Non‐linear and interacting effects of fire severity and time since fire may help explain how pyrodiversity promotes biodiversity in fire‐adapted systems. We built on previous research on avian responses to fire by investigating how complex effects of burn severity and time since fire influenced avian community composition across the northern Sierra Nevada, California. We conducted avian point counts from 2009 to 2015 in 10 fires that burned between 2000 and 2014, resulting in a chronosequence of 1–15 yr post‐fire. We estimated the effects of burn severity, time since fire, non‐linear and interacting effects of fire severity and time since fire, pre‐fire forest conditions, and several physiographic parameters on the density of 44 breeding bird species using hierarchical distance sampling models. In addition, we fit separate models to observations of each species in unburned forest to compare species’ densities between burned and unburned forests. At least one of the non‐linear or interaction fire effects was significant for 27 (61%) of the 44 bird species. The quadratic effect of time since fire was an important predictor of post‐fire densities of 20 species, illustrating the dynamic nature of this post‐wildfire avian community. Greater maximum densities were estimated at some combination of burn severity and time since fire than in unburned forest for 13 of the 44 (30%) species, only one of which reached maximum density following low‐severity fire. In contrast, all of the 12 species that were more abundant in unburned forest reached maximum post‐fire densities in fires that burned at low severity. Results from the study suggest that consideration of the non‐linear and interacting effects of fire severity and time since fire is important to fully understanding post‐wildfire responses for a majority of birds. Moreover, the study supports a growing body of literature that indicates mixed‐severity fire is essential for conserving avian diversity in many fire‐maintained systems.