Significance The mammary gland is functional for only a brief period of a female’s lifetime. During this time, it operates not for the survival of the individual, but for the survival of her species. Here, we visualize the nature of alveolar contractions in the functionally mature mammary gland, revealing how specialized epithelial cells, which possess the ability to behave like smooth muscle cells, undergo Ca ²⁺ -dependent contractions. We demonstrate that individual oscillators can be electrically coupled to achieve global synchrony, a phenomenon that has not yet been observed in the mammary gland. By imaging activity across scales, we provide a window into the organization, dynamics, and role of epithelial Ca ²⁺ oscillations in the organ principally responsible for sustaining neonatal life in mammals.