DNA Reveals New Details About Enigmatic Ivory-bills

September 6, 2006

From the toes of old woodpecker specimens, researchers gain a tool for searching for the Ivory-billed Woodpecker in the present, as well as a glimpse of the elusive bird’s past.

By Pat Leonard and Miyoko Chu

Male Ivory-billed Woodpecker, 1935, photo courtesy David Allen

According to the books, there is only one “Lord God” bird: the Ivory-billed Woodpecker. For years, many feared that it was extinct, both in the swampy forests of the southern United States and in the mountains of Cuba, the only other place ivory-bills have ever been found.

Now scientists mining ancient DNA from the toes of old woodpecker specimens have come up with new genetic information that may shed light on the elusive birds’ present as well as their past. Authors of the study, published in Biology Letters, extracted new DNA sequences from museum specimens that may help pinpoint evidence of surviving ivory-bills, based on feathers or other material gathered in the field. The DNA study also revealed that ivory-bills in North America and Cuba diverged from one another genetically about a million years ago. Because of their genetic differences, the authors suggest, the ivory-bills should be considered two species instead of one.

Robert Fleischer with ivory-bill specimens, photo by Carla Dove, NMNH

Led by Robert Fleischer, head of the genetics program at the Smithsonian National Museum of Natural History, the researchers extracted DNA from specimens of Cuban and North American Ivory-billed Woodpeckers, some of which were collected as long as 145 years ago. Except for the Cuban woodpecker’s slightly smaller size, the birds are nearly identical: big black-and-white woodpeckers with huge bills, flowing crests, and white lightning bolts shooting up their necks. Because they look so much alike, the Cuban and North American ivory-bills were thought to be especially closely related to one another.

Despite outward appearances, the new study suggests that the similar-looking Cuban and North American Ivory-billed Woodpeckers are no more closely related to each other than they each are to the Imperial Woodpecker, a bigger and somewhat more distinctive species from the highlands of Mexico, whose DNA was also sequenced for the study.   

Conservation implications

Many believe that the Imperial Woodpecker and the Cuban ivory-bill are extinct; there have been no confirmed sightings of Imperial Woodpeckers in more than a decade, and none of ivory-bills in Cuba since the 1980s. North American ivory-bills were also feared to be extinct until 2004, when searchers documented at least one in the Big Woods of eastern Arkansas.

Martjan Lammertink, photo by Rosemarie Attilio, Detroit Audubon

“Before the rediscovery in Arkansas, the main hope for ivory-bill conservation was in Cuba,” said Martjan Lammertink, a research scientist at the Cornell Lab of Ornithology and a coauthor of the study. “Showing these two birds are genetically distinct, even though they look similar, may bring renewed interest in the Cuban ivory-bill.”

Irby Lovette, director of the Lab’s Evolutionary Biology Program, said that study also shows the importance of the three woodpeckers as a group within their genus, Campephilus. “It’s now clear that the two ivory-billed subspecies and the Imperial Woodpecker are each other’s closest relatives. If we lose all three, we’ve lost a unique and spectacular evolutionary group of woodpeckers,” he said.

Knowing the code

Except for fleeting glimpses of Ivory-billed Woodpeckers, several seconds of video footage, and intriguing sounds, ivory-bills have remained elusive since their reappearance in 2004. Searchers have relied on high-tech tools such as remote video and audio recording devices, as well as NASA’s Laser Vegetation Imaging Sensor to locate the best potential habitat. In one case, they even collected black feathers from a search area in Arkansas and sent them to the Cornell Lab of Ornithology for DNA analysis. The results showed that the feathers were shed from a Pileated Woodpecker, an abundant species at the search site.

The new sequences from old museum specimens give researchers even more comparison material to work with in the future.  “We use the genetic sequences as a sort of bar code to compare DNA from material collected from the field—feathers or droppings, for example,” Fleischer said.

The Cuban ivory-bill: Baird’s bird?

Will field guides soon list two species of Ivory-billed Woodpeckers? Although the authors of the new study suggest that Cuban and North American ivory-bills should be considered separate species in their own right, the official decision rests with the American Ornithologists’ Union Committee on Classification and Nomenclature.

Lovette, a member of the committee, said decisions to split or lump species are usually based on multiple lines of evidence. “The new data are intriguing, but place these birds in the gray zone where some biologists would classify them as two species and others would retain them as just one,” he said. “These results will likely initiate an interesting debate on how we should classify these birds.”

If, at some point, the Cuban bird becomes officially recognized as its own species, the story of the woodpeckers’ shifting taxonomy will have come full circle. The Cuban Ivory-billed Woodpecker was named for an early Smithsonian Secretary, Spencer Baird: Campephilus principalis bairdii, in the subspecies nomenclature. But based on the work spearheaded by the Smithsonian, the species list might eventually read Campephilus bairdii, or Baird’s Ivory-billed Woodpecker. Until then, ornithologists will once again be involved in debate over the enduring enigma that is the ivory-bill.

Wandering Woodpeckers

Theories about how Ivory-billed Woodpeckers made it to Cuba have included the possibility that Native Americans transported the North American ivory-bill to that island as recently as 600 years ago. By showing that the Cuban population is genetically distinctive, the new study provides solid evidence that the woodpeckers were on the island long before people ever got there.

Martjan Lammertink, a researcher at the Cornell Lab of Ornithology, said the genetic data suggest a likely natural pathway of colonization: “From Central America, one group crossed during a low-water period from Yucatan (Mexico) to Cuba. Another group went to the Sierra Madre and became the Imperial Woodpecker, and the rest went farther north and became the North American Ivory-billed Woodpecker.”        

Because conditions were harsher in the mountains, researchers hypothesize that the Imperial Woodpecker became bigger and heavier than the other two to withstand the cold.








The original paper and supporting material is provided below courtesy of The Royal Society.

Mid-Pleistocene divergence of Cuban and North American ivory-billed woodpeckers

Biology Letters, May 16, 2006, DOI: 10.1098/rsbl.2006.0490

Robert C. Fleischer, Jeremy J. Kirchman, John P. Dumbacher, Louis Bevier, Carla Dove, Nancy C. Rotzel, Scott V. Edwards, Martjan Lammertink, Kathleen J. Miglia, and William S. Moore.

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