While analyzing the genetic data of five penguins, each of a different species, researchers at the University of Michigan discovered that all the birds were missing three of the five basic taste genes. "Based on genetic data, penguins are believed to have sour and salty tastes, but have lost sweet, umami, and bitter tastes,” researcher Jianzhi Zhang told the BBC, adding that the birds likely lost these taste genes when they evolved millions of years ago.
Zhang said that penguins may be unique in this deficiency. He told the HuffPost that “no other bird is known to have lost three tastes. As far as we know, most birds have both umami and bitter taste receptor genes.” Most, however, cannot taste sweetness.