Great black-backed gull stomach contents of great black-backed gulls was made up of birds, while a further 17% of stomach contents was made up of tern eggs alone. Adult or fledged juveniles of various bird species have also been predaceously attacked. Some fully-fledged or adult birds observed to be hunted in flight or on the ground by great black-backed gulls have included "Anas" ducks, ruddy ducks ("Oxyura jamaicensis"), buffleheads ("Bucephala albeola"), Manx shearwaters ("Puffinus puffinus"), pied-billed grebes ("Podilymbus podiceps"), common moorhens ("Gallinula chloropus"), terns, Atlantic puffins ("Fratercula arctica"), coots ("Fulica" ssp.), glossy ibises ("Plegadis falcinellus"), rock pigeons ("Columba livia") and even predatory birds
Tropical shearwater subspecies thought to number 3,000–5,000 pairs on Réunion and fewer than 100 individuals on Europa (reviewed by Brooke 2004), though it is thought there are many more breeding colonies on other islands in the Pacific. The population seems to be stable. Tropical shearwater The tropical shearwater ("Puffinus bailloni") is a seabird in the family Procellariidae formerly considered conspecific with Audubon's shearwater ("Puffinus lherminieri"). There are five listed subspecies of the tropical shearwater: The tropical shearwater is found in the tropical parts of the western Indian Ocean from east Africa to southern India and in similar regions of the Pacific from