INTER-POPULATIONAL SONG DIALECT DISCRIMINATION IN THE WHITE-CROWNED SPARROW

The fact that song types vary among coastal California populations of the White-crowned Sparrow (Zonotrichia leucoph ys nuttalli ) has been known for some time (Blanchard 1941). It was not until the advent of the sound spectrograph, however, that an unambiguous analysis of these inter-populational variations could be performed. Using this technique, Marler and Tamura (1962) foun’d that each male’s song type remains constant from year to year and that there are constant and distinctive differences among populations with respect to song type. They therefore refer to the songs of different populations as “dialects.” Of fundamental importance in determining the functional significance of these dialects is the question of whether or not the birds themselves discriminate among them. One approach to this question is to observe the behavioral responses of the individuals of one population to the recorded songs of their own and of other populations. Earlier work suggests that at least one function of song in the White-crowned Sparrow is territorial defense. A territorial male will respond with song (sometimes accompanied by chase and attack) to visual and/or auditory stimuli from another male intruding within his territory ( Blanchard 1939, 1941) . A study of vocal responses of captive male Whitecrowned Sparrows to recorded songs of their own and another species revealed a higher probability of response to the songs of their own species (Milligan 1966). Thus it seems reasonable to expect that male White-crowns can also discriminate among different dialects of their own species and that they would respond more strongly to playback of their own dialect. The central purpose of the present study was to test this hypothesis. In addition, data were accumulated on the seasonal changes in the response of male and