Understanding the drivers of seasonal migration among large herbivores is crucial for management and conservation. The forage maturation hypothesis predicts migration even at low population density, due to the benefits of increased access to newly emergent, high quality forage. We provide the first study comparing migration tendency of the two most widely distributed deer species in Europe, roe deer (Capreolus capreolus) and red deer (Cervus elaphus). The study was conducted in an area with a low population density of both species. We found that 94% of the GPS-collared red deer, but only 27% of the roe deer, migrated. This supports the forage maturation hypothesis in red deer only. Our study thus provides evidence of multiple causation of migration in ungulates, and is consistent with the hypothesis that the forage maturation hypothesis might be a more important driver for migration in grazers compared to browsers.