VOL. 19 (2) JUNE2001 Pacific Attacking 69

Pacific Gull Attacking Silver Gull and Response by a Flock of Silver

At about 1030h on 21 December 2000 at Currie Harbour, King Island, Thsmania, I was standing on the road near the wharf, about 3 m above the beach and about 30 m from the edge of the water. The sea was calm, and the sun shining from behind me. Visibility was excellent. I was using 10 x 25 binoculars. I became aware that in the water some 5 m out from the beach, an adult Pacific Gull pacificus was attacking an adult Silver Gull L. novaehollandiae. The Pacific Gull repeatedly bore down from behind on the Silver Gull, pressing it into the water so that several times it was fully submerged, including its head. On several occasions the Pacific Gull gripped the neck of the Silver Gull with its bill. The behaviour of the Pacific Gull resembled that of a carnivorous mammal attacking its prey. Both continually spread and flapped their wings, and it became apparent that the Silver Gull, although it could swim, could not fly. Whether this was caused by injuries inflicted by the Pacific Gull, or had been the situation before the attack, I am unable to say. It may be that the Silver Gull had been injured previously and was accordingly perceived by the Pacific Gull as easy prey. The Silver Gull swam towards the beach, while the attacks from the Pacific Gull continued. After a minute or less of this behaviour, a flock of about twenty Silver Gulls, which had been resting close by on the beach, took off and flew over and around the Pacific Gull, attacking it from above. When the victim reached the beach and walked out of the water, still trying, but unable, to fly, the Pacific Gull continued to attack, and the flock to defend it. They landed on the beach and surrounded the victim, closing in around it. Eventually the Pacific Gull abandoned the attack and flew away across the harbour, with one Silver Gull pursuing it closely and frequently diving on it. The other members of the flock remained on the beach, together with the victim. In many hours of idly watching gulls on beaches over many years, I do not remember ever seeing either inter-specific behaviour of this kind between a Pacific Gull and a Silver Gull, or any similar response by a flock of Silver Gulls to an attack on one of their number. The only record of similar behaviour by a Pacific Gull which is cited by Higgins & Davies (1996) is that of Stirling et al. (1970) at South Neptune Islands, South , who observed a Pacific Gull which 'caught a Crested Tern over the water and for about 20 minutes jumped on it, pecked it, and held it under the water, leaving it with broken feathers sticking out all over its body and unable to fly'. The authors did not know the reason for this behaviour. Other large avian prey taken by Pacific Gulls include Hoary-headed Grebes Poliocephalus poliocephalus and 'well-grown' Short-tailed Shearwaters Puffinus tenuirostris (Higgins & Davies 1996). The only record of similar behaviour by a flock of Silver Gulls cited by Higgins & Davies (1996) is that of Favaloro (1948) who recorded a flock of Silver Gulls at Lake Hawthorne, Mildura, Victoria, demonstrating around a Silver Gull chick which had fallen from its nest into the water. The observers AUS1RALIAN 70 BALMFORD WATCHER

Adult Pacific Gull, Stony Point, Vic., 2.9.1989 Plate 21 Photo: MJ. Carter considered that some of the adults were diving on the chick in a menacing manner. Eventually six birds piloted the chick to shore. This behaviour, insofar as it was protective, was analogous to that which I observed, but the victim in my case was a fully adult bird.

References Favaloro, N.J. (1948), 'Silver Gulls in north-west Victoria', Emu 41, 352-356. Higgins, P.J & Davies, S.J.J.F. (Eds) (1996), Handbook of Australian, New Zealand and Antarctic Birds, vol. 3, Oxford University Press, Melbourne. Stirling, I., Stirling, S.M. & Shaughnessy, G. (1970), 'The bird fauna of South Neptune Islands, South Australia', Emu 70, 189-192.

By ROSEMARY BALMFORD, 459 The Boulevard, East Ivanhoe, Victoria 3079 Received 15 January 2001 •