At the beginning of the 19th century millions of passenger pigeons migrated north in the spring in flocks large enough to darken the sky. When the flock arrived at a nesting site, the first day or two was spent in pairing. A male displayed with a circular nodding movement of the head and tried to hook its neck over a female's neck. If the female was receptive, the pair began to build a nest of sticks on which the female laid one white egg. Both male and female shared in incubating the egg (13 days) and feeding the young (15-17 days). For the first week the squabs were fed only pigeon's milk, produced in the crops of both parents. The young grew very fast, fledged in 14 days, and became independent a few days later. The adults fed on the ground and in trees or shrubs on beechnuts, acorns, seeds, berries, and invertebrates. Most calls of the passenger pigeon were harsh, loud variations of a loud "keck," repeated and modulated according to the message. It also uttered a soft "coo."

The first settlers to move west found the passenger pigeons an endless source of meat, fat, and feathers. In the 1850s the railroads began to extend their tracks westward; as a result, the birds could be shipped directly to city markets before they spoiled. Many persons became professional pigeon hunters. By 1880 the decrease in numbers had become irreversible. Some efforts were made to breed passenger pigeons in captivity, but with little success. The last passenger pigeon died in the Cincinnati Zoological Garden in 1914.

Scientific classification: The passenger pigeon belongs to the family Columbidae in the order of Columbiformes. It is classified as Ectopistes migratorius.