BirdLife International 2012. Ectopistes migratorius. IUCN Red List of Threatened Species. Version 2013.2
si.edu
Smithsonian Institution; it is believed that this species once constituted 25 to 40 per cent of the total bird population of the United States. It is estimated that there were 3 billion to 5 billion passenger pigeons at the time Europeans discovered America.
