Graduation date: 2006Radiotelemetry was used to study the seasonal movements and habitat use of adult westslope cutthroat trout Oncorhynchus clarki lewisi in Roberts Creek and Rail Creek, headwater tributaries of the John Day River, Oregon, from September 2000 to December 2001. The objectives were to (1) describe adult cutthroat trout life history in headwater streams by comparing seasonal movement patterns, and (2) assess seasonal habitat selection by comparing habitat use to availability. For seasonal comparison, only fish that survived with an active transmitter throughout winter, spring, and summer were used in the analysis. Sample size was 17 (mean fork length, 241mm) on Roberts Creek and 9 (mean fork length, 252 mm) on Rail Creek. In winter and summer, radiotagged fish were relatively sedentary on both Roberts Creek (median home ranges, 35 and 104 m, respectively) and Rail Creek (median home ranges, 104 and 112 m). In spring, 65% of fish in both streams moved over 100 m upstream to spawn; upstream movements were as long as 1,138 m (median, 271 m) on Roberts Creek and as long as 3,771 m (median, 311 m) on Rail Creek. Postspawning movements downstream were common; 82% of fish on Roberts Creek and 57% on Rail Creek showed homing behavior, returning in summer to the same channel unit they inhabited in winter. Fish length was positively correlated to total movement distance in spring on Roberts Creek but not on Rail Creek. Over 86% of the surface area of both creeks consisted of fast-water channel units. Instream large wood created the majority of habitat heterogeneity in both streams and radiotagged cutthroat trout were strongly associated with large wood pools throughout the year. Plunge pools were positively selected throughout the year on both streams. Headwater-resident populations of cutthroat trout are often considered nonmigratory; however, these radiotagged fish showed fluvial migratory behavior. These results demonstrate that habitat heterogeneity and connectivity are important life history requirements for fluvial headwater resident cutthroat trout.