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Flight Speeds among Bird Species: Effects of Allometry and Phylogeny

Flight Speeds among Bird Species: Allometric and
Phylogenetic Effects
Thomas Alerstam1*, Mikael Rosén1, Johan Bäckman1, Per
G. P. Ericson2, Olof Hellgren1 

1 Department of Animal Ecology, Lund University, Lund,
Sweden, 2 Department of Vertebrate Zoology, Swedish
Museum of Natural History, Stockholm, Sweden 

Flight speed is expected to increase with mass and
wing loading among flying animals and aircraft for
fundamental aerodynamic reasons. Assuming geometrical
and dynamical similarity, cruising flight speed is
predicted to vary as (body mass)1/6 and (wing
loading)1/2 among bird species. To test these scaling
rules and the general importance of mass and wing
loading for bird flight speeds, we used tracking radar
to measure flapping flight speeds of individuals or
flocks of migrating birds visually identified to
species as well as their altitude and winds at the
altitudes where the birds were flying. Equivalent
airspeeds (airspeeds corrected to sea level air
density, Ue) of 138 species, ranging 0.01?10 kg in
mass, were analysed in relation to biometry and
phylogeny. Scaling exponents in relation to mass and
wing loading were significantly smaller than predicted
(about 0.12 and 0.32, respectively, with similar
results for analyses based on species and independent
phylogenetic contrasts). These low scaling exponents
may be the result of evolutionary restrictions on bird
flight-speed range, counteracting too slow flight
speeds among species with low wing loading and too
fast speeds among species with high wing loading. This
compression of speed range is partly attained through
geometric differences, with aspect ratio showing a
positive relationship with body mass and wing loading,
but additional factors are required to fully explain
the small scaling exponent of Ue in relation to wing
loading. Furthermore, mass and wing loading accounted
for only a limited proportion of the variation in Ue.
Phylogeny was a powerful factor, in combination with
wing loading, to account for the variation in Ue.
These results demonstrate that functional flight
adaptations and constraints associated with different
evolutionary lineages have an important influence on
cruising flapping flight speed that goes beyond the
general aerodynamic scaling effects of mass and wing
The full article is available below:

Guy Leahy