The extent and spatial pattern of song-type sharing among neighboring males in one subspecies of Song Sparrow, Melospiza melodia cooperi, were examined in two San Diego County populations. Repertoire size averaged 9.6 song types per male (range 7 to 14). Song-type sharing was greatest between neighbors and declined with distance between territories. Adjacent neighbors shared an average of 22% of their song types. Variation in the amount of sharing between adjacent territory owners was high, ranging from 0% to 86% repertoire overlap. Results are consistent with the expected pattern produced by age-restricted learners that attempt to establish territories near tutors. The probability of a male surviving and remaining on his territory through the breeding and nonbreeding season increased as the fraction of song types shared with adjacent neighbors increased. The amount of song-type sharing may therefore be an indicator of a male's competitive ability to obtain a preferred territory near his tutors, or it may determine a male's effectiveness in using shared and unshared song types to communicate aggressive intentions.