Hummingbirds Fuel Hovering Flight with Newly Ingested Sugar

• Published in: Physiological and biochemical zoology Vol. 79; no. 6; pp. 1082 - 1087
• Main Authors: Welch Jr, Kenneth C., Bakken, Bradley Hartman, Martínez del Rio, Carlos, Suarez, Raul K.
• Format: Journal Article
• Language: English
• Published: United States The University of Chicago Press 01-11-2006
• Subjects: Animals; Birds - metabolism; Carbohydrate metabolism; Carbohydrate Metabolism - physiology; Carbohydrates - chemistry; Carbon dioxide; Carbon Isotopes; Dietary Carbohydrates; Energy Metabolism - physiology; Feeding Behavior; Flight muscles; Flight, Animal - physiology; Hovering; Hummingbirds; Insect flight; Lipid metabolism; Oxidation; Oxidation-Reduction; Protein metabolism; Selasphorus platycercus; Sugars
• ISSN: 1522-2152; 1537-5293
• DOI: 10.1086/507665

We sought to characterize the ability of hummingbirds to fuel their energetically expensive hovering flight using dietary sugar by a combination of respirometry and stable carbon isotope techniques. Broadtailed hummingbirds (Selasphorus platycercus) were maintained on a diet containing beet sugar with an isotopic composition characteristic of C3 plants. Hummingbirds were fasted and then offered a solution containing cane sugar with an isotopic composition characteristic of C4 plants. By monitoring the rates of CO2production and O2consumption, as well as the stable carbon isotope composition of expired CO2, we were able to estimate the relative contributions of carbohydrate and fat, as well as the absolute rate at which dietary sucrose was oxidized during hovering. The combination of respirometry and carbon isotope analysis revealed that hummingbirds initially oxidized endogenous fat following a fast and then progressively oxidized proportionately more carbohydrates. The contribution from dietary sources increased with each feeding bout, and by 20 min after the first meal, dietary sugar supported ∼74% of hovering metabolism. The ability of hummingbirds to satisfy the energetic requirements of hovering flight mainly with recently ingested sugar is unique among vertebrates. Our finding provides an example of evolutionary convergence in physiological and biochemical traits among unrelated nectar‐feeding animals.