While foraging, a predator is expected to try maximizing its net energy gain according to given internal and external conditions. Gulls are known to be dietary generalists, which promotes flexibility in diet, foraging habitat types and prey capture techniques. I investigated the effect of internal and external factors on the foraging behaviour of Herring and Great Black-backed gulls in coastal Newfoundland. I first examined how post-breeding failure and ice conditions affect the foraging behaviour and movement pattern of incubating Great Black-backed Gulls. I also conducted an at-sea experiment to investigate how capelin availability, along with flock size and species composition at multi-species feeding aggregations affect species-specific responses to supplemental food and foraging success of seabirds. Investigating the foraging ecology of gulls could help understand the relationship between foraging behaviour, seabird predation and gull population decline and help conservation of both gulls and other seabird species.