Wingbeat kinematics and energetics during weightlifting in hovering hummingbirds across an elevational gradient
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ORIGINAL PAPER
Wingbeat kinematics and energetics during weightlifting in hovering hummingbirds across an elevational gradient Derrick J. E. Groom1,2 · M. Cecilia B. Toledo3 · Kenneth C. Welch Jr.1,2
Received: 18 December 2015 / Revised: 8 July 2016 / Accepted: 9 July 2016 © Springer-Verlag Berlin Heidelberg 2016
Abstract Hummingbirds differentially modify flight kinematics in response to the type of challenge imposed. Weightlifting is associated with increases in stroke amplitude (the angle swept by the wings) to increase the angular velocity of the wings and generate the requisite lift, but only up to 160°. Conversely, flight in hypodense air is accomplished by increasing the angular velocity of the wing through increases in wingbeat frequency and stroke amplitudes, with larger increases in amplitude than seen in weightlifting flight. The kinematic differences between these two challenges may be facilitated by the lower energetic costs associated with overcoming drag and inertial forces over the wing during hypodense flight. Thus, we hypothesized that energetic expenditure is what limits the kinematics of weightlifting flight, with lower air densities permitting increases in angular velocity at comparatively lower costs. To explore the kinematic and energetic effects of air density and weightlifting on hovering flight performance, video and respirometric recordings of weightlifting were performed on four species of hummingbirds across
Communicated by G. Heldmaier. Electronic supplementary material The online version of this article (doi:10.1007/s00360-016-1016-y) contains supplementary material, which is available to authorized users. * Derrick J. E. Groom [email protected] 1
Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
2
Department of Cell and Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada
3
Instituto Bàsico de Biociências, Universidade de Taubaté, Taubaté, SP 12010‑180, Brazil
an elevational gradient. Contrary to our hypothesis, wingbeat frequency did not vary due to elevation. Instead, wingbeat frequency seems to increase depending on the power requirements for sustaining hovering flight. Furthermore, metabolic rates during hovering increased with angular velocity alone, independent of elevation. Thus, it appears that the differential responses to flight challenges are not driven by variation in the flight media. Keywords Hovering · Hummingbirds · Metabolism · Elevation · Load-lifting · Kinematics
Introduction Sustained hovering is one of the most demanding forms of flight a volant animal is capable of performing. In addition to maintaining the large power output necessary to hold position while hovering, animals that sustainably employ this mode of flight must also possess large power reserves to perform even more costly behaviors such as vertical ascent or to support increasing mass associated with feeding or egg formation. Production of elevated aerodynamic power output for such flight behaviors is achie
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