The functional significance of song sharing in the White-crowned Sparrow

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Abstract
The functional significance of learning a dialect has been a matter of considerable controversy. Some believe that birds learn dialects and mate assortatively according to those dialects to fixate adaptive genes within a habitat (the assortative mating theory). Others believe that birds learn dialects at sites settled after dispersal from their natal deme and that learning these songs gives them some kind of social advantage (the social adaptation theory). Color-marked female White-crowned Sparrows (Zonotrichia leucophrys) did not sing the same dialect as their consorts, and thus did not support the assortative mating theory. Birds singing alien dialects often mated and bred successfully. Hand-raised nestlings learned songs from live tutors but not from tapes when older than 50 days of age, beyond the age of dispersal. Critical examination of the literature revealed that there is no good evidence for restricted gene flow between dialect boundaries either from banding or isozyme studies. There is some evidence for birds changing dialects after dispersal from their natal area. Most available evidence tends to support the social adaptation theory.