Sexual Dimorphism in Vocal Control Areas of the Songbird Brain

TLDR

In canaries and zebra finches, male birds possess markedly larger vocal control areas, including a prominent area X in the lobus parolfactorius, whereas females have smaller or absent regions. These anatomical differences align with behavioral disparities, as testosterone can trigger singing in female canaries but not in female zebra finches, marking the first documented gross sexual dimorphism in a vertebrate brain.

Abstract

In canaries and zebra finches, three vocal control areas in the brain are strikingly larger in males than in females. A fourth, area X of the lobus parolfactorius, is well developed in males of both species, less well developed in female canaries, and absent or not recognizable in female zebra finches. These size differences correlate well with differences in singing behavior. Males of both species learn song by reference to auditory information, and females do not normally sing. Exogenous testosterone induces singing in female canaries but not in female zebra finches. This is believed to be the first report of such gross sexual dimorphism in a vertebrate brain.