Ryan P.G., Sommer E. & Breytenbach E. (2008) Giant petrels Macronectes hunting Northern Rockhopper Penguins Eudyptes moseleyi at sea. ARDEA 96 (1): 129-134

Adult penguins eaten at sea form a large proportion of the diet of giant petrels Macronectes spp. It is widely assumed that they are scavenged after being killed or injured by more agile predators such as fur seals Arctocephalus spp. We observed non-breeding Northern Giant Petrels M. halli hunting and killing Northern Rockhopper Penguins Eudyptes moseleyi offshore from a penguin colony on Nightingale Island, Tristan da Cunha. Penguins were killed at an average rate of 0.4 h–1 spent hunting by petrels. The most successful technique was a stabbing vertical lunge as a penguin surfaced or swam close to the surface near a petrel, but some were caught when a petrel dropped onto a group of penguins from the air, or when penguins fell back into the sea after attempting to land. Petrels also tried to sneak up on penguins resting on the surface by swimming towards them while lying flat on the water, but none of these ‘stealth’ attacks was successful. Penguins killed were grasped by the hind-neck and held underwater for 5–6 minutes until they stopped struggling, and then were eaten. Only 18% of penguins caught were killed; the remainder were dropped before they were subdued, apparently because they were not grasped correctly. One Southern Giant Petrel M. giganteus also attempted to catch penguins, but was not successful. Our observations suggest that not all penguins recorded in diet studies of giant petrels are scavenged.