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. OOO~Ol . then transformed to a habitat versus flow relationship by using the SI models in conjunction with hydraulic simulation models. This procedure follows the general procedures of the Physical Habitat Simulation (PHABS1M) for the Instream Flow Incremental Methodology (IFIM) (Bovee 1982). Habitat simulation models produced by Ziewitz (1987) and the Biology Workgroup (Carlson et al. 1990) have followed this procedure. Habitat criteria and suitability curves that represent those criteria were developed in workshops conducted by the Biology Workgroup (Shenk and Armburster, (draft) 1986) and U.S. Fish and Wildlife Service (USFWS 1987). Habitat criteria were integrated with a hydraulic simulation model by Ziewitz (1987) and the Biology Workgroup modeling subcommittee (Carlson et al. 1990) to produce the habitat simulation models. The modeling process of the Biology Workgroup underwent gradual evolution and refinement as additional data were obtained and as further analyses were conducted. The variation in the output between these models is attributable to uncertainties that exist in the most appropriate computational procedures, especially for the depth criteria. Among the models produced for the Biology Workgroup, Models C4R and C5R are the most recent and generally appear to be most favored by the modeling subcommittee. Models produced have thus far not been validated and should be considered preliminary. The Ziewitz model has not been updated since first produced in 1987. The criteria and basic assumptions developed early in this process, sometimes with a few data points and expert opinion, have been supported by more recent field data collected at confirmed whooping crane roost sights (see Appendix A, Figures AI-A3). All models display similar conformation with the habitat versus flow curves by converging at the range of highest habitat value from 2000 to 2500 cfs (Figure A4). Below this range, the combined suitability of water width and depths are diminished and, therefore, habitat value is reduced for all models. All models predict diminished overall suitability of roosting habitat above this range because all models predict diminished overall suitability of roosting habitat as depth increases. Further review and additional information recently collected at whooping crane roost sites eventually may enable alternate modeling approaches based on different hypotheses and criteria examined. Alternative models could be used to test habitat versus flow relationships to overcome some limitation of existing models or to enable better interpretations of model functions. Empirical Information A list of the confirmed whooping crane sightings on the Platte River since 1966 is provided in Table AI. The sighting in 1966 3