Radar studies have indicated that migrant birds possess an amazing understanding of wind patterns (Bellrose 1967). Birds can recognize many characteristics and select for favorable patterns. Head winds are as unfavorable to migration as is rain or snow because they greatly increase the labor of flight and cut down the speed of cross-country travel. If such winds have a particularly high velocity, they may force down the weaker travelers, and when this happens over water, large numbers of birds are lost. Moderate tail winds and cross or quartering breezes appear to offer the best conditions for the flight of migrants. Richardson (1971) found migrants traveling in different directions at different altitudes, but each group of birds was aided by a following wind. Thus we might expect natural selection to operate in favor of those birds that could recognize and respond to favorable wind patterns because it would reduce energy consumption and flight time on long-distance flights (Hassler et al. 1963). Soaring birds such as hawks, vultures, and storks are very dependent on proper wind conditions for migration. In the fall, often the best day to observe hawk migration in the eastern United States is on the second day after a cold front has passed providing there are steady northwest to west winds and a sunny day for production of thermals (Pettingill 1962). Considerable drifting may be observed in this group of birds because they are literally carried along by the wind or glide from one thermal to the next. Haugh and Cade (1966) found most hawks migrated around Lake Ontario when winds were 10 to 25 miles per hour, but, if the wind exceeded 35 miles per hour, most hawk migration stopped. In conclusion then, we can say that the weather may be the impetus for migration for many species, but it cannot stimulate a bird to migrate unless it is physiologically prepared. Arrivals on the ground are not necessarily indicative of the number of birds passing overhead. During the fall, peak migrations usually follow the passage of a cold front when the temperature is falling, the barometer is rising, winds are from the west or northwest, and the sky is clearing. In the spring, most migrants proceed north in the warm sector of a low when winds are southerly, warm, and moist, but rain, fog, or snow will often curtail the passage of migrants or prevent the initiation of a migration. Evolution of migratory behavior has probably resulted from the survival of birds capable of selecting those wind conditions, which reduce flight time and energy consumption, during their passage. =INFLUENCE OF TOPOGRAPHY=