Short and long-term changes in feeding ecology of Common Guillemots Uria aalge breeding in Witless Bay, Newfoundland, were investigated across three consecutive breeding seasons (1998-2000) and across decades (late 1970s to mid 1980s versus 1998-2000). The relationship between feeding rates and two chick growth parameters (mass and wing length) was also examined. From 1998-2000, observations were focused on the same subset of colour-ringed guillemots. Chick provisioning rates were highly variable within and across seasons. In all years, young guillemots were fed primarily medium-sized Capelin Mallotus villosus. In 1999 and 2000, their diets were supplemented with sandeel Ammodytes spp. Chick mass did not differ across years, however, a positive relationship existed between feeding rates and chick mass. Although no relationship was found between feeding rates and wing length, chicks reared in 2000 had longer wings than same aged chicks reared in 1998 and 1999. During unfavourable breeding conditions, wing growth may be prioritized to allow earlier departure. Overall, the diet and condition of Common Guillemot chicks reared in Witless Bay are similar to those reported in the 1970s and 1980s, despite important changes in Capelin biology and distribution in the Northwest Atlantic.