Laura Erickson’s For the Birds

Hummingbirds are strictly New World birds, found from south-central Alaska through Tierra del Fuego including the Caribbean Islands. There has never been a hummingbird sighting in Europe except when some Europeans tried to introduce them in the 19th century—few of the tiny birds survived being captured or the ocean voyage, and the ones that made it to Europe quickly died out in the foreign land where flowers had evolved to be pollinated by insects, not tiny birds.

Yet in 2004, German paleontologist Gerald Mayr took note of two tiny bird fossils sitting in a museum drawer in Stuttgart. They’d been unearthed in a clay pit south of Heidelberg and dated to the early Oligocene period, roughly 34–28 million years ago. To Mayr’s amazement, these fossils were clearly hummingbirds! Very primitive hummingbirds, not related to any living species, but belonging to what taxonomists call a “stem group,”—direct ancestors to living hummingbirds in the way that theropod dinosaurs were direct ancestors to all living birds. Mayr named them Eurotrochilus inexpectatus,meaning “unexpected European hummingbird.”

An even older fossil, found in Wyoming and dated to about 50 million years ago, was found in 2013 to be a predecessor to both hummingbirds and swifts before the two groups diverged.

Scientists had long believed that hummingbirds originated in South America, where their species diversity is greatest, but Eurotrochilus suggests the truth is much more complicated. Hummingbird bodies are so tiny and fragile that fossilization is difficult to begin with, and finding those fossils is even more difficult, which leaves their evolutionary history poorly documented or understood.

In 2014, Jimmy McGuire and Robert Dudley, of UC Berkeley, published a paper in Current Biology based on DNA data collected from 451 birds representing 284 species of hummingbirds and their closest relatives, in which they arranged the living groups in a family tree. They concluded that the branch leading to modern hummingbirds arose about 42 million years ago when they split from their sister group, the swifts and treeswifts. This probably happened in Europe or Asia, where Eurotrochilus was found.

They found their way to South America, possibly via Asia and a land bridge across the Bering Strait to Alaska, but no one knows for sure. The plants they feed on in the tropics co-evolved with hummingbirds, so it wasn’t like certain plants were waiting for them—hummingbird evolution drove the evolution of plant diversification in the Americas. But however they got there, when they reached South America about 22 million years ago, they quickly expanded into new ecological niches and evolved new species represented by nine distinct groups known today as topazes, hermits, mangoes, brilliants, coquettes, mountain gems, bees, emeralds, and the single-species group with the Giant Hummingbird.

About 12 million years ago, precursors of the bee and mountain gem hummingbird groups reached North America, which was still separated from South America by a few hundred miles of water. About 5 million years ago, hummingbirds reached the Caribbean. The bee hummingbirds, which originated in North America, participated in the Caribbean invasion, and even made their way back to South America alongside existing lineages.

DNA studies show that hummingbirds continue to evolve today, with the origination rate of new species exceeding extinction rates. And despite the fact that every one of them eats nectar and tiny insects, some places contain more than 25 species in the same small geographic area.

Teasing out hummingbird taxonomy, evolution, and simply how their tiny bodies work has given human scientists endless intellectual puzzles even as their paradoxical hardiness—some of these tiny birds thriving at extreme elevations in the Andes and all the way up to Alaska—along with their stunning beauty and spunky nature fill our hearts with both wonder and joy.