A vibrant hummingbird with a green crown feeds on a cactus flower in Costa Rica. John G. Fuller/I Ubiquitous/Universal Images Group (via Getty Images)
Everyone loves watching hummingbirds. Hummingbirds are small, brightly colored blurs that fly around, hover over flowers, and bravely defend ownership of feeders.
But for scientists who study hummingbirds, they offer more than just an interesting sight. With their small bodies and ferocious metabolisms, they live on a knife’s edge, sometimes having to shut down their bodies almost completely just to conserve enough energy to survive the night. Sometimes they have to travel thousands of miles across the open ocean.
Their nectar-rich diet raises blood sugar levels that can put a person into a coma. And their high-speed zoom flight can generate gravitational accelerations strong enough to cause fighter pilots to faint. The more researchers look into it, the more surprises there are hidden within its tiny body, the smallest in the bird world.
“They are the only birds in the world that can fly upside down or backwards,” says Holly Earnest, a conservation ecologist at the University of Wyoming. “They drink pure sugar, but they don’t die of diabetes.”
Ernest is one of a small number of researchers studying how hummingbirds cope with the extreme demands of their lifestyle. Here’s some of what scientists have learned about hummingbirds’ unique adaptations.
tackle work
For years, most researchers have known that hummingbirds spend only about 30 percent of their day in the energy-intensive activities of hopping from flower to flower and gulping down nectar, and spend most of the rest I thought of time as rest. But when physiological ecologist Anusha Shankar takes a closer look, she finds that they often work much harder than that.
Now at the Tata Institute of Fundamental Research in Hyderabad, India, Shankar is trying to figure out how the long-billed hummingbirds of southern Arizona spend their days. Using a combination of experimental methods, she measured the birds’ metabolic rates during various activities and estimated their total daily energy expenditure. Adding previously published data, Shankar was able to calculate the energy cost per minute of perching, flying and hovering, which are essentially three options for birds to spend their time. I did.
She then estimated how much time the birds must have spent each day feeding and perching.
“Ultimately, we found that it was very variable,” Shankar says. At the beginning of summer, when flowers are abundant, birds can meet their daily energy needs with just a few hours of feeding and can spend 70 percent of their day just perched, she found. But when the summer monsoon rains arrived and flowers became scarce, the birds in some locations perched only 20 percent of their waking hours and spent the rest of their time foraging.
“That’s 13 hours a day!” says Shankar. “It’s impossible to spend 13 hours a day running. I don’t know how they do it.”
Seriously calming down
Hummingbirds have a trick for regaining their energy reserves. When a bird is in danger of running out of energy, it enters a coma at night, and its body temperature drops to near the temperature of the surrounding air, sometimes only a few degrees warmer. It’s freezing. During coma, the bird appears almost comatose, cannot respond immediately to stimuli, and breathes only intermittently. Shankar estimated that this strategy could save up to 95% of the metabolic cost per hour on cold nights. This can be essential after days when bird food is lower than normal, such as after a thunderstorm. It also helps birds conserve energy to store fat before migrating.
Professor Shankar is currently studying which parts of the hummingbird’s physiology are prioritized during coma by examining essential gene products. “If you are a hummingbird functioning at 10 percent of your normal metabolism,” she asks, “what is that 10 percent keeping you alive?”
A ruby-bellied hummingbird is resting on a plant. Juan Jose Arango / VW PICS / Universal Images Group via Getty Images
One set of genes that birds seem to have left untouched is the set of genes that govern their biological clocks. “It’s important to do things at the right time when they’re in a coma,” Shankar says. For example, birds begin to wake up from their coma about an hour before sunrise, well before any visible light cues, to prepare for the day.
deal with sugar
To fuel their very high metabolic rate, hummingbirds suck about 80% of their body weight in nectar each day. That’s the equivalent of drinking nearly 100 20-ounce colas a day for a 150-pound person, and nectar is often much sweeter than soda.
Ken Welch, a comparative physiologist at the University of Toronto’s Scarborough College, says the human intestine can’t absorb sugar that quickly, which is one reason why eating too much soda or Halloween candy can make you sick to your stomach. states. Hummingbirds have leaky guts that cope with the onslaught by allowing sugar to enter the bloodstream between the intestinal cells, rather than just passing through them. This allows sugar to be quickly flushed out of the intestines before it can cause discomfort. This rapid transport and likely other adaptations allow hummingbirds to reach blood sugar levels as high as six times higher than humans, Welch says.
Having this much sugar in the blood causes serious physiological problems in people. This causes more sugar molecules to shine on the body’s proteins. This is a process known as saccharification. In the long term, excessive glycation causes many of the complications of diabetes, such as nerve damage. Welch says it’s still unclear how hummingbirds get around the problem of glycation, but clues are starting to emerge. For example, one study found that avian proteins contain fewer of the amino acids most susceptible to glycation than mammalian proteins, and that the remaining amino acids are often hidden deep within the protein and less exposed to circulating sugars. It turns out.
Other, as-yet-unknown strategies for dealing with hyperglycemia may one day have practical benefits in helping people manage their diabetes. “There could be a goldmine in the hummingbird genome,” Welch says.
perform metabolic reversal
By the end of each night’s fast, hummingbirds have nearly used up their sugar stores, which poses the opposite challenge to their metabolism. “How do you get up and fly?” Welch asks. “There’s nothing you can burn other than fat.”
He discovered that hummingbirds have evolved to be surprisingly agile at switching their metabolism from burning sugar to burning fat. “This requires major changes in the biochemical pathways involved,” Welch says. And it happens in a matter of minutes, much faster than other organisms can handle. “We would be very happy if we could control our fuel usage like that.”
To save water or not?
Sugar is not the only challenge posed by a nectar-rich diet. After all, nectar is mostly water, and birds that drink so much liquid have to remove 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, a retired ecophysiologist from the University of Wyoming.
But this brings further problems. If a hummingbird continues to produce dilute urine all night, it will likely die of dehydration before morning. To avoid that, hummingbirds shut down their kidneys every night. “In humans, you end up with what is considered acute kidney failure,” Martinez del Rio says. “The hummingbirds have to do this or they will urinate and die.”
Please fly slowly and high
The metabolic demands of hummingbirds are quite demanding even at sea level. However, many species live at high altitudes where the air is thinner, there is less oxygen, and there is less resistance to push against when hovering. Consider the world’s largest hummingbird, which lives in the Andes mountains at over 14,000 feet above sea level. This is higher than many helicopters can fly. To cope with these conditions, birds have evolved blood rich in hemoglobin, said Jesse Williamson, an ornithologist at Cornell University.
But as Williamson discovered, some birds face even tougher challenges. The giant hummingbird is large enough that researchers can attach satellite tracking tags and small geolocators to it. So Williamson and his colleagues decided to equip the birds with tracking devices. After spending thousands of hours trapping birds with nets, researchers were able to attach tracking devices to 57 birds using custom-made harnesses made from elastic jeweled cord.
A giant hummingbird (like the one pictured in the inset) wore a GPS tracker as it migrated from the coast of Chile to the highlands of the Andes. Just as human climbers gradually adapt to altitude, this bird ascended in a series of short ascents, then paused to adapt to conditions at high altitude. The entire journey took nearly three weeks. J.L. Williamson et al. / PNAS 2024
They collected tracking data from just eight birds, but even that small sample had some big surprises. Some of the birds lived in the Andean highlands all year round, while others, which turned out to be a separate, previously unrecognized species, migrated into the Andes. Andes is collected annually from its breeding grounds along the coast of Chile. This means that not only do they face the obvious challenges of a long journey of around 5,000 miles round trip, but they also face the need to adapt to thin air during the journey.
What is their secret? Do it gradually. “It’s very similar to how human climbers climb something like Mount Everest: they climb rapidly and then take breaks to acclimate,” Williamson said. “The journey takes months.”
As tracking technology becomes lighter and cheaper, researchers like Williamson hope to track smaller hummingbird species as well. Combined with other advances in research technology, this may lead to many new surprises about the ecology of these small and amazing birds.
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Filed Under: Anatomy, Animals, Biology, Birds, Flowers, Land Birds, Nature, Weird Animals, Wildlife
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