From the Winter 2025 issue of Living Bird magazine. Subscribe now.
A study that spanned the better part of the past decade has shed light on a centuries-old mystery: the migration patterns of the largest hummingbird in the world.
The Giant Hummingbird is a whopping eight times the size of a Ruby-throated Hummingbird—about the same length as a bluebird, albeit thinner and lighter. Its breeding range is giant as well, stretching thousands of miles along western South America.
For centuries, scientists have known that some Giant Hummingbirds are migratory and some aren’t. Giant Hummingbirds in the northern Andes of Peru and Ecuador are year-round residents. But the Giant Hummingbirds that breed in central Chile, in the southern part of the bird’s range, vanish during their nonbreeding season. “An unsolved mystery” is how the Atlas of the Breeding Birds of Chile 2011–2016 describes where these Chilean Giant Hummingbirds go after their breeding season ends.
New findings published in the journal Proceedings of the National Academy of Sciences in May 2024 included the astonishing discovery that these southern-breeding Giant Hummingbirds travel as far as any hummingbird on Earth—up to 5,200 miles round trip. And these lowland breeders cover those immense distances while ascending some of the tallest mountains in South America to more than 13,000 feet above sea level. What’s more, evidence shows that these long-distance travelers diverged genetically from their nonmigratory counterparts more than 2 million years ago.
“Out of more than 360 hummingbirds, several species can exceed 10 grams, but just barely. The Giant Hummingbird comes in at 20 to 30 grams—it was very improbable that this thing had evolved,” says Christopher Witt, a biology professor at the University of New Mexico and senior author of the new study, who has worked with Giant Hummingbirds since 2006. “It seemed like an unsuccessful evolutionary experiment with gigantism because, after 14 million years of evolution, it was only a single species. Or so we thought.”
“They Barely Look Like Hummingbirds”
Nearly 200 years ago Charles Darwin observed Giant Hummingbirds in central Chile, one of the places he stopped while sailing aboard the H.M.S. Beagle. His notes from the trip indicate that he saw “several of these birds in August, and was informed that they had only lately returned from the parched deserts of the north,” referring to the Atacama Desert in northern Chile. But no one from Darwin’s time to the present had been able to confirm this or any other hypothesis about where those Chilean birds were coming back from, or where they depart to after breeding each year.
“These are amazing birds,” says Jessie Williamson, a National Science Foundation Postdoctoral Fellow and Rose Postdoctoral Fellow at the Cornell Lab of Ornithology, and lead author on the study. “They barely look like hummingbirds. When they hover, you can actually see their wings—it makes them look almost like swifts.”
In 2016, Williamson was brainstorming projects for her PhD dissertation at the University of New Mexico when she learned about the mystery of the Giant Hummingbird’s unaccounted-for wanderings from Witt, her advisor. As they talked, they mused about the possibility that the Giant Hummingbird—at 7 or 8 inches long—is one of the few, maybe only, hummingbird species big enough to carry a tracking device.
“I couldn’t believe there was this huge gap in understanding of such a common and widespread species, and I got really excited about the possibilities,” Williamson says. So later that year she embarked on a mission to find out just where migratory Giant Hummingbirds go.
Affixing devices such as geolocators to any small bird is a challenge. On small songbirds such as warblers, these devices are often held on by a figure-8 harness that slides up the bird’s legs. But hummingbirds have tiny legs, too small for existing harnesses. So Williamson spent months designing a harness that would instead loop around the neck and wings of the Giant Hummingbird, effectively creating a backpack that was both lightweight and inexpensive (about 50 cents each to produce).
But even with this affordable innovation ready to deploy, capturing and tagging Giant Hummingbirds was easier said than done.
Williamson started by reaching out to potential collaborators in Chile. At the top of the list was Francisco Bozinovic, a biology professor at Pontifical Catholic University of Chile. Bozinovic was well connected in the regional ornithological community and had previously studied the energetics of Giant Hummingbirds. He provided Williamson with a home base for scouting Giant Hummingbird hotspots around the edges of the coastal city of Algarrobo, Chile. Bozinovic also introduced her to then-PhD student Natalia Ricote, a postdoctoral researcher at Chile’s Adolfo Ibáñez University, who would serve as one of Williamson’s key collaborators throughout the project.
As the project progressed, Williamson saw an opportunity to expand the scope of her study by comparing blood and genetic samples of Giant Hummingbirds across their entire range, which meant extensive field sampling of birds throughout the harsh high-altitude conditions of the Peruvian Andes. For this Williamson teamed up with Emil Bautista, a researcher with the Center for Ornithology and Biodiversity in Lima.
“There’s no way any of this could have happened without Emil,” says Williamson, noting that Bautista has more than 15 years of ornithological research experience in Peru. “He’s an incredibly gifted researcher … fast at setting mistnets and skilled at performing sensitive blood work. Plus he knows the terrain super well, and he’s dealt with local permitting before.”
“Giant Hummingbirds watch everything and they know their territories well,” says Bautista. “We had to be strategic in choosing sites for our nets. If Giant Hummingbirds see something unusual, they won’t visit that spot. They are more observant than other birds.”
At several sites, the shiny metal poles used to hold up the nets seemed to be warding off the birds, so the team began affixing the nets to cacti, the spines of which resulted in several minor but painful finger injuries. At another site, success eluded them until they had the idea to set their nets, which usually stand upright like volleyball nets, horizontally across a stream to catch the hummers as they dove for insects near the water’s surface.
In Chile, Williamson, Ricote, and a shifting cast of students and local scientists made five weeks-long forays over the course of three years into the sparsely populated hills surrounding Algarrobo to tag the migratory birds during their breeding season (November to February).
When all was said and done, they tagged 57 birds, 55 of which were fitted with light-level geolocators that record snapshots of sunlight that can be used to estimate a bird’s position. To get the data off of these geolocators, the scientists need to recapture the bird and retrieve the device. The team also outfitted two Giant Hummingbirds with more-expensive satellite tags, which relay a bird’s coordinates to satellites and then back to researchers in real time.
In November 2017, Williamson returned to Chile for 10 days in a failed effort to recapture a few of the tagged birds. The first failure was not too surprising, she says, since the breeding season was in full swing, with birds actively on nests and hard to capture. She returned in January 2018, but again the team failed to recapture any tagged birds. It was at this point that she began to wonder whether or not the whole endeavor might be hurtling toward failure.
But when she returned again in December 2018, her persistence finally paid off.
“There was one late-evening net run when I remember seeing the shape of the backpack before I even saw the bird,” Williamson recalls. “It was one of the top moments of my life.”
The extraordinary migration of a Giant Hummingbird
A satellite tag documented the extraordinary migration of a Giant Hummingbird. The bird started on its breeding grounds near sea level in Chile, then climbed to nearly 4,000 meters (more than 13,000 feet) over the course of a few weeks. It paused for days at a time along the way, in order to acclimate to lower-oxygen environments.
A Journey 5,200 Miles Long and 13,000 Feet High
Success led to success, and before long they recaptured six more of the tagged birds, giving the team seven geolocator tracks to analyze, along with the data from one of the satellite-tagged birds. (The other satellite tag stopped transmitting just a few weeks after deployment.)
The results were astonishing. The recaptured birds had traveled an average of 4,000 miles each on their round trips. One bird logged more than 5,200 miles total, about the same distance as a flight from Anchorage, Alaska, to Phoenix, Arizona, and back. That stat puts the Giant Hummingbird in the running for longest known hummingbird migration. (The current champ, Rufous Hummingbird, migrates from southern Alaska to Mexico and back.)
On their journey north, the birds followed the eastern side of the Andes, mingling with Giant Hummingbirds in Argentina, Bolivia, and Peru as they migrated through. After three to five months, the birds reached their destinations in the high Andes of central Peru. Their return trip was much quicker, lasting an average of just one month and following a migratory path roughly through, as Darwin had alluded to, the Atacama Desert in northern Chile.
While the geolocators were able to provide the mileage and approximate route that the birds used, it was the hummingbird with a satellite tag that highlighted the staggering ascent the Giant Hummingbirds make as they migrate through the tallest mountains in the Western Hemisphere. From its sea-level breeding grounds, it took just two days to climb to around 5,000 feet, followed by eight days of hanging out around that elevation. A second quick jump to an elevation of 8,000 to 10,000 feet was followed by a second pause of around nine days. Finally, about three weeks after the bird had set off from its breeding home, it reached altitudes above 13,000 feet. From there it would remain in the high Andes for the next several months.
According to Williamson, the go-stop-go cadence of the first three weeks of this Giant Hummingbird’s journey resembles the ascents of human mountain climbers who pause to allow their bodies to acclimatize to a higher altitude where less oxygen is available. To get a fuller picture of how these distinct resident and migratory populations of Giant Hummingbirds differ in other aspects of their biology, Williamson compared blood and genetic samples from birds captured at low elevations in Chile, high elevations in Peru, and from museum specimens dating back to the 1800s.
Daniel Cadena—a biology professor at the University of the Andes in Colombia who studies avian physiology and evolution, and who was not involved in the study—wrote a commentary in the science journal PNAS explaining how these birds can accomplish their mountain-climbing feats: “Individuals do not move continuously. Instead … [there are] times when they move upslope, and various pauses during which they acclimate, increasing the concentration of hemoglobin and hematocrit in their blood.”
Intriguingly, the team’s analyses of gene segments related to hemoglobin from migratory and nonmigratory birds showed the same adaptations for efficiently transporting oxygen. Yet despite this one shared trait, further genomic analyses showed that the resident and migratory populations of Giant Hummingbirds have been separate species for at least 2 million years.
Williamson was astonished upon first viewing the results of the genomic analyses of birds from across the range of the species: “It was amazing how clear the separation was.”
Based on the migration tracking and genetic analyses, the authors of the study recommend that the Giant Hummingbird should officially be split into two species—the high-elevation resident Northern Giant Hummingbird and the migratory Southern Giant Hummingbird. Previous research had identified these two forms as subspecies. The new results, say study authors, reveal stark differences in migration patterns, blood physiology, genetics, and morphology that provide evidence for the governing bodies of avian taxonomy to consider recognizing Giant Hummingbirds as two species.
“Giant Hummingbirds are outliers within the hummingbird family,” wrote Cadena in PNAS, referring not just to their size but also the extremely broad ecological niche they occupy, from the high-altitude plains of Peru to the coastal lowlands of Chile. “This anomalous niche is … an artifact of outdated taxonomy, and is explainable by the finding that they actually represent two species.”
