Once the most common bird in the world, numbering in the billions, the passenger pigeon disappeared from this world 100 years ago yesterday. The 19th century ornithologist and artist John James Audubon once noted a flock that darkened the sky for days as it flew overhead. Hunting and deforestation quickly decimated the species. The last such pigeon, Martha, died 1 September 1914, in an Ohio zoo and helped kick off conservation efforts. Many media took note of this solemn anniversary yesterday, which came on the heels of a genome analysis of passenger pigeons that suggest population booms and busts contributed to its demise.