The Passenger Pigeon used to be one of the most numerous bird in the world. They lived in enormous flocks and during migration it was possible to see flocks of them a mile wide and 300 miles long, taking several hours to pass and containing up to a billion birds. They could literally shade sky and when they would all settle somewhere the droppings could kill sections of forest. We have no modern equivalent to this. You have never seen anything that compare.

They went from the estimated 5 billion birds at the beginning of the 19th century to the last known one dying in 1914. They were killed on mass by commercialized hunting for meat. One of the methods for hunting them was to take live pigeon and sew its eyes shut. It would be tied to a wooden stool. The fluttering of the bird would attract other pigeons to see what was wrong. The hunters would then drop a net on them and crush their heads between fingers and thumbs. This incidentally may be the origin of the term stool pigeon.

nods to the http://thememorypalace.us, http://en.wikipedia.org/wiki/Passenger_Pigeon, and http://www.petermaas.nl/extinct/speciesinfo/passengerpigeon.htm for the info.