title: Hovering energetics and thermal balance in Anna's hummingbirds (Calypte anna).
abstract: We studied the energetics of hover-feeding Anna's hummingbirds, using three different simultaneous techniques: heat loss as estimated via thermal imaging, metabolic rate as measured at a feeder mask using flow-through respirometry, and aerodynamic power estimated from wingbeat kinematic data. These three methods yielded comparable estimates of power output at ambient air temperatures ranging from 18 degrees to 26 degrees C, whereas heat imbalance at higher air temperatures (up to 34 degrees C) suggested loss by mechanisms other than convection and radiation from the body, such as evaporative cooling and enthalpy rise associated with exhaled air and excreted water and convective heat loss from the patagia. Hummingbirds increased wingbeat frequency and decreased stroke amplitude as air temperature increased, but overall muscle efficiency was found to be approximately constant over the experimental range of air temperatures.
authors.affiliation: Department of Integrative Biology, University of California, Berkeley, California 94720, USA. devangel@berkeley.edu
authors.forename: Dennis
authors.initials: D
authors.lastname: Evangelista
authors.forename: María José
authors.initials: MJ
authors.lastname: Fernández
authors.forename: Madalyn S
authors.initials: MS
authors.lastname: Berns
authors.forename: Aaron
authors.initials: A
authors.lastname: Hoover
authors.forename: Robert
authors.initials: R
authors.lastname: Dudley
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D001833:Body Temperature Regulation; D004734:Energy Metabolism / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D008297:Male; D013696:Temperature