Today marks a sad centennial: the 100th anniversary of the extinction of the passenger pigeon (Ectopistes migratorius), a species once so abundant that their flocks blacked out the skies of North America. Today the only passenger pigeons that remain are a handful of preserved specimens gathering dust in museum drawers and exhibits. These stuffed and mounted dead birds serve as a stark reminder, telling us that we did this, and yes, we'll undoubtedly do it again.

The passenger pigeon: Gone, but not forgotten.

Photo: Tim Lenz via Flickr. Used under Creative Commons license