The Passenger Pigeon may be the only species for which the exact time of extinction is actually known. 

With Martha's passing, all future encounters with Passenger Pigeons will be limited to static images in books and photographs.  'Tis a sad legacy we leave our children.

In the early 1800s, their populations contained more individuals than all the other North American birds combined.  Passenger Pigeons were so plentiful, the sky literally turned black when the birds took to flight.  A single flock may have consisted of more than 2 billion birds.

Passenger Pigeons were a very popular item on the dinner menu, and were widely sought after by hunters as a game bird, and for sport. The birds were harvested in quantity, and made easy targets because of the large, congregating flocks during migration and nesting. No restrictions were ever placed on the harvest. There were no bag limits, no regulated hunting season, nothing...ever.  As a result, their populations soon collapsed.

Overharvest is considered the primary catalyst that led to the extinction of the Passenger Pigeon. Once their numbers had declined, factors like natural mortality, and the loss of habitat due to commercial development quickly pushed them over the edge, unable to sustain viable breeding populations.  In a short 50 years, their numbers plummeted from billions of birds to one lone survivor. She was named "Martha" in honor of George Washington's beloved wife. She died alone in captivity at the Cincinnati Zoo.

The Passenger Pigeon looked very similar to a Mourning Dove, only larger, and without the black spot on the side of the neck.

The head and rump of the Passenger Pigeon was slate blue, the back was slate gray, and the breast was a red wine color.  Males were brighter in color than females.

Today, there are many species whose entire existence hangs in the balance. Their fate depends on whether or not WE choose to allow the species to go extinct.