There’s a review of A Feathered River Across the Sky: The Passenger Pigeon’s Flight to Extinction that’s worth reading. I’ll probably end up getting a copy of the book at some point, but, according to the review, the book doesn’t address the most interesting question about the passenger pigeon.

I’ve never found the question of how the passenger pigeon went extinct to be especially interesting. It’s a case of firearms and poor (human) predator avoidance strategies, combined with the human desire to kill them all (or not caring if we did). We nearly did the same thing with the bison, but we realized, when there were roughly 100 left, that exterminating them might be a bad thing, so they didn’t disappear for good. Except in minor details, we have a very good idea of what drove the passenger pigeon to extinction: us.

So what is the interesting question? How did they become so damn abundant?

Here’s what I mean by abundant:

The passenger pigeon was also the most numerous bird species in North America, and possibly the world, dominating the eastern half of the continent in numbers that stagger the imagination. In 1813, John James Audubon saw a flock—if that is what you call an agglomeration of birds moving at sixty miles an hour and obliterating the noonday sun—that was merely the advance guard of a multitude that took three days to pass. Alexander Wilson, the other great bird observer of the time, reckoned that a flock he saw contained 2,230,272,000 individuals. To get your head around just how many passenger pigeons that would mean, consider that there are only about two hundred and sixty million rock pigeons in the world today. You would have to imagine more than eight times the total world population of rock pigeons, all flying at the same time in a connected mass….

In their wake, passenger pigeons left behind denuded fields and ravaged woods; descriptions conjure up those First World War photographs of amputated trees in no man’s land. “They would roost in one place until they broke all the limbs off the trees,” one old-timer recalled, “then they would move to Joining timber & treat it likewise, then fire would break out in the old Roost and Destroy the remainder of the timber.” Their droppings, which coated branches and lay a foot thick on the ground, like snow, proved toxic to the understory and fatal to the trees.

One hunter recalled a nighttime visit to a swamp in Ohio in 1845, when he was sixteen; he mistook for haystacks what were in fact alder and willow trees, bowed to the ground under gigantic pyramids of birds many bodies deep. As late as 1871, a single nesting ground in Sparta, Wisconsin, covered eight hundred and fifty square miles, hosting more than a hundred million birds.

Here’s what interesting: last time I checked (and that was a few years ago, so maybe there’s new scholarship on this question), these massive flocks were a relatively recent phenomenon. There’s very little pre-1500s evidence that the passenger pigeon was very common. It doesn’t appear to have been part of the diet of the Mississipian cultures, for example, which one would expect if it were so abundant. When you consider the ecological havocon a local scale that these flocks could wreak–especially for cultures that used acorns as a foodstuff–there’s no evidence of these flocks as a cultural phenomenon from the pre-1500s (though, in fairness, there isn’t much of a cultural record).

I can’t help think that the near-annihilation of Native Americans in the continental U.S.–often by disease before most whites encountered them*–had a significant effect on the passenger pigeon. Agricultural systems collapsed. If the U.S. agricultural system imploded, it’s easy to imagine that there could be tremendous effects on the ecology of various domesticated and wild organisms. On top of that, many of the surviving Native Americans shifted to a more nomadic lifestyle, which also would have changed land use patterns.

I’m waiting for the book that tells us how the passenger pigeon became so dominant.