It is often said the passenger pigeon, once among the most abundant birds in North America, traveled in flocks so enormous they darkened the skies for hours as they passed. The idea 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 J. Novak, a young biologist who is backed by some big names, including the Harvard geneticist George Church.
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.
Some scientists say even if the passenger pigeon is re-created, it's unlikely to be viable as a species in today's ecosystem.
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 behaviours make the bird particularly susceptible to dying out again.
"Much of their breeding and wintering habitat is gone," says Scott C. Yaich, director of conservation for Ducks Unlimited, and the animal's primary breeding-season food -- beech mast, the nuts of a beech tree -- is limited.
The birds "simply couldn't be restored to a landscape that is so radically altered from the one to which they were uniquely adapted," says Yaich.
Other experts say given the nesting behaviour of the passenger pigeon, releasing a handful of birds into the wild would be a losing proposition.
The mainstream view of passenger pigeon ecology is they used a reproductive strategy called predator satiation. The recent cicada invasion in the Northeast is one example of this strategy. Each cicada is individually easy to catch in its slow, bumbling flight. But there are so many millions of cicadas in a spot at one time they are able to finish mating and laying eggs before predators have had time to eat all of them. If only a few thousand cicadas emerged at once, then most of them would probably be eaten before they were able to reproduce. In this way, the cicada's survival depends on showing up in hordes.
Passenger pigeons succeeded through a similar sort of mob rule. Individually, their behaviour was borderline reckless. They built flimsy nests, often dangerously low to the ground. The nests were built so hastily when bad weather would slow down construction, a female would sometimes be forced to lay her eggs on the ground. When the young were ready to leave the nest -- after only 14 days of development -- they would spend their first few days on the ground, vulnerable to any hungry predator. Passenger pigeons could get away with such behaviour because of their incredible numbers.
-- Washington Post