Changes in the relative numbers of wintering rough-legged hawks flying and standing were analyzed in relation to several environmental variables. One-third of all the birds recorded (178 of 534) were flying when first seen. The data indicate that local weather conditions are important in determining rough-legged hawk activity in winter. Optimum conditions for flight occurred with high wind velocity, clear skies, rising air pressure, low relative humidity, and high temperature. There was no statistically significant difference in hawk activity at different times of day. The fact that activity was correlated with several variables indicates that the rough-legs react to the end product of numerous interrelated and interacting variables, including those tested.