Species Recovery Objectives for Four Target Species in the Central and Lower Platte River

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the entire population is desirable. Aerial surveys are the only practical way to survey a large area. The surveys begin at daybreak by flying over the river from east to west or vice versa. The flights are expensive. Despite the large, white coloration of the adult birds, past surveys have overlooked some birds that were confirmed by ground observations. Whooping cranes begin leaving the river roost at daybreak to fly to feeding areas. As the aerial survey progresses, and time passes, an increasing number of cranes have already moved outside the survey area. Consequently, daily aerial surveys provide incomplete counts of whooping crane use or presence. If managers cannot adequately measure use, then failure to meet some numbers objective could be improperly interpreted. For example, if managers are not able to demonstrate achievement of stated objectives, even though habitat management has occurred, then some may argue that habitat management should stop. In reality, the habitat management might have been ideal, but survey techniques may have been unable to confirm that because of the low numbers of birds and erratic use. The draft protocols (December 11, 2000) being developed for monitoring whooping crane use on the Platte River are conceptually sound given the limitations of surveys. For example, there are sometimes problems with weather patterns that can prevent survey flights for extended periods of time. Additional improvements should be made to existing survey techniques and methods. B.5.2. Statistical Analyses There is a question about the statistical significance that could be placed on any increased whooping crane use of the central Platte River. As habitat improvements are made along the central Platte River, it is expected that whooping crane use would gradually increase. Because the AWP is small, the numbers counted will be low, and year to year river use has been highly variable in the past. Weather conditions in any given year can strongly influence whether whooping cranes stop on the Platte River.63 For example, in some years, strong winds have pushed cranes east or west of their principal migration pathway so they did not fly over the central Platte River.64 Weather conditions in some years may result in most whooping cranes overflying the Platte River before the time of day they need to go to roost. The low numbers involved and the variability of river use makes it difficult to statistically evaluate the significance of any increase or decrease in river use. If statistical 63 Kuyt, E. 1992. Aerial radio - tracking of whooping cranes migrating between Wood Buffalo National Park and Aransas National Wildlife Refuge, 1981 -1984. Occas. Pap. 74, Canadian Wildlife Service, 53pp. 64 Wally Jobman, U.S. Fish and Wildlife Service, Grand Island, Nebraska. Personal Communication: September 2000. 23