VOL. 24 (4) DECEMBER 2007 167 AUSTRALIAN FIELD ORNITHOLOGY 2007, 24, 167–179 Another Form of Fairy Tern Sterna nereis Breeding in Australian Territory MIKE CARTER1 and SIMON MUSTOE 2 130 Canadian Bay Road, Mount Eliza, Victoria 3930 (Email: [email protected]) 2Applied Ecology Solutions, 39 The Crescent, Belgrave Heights, Victoria 3160 Summary Five Fairy Terns Sterna nereis were seen on East Diamond Islet (17°25′S, 151°05′E) in Australia’s Coral Sea Territory on 13 December 2006. A newly fledged juvenile begging from an adult indicated that they had bred locally. Within Australian territory, only the nominate subspecies has previously been recorded breeding, with the nearest known nesting site being in New South Wales over 2000 km away. Of the three described forms of Fairy Tern, the East Diamond Islet birds were most similar morphologically to the New Caledonian subspecies exsul, which is known to breed in the Chesterfield Islands ~800 km to the east. Two specimens found in 1950 on Heron Island, Queensland, are considered to be of that taxon. In New Caledonia, exsul is rare and declining and is genetically isolated from other subspecies in Australia and New Zealand. This discovery on East Diamond Islet is significant as it enlarges the range of the Fairy Tern in the Pacific and brings an additional taxon under the protection of Australian conservation legislation. Introduction Three subspecies of the Fairy Tern Sterna nereis are recognised and, according to R. Schodde (Research Fellow, CSIRO Division of Wildlife and Ecology, pers. comm.), this taxonomy is unlikely to change in the near future. All known forms occur in Australasia (Higgins & Davies 1996). The nominate subspecies nereis has a disjunct coastal distribution around Tasmania and mainland Australia westwards from eastern Victoria, rarely but increasingly also in southern New South Wales (Alan Morris in litt. 14 June 2007), through South Australia and Western Australia north to the Dampier Archipelago (Higgins & Davies 1996; Barrett et al. 2003). The Australian population has been variously estimated at approximately 2000 breeding pairs (Hill et al. 1988) and 6000 mature birds (Garnett & Crowley 2000; BirdLife International 2004) but is now in serious decline because of population loss in the Coorong, South Australia (Garnett 2007). Subspecies davisae is a rare and endangered form restricted to northern New Zealand. Hansen (2004) considered it to be New Zealand’s rarest indigenous breeding bird, with a population estimated at 35–40 individuals. The third subspecies exsul was formerly considered to breed only in New Caledonia and possibly the Loyalty Islands and other unknown sites in the south- western Pacific Ocean (Higgins & Davies 1996). Although Doughty et al. (1999) considered the Fairy Tern to be a ‘fairly common resident around the coasts of New Caledonia’, the IUCN Red List of Threatened Species assessment in 2004 considered that the total population might be only 100 pairs (Bird Life International 2004). Current research supports the view that the species is rare in New Caledonia and it has been described by some authorities as on the ‘verge of extinction’ (Benoit & Bretagnolle 2002). A declining population of ‘less than ten pairs’ is claimed for AUSTRALIAN 168CARTER & MUSTOE FIELD ORNITHOLOGY the Southern Lagoon of New Caledonia in BirdLife International (2004), but 25 pairs were recorded there during a visit by Massey University (New Zealand) in 2004 (Brunton 2005). However, Fairy Terns were reportedly absent from this location ‘between 1993 and 1996’ (Benoit & Bretagnolle 2002). Elsewhere, there may be 40–50 pairs in the Chesterfield Islands, a French possession midway between the centre of Australia’s Coral Sea Territory and New Caledonia (Barre & Dutson 2000; Bourne et al. 2005) (Figure 1). Two specimens collected by J.A. Keast on Heron Island, Queensland, on 20 and 21 January 1950 (Higgins & Davies 1996; label data from Australian Museum, Sydney) are considered to be of this subspecies. The few other Queensland reports of Fairy Terns (all sightings) are regarded as ‘unconfirmed’, but if correct we believe that they are unlikely to be S.n. nereis. On 13 December 2006 during a research cruise in Australia’s Coral Sea Territory, five Fairy Terns—a begging juvenile, two adults and two immatures— tentatively identified as being of the New Caledonian subspecies exsul, were found on East Diamond Islet (17°25′S, 151°05′E) (Figure 1). Because the bill of the juvenile was not fully developed, being short and blunt, and because the plumage retained some buff on the head, mantle, scapulars, and wing-coverts, we concluded that the bird had recently fledged. East Diamond Islet is >800 km from the hitherto nearest known breeding location for Fairy Terns, the Chesterfield Islands. It is inconceivable that this juvenile could have flown that distance, and it must therefore have been reared either on East Diamond Islet or another nearby islet. A series of photographs, some of which are in Plates 35–37 was obtained. These provide the first positive evidence for Australian territory of live birds and breeding of a taxon of Fairy Tern other than the nominate subspecies. Habitat The Diamond Islets are roughly at the centre of Australia’s Coral Sea Island Territory. Together with the adjacent Tregrosse Reefs, they embrace an area measuring ~90 km east to west and 50 km north to south and include four small islands, South, West, Central and East Diamond Islets, and a few sand cays. East Diamond Islet is located at the north-eastern extremity of the reef system and is 14, 28 and 36 km from Central, West and South Islets respectively. The next closest land is a small cay immediately west of Nellie Cay in the Lihou Reef, which is 43 km to the south-east. None of these other islets was visited. East Diamond Islet is a coral cay shaped like an elongated triangle with a north-east–south-west alignment ~1 km long and 200 m across at its widest point. It has a sandy substrate of coral grit, with some rocky limestone outcrops. Its highest point is probably <3 m above the high-tide line. Octopus Bush Argusia argentea dominates the fringing vegetation, and the interior is covered with terrestrial creepers, tall grass and herbs. All but the central eastern portion of the islet is surrounded by barrier reef. This forms a shallow lagoon-type habitat extending up to ~1 km from the shore. Although the sheltered north-western shoreline consists entirely of a sandy beach, the opposite shore exposed to the south-east trade winds is ~70% rock and 30% sand. Fairy Terns were found loafing on a sandy spit at the northern tip and on a rockier point at the south-western corner of the islet. The islet is host to a variety of seabirds. Those observed breeding during our visit were Wedge-tailed Shearwater Puffinus pacificus, Red-tailed Tropicbird Phaethon rubricauda, Masked Booby Sula dactylatra, Red-footed Booby S. sula, VOL. 24 (4) DECEMBER 2007Fairy Tern: Another Form Breeding in Coral Sea 169 Figure 1. Location of East Diamond Islet and Lihou Reef Brown Booby S. leucogaster, Great Frigatebird Fregata minor, Lesser Frigatebird F. ariel, Sooty Tern Sterna fuscata, Common Noddy Anous stolidus and Black Noddy A. minutus. Black-naped Terns Sterna sumatrana (~30) had flying young, so like the Fairy Terns are presumed to have bred either there or somewhere nearby. About eight Crested Terns S. bergii were also present. Migrant waders observed were Whimbrel Numenius phaeopus (1), Wandering Tattler Heteroscelus incanus (1), Ruddy Turnstone Arenaria interpres (13), Red-necked Stint Calidris ruficollis (4) and Pacific Golden Plover Pluvialis fulva (35). We estimated that, including juveniles, up to 30 Buff-banded Rails Gallirallus philippensis were present. Behaviour The first two Fairy Terns, an adult and an immature, were found during a morning visit near high tide, loafing with Crested and Black-naped Terns near the AUSTRALIAN 170CARTER & MUSTOE FIELD ORNITHOLOGY water’s edge on the sand-spit at the north-western tip of the islet. The adult Fairy Tern [Plate 37 (C)] was reasonably tolerant of the approaching observers, remaining on the beach when the other terns moved off. This permitted sustained study allowing its identity to be confirmed. Eventually, however, it flushed and at first flew a short distance out to sea where it started to hover as if about to dive for food, but soon abandoned the attempt and flew westward, disappearing into the far distance at a height of about 50 m. It gave the impression that it was moving to another roosting site, presumably Central Diamond Islet. The immature appeared to disperse more locally with the Black-naped Terns. A return visit in the afternoon located three different Fairy Terns (plumage differences clearly discernible in some of the photographs) on the spit at the south- western end of the island, this time associating with Pacific Golden Plovers and Red-necked Stints. The Terns in this group, which consisted of a juvenile begging from an adult and an immature (Plate 35), were more confiding than the waders and when on the beach stayed close together. The adult from this group was observed fishing offshore [Plate 37 (F)], hovering some 8 m above the sea. The flight of the birds was typical of the species as observed in southern Australia, swift-flying with continuous quick wing-beats when in direct flight (more like a calidrid wader than the more leisurely, graceful flight of a Black-naped Tern). When hovering, the body was inclined with the head up but bent forward and down so that the bill was vertical. The tail was depressed, and the wing-beats rapid. Identification to species level All five terns seen were photographed and are shown in Plates 35–37.