The northern fulmar Fulmarus glacialis is a medium-sized seabird with a broad, circum-polar range in the northern hemisphere, and is the only petrel that inhabits the High Arctic. We used stomach analysis and stable isotopes (delta N-15, delta C-13) of muscles to examine the diet of 179 fulmars during the breeding season at 4 locations in Arctic Canada, to compare diet to those from studies conducted in these regions >2 decades earlier. Across sampling locations, cephalopods, polychaetes and crustaceans dominated dietary remains in fulmars, although there was some regional variation. Both stable isotopes and stomach dissections showed that a seasonal shift in diet occurred in May, after which fulmars fed at a higher trophic level, suggesting a difference in winter/migration diet and breeding season diet. After migration, fulmar digestive organs decreased markedly in size, and by the time chicks were hatching, these organs were still 17 to 39% smaller than their size when birds arrived at the colony. Despite ongoing changes in the marine environment in much of the Arctic due to global warming, recent fulmar diet samples were similar to samples collected in the 1970s and 1980s, except that a higher proportion of recent collections contained fish.