passenger pigeon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An extinct migratory pigeon (Ectopistes migratorius) that was abundant in North America until the late 1800s.

from The Century Dictionary.

• noun The common wild pigeon of the United States, Ectopistes migratorius: so called from its very extensive wanderings in search of food. See Ectopistes.

from the GNU version of the Collaborative International Dictionary of English.

• (Zoöl.) A once common wild pigeon of North America (Ectopistes migratorius), now extinct. It was so called on account of its extensive migrations.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun an extinct bird of the species Ectopistes migratorius

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun gregarious North American migratory pigeon now extinct