Passenger pigeon.
New Yorker has an interesting read on why the passenger pigeon became extinct (and how that led to the preservation of bison). It's odd to think that flocks of the birds numbering in the billions could be completely exterminated in a span of fifty years, but so it went.
They were easy to catch - they could be knocked out of the sky with a club, very often - and in the days before refrigeration, they were an easy source of protein. And they could decimate crops, even forests as well. Imagining so many birds perching in trees that the branches snapped is difficult, but hundreds of pigeons were killed nightly by such events.
It was largely the railroads and electricity, however, that doomed them:
As long as America was rural and untraversed by railroads, the killing did not seem to do much more than dent the vast pigeon population. After the Civil War, however, things began to change rapidly. You could find out by telegraph where pigeons were nesting, get there quickly by train, and sell what you killed to a city hundreds of miles away. Soon market hunters began operating on an enormous scale, cramming tens of thousands of birds into boxcars—especially after Gustavus Swift introduced the refrigerator car, in 1878. This meant that rural migrants to growing cities could still get wild game, and the well-heeled could eat Ballotine of Squab à la Madison, served by a new class of restaurant, like Delmonico’s, in New York, where fine dining was becoming a feature of urban life. All this coincided with an explosion in logging, which began destroying the habitat of pigeons just as hunters were destroying the pigeons themselves.
Once they became a commodity, there was nothing to save them; they fell victim not to pure human greed, but to a complex dynamic involving technological development, urbanization, and the environmental issues inevitably accompanying both. At the same time, it was this extinction event, perhaps more than any other single issue, that led to the rise of conservation efforts - which is largely why bison still roam parts of the country today.
And combined with the exponential increases in technological prowess, there are serious efforts underway toward the establishment of the Second Cooing:
De-extinction became big news after a conference last March—sponsored by Revive & Restore, ted, and National Geographic—broadcast plans to take passenger-pigeon genes recovered from the toe pads of museum specimens, combine them with genes from the band-tailed pigeon (the genetic next of kin), and use them to modify another bird, possibly a chicken, so that it would lay a passenger-pigeon egg that could be raised by a band-tailed pigeon but taught to flock by a homing pigeon.
Alternatively, the squabs could be hand-raised, much as we do with California Condors today, before being mentored by homers. But what do we do if, as may well be the case, the birds require huge flock-sizes to survive?
