March ] ROBERTSON: Pacific & Dominican 5 1977 Identification of Pacific and Dominican By B. l. Robertson, 30 Naples Road, Mentone, Vic. 3194 SUMMARY Unusual plumages are described for the Pacific Gull pacificus and the Dominican Gull L. dominicanus and explanations for their occurrence are proposed. Various records of Pacific and Dominican Gulls are discussed in relation to new information presented. It is suggested that bill characteristics are the most reliable for distinguishing between Pacific and Dominican Gulls. INTRODUCTION The Dominican Gull Larus dominicanus has extended its range considerably since its first sighting in in 1943. The Pacific Gull L. pacificus has also undergone marked changes in its distribution this century (McGill, 1955). Serventy, et al. (1971 ) summarise the present distribution of both gulls. The distinctive characteristics of Pacific and Dominican Gulls have been recorded by Mathews (1912), North (1914), Oliver (1930), Merilees (1969, 1970), Slater (1970), Serventy, et al., and Simpson (1972). RESULTS On April 10, 1976, I observed four Pacific Gulls on the beach at Edithvale (mid-eastern side of Port Phillip Bay), Victoria. One of these gulls had a black sub-terminal band on its tail, typical of the Pacific Gull (Figure 1). The other three gulls had white tails, thus resembling Dominican Gulls (Figure 2). On April 15, at Edithvale, I was only fifteen metres from the gulls with white tails and close examination of them using 7 x 50 binoculars confirmed that they were Pacific Gulls. On April 18, I returned to Edithvale and found two Pacific Gulls both of which had an indistinct or partial black sub-terminal band on their tails (Figure 3). In Wellington, New Zealand, on May 17, I observed and photo­ graphed a Dominican Gull with plumage characteristics resembling those of the Pacific Gull (Figure 4). DISCUSSION Although none of the were colour-banded, it is highly probable that the two Pacific Gulls with the partial black band were two of the three Pacific Gulls with no black sub-terminal tail band which I saw the previous week. The absence of the black band and the persence of a partial black band seem related to the moult cycle of the . It appears that these three Pacific Gulls moulted all their retrices simultaneously or in quick succession, leaving only the long white tail coverts. Thus, the white tails appeared shorter and more tapered than the broad, fan-shaped tail as in Figure 1. The presence of the partial black sub-terminal band is probably due to the retrices of the next feather generation as they grow longer and emerge through the tail coverts. This would explain why the band is more discernible at the edges of the tail. The bird in Figure 3 is in an advanced state of moult as is shown by the absence of a number of feathers from the left wing Fig. I. Pacific Gull at Edithvale, Victoria, on April 16, 1976. Note the black sub-terminal tail band and the feathers moulted from the right wing. Pla te 2 Photo by B. S. Robertson

- probably primaries 7 and 9 and distal secondaries 6, 7, 8, 9 and 10. The bird in Figure 1 also appears to have moulted a number of distal secondaries from its right wing. Whether this moulting of a number of feathers together or in rapid succession is widespread in Pacific Gulls will only become evident with futher study. In the Dominican Gull, Kinsky (1963) found an ordered pattern of moult, with the middle pair of retrices being the first shed and replaced, and these are followed sequentially until the outer sixth pair is replaced. According to Payne ( 1972), moult begins at certain points or loci in a feather series and a wave of feather replacement progresses from each of these points through a series of neighbouring feathers. The occurrence of Pacific Gulls with white tails has been re­ corded previously. According to North (1914) the tail feathers of the Pacific Gull are white and, usually but not always, crossed with a sub-terminal band of brownish-black. McGill (1943) be­ lieves that North based his remarks on two incorrectly identified Pacific Gulls in the Australian Museum collection, . Wood (19 55) presents a contradictory account of the sighting of a Fig. 2. Dominican Gull in Wellington Harbour, New Zealand, on May 17, 1976. Plate 3 Photo by 8 . S. R obertson

Dominican Gull: "One bird that flew within twenty feet of the car was noted to have the pure white tail of Larus dominicanus. It lacked the rounded, plumpness of pacificus, and the strawberry flush at the point of the upper and lower mandibles was more extensive and deeper in colour than in that ". I believe he saw a Pacific Gull with a white tail. Eckert (197 1 ) recorded the occurrence of a pair of Pacific Gulls with white tails on Eyre Island, South Australia. The female was collected and examina­ tion showed that the retrices had completely moulted, the new ones not having grown sufficiently for the black sub-terminal band to be visible. Cooper (197 5) recorded an "apparent hybrid" between the Dominican and Pacific Gull at Wilson's Promontory, Victoria. His discription of the tail corresponds with Figure 3; hence he was probably observing a moulting Pacific Gull.

Pacific Gulls breed in spring and early summer (Serventy, et al., 1971). The dates on which Pacific Gulls with unusual tail plumages have been seen are: Wood (1955) on March 24, 1955; Cooper (197 5) on April 3, 1966; Eckert (1971) on February 23, 1969; and the author on April 10, 1976. Simpson ( 1972) noted Fig. 3. Pacific Gull at Edithvale, Victoria, on April 18, 1976. Note the partial black sub-terminal tail band and feathers moulted from the wings. also present. Plate 4 Photo by B. S. Robertson

that during March the tail is moulted, becoming irregular and short, often causing the black sub-terminal tail band to be totally absent or represented in patches. Thus, all sightings have been in late summer and autumn, and are probably related to the simul­ taneous moulting of a group of feathers during a post-breeding moult. The Pacific Gull is not found in New Zealand (Kinsky, pers. comm.). Sightings have been reported but these have proved to be Dominican Gulls in late second year plumage (Figure 4). The second year tail acquired during the birds first full moult is very variable in colouring. The colouring of the tail is not dependent on the colour type a bird may develop, thus second year birds in a very advanced state of colouring can have pure black tails (Kinsky, 1963). Since ecological interactions between the Pacific and the Do­ minican Gull may occur, it is important that accurate records of their distribution be made. In view of the unusual plumages mentioned for both species and the consequent possibility of misidentification, I suggest that more emphasis be placed on bill and less on tail characteristics when identifying Pacific and Dom­ inion Gulls. Merilees ( 1970) illustrates clearly the differences in Fig. 4. Dominican Gull in Wellington Harbour, New Zealand, on May 17, 1976. Note the presence of a black tail. Plate 5 Photo by B. S. Robertson

size and shape of the bills of the two gulls. The bill of the Pacific Gull is large and orange-yellow with the tips of both mandibles boldly marked orange to plum red. The bill of the Dominican Gull is yellow with red gonys (Serventy, et al. , 1971). Finally, the Editor has kindly drawn my attention to the paper by van Tets (Australian Bird Watcher 7 ( 1) : 11) in which the sightings by Boeke! (1976) of a Dominican Gull at Gove Penin­ sula, N.T., is considered to be L . f. fusca - Scandinavian Lesser Black-backed Gull. This species also has a plain white tail in adult plumage. Its possible future presence in more northerly regions should be considered by persons studying the large gulls in Australia.

ACKNOWLEDGEMENTS I am grateful to Mr. F. C. Kinsky, Dominion Museum, Wel­ lington, and Mr. A. R. McEvey, National Museum, Melbourne, for access to the skins held in their collections and for their valuable discussions. I would also like to thank Dr. A. A. Martin, Melbourne University, for helpful criticism of the manuscript. 10 MORRIS: Little Falcon hunting [ Bird Watcher

REFERENCES Boeke!, C., 1976. Extension of Range of the Dominican Gull. A ust. Bird Watcher 6 : 162-167. Cooper, R. P. , 1975. The Avifauna of Wilson's Promontory. Part 4. Aust. Bird Watcher 6 : 17-34. Eckert, J., 1971. Birds of the Franklin Islands and Eyre Island, South Australia. Emu 71 : 61-64. Kinsky, F. C., 1963. The Southern Black-backed Gull (Larus dominicanus) Lichtenstein. Measurements, Plumage Colour and Moult Cycle. Rec. of Dam. Mus. 4 : 149-219. Mathews, G. M., 1912. Birds of Australia. Vol. 2. Witherby and Co., London. McGill, A. R., 1943. Probable Occurrence of the Southern Black­ Backed Gull in Australia. Emu 43 : 65-66. McGill, A. R., 1955. The Two Larger Gulls in Eastern Australia. Emu 55 : 90-98. Mer ilee~, W. J., 1969. Bird in the Hand. The Dominican Gull. Laru.< dominicanus. Aust. Bird Bander 7 : 62-63. Merilet>s, 1970. Field Characters of the Dominican Gull. Aust. Bird Watcher 3 : 272-274. North. A. J., 1914. Nests and Eggs of Birds found Breeding in Australia and Tasmania. Vol. 4. Australian Museum, Sydney. Oliver, W. R. B., 1930. New Zealand Birds. Coulls Somerville Wilkie Ltd., Wellington. Payne, N. B., 1972. Mechanisms and Control of Molt. In: Farner, D. S. and King, J. R., 1972. Avian Biology. Vol. II. Academic Press, New York. Serventy. D. L. , Serventy, V. and Warham, J., 1971. The Hand­ book of Australian Sea-Birds. A. H. and A. W. Reed, Sydney. Simpson, K. N . G., 1972. Birds in Bass Strait. A. H. and A. W. Reed Pty. Ltd., Sydney. Slater, P., 1970. A Field Guide to Australian Birds. Vol. I. Non­ Passerines. Rigby Ltd., Adelaide. Wood, P. J., 1955. Victorian Records of the Dominican Gull. Emu 55 : 157.

Little Falcon hunting in pre-dawn gloom. On October 23, 1976, while standing on the western edge of Lake Corangamite, western Victoria, at 0500 hours in the cold, charcoal-grey dimness before sunrise, I was surprised to observe the following: the alarm calls of Spur-winged Plover Vanellus miles novaehollandiae and Little Grassbird Megalurus gramineus, which I thought were voiced at my intrusion, were in fact directed elsewhere. An adult male Little Falcon Falco longipennis was seen flying rapidly over the mudflats in an erratic, zig-zag course, but progressing from west to east at about 5 metres above the ground. The hunting bird was gone into the darkness in a moment, and it is the first falcon I have seen hunting in what could be considered noctural condi­ tions. First light was not until 0505 hours. By F. T. Morris, 13 Bellett St. , Camberwell, Victoria. 3124.