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"probable" sightings may make allowances for differences in effort to confirm <br />"Probable" sightings in the past. However, the greatest emphasis should be on <br />"confirmed" sightings. Sightings may be one bird or a number of birds. As the <br />AWP has increased since 1940, there has been an increase in the number of birds <br />per sighting. That pattern will likely continue, therefore, there is a need to <br />consider both the number of birds and number of sightings in interpreting trends <br />and evaluating management activities. The following formulas should be used to <br />determine the annual ratios: <br />ratio for fall use = fall sightings and (separ) no of cranes in the fall <br />winter total at Aransas NWR <br />ratio for spring use = spring sighting. and (separately) no of cranes in the spring <br />number departing Aransas NWR in spring <br />These population ratios should be successfully tested and endorsed before they <br />are used as standardized means of crane detection. <br />B.7.2. Index of Bird Use Days <br />Whooping crane distribution along the Platte River, in relation to managed areas, <br />is another means of evaluating benefits of habitat management. There is a need <br />to have a whooping crane use index of bird days on the river as an additional <br />measure of habitat attractiveness. This information is available in post -1984 <br />whooping crane use data. A bird day is defined as one whooping crane sighted in <br />the Platte River Valley on one day. Each additional day that the same bird is <br />present is counted as another use day. <br />Therefore, two indices could be measured: (1) the proportion of the population <br />stopping on the Platte River in the spring and fall, and (2) the number of bird days <br />of use in the spring and fall. The comparisons should begin immediately. There <br />is a need to recognize that there may be a lag time between management actions <br />and bird responses. <br />B.7.3. Habitat Suitability Models <br />This report recommends using habitat suitability models68 as additional tools to <br />evaluate habitat and habitat changes for whooping cranes. The following models <br />are identified: <br />Model A - estimate �xistin suitable habitat I <br />existing suitable habitat I +n <br />68 Dale Strickland, WEST, Inc. and Executive Director, Platte River Cooperative <br />Agreement, Cheyenne, Wyoming. Personal recommendations made at Follow -up <br />Whooping Crane Workshop, February 15, 2001. <br />26 <br />