Observation of killer whale (Orcinus orca) possibly eating penguins in Terra Nova Bay, Antarctica

(Jehl et al. 1980, Thomas et al. 1981, Branch & Butterworth 2001, Pitman & Ensor 2003). As in the Northern Hemisphere where killer whales manifest three ecotypes (resident, transient and offshore) (Jones 2006), three forms of killer whale have been described in Antarctic waters (Pitman & Ensor 2003). Such ecotypes, defined as A, B and C, differ from one another, on the basis of body size, color pattern, habitat preferences and food habits. However, no detailed information on the diet is available. It is generally believed that the A form is a mammal eating species, while the B form preys on pinnipeds (possibly including penguins and whales) and the C form is a fish eater targeting toothfishes (Dissostichus spp.) (Berzin & Vladimirov 1983). The present note, describes an observation of Adélie penguin (Pygoscelis adeliae (Hombron & Jacquinot)) killer whale B form interaction at Tethys Bay, (Terra Nova Bay, western Ross Sea). The observation took place during an aerial survey conducted by helicopter in the coastal area surrounding the Italian Station Mario Zucchelli (74°41'S, 164°07'E) between 5 January and 2 February 2004. The survey, aimed at investigating the presence and distribution of cetaceans, involved regular daily observations, carried out along the seasonal pack ice edge between the Drygalski Ice Tongue and Edmonson Point. The observation, took place on 21 January 2004, at 10:07 am local time, during a flight on the way back to the Italian Station. We observed a killer whale group composed of four adults (two males, two females), one juvenile and one calf close to the pack ice edge. A group of Antarctic skuas (Catharacta maccormicki Saunders), a scavenger bird, were observed in the same area, skim feeding, circling above and following the killer whale movements. We decided to use a small vessel to find and follow the killer whales in order to photo-identify and observe them. At 10:35 am we visually re-located the group after heading the vessel towards the initial GPS sighting position recorded from the helicopter. Group composition was the same, but a slight modification in the group formation was noted. Animals were moving offshore in two subgroups and were followed by the skuas. Animals in both subgroups zigzagged slowly in open waters and were observed spyhopping three times, a behaviour interpreted as looking over an ice floe which was adrift. The orcas then moved on each side of the floe. A group of 3–5 Adélie penguins were also present in the area. The penguins were moving slowly and began porpoising as soon as the killer whales began pursuing them. Following the interaction, we observed an escaping penguin with the right wing cut off. This individual was not sighted again. We interpreted this change in behavior as evidence of an aggressive interaction having taken place. A few minutes after this occurrence, a second interaction was observed. The larger male surfaced slowly with an Adélie penguin in its mouth, followed by the smaller male and the juvenile. This phase lasted 20 seconds. At the second surfacing bout, the penguin was in the female’s mouth. The female moved very slowly with a sudden 90° swerve in which the penguin emerged nearly out of the water. This change in direction lasted 30 seconds and turned into a zigzag in which the penguin seemed free to move itself laterally, despite the facts that the posterior part of the body was in the killer whale mouth. Just before the last dive the female nearly stopped, ventilated, arched the body and dived. This penguin was not see again as well as all the others. The observed killer whales were identified as B form on the basis of the dark gray dorsal cape and a large white eye patch oriented parallel to the body axis (Pitman & Ensor 2003). Identification was confirmed by the photographs. Although some records have been reported (Guinet 1992), it has been suggested that birds are not a significant food resource for killer whales (Ford et al. 1998) and bird predation represent a training activity for chasing and hunting (Ford et al. 1998). Moreover, Adélie penguins do not represent an appropriate prey for killer whales as they are a fast swimming and light species (Ballard & Ainley 2005). To date the few reported killer whale interaction of penguins have been attributed to the C form (Pitman & Ensor 2003, Ballard & Ainley 2005). Pitman & Ensor (2003) do not speculate on the nature of the interaction whilst Ballard & Ainley (2005) inferred that the motivation for the event was training because of the presence of young whales, no penguin consumption occurred and floating carcasses were picked up by skuas. In our observation, no Antarctic Science 19 (1), 95–96 (2007) © Antarctic Science Ltd Printed in the UK DOI: 10.1017/S0954102007000132