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
Puffinus and often give eerie contact calls on their night-time visits. They lay a single white egg. They feed on fish, squid and similar oceanic food. Some will follow fishing boats to take scraps, notably the sooty shearwater; these species also commonly follow whales to feed on fish disturbed by them. Traditionally, "Puffinus" has been grouped with the "Procellaria" and "Calonectris" shearwaters. However, more recent results have determined that the genus is apparently paraphyletic and while in part very close to "Calonectris", forms a clade with the genera "Pseudobulweria" and "Lugensa", which were formerly presumed to be gadfly petrels, and can