The Passenger Pigeon, once probably the most numerous bird on the planet, made its home in the billion or so acres of primary forest that once covered North America east of the Rocky Mountains. Their flocks, a mile wide and up to 300 miles long, were so dense that they darkened the sky for hours and days as the flock passed overhead. Population estimates from the 19th century ranged from 1 billion to close to 4 billion individuals. Total populations may have reached 5 billion individuals and comprised up to 40% of the total number of birds in North America (Schorger 1995). This may be the only species for which the exact time of extinction is known.
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