© Marcel Burkhardt
Liechti, F. & L. Bruderer (2002)
Wingbeat frequency of barn swallows and house martins: a comparison betweenfree flight and wind tunnel experiments.
J. Exp. Biol. 205: 2461–2467
The flight paths and wingbeat patterns of 39 barn swallows (Hirundo
rustica) and 26 house martins (Delichon urbica) were recorded by
tracking radar duringthe spring migration. Depending mostly on flight angle,
hirundines performed anything from continuous flapping flight during climbing to
single pulse-like wing beats during descent. Unlike most other passerines,
hirundines rarely showed regular flapping and rest phases, allowing them to be
distinguished from other bird migrants by radar echo signatures. Effective
wingbeat frequency (Feff)was calculated as the mean number of wing beats per
second, including non-flapping phases. Under comparable flight conditions, Feff
was higher in house martins than in barn swallows. Within species, Feff values
were higher during climbing and slow flying than during descent. Of the variance
in Feff, 71% could be explained by climbrate, air speed and species; similar
results were obtained in the wind tunnel. Under comparable flight conditions,
barn swallows and house martins in free flight had significantly lower values of
Feff than individuals in windtunnel experiments (by 40% and 32%, respectively).
This difference may at least partly be due to the shorter wings of the juveniles
tested in the wind tunnel during autumn. However, it seems unlikely that this
can account for all ofthe large difference. It is suggested that wind
tunnelexperiments might overestimate birds´ flight costs compared with free
Keywords: barn swallow, Hirundo rustica, house martin, Delichon urbica, wingbeat pattern, intermittent flight, effective wingbeat frequency, wind tunnel, free flight, flight costs.