The emergence and persistence of partial migration

Dongmin Kim , Ellen Aikens, Teresa Pegan, Paul Moorcroft, Jesús Pinto-Ledezma

Partial migration, where some individuals in a population migrate while others remain resident, is a widespread and complex behavioural phenomenon arising from the interplay of genetic, developmental, social, and environmental processes. These mechanisms often interact, as migratory strategies can be shaped by genetic variation, individual experience, social learning, and fluctuating environmental pressures. With rapid advances in our ability to study the genetic, social, developmental, and ecological determinants of migration, it is timely to revisit long-standing questions of how individual-level processes generate partial migration (emergence) and how migratory and resident strategies persist within populations over generations (persistence). Here, we provide evidence across different taxa to examine how interacting mechanisms shape both the emergence and persistence of partial migration. We focus on two linked questions: (1) why individuals within a population adopt different movement strategies, and (2) how the coexistence of migratory and resident individuals persists across generations. We further emphasize the importance of spatial and temporal scale in linking individual-level mechanisms to population-level patterns, as mismatches in scale can alter inference about underlying processes. This integrative perspective highlights how multiple mechanisms jointly structure variation in migratory behaviour and provides a framework for generating testable hypotheses and developing biologically realistic eco-evolutionary models. Beyond partial migration, this perspective may also help clarify how similar interacting processes shape other forms of animal movement across species and ecosystems.