Flight characteristics of birds: I. radar measurements of speeds

This is the first part of a study on flight characteristics of birds and pr esents an annotated list of flight speeds of 139 western Palearctic species . All measurements were taken with the same tracking radar and corrected fo r wind influence according to radar-tracked wind-measuring balloons. Graphi cal presentation of the birds' air speeds emphasizes the wide variation of speeds within species and allows easy comparison between taxonomic groups, species, and types of flight. Unlike theoretical predictions, speeds increa se only slightly with size. The larger species seem to be increasingly limi ted to speeds close to their speed of minimum power consumption V-mp. Relea sed birds, apparently reluctant to depart with migratory speed, fly at cons iderably lower speeds than migrating conspecifics. While large birds seem t o be limited to speeds around V-mp, smaller birds seem to be capable of sel ecting between various speeds, approaching predicted V-mp when tending to r emain airborne at low cost, but flying at much higher speeds when tending t o make best progress at low cost (around predicted speed of maximum range V -mr). Predictions of air speeds by aerodynamic models proved to be too low for small birds because the models do not account for the gain in speed att ained by the reduction in profile drag during bounding flight of small pass erines. The models predict excessive speeds for large birds because the pow er output available for flight seems to decline much more with size than pr eviously assumed.