Meeting Abstract
During the day, hummingbirds quickly metabolize floral nectar to fuel the high metabolic demands of hovering flight. At night, hummingbirds are unable to forage, and must rely on stored energy reserves to fuel their nocturnal metabolism. 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 beginning of 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. We predicted that hummingbirds would first exhaust crop-stored sugar, and subsequently metabolize fat stores as the primary fuel until their first feeding the following morning. Hummingbirds were fed a 13C-enriched sugar solution before lights out and held in respirometry chambers overnight without food. Respiratory exchange ratios (RER) and breath stable isotope signatures (δ13C) indicate that the hummingbirds metabolized labeled sugar for less than 2 h and used fat as the fuel for the remainder of the night. Overall, this study provides insight into how hummingbirds can shift fuel usage at night in order to optimize their daily energy budget.
