Ecological correlates of hovering flight of hummingbirds

Simultaneous recordings of oxygen consumption and wing kinematics were collected from hummingbirds hovering at artificial flowers of different dimensions or when loaded by the addition of small weights to simulate increased fat stores. Hovering at wide-diameter flowers required increased wingbeat frequencies to compensate for decreased wingbeat amplitude, and it was 5 % more metabolically expensive than at narrow flowers. Loaded birds increased their wingbeat amplitude to support the extra load whilst maintaining a nearly constant wingbeat frequency. A 10 % increase in load required a 5.7 % increase in mass-specific oxygen consumption. Although the variation in wing kinematics was associated with an increased metabolic cost, there was very little effect on fl ight efficiency. This ability to vary wing kinematics allows hummingbirds to exploit a wide range of flower types and to accommodate increased energy stores for seasonal migration