Hummingbirds feel the sweet lure of nectar, but they taste it in the most unexpected of ways.
This group of feathered friends doesn’t have a sweet taste receptor, which means they shouldn’t be able to taste sweet at all. But a new study published Thursday in Science reveals that hummingbirds have repurposed their umami receptor (which recognizes meaty and savory flavors) to be able to taste nectar’s sweetness.
“There are not many cases of such a complicated function being regained over the course of evolution,” which makes it a unique example to study, said Maude Baldwin, a doctoral student at Harvard University and lead author of the new study.
The mystery surrounding the hummingbird’s ability to taste began a decade ago, when researchers first published the complete sequence of the chicken genome. The chicken was the first bird to have its complete genome sequenced, and the data revealed many of its secrets. The chicken, the researchers found to their surprise, didn’t have a functioning sweet taste receptor. While sugar might not taste bad to chickens, they didn’t seek it out, either.
Because this trait is shared by many different groups of birds, scientists believe that some of the birds’ ancestors, such as the small, four-legged dinosaurs from which they likely descended, also lacked a sweet taste receptor.
Baldwin and other ornithologists noticed a problem. Lacking the ability to taste sugars might not be a problem for birds that eat bugs, but plenty of birds, such as hummingbirds, live entirely on nectar, which is almost completely sugar. Without sweet taste receptors, how could they find food?