SONG DIALECTS AS BARRIERS TO DISPERSAL: A RE-EVALUATION.

Abstract

Although much has been written on the subject of song dialects in birds (reviews in Thielcke, 1969; Lemon, 1975; Bitterbaum and Baptista, 1979), few data exist testing the current theories regarding the adaptive significance of these vocalizations. Two popular ideas presented by Marler and Tamura (1962) and Konishi (1965), and developed by Nottebohm (1969), are that: 1) song dialects reduce gene flow across demes by attracting birds to settle near their place of birth on hearing their familiar natal song; 2) females select males that sing their own song for mates, thus promoting deviation from panmixia. Baker (1975) and Baker and Mewaldt (1978, 1979) have tested the first using biochemical and capture/recapture techniques on sedentary White-crowned Sparrows (Zonotrichia leucophrys nuttalii). Between 1975 and 1979, we conducted a similar study on the same species at the Presidio (P) of San Francisco (see map, Fig. 1). The habitat consists of coastal soft chaparral, and is, therefore, similar to that of the Point Reyes Peninsula, 38 km to the northwest, where Baker and Mewaldt (1978) conducted their study. One might expect the local dispersal biologies of the two populations to be similar. The Presidio study area is unusual; while most birds sing the local (Presidio) dialect within the 1.5 km by 370 m area, scattered throughout this population are breeding birds singing the dialect of the adjacent San Francisco city. Additional data were gathered at a site 5.6 km south at Twin