightings were treated as a subset representative of <br />whooping crane use of the river. Although many reports of <br />whooping cranes are received from the public by the U.S. Fish and <br />Wildlife Service, Game and Parks commission, and Whooping Crane <br />Trust, a relatively low number are confirmed due to late <br />reporting, inability to locate reported birds, or <br />misidentification by observers. On some occasions the birds have <br />been in the area for several days before they are reported to <br />authorities, or before their presence could be confirmed. It is <br />probable that some whooping crane use has not been observed and <br />that some observations are probably not reported. <br /> <br />Information in Appendix A was examined first by discounting the <br />repeated observations of whooping crane groups at different <br />locations and by repeated use on sequential dates. This results <br />in 25 confirmed sightings of whooping cranes groups on the river <br />since 1966 (Table 1). Sixteen of the confirmed sightings <br />occurred during spring and 9 during fall. <br /> <br />The flows at the time of whooping crane sightings also were <br />compared with daily flows (USGS Grand Island gage, 1966-1989, <br />1990-1992 provisional) that have occurred during the migrational <br />period. This was done by first computing the modal date of crane <br />sightings in Nebraska during the spring and fall migration <br />periods. Then the statistical distributions of daily flows that <br />occurred from 15 days before to 15 days after those dates were <br />cDmputed. <br /> <br />Platte River flows at the time of confirmed whooping crane use <br />frequently fell in a range from 1800 to 2300 cfs; ten (40%) of <br />the 25 observations occurred in that range. By comparison, the <br />historical gaging records indicate 11 percent of the daily flows <br />during the combined spring and fall migration periods fell within <br />the 1800-2300 cfs range. Flows near 2000 (+;-200) cfs have <br />recurred as a point of significance in reviewing available <br />information on whooping crane use and is consistent with roosting <br />model outputs. A flow of 2000 appears to provide a good <br />combination of habitat suitability assigned by the habitat <br />simulation models (i.e., depth, wetted area, shallowly submerged <br />sandbars) . <br /> <br />Five (20%) of 25 confirmed observations have been at flows less <br />than 1200 cfs. In comparison, 25 percent of the daily flows <br />during the spring migration period and 40 percent of the daily <br />flows during the fall migration period (1966-1992) were less than <br />1200 cfs. Flows of 1200 to 1300 have previously been suggested <br />to be a range with some assignable value. Speculatively, this <br /> <br />4 <br />