Scientists solve giant hummingbird mystery — with the help of tiny backpacks

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The world’s largest hummingbird has been hiding in plain sight for centuries — and scientists only discovered the species is distinct from another giant species after attaching tiny backpacks to hummingbirds to understand migration patterns.

Along the way, researchers also identified the longest hummingbird migration journey, which spans a 5,200-mile (8,368-kilometer) round trip, or about the distance between New York City and Buenos Aires.

Questions around the giant hummingbird of South America have persisted since naturalist Charles Darwin first observed them in 1834 during his expedition aboard the HMS Beagle.

Darwin observed the birds, which are about eight times the size of typical hummingbirds, breeding along the Pacific coast of Chile, but then they seemed to completely vanish after breeding. He speculated that the giant hummingbirds migrated to the Atacama Desert region, located in northern Chile.

Now, new research has revealed that there are two distinct species of giant hummingbird in South America — the northern giant hummingbird that lives year-round in the Andes, and the migratory southern giant hummingbird — and they have been evolving separately for millions of years.

A southern giant hummingbird is seen flying from its breeding grounds in central Chile. - Chris Witt
A southern giant hummingbird is seen flying from its breeding grounds in central Chile. - Chris Witt

A new study describing the birds appeared Monday in the journal Proceedings of the National Academy of Sciences.

“There aren’t many animal migrations of large, charismatic species that are still totally unknown, but that was the case for southern giant hummingbirds,” said lead study author Jessie Williamson, a National Science Foundation Postdoctoral Fellow and Rose Postdoctoral Fellow at the Cornell Lab of Ornithology in Ithaca, New York. “We wanted to finally solve this mystery.”

Designing backpacks for hummingbirds

Giant hummingbirds differ from hundreds of other hummingbird species in many other ways.

“Everything about the giants is anomalous — they are not only far larger (two times or more) than the second largest hummingbird — but their wingbeats and heartbeats are far slower,” Williamson said. “And their wings are proportionately longer, so they have a completely unique appearance in flight — almost like a hovering swift.”

Swifts are medium-size fast-flying birds included in the family Apodidae, which also includes hummingbirds.

But studying hummingbirds, no matter their size, is an arduous task. The team worked with local landowners and residents of villages across Peru and Chile during fieldwork.

“Capturing Giant Hummingbirds is very challenging,” said study coauthor Emil Bautista, researcher at the Centro de Ornitología y Biodiversidad in Lima, in a statement. “They watch everything, and they know their territories well. 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.”

The research team spent nine months camping in rural parts of Chile and Peru, working from sea level to the steep, cactus-strewn slopes of the Andes and going without electricity or running water for weeks at a time, Williamson said.

Williamson designed a backpack harness, using a type of jewelry cord to attach a microtracking device to 57 hummingbirds in Chile.

“Designing appropriate backpack harnesses for giant hummingbirds took two field seasons of trial and error, including practicing the harness design on a stuffed hummingbird finger puppet … with a paper maché mock-up geolocator device, plus lots of consultation with colleagues who have experience tracking small migratory birds,” Williamson said.

A southern giant hummingbird is fitted with a tiny backpack-like geolocator tracking device in central Chile. - Jessie Williamson
A southern giant hummingbird is fitted with a tiny backpack-like geolocator tracking device in central Chile. - Jessie Williamson

The geolocator backpacks weighed 0.3 grams and were designed to be small and light enough so they didn’t interfere with the birds’ style of flight.

Williamson published a paper describing her design and how to safely attach it to hummingbirds in the Journal of Avian Biology in June 2021.

“Hummingbirds are challenging to work with because they are lightweight with long wings and short legs. They’re nature’s tiny acrobats,” she said.

But it wasn’t enough to catch the birds, attach the backpacks and release them — the birds had to be recaptured for the team to collect the data.

The researchers were able to retrieve data from eight of the geolocators by recapturing the birds using fine mesh nets called “mist nets,” commonly used by ornithologists, Williamson said.

What the team discovered was that migratory southern giant hummingbirds are like human mountaineers.

High-altitude bird flights

The geolocator data revealed that migratory giant hummingbirds can ascend from sea level to more than 13,000 feet (3,962 meters) in elevation, and their travels brought them as far north as the Peruvian Andes.

But the birds don’t just fly directly to these towering altitudes. Instead, like mountaineers, they pause during their ascent for days at a time to allow their blood and lungs to acclimate to lower oxygen levels.

By tracking the birds’ migration with geolocators and satellite transmitters, the scientists discovered what they believe to be the longest known hummingbird migration, spanning 5,200 miles (8,368 kilometers) from the Chilean coast up to the Andes in Peru and back.

As the researchers studied the birds and compared them with genetic data from museum specimens, they realized there were two types of giant hummingbirds.

“Nobody had figured out where migratory giant hummingbirds go because they were hiding among the non-migratory giant hummingbirds,” said senior study author Christopher Witt, professor of biology and director of the Museum of Southwestern Biology at the University of New Mexico, in a statement. “The two forms of giant hummingbird look almost identical — for centuries, ornithologists and birders never noticed that they were different. We couldn’t have figured this out without the miniaturized trackers.”

A shift in migratory behavior likely drove the difference between the two species. By studying museum species, including a 154-year-old specimen, the researchers realized that the two types of giant hummingbird had been evolving separately for about 3 million years.

“They are as different from each other as chimpanzees are from bonobos,” Witt said. “The two species do overlap on their high elevation wintering grounds. It’s mind-boggling that until now nobody figured out the Giant Hummingbird mystery, yet these two species have been separate for millions of years.”

The northern giant hummingbird, which lives in the high Andes year-round, has a different lung and blood capacity compared with the southern giant hummingbird.

After realizing the two birds were entirely different species, the study team named the northern giant hummingbird Patagona chaski, a nod to chaskis, the Quecha word for messengers, of the Inca Empire. Quecha is a group of indigenous languages used across Peru and neighboring countries.

“Chaski runners were surefooted sprinters, capable of speed and endurance on steep slopes, in part due to high-capacity lungs and rigorous aerobic training at high elevations,” the authors wrote in the study.

New bird mysteries emerge

The researchers reported that both populations of giant hummingbirds are stable, and some can even be seen enjoying nectar from backyard feeders.

A southern giant hummingbird is shown poised for take-off. - Chris Witt
A southern giant hummingbird is shown poised for take-off. - Chris Witt

Now that the two distinct species have been confirmed, the team wants to better understand how the populations interact, especially when they live in the same parts of the Andes during the winter.

“We have to figure out where these two forms come together and how they interact,” Witt said. “Do they compete, is one dominant over the other, how might they partition resources, and do they mix or spatially segregate within the winter range? Lots of interesting questions to pursue!”

Williamson also wants to work with botanists to understand how the birds’ migration patterns may have coevolved with the flowering plants the birds use for sustenance on their journeys.

“I’m really interested in how Southern Giant Hummingbirds make such dramatic shifts in elevation during migration,” Williamson said. “They’re like miniature mountain climbers. How do they change their physiology to facilitate these movements?”

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