1. Air speeds of migrating birds observed by ornithodolite and compared with predictions from flight theory by C. J. Pennycuick, Susanne Åkesson, and Anders Hedenström Interface Volume 10(86):20130419 September 6, 2013 ©2013 by The Royal Society

2. Power curves calculated for sea-level air density from Flight 1.24, using mass and wing span from table 1, and values of k = 0.90 for the induced power factor and Cdb = 0.10 for the body drag coefficient. C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society

3. Mean flying heights above the water surface for the 31 species in our sample. C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society

4. Track of a Brent Goose, one of a flock of 36, shown in Google Earth from the KML file. C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society

5. Observing set-up and wind sources. C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society

6. Double-logarithmic plot of equivalent air speed (mean of run means) versus body mass. C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society

7. Log-linear plot of the ratio of the mean air speed (Va) to a ‘Reference speed’, which is Vmp for the upper line (filled circles), and Vmr for the lower line (open circles). C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society

8. Bewick's Swan (Cygnus columbianus), showing separation and upward bending of the primaries at the wing tip, when the wing is highly loaded in the downstroke of flapping flight, and the lift coefficient is high. C. J. Pennycuick et al. J. R. Soc. Interface 2013;10:20130419 ©2013 by The Royal Society