title: Metabolic substrate use and the turnover of endogenous energy reserves in broad-tailed hummingbirds (Selasphorus platycercus).
abstract: We fed broad-tailed hummingbirds (Selasphorus platycercus) diets of contrasting carbon isotope composition and measured changes in the delta(13)C of expired breath through time. By measuring the delta(13)C in the breath of fed and fasted birds we were able to quantify the fraction of metabolism fueled by assimilated sugars and endogenous energy reserves. These measurements also allowed us to estimate the fractional turnover of carbon in the hummingbirds' energy reserves. When hummingbirds were feeding, they fueled their metabolism largely ( approximately 90%) with assimilated sugars. The rate of carbon isotope incorporation into the energy reserves of hummingbirds was higher when birds were gaining as opposed to losing body mass. The average residence time of a carbon atom in the hummingbirds' energy reserves ranged from 1 to 2 days.
authors.affiliation: Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA. scarlet@uwyo.edu
authors.forename: Scott A
authors.initials: SA
authors.lastname: Carleton
authors.forename: Bradley Hartman
authors.initials: BH
authors.lastname: Bakken
authors.forename: Carlos Martínez
authors.initials: CM
authors.lastname: Del Rio
mesh_terms: D000818:Animals; D001717:Birds / Q000378:metabolism*; D002247:Carbon Isotopes; D004734:Energy Metabolism / Q000502:physiology*; D008297:Male; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes