Song in birds is generally associated with territorial defense, reproduction, and maintenance of the pair bond (Thorpe 1961; Marler and Hamilton 1966). Since the songs of most species are distinctive even to the human ear, it has long been supposed that they aid in the reproductive isolation of one species from another (Marler 1960). The males of many species have been found to react to playback of a song of their own species in a manner typically including vocalizations, movement toward the sound source, and visual displays. Other species' songs do not elicit such reactions (Dilger 1956; Thielcke 1962; Lanyon 1963; Stein 1963; Gill and Lanyon 1964; Ficken and Ficken 1967; Lemon and Herzog 1969; Thompson 1969; Schubert 1971; Emlen 1972). As well as the differences between species, dialects or consistent differences between nearby populations may occur within the songs of one species. Dialects have been shown to exist in a wide variety of songbirds, including the Chaffinch (Fringilla coelebs) (Marler 1952), Short-toed Tree Creeper (Certhia brachydactyla) (Thielcke 1961), Great Tit (Parus major) (Gompertz 1961), Whitecrowned Sparrow (Zonotrichia leucophrys) (Marler and Tamura 1962), Mistle Thrush (Turdus viscivorus) (Isaac and Marler 1963), Cardinal (Cardinalis cardinalis) (Lemon 1966), Pyrrhuloxia (Pyrrhuloxia sinuata) (Lemon and Herzog 1969), Chingolo (Zonotrichia capensis) (Nottebohm 1969), Indian Hill Mynah (Gracula religiosa) (Bertram 1970), Rufous-sided Towhee (Pipilo erythrophthalmus) (Kroodsma 1971), and Vesper Sparrow (Pooecetes gramineus) (Kroodsma 1972). Behavioral responses to dialects have not been widely studied, but in the species which have been investigated, responses were stronger to songs of the birds' own dialects, as in the Cardinal (Lemon 1967), the Indian Hill Mynah (Bertram 1970), and the Whitecrowned Sparrow (Milligan and Verner 1971). Each male Song Sparrow (Melospiza melodia) possesses a repertoire of several different song patterns, each of which is repeated several times before another is begun. Although neighbo ing birds rarely have entire song patterns which are identical to one another, they usually have some elements within the patterns in common. Shared elements have been noted for birds in southern Quebec (Harris d Lemon 1972) and in Maine (Borror 1965), although Mulligan (1966) makes no such claims for birds in California.