Using comprehensive faculty hiring data from US degree-granting institutions (2011-2023), we investigate how academic departments manage their size over time. Despite growth in overall faculty numbers, departments maintain a remarkably consistent size distribution, with an average of 18 faculty members. We find that departments actively regulate their size through coordinated hiring and departure patterns. After years with many faculty departures, departments systematically reduce further attrition and increase hiring the following year, compensating for losses to maintain optimal size. This suggests that departments function as self-regulating units within the organization. Our ongoing work explores whether departments that deviate too far from this characteristic size split or merge, while also investigating implications for gender parity, as attrition-hiring cycles may create opportunities for improving faculty diversity.