During the summers of 1963 and 1964, while in northern Michigan, I used a Doppler radar unit to determine flight-speed of birds. The radar unit is described. I recorded 1,628 speeds of 17 species. The speeds of eight colonial species were analyzed in detail. With the exception of one sample, all speeds were taken of birds flying under "natural" conditions. Flight-direction was recorded with relation to wind. Mean flight-speeds ranged from 12.9 miles per hour for Cliff Swallows flying into winds at 20 miles per hour to 34.7 miler per hour for Herring Gulls flying with winds at 6 to 15 miles per hour. Wind velocity affected the flight of most birds. The effect was less for birds flying into the wind than for those flying with the wind. Speeds of birds flying across the wind were, for the most part, not significantly different from those of birds flying without wind. The mean flight-speed for feeding Bank Swallows was faster than that for birds flying near the colony. Herring Gulls were faster than Ring-billed Gulls. Common Terns flew faster than Black Terns. Bank Swallows and Purple Martins were faster than Barn and Cliff Swallows.