(Inside Science TV) -- It's the smallest bird on the planet and no animal has a faster metabolism -- roughly 100 times that of an elephant. Yes, the humble hummingbird is certainly a winged wonder.
"When they're flying they beat their wings 200 times a second, their heart can beat up to 20 times a second, and when they're feeding they can stick their tongues out 17 times a second," said Maude Baldwin, a PhD student of biology at Harvard University in Cambridge, Massachusetts.
To keep up their speedy pace, a hummingbird's main fuel is sugar.
"Their main source of their energy is from carbohydrates in nectar," said Baldwin.
But here's the thing that's stumped scientists like Baldwin, for years: she knows hummingbirds have a taste for sweets, but they shouldn't. Like other birds, hummingbirds lack sweet-taste receptors on their tongues. So in theory, they shouldn't be tempted by any sugary tastes.
"We wanted to see if hummingbirds actually taste sugar or if they're just attracted to the calories in the nectar, if it was like they were getting a sugar high," Baldwin said.
In an experiment, researchers put out hummingbird feeders. One feeder contained plain water, and the other feeders contained water with different artificial sweeteners. Researchers then watched the hummingbirds' reactions to each feeder.
"We used high-speed cameras to figure out how quickly they could discriminate between water and sugar," explained Baldwin.
The hummingbirds quickly rejected the plain water and all artificial sweeteners, except for one that is used as a sweetener in toothpaste. But, what repelled the hummingbirds from the water and other artificial sweeteners and attracted them to the toothpaste sweetener when they have no sweet receptors?
"So they use instead their savory receptor," remarked Baldwin.
Scientists know that the tongue can detect five different kinds of tastes: sweet, sour, salty, bitter and savory, also known as "umami."
At some point in the hummingbirds' evolution, a taste receptor transformed from one that's normally used to detect umami flavors, into one that's used to taste sweets instead.
"So hummingbirds…they’ve evolved a new way to taste sugar," said Baldwin.
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Maude Baldwin, Harvard University