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Diversity 2019, 11(1), 9; https://doi.org/10.3390/d11010009

Metabolic Fates of Evening Crop-Stored Sugar in Ruby-Throated Hummingbirds (Archilochus colubris)

1
Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON M1C 1A4, Canada
2
Department of Ecological & Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2, Canada
*
Author to whom correspondence should be addressed.
Received: 30 November 2018 / Revised: 27 December 2018 / Accepted: 5 January 2019 / Published: 15 January 2019
(This article belongs to the Special Issue Stable Isotopes in Ecological Research)
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Abstract

During the day, hummingbirds quickly metabolize floral nectar to fuel high metabolic demands, but are unable to feed at night. Though stored fat is the primary nocturnal metabolic fuel, it has been suggested that hummingbirds store nectar in their crop to offset fat expenditure in the night or to directly fuel their first foraging trip in the morning. We examine the use of crop-stored sugar in the nocturnal energy budget of ruby-throated hummingbirds (Archilochus colubris) using respirometry and 13C stable isotope analysis. Hummingbirds were fed a 13C-enriched sugar solution before lights-out and held in respirometry chambers overnight without food. Respirometry results indicate that the hummingbirds metabolized the sugar in the evening meal in less than 2 h, and subsequently primarily catabolized fat. Breath stable isotope signatures provide the key insight that the hummingbirds converted a substantial portion of an evening meal to fats, which they later catabolized to support their overnight metabolism and spare endogenous energy stores. These results show that the value of a hummingbird’s evening meal depends on how much of this energy was converted to fat. Furthermore, this suggests that evening hyperphagia is an important energy maximization strategy, especially during energetically expensive periods such as migration or incubation. View Full-Text
Keywords: nocturnal energy management; hummingbirds; fuel-use; stable isotopes; respirometry; crop storage; metabolism; respiratory exchange ratio nocturnal energy management; hummingbirds; fuel-use; stable isotopes; respirometry; crop storage; metabolism; respiratory exchange ratio
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Eberts, E.R.; Dick, M.F.; Welch, K.C., Jr. Metabolic Fates of Evening Crop-Stored Sugar in Ruby-Throated Hummingbirds (Archilochus colubris). Diversity 2019, 11, 9.

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