Everyone loves to watch hummingbirds, those tiny, brightly colored, fuzzy creatures that flit about, hover over flowers and combatively defend ownership of feeders.
But to the scientists who study hummingbirds, they offer more than just entertainment: Their small size and rapid metabolism mean they lead a dangerous life, sometimes forcing them to move almost entirely to conserve enough energy to survive the night or cross thousands of miles of ocean.
Their diet of nectar produces blood sugar levels that would put a human into a coma, and their soaring flight can generate enough G-forces to knock a fighter pilot unconscious. And the more researchers study these tiny creatures, the more surprises they find hidden within the tiny bodies of the avian kingdom.
“They are the only birds in the world that can fly upside down and backwards.” Holly Ernest“They’re not going to die of diabetes if they drink pure sugar,” says University of Wyoming conservation ecologist David Schneider.
Ernest is one of a handful of researchers studying how hummingbirds cope with the extreme demands of their lifestyle. Here, we share some of what scientists have learned about hummingbirds’ unique adaptations.
Make an effort
For many years, most researchers assumed that hummingbirds spent about 30 percent of their day engaged in the energy-intensive activity of flying from flower to flower and drinking nectar, and most of the rest of the time resting. But physiological ecologists have discovered that Anusha Shankar When I looked closely, I found that they were usually working much harder than they actually were.
Shankar, now at the Tata Institute of Fundamental Research in Hyderabad, India, set out to understand how southern Arizona hummingbirds spend their day. Using a combination of experimental techniques, he measured the birds’ metabolic rates during different activities to estimate their total daily energy expenditure. Combined with previously published data, Shankar was able to calculate the energy cost per minute of the three basic ways birds spend their time: perching, flying, and hovering.
She then estimated how much time each day the birds spent feeding and perching.
“It turns out it’s very variable,” Shankar says. They found that during the early summer when flowers are in full bloom, birds can meet their daily energy needs with just a few hours of feeding, spending 70 percent of the day simply perched. But as the summer monsoon rains arrive and flowers thin out, in some places the birds can’t. They only spent 20% of their day perched, the rest of the time feeding..
“13 hours a day!” Shankar says. “There’s no way I could run 13 hours a day. I don’t know how I do it.”
Really calm down
Hummingbirds have a trick up their sleeves to burn through their energy reserves: When they’re running low, they go into torpor at night, lowering their body temperature to roughly the same as the air around them, which can be just a few degrees above freezing. During torpor, the bird becomes almost comatose, unable to respond quickly to stimuli, and able to breathe only intermittently. Shankar calculates that this strategy can save up to 95 percent of metabolic costs per hour during cold nights. It’s essential on days when hummingbirds eat less than usual, such as after a thunderstorm. It also helps them conserve energy to build up fat stores before migrating.
Shankar is currently studying which parts of hummingbirds’ physiology they prioritize during hibernation, looking at which gene products are essential for them to function. “If hummingbirds are functioning at 10 percent of their normal metabolism, what does that 10 percent do to keep them alive?” she asks.
