Hovering on a high fructose diet: hummingbirds can fuel expensive flight with glucose or fructose

Chris Chin Wah Chen and Kenneth Collins Welch, Jr. in Functional Ecology a Journal of the British Ecological Society

"Unlike humans, some animals evolved on a sugar diet equally rich in glucose and fructose. Hovering hummingbirds are rare among vertebrates in their ability to rapidly make use of ingested sugars to fuel energetically expensive hovering flight, powering up to 100% of their metabolic needs with the sugars they drink, while humans athletes max out at around 30%. Until now, we haven't understood to what extent hummingbirds can use the 50% of the sugar in their nectar meals that is glucose versus the 50% that is fructose. Our study shows that hummingbirds begin using newly ingested sugars to fuel hovering flight within minutes and can fuel as much as 100% of their intense hovering metabolism with either glucose or fructose. This suggests that hummingbirds may even be able to oxidize fructose in flight muscle tissues at rates high enough to satisfy metabolic demands that are, pound for pound, 10 times those of an elite human athlete.

By relying on newly ingested sugars to fuel flight hummingbirds can reserve precious fat stores to see them through the overnight fasting period, or to power migratory flights. These results hint at unique adaptations for fructose use in hummingbird muscles and demonstrate the remarkable convergence of diet, behaviour, and most notably, physiology that enables their high energy lifestyle."

You can read the paper free online here
Chen, C. C. W., Welch, K. C. (2013), Hummingbirds can fuel expensive hovering flight completely with either exogenous glucose or fructose. Functional Ecology. doi: 10.1111/1365-2435.12202

A male ruby-throated hummingbird (Archilochus colubris) hovers at a feeder placed inside a respirometry mask.