1. The migratory movements of wild animals can promote abundance and support ecosystem functioning. For large herbivores, mounting evidence suggests that migratory behavior is an individually variable trait, where individuals can easily switch between migrant and resident tactics. The degree of migratory plasticity, including whether and where to migrate, has important implications for the ecology and conservation of large herbivores in a changing world. 2. Mule deer (Odocoileus hemionus) are an iconic species of western North America, but are notably absent from the body of literature that suggests large herbivore migrations are highly plastic. We evaluated plasticity of migration in female mule deer using longitudinal GPS data collected from 312 individuals across 9 populations in the western US, including 882 animal-years (801 migrants and 81 residents). 3. We followed both resident and migratory mule deer through time to determine if individual animals switched migratory behaviors (i.e., whether to migrate) from migratory to residency, or vice versa. Additionally, we examined the fidelity of individuals to their migration routes (i.e., where to migrate) to determine if they used the same routes year after year. We also evaluated if age and reproductive status affected propensity to migrate or fidelity to migratory routes. 4. Our results indicate that mule deer, unlike other large herbivores, have little or no plasticity in terms of whether or where they migrate. Resident deer remained residents, and migrant deer remained migrants, regardless of age, reproductive status, or number of years monitored. Further, migratory individuals showed strong fidelity (>80%) to their migration routes year after year. 5. Our study clearly shows that migration plasticity is not ubiquitous among large herbivores. Because of their rigid migratory behavior, mule deer may not adapt to changing environmental conditions as readily as large herbivores with more plastic migratory behavior (e.g., elk). The fixed migratory behaviors of mule deer make clear that conservation efforts aimed at traditional seasonal ranges and migration routes are warranted for sustaining this iconic species that continues to decline across its range.