Environmental History, DNA, and Passenger Pigeons

The story of the passenger pigeon has always seemed strange to me (and to others).  It's not just that humans managed to push to extinction this once incredibly abundant bird, or that, unusually, the path of extinction can be tracked down to the last day of the last survivor: Martha in the Cincinnati Zoo, on September 1, 1914.

It's just that it seems so unlikely that a population of tens of billions could go to zero in just a few decades.  Whenever the story comes up in my environmental studies courses I review the usual explanations: mass market hunting, elimination of habitats, and so on.  But those always seemed unsatisfying: surely some populations somewhere could hold on, remote from hunters and landscape changes, just as other species have.

So recent studies of passenger pigeon genomes are interesting, because of what they tell us about how evolution and natural selection affected their prospects.  The bottom line (or at least a plausible hypothesis) is that the pigeons were so vulnerable because they were adapted to live in large flocks; once those flocks were drastically reduced, they could not hold on -- becoming too scarce to survive.

It's an interesting twist on our understanding of the history of this and other once-abundant species.  And a useful reminder of the value in environmental history of keeping current on recent developments in the scientific study of the history of life.