The Passenger Pigeon or Wild Pigeon (Ectopistes migratorius) is an extinct North American bird. The species lived in enormous migratory flocks until the early 20th century, when hunting and habitat destruction led to its demise. One flock in 1866 in southern Ontario was described as being 1 mi (1.5 km) wide and 300 mi (500 km) long, took 14 hours to pass, and held in excess of 3.5 billion birds. That number, if accurate, would likely represent a large fraction of the entire population at the time. Some estimate 3 to 5 billion Passenger Pigeons were in the United States...