Iberia is a very important wintering area for several species of European seed-eating passerines, including the reed runting Emberiza schoeniclus. The dynamics and structure of its wintering population remains unknown over large areas, especially in northern Iberia. This study aimed to test (1) whether northern Iberia is a stop-over region rather than a wintering area for non-breeding nominate race reed buntings; (2) whether sex and age ratios indicate a higher proportion of immature males and whether such ratios differ from those found in regions further south; (3) whether wing morphology varies at different stages of the non-breeding season, thus possibly revealing differential migration by different populations. Reed buntings were mist-netted weekly from October to April in a reedbed in the Ebro Valley, northern Iberia, between 2003 and 2009. The zone was used mainly by reed buntings stoppingover in this area during the autumn migration period but also, to a lesser extent, by an apparently stable population that overwintered in this zone. The high proportion of females supports the hypothesis that Iberia plays a major role as a destination area for female reed buntings during the non-breeding period. Seasonal variation in wing morphology suggests that populations of very distinct origin occur but the temporal patterns of their occurrence still remain unresolved. Our results suggest that longwinged reed buntings, which presumably have travelled from more distant regions, are more abundant in mid-winter.