Marine species occupy broad geographical ranges that encompass varied habitats. Accordingly, resource availability is likely to differ across a species range and, in-turn, this may influence the degree of dietary specialization. Gentoo penguins Pygoscelis papua are generalist predators occupying a range of habitats with a large breeding range extending from Antarctica to temperate environments. Using the most extensive stomach content data set on gentoo penguins this study investigated their feeding ecology at the Falkland Islands (52°S, 59.5°W), the world’s largest population. Sampling occured in consecutive breeding seasons (2011–2013), across multiple foraging habitats utilizing stomach content data and carbon and nitrogen stable isotope values of feathers. The first species specific description of diet at this scale for the Falklands revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). Niche width, relating to both stomach content and stable isotope data related to the surrounding bathymetry. Birds from colonies close to gently sloping, shallow waters, fed primarily on benthic prey and had larger niche widths. The opposite was observed at a colony surrounded by steeply sloping, deeper waters. Therefore, gentoo penguins at the population level at the Falklands are indeed generalists, however, at individual colonies some specialization occurred to take advantage of locally available prey, resulting in these birds being classified as Type B generalists. Hence, future studies must account for this intra-colony variation when assessing for factors such as inter-specific competition or overlap with anthropogenic activities.