Based on 13 y of trapping data, captures of the western harvest mouse (Reithrodontomys megalotis) in northeastern Kansas decreased significantly in summer. Reduced rates of capture could have arisen from reduced numbers or behavioral changes. We found a slight decrease in persistence rates in summer, so in June and July 2002, we placed traps on elevated platforms to test whether R. megalotis might be scansorial in summer. Elevated traps were significantly more successful than surface traps. We concluded that apparent disappearance of R. megalotis in summer was attributable to changes in behavior rather than emigration or death.