ANDROGEN CONTROL OF VOCAL CONTROL REGION VOLUMES IN A WILD MIGRATORY SONGBIRD (JUNCO-HYEMALIS) IS REGION AND POSSIBLY AGE-DEPENDENT

Previous laboratory studies have shown that photoperiodic adult songbi rds experience seasonal variations in singing frequency that correlate with plasma androgen levels, as well as changes in the brain regions that control singing (vocal control regions). The present study invest igates naturally occurring seasonal changes in the sizes of these regi ons in a wild migratory species (dark-eyed junco, Junco hyemalis), wit h samples from adolescence to postbreeding fall migration. In adult ma les, the volumes of the vocal control regions area X and the higher vo cal center (HVC) were large during the breeding season when birds were singing and androgen levels were high, and decreased in size after th e breeding season when singing had stopped and androgen levels were lo w. HVC volume in adolescent males caught in the fall (no singing), whe n plasma androgen levels were low, was smaller than in breeding adults , thereby following the seasonal pattern of change in plasma androgen levels. In adolescent males, however, area X volume was the same as in breeding adults. Thus, area X size in adolescent male juncos may be t estosterone independent. The seasonal pattern of robust nucleus of the archistriatum volume was similar to that of the HVC. The volumes of n either the magnocellular nucleus of the anterior neostriatum nor the n ucleus rotundus, a control region, differed seasonally. Castration of breeding adult males caused both area X and HVC volumes to decrease co mpared to castrated controls with testosterone replacement, indicating that maintenance of these two region volumes is testosterone dependen t in adults. (C) 1997 John Wiley & Sons,Inc.