Bay Nature magazineOctober-December 2017

Ask the Naturalist

Ask the Naturalist: What Do Hummingbirds Taste?

September 25, 2017

Do birds like hummingbirds have taste buds? —Sarah Rabkin, Soquel, CA

Birds do have taste buds, which help them avoid toxic foods and choose preferred food items. But they don’t have nearly as many as mammals do. For example, parrots have about 400 taste buds, whereas humans have anywhere from 2,000 to 8,000. And avian taste buds are mainly not located on the tongue, but mostly in the back of the oral cavity or, in some birds, at the tip of the bill. This enables ducks and shorebirds to easily identify choice items or poisonous ones before actually putting them in the mouth.

Vertebrates share a family of taste receptors called T1Rs. Without getting into too much detail, the interaction between two of these receptors enables some vertebrates to detect savory elements like amino acids and proteins, which are present in things they may eat such as other animals and grain. The interaction between other members of this receptor family enables other vertebrates, for instance primates like us, to taste sugar.

Birds evolved from reptiles, in particular the theropod dinosaurs. These carnivorous ancestors didn’t search out energy-rich sugars, but instead concentrated on eating fleshy organisms. Their taste buds apparently were sensitive to chemicals present in animals, but not to sugar. Because most theropods and most birds had no reason to detect sweetness in order to survive, it is thought that they lost the genes that produce receptors to detect sugars. Generally, modern birds can only detect the savory chemicals that are present in seeds and insects.

Hummingbirds, however, are an outlier among birds. They consume plant nectar equaling up to three times their body weight daily by visiting literally hundreds of flowers. They can distinguish between various concentrations of sugars in solution, and they also like some, but not all, artificial sweeteners.

The poor things are fooled like the rest of us.

Maude Baldwin, a researcher with the Max Planck Institute for Ornithology in Germany, has done extensive research on the hummingbird’s abilities. She found that there were apparently a number of mutations in genes that switched hummingbird taste receptors from detecting savory substances to recognizing sugary substances. How did this evolve? Perhaps as ancestral hummingbirds were looking for insects and probing flowers they accidentally poked into the sugar-rich nectar of flowers. This superfood may have given those hummingbirds a reproductive advantage over hummers that stuck to the old food, thereby selecting for the ability to taste sugar.  So hummingbirds began to concentrate on flowers and some flowers in turn coevolved to attract hummingbirds. There are several other avian groups that concentrate on nectar: sunbirds and tanagers, for example. Ongoing research will explore the mechanism for how those birds detect sweetness.

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