Hummingbirds dont visit feeders to quench a thirst. They have a taste for sweetness, like us, although different receptors on their tongues (T1R1 + T1R3).
Now, we learn that songbirds taste it too. Several avian ancestors emerging in Australia 30 million years ago evolved it independently (convergent evolution) and kept it as they radiated across the world. The receptor is a modification of the savory receptor (umami), not so surprising considering dinosaur ancestry. Sugar packs calories. That songbirds represent 40% of all birds today suggests the adaptation contributed to their success. Thats a sweet excuse for us to cover embarrassment at a sweet tooth.
