The Rufous Hummingbird's expansive range, which extends from southern Alaska to Mexico, is just one example of how the hummingbird family has evolved to be highly successful in the Western Hemisphere. Photo: Vince Streano/Audubon Photography Awards

Science

The Origins of Hummingbirds Are Still a Major Mystery

There is a dazzling diversity of the tiny birds in the Americas, but recent discoveries trace their evolution back to Europe—where today there are no nectar-feeding species.

In East Africa, you’ll find little birds with purple heads and red chests flitting from flower to flower for nectar. Across the Indian Ocean you can see brown and yellow birds with iridescent neck patches hunting spiders among the jungle leaves. These species and their relatives are abundant across the tropics in Africa and Asia; they’re brightly colored and they all drink nectar. But none of them are hummingbirds.

Back in 1557, Jean de Léry published a journal of his travels to Brazil. In it was one of the first descriptions of hummingbirds to reach the Old World. Early European explorers like Léry had never seen anything like the fearless, tiny birds that buzzed around their heads when they reached the Americas. As a result, hummingbirds quickly joined the birds-of-paradise as must-haves for any natural history collection and Victorian drawing room. In 1851, the Crystal Palace in London exhibited more than 300 hummingbird specimens, dazzling crowds, along with Queen Victoria herself.

The obsession is understandable. Hummingbirds come in a jewel-like assortment of colors and are so dexterous, they can hover still for seconds and fly backward. They also have one of the most diverse avian families in the world, boasting about 350 known species across North and South America. Sunbirds, the prime nectar-feeding birds of the Old World, have fewer than 150.

But once upon a time, tens of millions of years ago, hummingbirds did zip around the hills and forests of Europe. According to Jim McGuire, it all started about 42 million years ago, when hummingbirds broke away from the swifts, their closest living relatives. McGuire, an integrative biologist at University of California Berkeley, calculated this date by examining genetic variation across living hummingbird species and using that information to piece together an approximate evolutionary timeline.

The plot, McGuire says, thickens at the 30- to 35-million-year mark. The oldest hummingbird fossils we’ve discovered come from this period—but they aren’t American. Instead, they were unearthed in southeastern Germany.

Gerald Mayr is the paleontologist at the Senckenberg Research Institute in Germany who identified the fossils as hummingbirds in 2004. (He named the species Eurotrochilus inexpectatus to reflect his surprise at the finding.) One look at the short upper wing bones on the specimen and he knew: They looked just like the unusual “short and stocky humerus” that help modern-day hummingbirds with their aerial acrobatics.

Dug up by private collectors in Frauenweiler, Germany, Eurotrochilus inexpectatus was identified as an ancient hummingbird, largely by the structure of its wings. Photo: Sven Tränkner/Senckenberg Research Institute

Since then, at least six more hummingbird fossils have popped up in Germany, Poland, and France. The similarity between these fossils and New World hummingbirds could be an example of convergent evolution—when two species are not closely related yet develop similar traits over time by adapting to similar environments—but McGuire and Mayr both believe the family probably originated in Eurasia and somehow migrated to the Eastern Hemisphere. "It is still theoretically possible that those fossil hummingbirds are not really hummingbirds but another bird group," McGuire says. But after closely comparing the morphology of the fossils to modern hummingbirds, he thinks convergent evolution is "unlikely" in this case.   

That still leaves a gaping hole in hummingbird history, however. Modern hummingbirds evolved in the Americas around 22 million years ago, according to McGuire’s estimates, but we don’t have any fossils from the West that are older than 10,000 years ago. “We basically have no fossil material we can use” in the New World to figure out how to connect the dots, says McGuire. 

There’s also the question of how. McGuire and Juan Francisco Ornelas, an evolutionary biologist at The Institute of Ecology in Mexico, speculate that the birds used the former land bridge between Siberia and Alaska to move from Eurasia to the Americas. Neither scientist is satisfied with that option, but it seems more viable than a trans-Atlantic route; while hummingbirds are migratory and capable of traveling long distances, it’s unlikely they could traverse an entire ocean without stopping.

And finally, there’s the question of why. Did hummingbirds relocate after the climate in Europe shifted from tropical to temperate? If that were the case, they would have just migrated to Africa or Asia, where sunbirds currently thrive, Mayr says. Food could have been another issue, but given that Europe has a broad diversity of deep-necked, nectaring plants, the birds should have had plenty of options before they disappeared, Ornelas says.

Mayr’s best guess is that other nectar-feeding species like sunbirds outcompeted hummingbirds in the Old World. “But that’s pure speculation,” he concedes. And it doesn’t fully explain why the family died out in mainland Europe, where there are no sunbirds, honeycreepers, or any other bird that survives on nectar.

Meanwhile, there was little competition for hummingbirds in the New World, so they were able to expand rapidly and furiously. Today they can be found wherever there are flowers to pollinate: Rufous Hummingbirds have been spotted as far north as Alaska and the Green-backed Firecrown makes its home in the Juan Fernandez Islands off South America. In fact, the only avian family in the Americas that’s more successful and diverse is the tyrant flycatchers, says Sheri Williamson, who wrote the Peterson Field Guide to Hummingbirds of North America.

While hummingbirds can hover in midair as they feed, the Greater Double-collared Sunbird has to perch on plants to drink nectar. Photo: Patrick Chauvet/Audubon Photography Awards

Of course, an animal’s current range isn’t always a great measure of where its ancestors lived, McGuire says. Hummingbirds could have occupied multiple continents and then for whatever reason, went extinct everywhere but the Americas. What’s more, they aren’t the only birds to have a shadowy past, Mayr says. Modern hoatzins, for example, dwell in South America alone, but Mayr has identified fossils in Africa and Europe.

Until scientists discover more fossils on both sides of the Atlantic, the hummingbird mystery is a tough one to solve. But what we do know about hummingbird evolution so far is fascinating. “Hummingbirds can be very resource-specific in terms of their needs; they evolve relatively quickly into actual separate species that look similar and have different needs and genetics,” says Geoff LeBaron, the Christmas Bird Count director for Audubon.

McGuire, meanwhile, believes that hummingbirds are still breaking off into new species. As part of his molecular-phylogeny research, he’s created “species-accumulation curves” to graph the change in diversity over time. Once hummingbirds have evolved to fill all the ecological niches they possibly can, he expects the curve to flat line. But they aren’t close to maxing out yet, he says.  

Going forward, it will also be important to track how climate change interferes with hummingbird evolution. “[Their] migration is starting to vary due to climate change that may be impacting plant bloom times,” says Kathy Dale, director of science technology at Audubon. Dale is in charge of monitoring these differences through Hummingbirds at Home, a community science project that logs hummingbird sightings throughout the year. Through data, it could end up being much easier to forecast the future of these birds than it is to piece together their past.

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