AGE-RELATED AND BEHAVIOR-RELATED VARIATION IN VOLUMES OF SONG CONTROLNUCLEI IN MALE EUROPEAN STARLINGS

There is considerable interindividual variation in the volumes of song control nuclei, Sex and physiological condition appear to contribute to these differences; however, these factors alone do not account for all of the variation, Studies have attempted to relate differences in song behavior(i.e., song repertoire size) to variation in song nucleus volume, but have met with mixed success, In this article, two studies are presented that used male European starlings (Sturnus vulgaris) to explore the relationship between song nuclei volumes and age-related differences in song behavior and interindividual variation in song beh avior in adults, The results of the first study showed that song reper toire size and song bout length were significantly greater in older ad ult than in yearling males, In addition, the volumes of the high vocal center (HVC) and nucleus robustus archistriatalis (RA) were significa ntly larger in older adults than yearlings, Area X of the parolfactory lobe did not differ significantly in volume between the two age class es, In the second study, both HVC and RA volume correlated positively with song bout length but not repertoire size among adult birds, Based on these results a new hypothesis is presented that states that varia tion in song nuclei volumes in starlings relates more to the amount of song produced than to the number of song types stored in memory. (C) 1996 John Wiley & Sons, Inc.