The High-Flying Lives of Hummingbirds: A Dive into Their Extraordinary Existence

Hummingbirds are a delight to observe — petite, vividly colored flashes that zip around, hovering at flowers and fiercely guarding their territory over a feeder.

However, for the researchers who examine them, hummingbirds provide much more than mere amusement. Their small dimensions and rapid metabolism imply they live life on the edge, occasionally needing to nearly halt their bodily functions just to save enough energy to endure the night — or to traverse thousands of miles, sometimes over open water.

Their nectar-rich nutrition leads to blood sugar levels that would send a human into a coma. Furthermore, their swift, darting flight can generate g-forces high enough to cause a fighter pilot to lose consciousness. The deeper scientists investigate, the more astonishing discoveries await within these tiny creatures, which are the smallest in the avian realm.

“They are the sole bird species that can maneuver upside down and backward,” states Holly Ernest, a conservation ecologist from the University of Wyoming. “They consume pure sugar and don’t suffer from diabetes.”

Ernest belongs to a small group of scientists examining how hummingbirds manage the extreme strains of their existence. Here’s some of the insights researchers have gained regarding the remarkable adaptations of these birds.

Commit to the effort

For many years, the majority of researchers believed that hummingbirds spent roughly 30% of their day engaged in the energy-draining act of flitting from bloom to bloom and consuming nectar while resting for the remaining duration. However, upon conducting a detailed examination, physiological ecologist Anusha Shankar discovered that they are often putting in much more effort than previously thought.

Shankar, currently affiliated with the Tata Institute of Fundamental Research in Hyderabad, India, aimed to determine how broad-billed hummingbirds in Southern Arizona distribute their daily activities. Employing a combination of experimental techniques, she gauged the birds’ metabolic rates during different behaviors and estimated their total daily energy consumption. By incorporating previously published data, Shankar calculated the energy expenditure per minute for perching, flying, and hovering — essentially, the three primary activities a bird might engage in.

She subsequently inferred how much time the birds must allocate to feeding versus perching throughout a day.

“We discovered that it’s incredibly variable,” Shankar explains. During the early summer when flowers abound, the birds could fulfill their daily energy requirements with as little as a few hours of feeding, devoting as much as 70% of the day simply perching, she noted. But when flowers became less prevalent following the onset of summer monsoon rains, birds at one location perched only 20% of the time and dedicated the remainder of the day to feeding.

“That’s 13 hours a day!” Shankar remarks. “There’s no way I can manage 13 hours a day running. I have no idea how they accomplish it.”

Incredibly relaxed

Hummingbirds possess a strategy to help them stretch their energy reserves: When a bird risks depleting its energy, it may enter a torpid state at night, lowering its body temperature almost to that of the surrounding air — sometimes merely a few degrees above freezing. While in torpor, the bird appears almost lifeless, unable to react swiftly to stimuli, and only breathes intermittently. This tactic can result in savings of up to 95% of hourly metabolic expenses during cold nights, as calculated by Shankar. This tactic is vital after days when a bird has not fed sufficiently, such as after a thunderstorm. It also aids birds in conserving energy to accumulate fat before migration.

Shankar is currently investigating which aspects of their physiology hummingbirds prioritize while in torpor, analyzing which gene products are essential for them. “If you’re a hummingbird operating at 10% of your normal metabolism, what is that 10% that’s sustaining your life?” she inquires.

One category of genes that these birds appear to conserve untouched is those linked to their internal clock. “It’s crucial for them to perform tasks at the correct time while in torpor,” Shankar states. To prepare for the day, for instance, the birds begin to awaken from their torpid state approximately an hour prior to sunrise, well before the arrival of visible light cues.

Manage the sugar

To sustain their elevated metabolic rate, hummingbirds consume around 80% of their body weight in nectar daily. This amount is akin to a 150-pound individual drinking almost one hundred 20-ounce sodas each day — and nectar is frequently far sweeter than soda.

The human digestive system cannot absorb sugar so rapidly, contributing to the reason why overindulging in soda or Halloween candy can upset the stomach, explains Ken Welch, a comparative physiologist at the University of Toronto at Scarborough. Hummingbirds manage the influx by possessing porous guts enabling sugars to enter the bloodstream between gut cells rather than solely through them. This expedites the delivery of sugar from the gut before it can cause discomfort. This rapid transport, along with likely other adaptations, permits hummingbirds to attain blood sugar concentrations up to six times higher than those found in humans, according to Welch.

Such elevated sugar levels in the bloodstream result in serious physiological concerns for humans. It causes increased sugar molecules to adhere to body proteins, a phenomenon known as glycation; over time, excessive glycation contributes to many complications associated with diabetes, like nerve damage. The method by which hummingbirds evade the issues linked to glycation remains unclear, Welch notes, but early hints are beginning to surface. For instance, one study has shown that bird proteins are comprised of fewer of the amino acids most susceptible to glycation compared to mammalian proteins, and those that are present are typically concealed deep within the protein structure where they are less exposed to circulating sugars.

Other, yet unidentified, mechanisms for addressing high blood sugar might potentially offer tangible advantages for managing diabetes in humans. “There may be a treasure trove within the hummingbird genome,” asserts Welch.

Execute a metabolic shift

By the conclusion of its nighttime fast, a hummingbird has almost exhausted its sugar reserves — leading to an entirely different metabolic hurdle. “How does it awaken and fly?” Welch questions. “There’s merely fat left to combust.”

Hummingbirds have adapted to be extraordinarily adept at transitioning their metabolism from sugar-burning to fat-burning, as he discovered. “This necessitates a significant transformation in the biochemical pathways involved,” Welch explains — and it occurs within minutes, at a pace far exceeding that of other organisms. “If we could command such control over our fuel utilization, we’d be thrilled.”

Conserve water — or not

Sugar isn’t the only issue presented by a nectar-rich diet. After all, nectar primarily consists of water — and birds that consume so much liquid must excrete

of the majority, without forfeiting electrolytes. Consequently, the kidneys of hummingbirds are exceptionally evolved to reclaim electrolytes prior to their elimination. “They urinate nearly pure water,” remarks Carlos Martinez del Rio, an ecophysiologist formerly affiliated with the University of Wyoming.

However, this leads to another issue: If a hummingbird were to continue producing diluted urine throughout the night, it would perish from dehydration before dawn. To prevent this, hummingbirds incapacitate their kidneys each night. “They enter a state that in humans would be deemed acute renal failure,” explains Martinez del Rio. “Hummingbirds must do this; otherwise, they’d urinate themselves to demise.”

Ascend gradually

The energetic requirements for a hummingbird are challenging enough at sea level. Yet, numerous species inhabit high altitudes, where the thin atmosphere has lower oxygen levels and offers diminished resistance during hovering. Take the giant hummingbird, the largest in the world, which resides in the Andes Mountains at heights exceeding 14,000 feet — higher than many helicopters can ascend. To adapt to these circumstances, these birds have developed blood that is richer in hemoglobin, states Jessie Williamson, an ornithologist at Cornell University.

Nonetheless, some of these birds encounter an even greater challenge, as Williamson discovered. Giant hummingbirds are sizable enough that researchers can affix satellite tracking devices along with smaller geolocators. Therefore, Williamson and her team opted to equip the birds with trackers. After countless hours spent attempting to capture these birds using nets, the researchers successfully attached trackers to 57 individuals using custom-made harnesses crafted from elastic jewelry cord.

Although they retrieved tracking information from merely eight birds, even that limited sample presented a significant surprise: Some of the birds inhabited the high Andes throughout the year, while others — which turned out to be a distinct, previously unrecognized species — migrate annually to the Andes from breeding areas along the Chilean coast. This indicates they confront not just the evident challenges of a prolonged migration — a round trip of approximately 5,000 miles — but also the necessity to acclimatize to thinner air en route.

What’s their strategy? To do so incrementally. “It resembles the approach of human mountaineers approaching summits like Mount Everest, with spurts of climbing followed by acclimatization pauses,” explains Williamson. “The excursion takes months.”

With tracking technology becoming lighter and more affordable, researchers like Williamson aspire to study smaller hummingbird species as well. This, combined with advancements in research tools, may reveal many more surprises regarding the biology of these remarkable, tiny birds.

This article originally appeared in Knowable Magazine, a non-profit outlet focused on making scientific insights accessible to all.

Sign up for our weekly newsletter to receive more English-language news coverage from EL PAÍS USA Edition