Breeding within a seabird colony can have positive and negative effects for smaller passerine species. For example, they may profit from the anti-predator behavior of the seabirds as well as from the influx of food and nutrients brought into the community. However, these possible benefits might be offset by seabird predation. For instance, gulls are not only fierce defenders of their colony, but also opportunistic feeders. Here, we report predation of Glaucous-winged Gulls (Larus glaucescens) on Sooty Fox Sparrows (Passerella iliaca fuliginosa), Song Sparrows (Melospiza melodia), and a European Starling (Sturnus vulgaris), observed on Mandarte Island, British Columbia, Canada. These observations provide new evidence for dietary supplements of Glaucous-winged Gulls and for a disadvantage of passerine life in a Glaucous-winged Gull colony.