You can’t take anything for granted anymore. Hummingbirds, for instance—like the Bay Area’s permanent-resident Anna’s, spring-nesting Allen’s, and migrant rufous. There are about 340 living species of these small, hyperactive, nectar-feeding birds, and they’re all found in the Western Hemisphere. Their greatest diversity is in the Central American and northern South American tropics, leading biologists to conclude that the family evolved there before colonizing the temperate regions. Hummingbirds were always thought to be as American as succotash, or ceviche.
Not so, says ornithologist Gerald Mayr of the Senckenberg Research Institute in Frankfurt. Hummingbirds are from Germany.
In a recent issue of Science, Mayr described a 30- to 34-million-year-old fossil discovered in a clay pit in the German state of Baden-Wurttemberg. The tiny skeleton is almost identical to that of a modern hummingbird. Its needle-like beak is more than twice as long as the skull; its wingbones are modified for hovering flight. Mayr named his find Eurotrochilus (“European hummingbird”) inexpectatus.
Inexpectatus is an understatement. “My mind is a little blown,” commented one American biologist.
Hummingbirds, like most small, delicate-boned vertebrates, have not left an extensive fossil record. The oldest unequivocal hummingbird remains, from Central America, date back a mere million years. Mayr has claimed other specimens from 49-million-year-old deposits in Germany and 30-million-year-old sites in the Caucasus as protohummers, but these are less complete than Eurotrochilus and appear to have been in some ways more like swifts than modern hummingbirds.
The new discovery seems to clinch the case for the European ancestry of hummers. As counterintuitive as it seems, that shouldn’t be too much of a shock, though. Many organisms evolved in one continent, migrated to others, then died out in their original homeland. Horses and rhinos began as native North Americans; not to mention camels. There was a lot of traffic over Beringia and other ancient landbridges.
You might wonder how the founders of the American hummingbird lineage made it across the North Atlantic. No problem. When the dinosaurs were wiped out 65 million years ago, Eurasia and North America were still united in the supercontinent Laurasia, the northern counterpart to Gondwanaland. While tectonic rifts then opened up in the Arctic regions, broad land corridors still connected North America with Greenland, Greenland with Scandinavia and Scotland. The last such link, the DeGeer Landbridge, was not broken until 36 million years ago. There were lots of potential flight paths for early hummers. And the higher latitudes were pretty balmy, with broadleaf forests growing almost as far north as the pole.
Mayr hasn’t speculated in print as to why hummingbirds would have gone extinct in the Old World. But they may have left tantalizing clues to long-vanished partnerships with flowering plants: what naturalist Connie Barlow has called “ghosts of evolution.”
Plants pollinated by hummingbirds share a number of characteristics.
Many have tube-shaped flowers, to accommodate a hummer’s long beak and probing tongue. Some, like fuchsias, have pendent flowers; if your pollinator can hover, there’s no need to provide a perch. Red is a prevalent color. Insects are blind to red, but hummers and other birds are ultrasensitive to that end of the spectrum. On Santa Cruz Island off the Southern California coast, the yellow-blossomed bush monkeyflower is pollinated only by bees, while the red island monkeyflower attracts hummingbirds. Experiments with other monkeyflower species have shown that small mutations in the genes that control flower color can have dramatic effects on pollinator preference.
Compared with insects, hummers don’t seem to have much of a sweet tooth. The nectars of the flowers they service have relatively low sugar concentrations, in the neighborhood of 20 percent, mostly sucrose. And since birds have a limited sense of smell, hummer-pollinated flowers tend to be unscented.
Hummingbirds aren’t the only avian pollinators, of course. Other families—the sunbirds of Africa and Asia, the honeyeaters of Australia and the South Pacific—have made their own arrangements with flowering plants. But none of these birds have evolved the ability to hover by rotating their wings in a figure-eight pattern. Only hummingbirds can do that.
Gerald Mayr points out that a handful of Old World plants—an East African bellflower, a Himalayan impatiens, some Asian members of the heath family—have flowers that look as if they evolved to attract hummingbirds. I was able to find a picture of one of these, a Southeast Asian shrub called Agapetes serpens. Its flowers are tubular, pendent, and fire-engine red. Any hummer would love them. Mayr thinks bees may have taken over the pollinator role for these plants after the extinction of Eurasian and African hummingbirds.
My trusty Hortus Third, the one-volume encyclopedia of plants cultivated in North America, says Agapetes has been grown in California. So it’s highly probable that somewhere, in someone’s garden, a California hummingbird—Anna’s or Allen’s, rufous, Costa’s or black-chinned—has nectared at an Agapetes, and an old partnership has been renewed.