During natural colonization events, songs are expected to change as a result of both selection and drift-like processes. We studied song variation within a small isolated population of dark-eyed juncos, Junco hyemalis, which became established in an unusual environment on the University of California at San Diego (UCSD) campus in the early 1980’s, and compared this variation with the native range. At UCSD, the average repertoire size is 4.2 song types/male, which is similar to that in the native range. There is a low level of song-type sharing across the population. Typically a male shares at least one song type with on average 40% of his neighbors, and song-type sharing decreases rapidly with distance. Thus song-type diversity is high, and in this respect appears similar to that in ancestral mountain populations. These results suggest a moderate to large number of males founded and/or subsequently immigrated into the UCSD population, but several selection mechanisms, if coupled with a high cultural mutation rate, may also favor high song-type diversity. When combined with results from a previous study, songs are significantly shorter at UCSD than in the mountain population we studied. It appears that founder effects have not influenced the evolution of songs in this population. More generally, if song-type diversity and other features of song result from various social and natural selection pressures, many of these pressures may have remained similar between the native and the recently established population.