Across their entire Atlantic breeding range, Atlantic puffins (Fratercula arctica) have experienced decreases in food availability, often leading to population declines. The species is one of the most numerous seabirds in Føroyar (Eng. the Faroe Islands) but has faced apparent, unquantified population declines. To better understand the underlying processes of this decline in Føroyar, we studied the change in the average, estimated age of puffins (i.e., the population age structure) harvested over a 20-year period (1989-2008). We assessed how the population age structure changed over time and in relation to food availability indices (i.e., phytoplankton primary production, juvenile fish; data available online - see publication). We showed that the average age of the birds in the population increased over time during the studied period, as the contribution of younger age classes declined, and cohort sizes decreased. Further, we showed that population age structure was significantly affected by food availability in the hatch year and the years preceding the hatch year but was hardly related to food availability in the harvest year. Our study thus suggests that reduced reproductive success driven by variability in foraging conditions is an important factor in the Atlantic puffin population decline in Føroyar.