An estimated one in four North American birds was a passenger pigeon...

... on the eve of European settlement. By the end of 1914 they were all gone... every last one. Their flocks could, famously, darken the sky... and apparently also whiten the earth. For some reason the story I remember from childhood was that farmers shot them in large numbers to protect their crops, but they were in fact killed for food, and also suffered from habitat destruction as the continent was deforested. Their catastrophic decline after 1870, interestingly, coincided closely with the near-extermination of the American bison. The railroad plays a key role in the conventional wisdom about both events: trains allowed large numbers of hunters to travel to where the massive herds or flocks were passing, and pick them off with rifles or capture large numbers in nets. When it comes to the buffalo, however, this story is decidedly incomplete, if not wrong, as economist Scott Taylor has shown in his excellent article, "Buffalo Hunt...." The discovery of a new tanning process facilitated an export market for bison hides and thus an elastic (nearly limitless) international demand. With the price maintained by the export market, and absent regulation, mass extermination was the likely and eventually actual outcome. Presumably there was no international trade in pigeon meat or feathers, but the domestic market for meat was sufficiently large to maintain a profitable price. Hunting proceeded all the way to the point where the number of these highly social birds fell below the critical level, and the population imploded.