FLIGHT SPEED OF FORAGING COMMON NIGHTHAWKS (CHORDEILES MINOR) - DOES THE MEASUREMENT TECHNIQUE MATTER

We collected data for flight speeds of foraging common nighthawks (Cho rdeiles minor) flying under natural conditions using a Doppler radar a nd compared them with data collected by timing flights over a known di stance For the same species. We also compared our Doppler radar measur es of flight speed with the values of minimum power speed (V-mp) and m aximum range speed (V-mr) predicted from aerodynamic models. Our measu rements showed that under natural conditions, nighthawks flew at 6.5 /- 1.1 m-s(-1), significantly faster than the 5.3 +/- 1.2 m-s(-1) deri ved by timing flights over measured distances. Doppler measurements in dicate that on average, nighthawks flew significantly faster than the predicted V-mp, but slower than the predicted V-mr although there was considerable variation. Our results confirm that the method of measuri ng flight speeds can be important and suggest that the mechanics of hu nting insects and not energetics, may be most important in determining the flight speed used by foraging common nighthawks.