Publications

    

    Bruderer, B. & A. Boldt (2001)

    Flight characteristics of birds: Part I: radar measurements of speeds.

    Further information

    Ibis 143: 178–204

    Contact

    bruno.bruderer@vogelwarte.ch

    Abstract

    This first part of a study on flight characteristics of birds presents a commented list of flight speeds measured by radar. It includes 139 western Palearctic species. All measurements were taken by the same tracking radar and corrected for wind influence according to radartracked wind-measuring balloons. The graphical 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 increase only slightly with size. The larger species seem to be increasingly limited to speeds close to their speed of minimum power consumption Vmp. Released birds, apparently reluctant to depart with migratory speed, fly at considerably lower speeds than migrating conspecifics. While large birds seem to be limited to speeds around Vmp, smaller birds seem to be capable of selecting between various speeds, approaching predicted Vmp when tending to remain airborne at low cost, but flying at much higher speeds when tending to make best progress at low cost (around predicted speed of maximum range Vmr). 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 which is attained by the reduction in profile drag during bounding flight of small passerines. The models predict too high speeds for large birds because the power output available for flight seems to decline much more with size than previously assumed.