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Passenger pigeons may come back from the dead

It is often said that the passenger pigeon, once among the most abundant birds in North America, traveled in flocks so enormous that they darkened the skies for hours as they passed. The idea that the bird, which numbered in the billions, might disappear seemed as absurd as losing the cockroach. And yet hunting and habitat destruction pushed the animal to extinction. Martha, the last known passenger pigeon, died in 1914 at the Cincinnati Zoo.

Plans are afoot to bring back the bird by using a weird-science process called de-extinction. The work is being spearheaded by Ben Novak, a young biologist who is backed by some big names, including Harvard geneticist George Church. The idea was recently promoted at a
TEDx meeting in Washington, D.C., and is being funded by Revive and Restore, a group dedicated to the de-extinction of recently lost species. (Other candidates include the woolly mammoth and the dodo.)

Novak’s idea takes a page from Jurassic Park, in which dinosaur DNA was filled in with corresponding fragments from living amphibians, birds and reptiles. Working with Church’s lab and Beth Shapiro, an evolutionary biologist at the University of California at Santa Cruz, Novak plans to use passenger pigeon DNA taken from museum specimens and fill in the blanks with fragments from the band-tailed pigeon. This reconstituted genome would be inserted into a band-tailed pigeon stem cell, which would transform into a germ cell, the precursor of egg and sperm. The scientists would inject these germ cells into developing band-tailed pigeons. As those birds mate, their eventual offspring would express the passenger pigeon genes, coming as close to being passenger pigeons as the available genetic material allows.

The process is not the same as cloning. Novak’s approach would use a mishmash of genes recovered from different passenger pigeons, resulting in birds as unique as any from the original flocks. Most pigeons mature and reproduce quickly enough that the de-extinction process could be completed in less than a year. Producing a flock large enough to release into the wild would take at least another decade.

Novak said he is confident the procedure will work. “Essentially, the genomes of the band-tailed pigeon and the passenger pigeon, I think, will prove to be similar enough to easily convert one to the other,” he said. In fact, he said, “making the passenger pigeon genome right now will be easier than making the first living passenger pigeon hatch from an egg.”

Experts say there is little question that re-creating the pigeon is technically possible. Indeed, the genome of the woolly mammoth has largely been sequenced using elephant DNA as a scaffolding. Complete, working genomes of dogs, sheep, horses, cows and other species have been artificially inserted into egg cells to produce living organisms.

But the project still faces many challenges, among them the contamination of much of the DNA specimen.

The hundreds of passenger pigeons in museum collections have been exposed to heat and oxygen. Specialized equipment would be used to identify the surviving fragments of DNA and reassemble them into working genes. It’s a painstaking process that could take years.

But the larger problem, say some scientists, is that even if the passenger pigeon is re-created, it’s unlikely to be viable as a species in today’s ecosystem. Novak’s plan is to breed the first new generations of the bird in captivity. But eventually he hopes to release the animal into the wild.

Such a proposition, some experts say, poses a number of fundamental problems: There is some question as to whether today’s forests can support a restored passenger pigeon population, and its nesting behaviors make the bird particularly susceptible to dying out again.

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