We conducted studies of bird and bat mortality at the Nine Canyon Wind Energy Project located in Benton County, Washington. Fatality searches were conducted between September 2002 and August 2003, with a search conducted approximately every two weeks during spring, summer and fall (March - October), and once a month during the winter (November - February). A total of 19 searches were conducted at each of the 37 Nine Canyon turbines and the one unguyed permanent meteorological tower. Experimental trials were conducted to estimate searcher efficiency and carcass removal (scavenging, etc.). Mean searcher efficiency was 44% for small-sized casualties and 78% for large-sized casualties. These rates are very similar to those observed from on-going monitoring at the Stateline Wind Power Project located approximately 12 miles southeast of Nine Canyon. Mean carcass removal time, the average time it takes for a scavenger or other measure to remove a carcass, was estimated to be approximately 11 days for small birds and 33 days for large-sized birds. The carcass removal rates are higher at Nine Canyon than at Stateline. The observed number of fatalities and the results of the experimental bias trials were used to estimate mortality. Thirty-six bird and 27 bat fatalities for which collision with turbines or vehicles could not be ruled out, were found within or very near the search plots. Some of these may not have been killed by turbines or vehicles, but are conservatively included. Horned larks comprised 47% of the fatalities, ring-necked pheasants comprised 14% of the fatalities and western meadowlarks comprised 6% of the fatalities. No other individual species was documented more than once. Two raptor fatalities (American kestrel and short-eared owl) were discovered within the search plots. Estimated mortality was 3.59 bird and 3.21 bat fatalities per turbine per year. Cause of fatalities could have been strikes with turbine towers or blades, collision vehicles traveling along project roads or other non-project related causes. When standardized to the area swept by rotors of the individual turbines, per turbine fatality estimates are within the range observed at other wind projects in the west and mid-west. These results provide an estimate of the mortality expected at the Nine Canyon Wind Power Project or at future wind developments with similar characteristics.