Aerial shaking performance of wet Anna's hummingbirds

Abstract

External wetting poses problems of immediate heat loss and long-term pathogen growth for vertebrates. Beyond these risks, the locomotor ability of smaller animals, and particularly of fliers, may be impaired by water adhering to the body. Here, we report on the remarkable ability of hummingbirds to perform rapid shakes in order to expel water from their plumage even while in flight. Kinematic performance of aerial versus non-aerial shakes (i.e. those performed while perching) was compared. Oscillation frequencies of the head, body and tail were lower in aerial shakes. Tangential speeds and accelerations of the trunk and tail were roughly similar in aerial and non-aerial shakes, but values for head motions in air were twice as high when compared with shakes while perching. Azimuthal angular amplitudes for both aerial and non-aerial shakes reached values greater than 1808 for the head, greater than 458 for the body trunk and slightly greater than 908 for the tail and wings. Using a feather on an oscillating disc to mimic shaking motions, we found that bending increased average speeds by up to 36 per cent and accelerations of the feather tip up to fourfold relative to a hypothetical rigid feather. Feather flexibility may help to enhance shedding of water and reduce body oscillations during shaking.

Flying in the rain: hovering performance of Anna's hummingbirds under varied precipitation

“…Hummingbirds flying in the rain V. M. Ortega-Jimenez and R. Dudley 3999 water penetration and offer effective thermal insulation [8,9,17]. Moreover, hummingbirds have the ability to perform rapid body shakes even in flight to remove almost completely any water adhered to the body [18]. Aerodynamic studies indicate a reduction of lift and an increase in airfoil drag as precipitation increases [1 -3].…”

Into turbulent air: size-dependent effects of von Kármán vortex streets on hummingbird flight kinematics and energetics

“…Interestingly, von Kármán vortex streets persist as a dominant flow structure within vegetational canopies [10], even amidst the complexity of interacting wakes, and thus represent a well-characterized unsteady regime with which to probe biomechanical responses of volant taxa to natural flow fluctuations. In this regard, hummingbirds are of particular utility because of their capacity to engage in sustained feeding bouts from flowers over a range of orientations [11] and under challenging environmental conditions, including reduced air density [12], fast forward flight [13] and while flying in rain [14,15]. Thus, the associated maintenance of stability more generally is an obvious feature of flight in this taxon.…”

Cleanliness is next to godliness: mechanisms for staying clean

“…6D). Such motions have been found to help mammals, birds and mosquitoes expel accumulated water (Dickerson et al, 2012;Ortega-Jimenez and Dudley, 2012;Dickerson and Hu, 2014). Shaking mammals can impart accelerations of 10-70 g to adhered water (Dickerson et al, 2012).…”