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from being designated critical habitat, they were successful in reducing the area involved from 2600 to about 250 square miles. The pair of statements above sunmarize a fairly complex chain of logic connecting the MBPP to the future of the whooping crane: 1. MBPP will increase water consumption from the Laramie River. 2. Increased consumption from the Laramie will reduce flows downstream 1n the critical habitat region on the Platte. 3. Reduced flows in the Platte will allow the encroachment of tall vege- tation in the channel of the river. 4. Because the cranes will roost only on open sandbars, the encroachment of vegetation will reduce the area suitable for roosting by cranes. 5. A reduction in the roosting area suitable for cranes will either cause crowding, which will result in stress and increase the chances of catastrophic disease outbreaks, or force the whoopers to seek alternative roosting sites in the Central Flyway, which may be less suitable. 6. An inadequate supply of roosting sites in the Central Flyway will increase the cranes' mortality or decrease the birth rate, or both, thereby reducing the species' chances of survival. To get an idea of the standards of proof implicit in actions under the Endangered Species Act, this chain will now be considered in more detail. 1. MBPP will increase water consumption from the Laramie River. The original plan for MBPP estimated annual water consumption for power production to be 20 000 to 30 000 acre-ft/yr. The dam also may make economically feasible the Corn Creek Irrigation Project in Goshen County, which has a prior right to 22 500 acre-ft/yr. In addition, annual evaporative losses from Grayrocks Reservoir were expected to average 8000 to 9000 acre-ft/yr. Thus, total con- sumption attributable to MBPP could be as much as 60 000 acre-ft/yr.* 2. Increased consumption from the Laramie will reduce flows downstream 1n the Critical Habitat region on the Platte. If all other depletions remain unchanged, it seems obvious that consumption at Grayrocks will reduce the average annual flow at Overton, Nebraska, which is located toward the western end of the critical habitat. However, it will not be a one-for-one reduction *Goshen County is in the eastern part of Wyoming on the Nebraska line. This makes the Corn Creek project a transbasin diversion with respect to the Laramie, but not with respect to the North Platte. Therefore, the North Platte will receive return flows from Corn Creek. 34