In his review of Joel Greenberg's book "A Feathered River Across the Sky: The Passenger Pigeon's Flight to Extinction," "The New Yorker's" Jonathan Rosen explains how the passenger pigeon could "vanish after near-ubiquity."
The short answer is that it tasted good. Also, it was easy to kill and so abundant that it often seemed, in the days before refrigeration, like the quail that fell on the Israelites in Exodus. In 1781, after a crop failure, a flock of pigeons saved a large swath of New Hampshire from starvation.
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....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.
A key point in the extinction was how human advances in technology outpaced the evolution of consciousness regarding wildlife conservation. Rosen writes:
We did hunt the passenger pigeon to death, even if we didn't quite understand at the time what we were doing. We also might have saved it, at least in token form, if only our technological genius and our conservation consciousness -- two things that set us apart from other animals -- had come together sooner.
However, as Rosen points out, just because modern societies have gained a more widespread understanding and appreciation of conservation, in many ways we have yet to learn the lessons of the past:
Human beings live in their historical and cultural contexts as much as passenger pigeons lived in fields, trees, and sky; it is important to remember, for example, that rural people hunted for food in the days before factory farming and supermarkets. The chicken industry in this country alone kills more than seven billion birds a year -- far more than the total number of passenger pigeons at their peak. Nobody in the nineteenth century had figured out how to make the slaughter of the birds sustainable, but it is worth wondering what we would think of the passenger pigeon, and ourselves, if they had
Read the rest of the review here.