Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role i n mate attraction. During the breeding season courtship song occurs prior t o copulation and appears to reflect male sexual arousal. Outside the breedi ng season starlings sing, but song appears unrelated to reproduction. The a romatization of testosterone mt likely within the medial preoptic nucleus ( POM), is critical for the expression of male sexual arousal. The present st udy was performed to determine whether seasonal changes in the POM might re late to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were e xamined both during and outside of the breeding season in male starlings. S ong was also recorded at these times both with and without a female present . The POM was largest and contained dense aromatase immunostaining only dur ing the spring breeding season, when T concentrations were highest and male s responded to a female with an increase in courtship song. Outside the bre eding season the volume of the POM was small, T concentrations were low, an d males displayed no changes in song expression in response to female consp ecifics. Song bout length was positively related to POM volume, and males s ang longer songs in spring. Only males with nestboxes in spring responded t o a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall , the findings suggest that T-dependent plasticity and aromatase activity w ithin the POM might regulate courtship singing in a wild songbird. (C) 2000 Academic Press.