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WASHINGTON — For such small creatures, hummingbirds have racked up an huge list of claims to fame.
They are the smallest birds and the smallest warm-blooded animals on Earth. They have the fastest heart and the fastest metabolism of any vertebrate. They are the only birds that can fly backward. And scientists reported on Thursday that they also have a complicated evolutionary history.
Researchers constructed the family tree of these nectar-eating birds using genetic information from most of the world's 338 hummingbird species and their closest relatives. They said hummingbirds can be divided into nine groups, with differences in size, habitat, feeding strategy and body shape.
They boast a unique set of capabilities, said University of New Mexico ornithologist Christopher Witt, one of the scientists in the study published in the journal Current Biology. "They can hover stationarily or move in any direction with precision, even in a strong wind. They also have the highest rate of energy consumption per gram of any animal," Witt said.
Lead author Jimmy McGuire, a biologist at the University of California at Berkeley, said hummingbirds "have to constantly feed because they're powering this system that has such great energy requirements."
"Many of these hummingbirds go into torpor at night so that they don't starve to death overnight, which is pretty cool. They're just operating on the extremes," McGuire said.
Hummingbirds now live only in North America, Central America, South America and the Caribbean, but the oldest hummingbird fossils were unearthed in Europe. That indicates that the birds once enjoyed a much larger range and disappeared from the Old World for unknown reasons, the researchers said.
The hummingbird evolutionary lineage split from a related group of small birds called swifts and treeswifts about 42 million years ago — most likely in Europe or Asia — and by 22 million years ago the common ancestor of all present-day hummingbirds found its way to South America, the researchers said.