Other, as yet unknown strategies to cope with high blood sugar may one day yield practical benefits for managing diabetes in people. “There could be a gold mine in the genome of the hummingbird,” says Welch.
Do a metabolic flip
By the end of its nightly fast, a hummingbird has nearly depleted its sugar stores—which poses an opposite metabolic challenge. “How does it wake up and fly?” Welch asks. “There’s nothing but fat available to burn.”
Hummingbirds have evolved to be remarkably nimble at switching their metabolism from sugar-burning to fat-burning, he has found. “This requires an enormous shift in the biochemical pathways that are involved,” Welch says—and it happens in mere minutes, far more quickly than other organisms can manage. “If we could have that kind of control over our fuel use, we’d love that.”
Save water—or not
Sugar isn’t the only challenge posed by a nectar-rich diet. After all, nectar is mostly water—and birds that drink in so much liquid must get rid of most of it, without losing electrolytes. As a result, hummingbird kidneys are highly adapted to recapture electrolytes before they are excreted. “They pee almost distilled water,” says Carlos Martinez del Rio, an ecophysiologist now retired from the University of Wyoming.
But that brings a further problem: If a hummingbird kept producing dilute urine overnight, it would die of dehydration before morning. To avoid that, hummingbirds shut down their kidneys every night. “They go into what, in a human, would be considered acute renal failure,” says Martinez del Rio. “Hummingbirds have to do this, or they would piss themselves to death.”
Fly high—gradually
The metabolic demands on a hummingbird are tough enough at sea level. But many species live at high elevations, where thin air contains less oxygen and offers less resistance to push against when hovering. Consider the giant hummingbird, the world’s largest, which can live in the Andes Mountains at elevations over 14,000 feet—higher than many helicopters can fly. To cope with these conditions, the birds have evolved more hemoglobin-rich blood, says Jessie Williamson, an ornithologist at Cornell University.
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