Male and female bodies are both sexually specialized, yet studies of sexual dimorphism predominantly focus on male specializations in ornamentations, brain circuits, and behaviors. The same is true of birdsong in the Zebra Finch (Taeniopygia guttata), where males learn to sing complex vocalizations, called songs, while females do not. Most work has focused on the specializations that males might have, and that females might lack, to promote singing. Other recent work indicates that song is widespread and ancestral across songbirds and more recently lost in the female Zebra Finch, and partially regulated by sex hormones. These theories are supported in part by well-documented brain circuit differences between males and females. However, relatively less attention has been paid to the syrinx, the songbird vocal organ analogous to the human larynx, and the ultimate output of brain circuits controlling vocal behavior. In particular, the female syrinx has been vastly understudied, and this gap prevents understanding potential synaptic differences underlying the sexually dimorphic vocal behavior in this species. In this thesis, I examined synapses and other neuromuscular features in the syrinx of males and females. First, I examined these features in adults, finding a surprising sex difference that is not male-biased, but instead female-biased. The adult female syrinx uniquely has a predominance of weaker en grappe synapses, which do not form a typical central motor endplate band in the muscle, and are biased towards smaller and weaker muscle fibers. Drawing on other well-studied models, these results suggest that female syrinx synaptic peculiarities might be an anatomical correlate of song suppression in this species. Second, I asked how these adult sexual dimorphisms develop, and whether one sex is specialized at the start relative to the other, or if they both specialize with sex-specific developmental programs. I find that both sexes have a common starting point of neuromuscular systems, and during developmental song learning, there is a divergence of these features. This implies two unique developmental programs leading to each adult phenotype, and further argues that both sexes are specialized at the level of syrinx synaptic morphology, likely in service of enhanced song production in males, and relative song suppression in females depending on species. Third, I manipulated hormonal systems starting early in life to alter singing behavior, i.e., to suppress male song learning and production, and to spur females to learn and produce songs. This data is preliminary and descriptive in nature, but is intriguing for at least two reasons. First, it indicates the morphology and organization of vertebrate-typical en plaque synapses is tied in large part to song production. Second, it implies that song suppression is particularly tied to the presence of en grappe synapses outside the motor endplate band region of the vocal organ. Altogether, these results broadly argue that the female synaptic specializations are the anatomical substrate of song suppression in Zebra Finches. Specifically, my data suggests that the location of en grappe synapses, either in endplate bands or out, is the strongest correlation to singing. They also suggest a mechanism by which an evolutionary loss of behavior may ultimately be realized at the level of synapses.