Hummingbirds can detect the sweetness of nectar because of a taste receptor that took an unexpected evolutionary path, researchers say.

Nectar is known to make up about 75 percent of a hummingbird’s diet. But birds seem to lack the receptor that vertebrates normally use to taste sweetness, as scientists discovered when they sequenced the chicken genome in 2004.

“We thought, if the chicken is missing the sweet receptor, then maybe all birds are,” said Maude Baldwin, a biologist at Harvard and an author of the new study, published in Science. “And if all birds are, then birds that eat nectar, like hummingbirds, have to be tasting sugar in a new way. It was a big puzzle.”

To find the answer, Ms. Baldwin and her colleagues scanned whole-genome sequences of 10 bird species, looking for a receptor that would respond to sweets. They found that in hummingbirds; the receptor highly responsive to sugar was one normally used by vertebrates, including chickens, to detect umami, the savory flavor in foods like mushrooms and soy sauce.