MODELING BIRD SONG DIALECTS - THE INFLUENCE OF REPERTOIRE SIZE AND NUMBERS OF NEIGHBORS

Computer simulation was used to examine whether the distribution of song types in a population of birds, and the changes in those present over time, are likely to be influenced by whether or not individuals have repertoires and by the number of neighbours from which a bird can copy. It is predicted from these simulations that having more neighbours will lead to song types lasting for less time in the population, to greater sharing of song types between birds, to song types being shared by spatially separated groups of birds more often, and to a lower proportion of the repertoire being shared between neighbours. Where repertoire sizes are larger the simulations suggest that song types should persist for longer, but they predict little effect on the number of birds sharing a type and no tendency for these birds to split into separate groups. The larger the repertoire the smaller the proportion of it expected to be shared between pairs of neighbours. Comparison with data on the frequency of different songs in a chaffinch population gave a goodness of fit of the simulations to the data that did not vary with repertoire size. However, more simulations with four neighbours matched the data than did ones with two or eight. This number of neighbours was also the most realistic for the population in question. It is concluded that both repertoire size and numbers of neighbours are likely to have a marked impact on various aspects of song distribution in wild populations. © 1990 Academic Press Limited.