Functional Dependence of the Power for Hovering on Wing Disc Loading in Hummingbirds

Abstract

The mass-specific power input (metabolic cost) of hovering is independent of body mass but is proportional to the 0.5 exponent of wing disc loading for the sample considered here. The efficiency of converting energy metabolism to aerodynamic power is approximately constant at 6.23% in hummingbirds with a wide range of body mass and wing disc loading. Actuator wing disc theory of helicopter aerodynamics appears adequate for comparing the energetic cost of hovering flight among hummingbirds. Differences in the power input for hovering due to differences in wing disc loading are greater for larger hummingbirds than for smaller ones. Impaired integrity of the outer portion of the wing disc caused by molt or breaking primaries 8, 9, or 10 greatly increases the required power for hovering. The unusual nonsequential pattern of primary-feather molt in hummingbirds may be of adaptive value in that it results in the most rapid restoration of the integrity of the wing disc.