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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, and the ocean voyage killed most of them. The ones that did make it to Europe quickly died out in a very 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 28–34 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, Christopher Witt, J.V. Remsen, Jr., Ammon Corl, Daniel L. Rabosky, Douglas L. Altshuler, and Robert Dudley published a paper in Current Biology “Molecular Phylogenetics and the Diversification of Hummingbirds” 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.
That phylogenetic arrangement, created over a decade ago, has been modified with new information. The Cornell Lab of Ornithology just released, on their Birds of the World website, a Phylogeny Explorer, a flexible visualization of the phylogenetic relationships of all birds based on available scientific information from numerous sources, which will be updated annually. As a member of the American Ornithological Society, I have access to Birds of the World, which has a paywall, but the Phylogeny Explorer may be accessed, at least for a while, without a subscription.
Hummingbirds 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. (I personally like to think that ancestors of the hardy little Rufous Hummingbird were the ones who made the jump.) The plants hummingbirds feed on in the tropics co-evolved with them, so it wasn’t like certain plants were lying in wait as a welcome committee—hummingbird evolution was a major driving force in the evolution of plant diversification in the Americas. For example, the unique Sword-billed Hummingbird co-evolved with Passiflora mixta, which produces nectar at the bottom of its exceptionally long corolla tubes, requiring a bird with an exceptionally long bill to access.
However they got there, when hummingbirds 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…
…jacobins and 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 hummingbird 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 bodies work has given human scientists endless intellectual puzzles even as the tiny birds’ paradoxical hardiness—some thrive 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.
I love the way you teach us the science as well as the beauty and charm of birds!