Where do hummingbirds get their sweet tooth?

It's one of the most astounding images in nature: a hummingbird hovering above a flower, wings flapping up to 200 times a second, as it feeds on the nectar. Now a study involving an Irish scientist has shed light on the evolutionary mystery of how the birds taste that sweetness: hummingbirds have hacked together their own kind of taste receptor.

Birds appear to have descended from dinosaurs that lost their sweet tooth, explains Dr Mary O'Connell, a lecturer and Fulbright scholar at Dublin City University's school of biotechnology and co-author of a study in the journal Science.

"The ability to taste sweetness is governed by the combination of two proteins, and by looking at genetic information we discovered that the dinosaurs completely lost one of these proteins.

“All birds therefore lack sweet taste perception. So, how is it that hummingbirds feed on nectar? Are they able to taste sweetness in some alternative way?”

Through genetic, behavioural and molecular studies, O’Connell and colleagues in the United States and Japan discovered that hummingbirds have remodelled the “umami” taste receptor, which we use to pick up on savoury foods with “brothy” flavours, such as mushrooms and soy sauce.

“Hummingbirds, unlike their closest relatives the insectivorous swifts, have evolved the ability to taste sweetness by repurposing their umami taste receptor.”

This adaptation created new opportunities for the species, adds O’Connell. “Changing how they perceived taste allowed them to colonise a new ecological niche and radiate into more than 300 species,” she says.