Supplementation of wild populations with captive-bred individuals is often ineffective for boosting long-term productivity of wild populations. On the other hand, it remains unknown whether supplementation can act to maintain life-history variation in natural habitats, which is also important for the long-term persistence of populations and species. Partial migration, in which both migratory and resident individuals are maintained in a population, is commonly found across animal taxa. However, human-induced habitat fragmentation continues to cause rapid...