Introduced to North America in the early 17th-century by colonists who brought domestic pigeons to Atlantic coast settlements ( Schorger 1952a ), the Rock Pigeon (formerly the Rock Dove) is now feral and lives broadly on the continent. Wild Rock Pigeons, native to Europe, North Africa, and western, southwestern, west-central, and southern Asia, gave rise to domestics as a result of artificial selection by humans ( Darwin 1868 ). Domestics readily go feral, and have done so widely throughout the world ( Long 1981 ).
Domestic and feral pigeons are among the most intensively studied of all birds. Knowledge of avian flight mechanics, thermoregulation, water metabolism, endocrinology (prolactin was discovered through work with pigeons [ Riddle et al. 1932 ]), sensory perception, orientation and navigation, learning (the original subjects in Skinner boxes), genetics of color, pattern, behavior and other characteristics, and Darwinian evolutionary biology have depended heavily on research using domestic and feral Rock Pigeons. The total scientific literature referring to these birds is enormous, and can only be sketched here. Recent reviews include those of Abs ( Abs 1983b : physiology and behavior), Baldaccini ( Baldaccini 1986 : homing pigeons), Cramp ( Cramp 1985a : wild C. livia), Goodwin ( Goodwin 1983b : general biology of the family), Haag ( Haag 1991 : behavior), Hollander ( Hollander 1983 : pigeon genetics), Granda and Maxwell ( Granda and Maxwell 1979 : neural basis of behavior), Levi ( Levi 1965 : domestic breeds; Levi 1974 : general biology), Murton and Westwood ( Murton and Westwood 1977 : reproduction), and Berthold ( Berthold 1991 : navigation). Darwin ( Darwin 1859 , Darwin 1868 : evolutionary theory) should be noted irrespective of date. In addition, a monographic treatment of feral pigeons ( Johnston and Janiga 1995 ) provides another comprehensive review of Rock Pigeon biology with an extensive bibliography.
Despite all this work, the breeding biology and population ecology of this species remain poorly known and little studied, especially in the wild.
Body size and plumage color of Rock Pigeons vary appreciably, usually clinally, in wild populations; plumage variation is nearly limitless in polymorphic domestic and feral birds. Geographic size and color variation is recognized in Eurasia and Africa by use of several subspecies ( Cramp 1985a ), but such variation in feral populations has not been partitioned subspecifically. This species' presence in North America dates from 1606 (at least) with feral individuals existing soon afterwards ( Johnston and Janiga 1995 ). Biology of ferals has been largely ignored in North American ornithology, so some of the basic information on life history comes from studies of European ferals, confined ferals, and domestics of several varieties.