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Surprises in genetic study will shake up birds' family tree

June 28, 2008|Jeremy Manier and Tim De Chant | Chicago Tribune

CHICAGO — When a falcon swoops from the sky to seize its prey, no one would mistake the predator for a gaudy parrot.

Yet the secret kinship of falcons and parrots is one of many surprises in a landmark genetic study of 169 bird species published by Field Museum researchers.

One likely consequence of the study in Friday's edition of the journal Science is a reordering of the field guides that many of America's 80 million bird-watchers use.

"This is the most important single paper to date on the higher-level relationships of birds," said Joel Cracraft, curator of birds at the American Museum of Natural History in New York, who was not part of the study.

Birds' family tree has long stumped scientists. Many previous studies relied on painstaking comparisons of outward characteristics and behaviors.

Genetic comparisons can tell a deeper story, so the Field Museum launched a five-year effort with seven other institutions to do an unprecedented analysis. They discovered many cases in which seemingly similar birds were merely distant relatives and other birds long assumed to be unrelated turned out to be closely linked.

The analysis showed that falcons are more closely related to parrots than to such other hunters as hawks and eagles. If true, the finding would mean that falcons do not even belong in the scientific order originally named for them.

"It's kind of crazy to us too," said Shannon Hackett, a lead author of the study and associate curator of birds at the Field Museum. "People have been studying birds a long time, but now we're in a time when we should question everything, because for the first time we have the tools to answer these questions."

The bird project was part of a larger, federally funded effort called Assembling the Tree of Life, which aims to trace the evolutionary origins of all living things.

Using birds to study evolution is nothing new -- the diversity of Galapagos finches helped fuel Charles Darwin's theory of evolution. But many details of avian evolution remained a mystery, in part because the animals' light, hollow bones left few fossils.

Genetic studies can reconstruct evolutionary links by comparing small changes that have accumulated within the genes of different species. But studying birds that way posed a challenge because the major bird groups emerged in quick succession more than 65 million years ago, making their genetic changes harder to decipher.

The new lineage helps show how evolution works, experts said. Although falcons do not appear closely related to hawks, each species developed similarly shaped beaks and talons to hunt prey -- an evolutionary process that biologists call convergence.

Although conclusions like the falcon-parrot link may rattle some bird specialists, Joel Greenberg, an expert bird-watcher and editor of an anthology of Chicago nature writing, said such surprises can deepen the delight of studying birds.

"This may be one more of God's little jokes," Greenberg said.

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