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Wing kinematics and morphology are influential upon the aerodynamics of
flight. However, there is a lack of studies linking these variables to
metabolic costs, particularly in the context of morphological adaptation
to body size. Furthermore, the conversion efficiency from chemical energy
into movement by the muscles (mechanochemical efficiency) scales with mass
in terrestrial quadrupeds, but this scaling relationship has not been
demonstrated within flying vertebrates. Positive scaling of efficiency
with body size may reduce the metabolic costs of flight for relatively
larger species. Here, we assembled a dataset of morphological, kinematic,
and metabolic data on hovering hummingbirds to explore the influence of
wing morphology, efficiency, and mass on hovering metabolic rate (HMR). We
hypothesize that HMR would decline with increasing wing size, after
accounting for mass. Furthermore, we hypothesize that efficiency will
increase with mass, similarly to other forms of locomotion. We do not find
a relationship between relative wing size and HMR, and instead find that
the cost of each wingbeat increases hyperallometrically while wingbeat
frequency declines with increasing mass. This suggests that increasing
wing size is metabolically favourable over cycle frequency with increasing
mass. Further benefits are offered to larger hummingbirds due to the
positive scaling of efficiency.
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