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. As these terns were very small, only about half the size of the accompanying Black-naped Terns [see Plate 37 (B)], specific identification in the field required separation only from the Little Tern Sterna albifrons. However, when no size comparison was available, either in the field or in photographs of single birds, some confusion with the Black-naped Tern occurred, particularly with regard to juvenile and immature birds. The absence of a black line extending from the eye to the bill immediately eliminates adult Little Tern in breeding plumage, but the birds’ mainly dark bills and feet suggest Little Tern in non-breeding plumage (Higgins & Davies 1996). However, all the birds were too pale for Little Tern, and the adults had the broad white forehead typical of Fairy Tern in breeding plumage. The only contra- indication to that conclusion was the bare-part colouration: Fairy Terns in breeding plumage on mainland Australia, subspecies S.n. nereis, have wholly bright-yellow- orange bills and bright-orange legs and feet (Higgins & Davies 1996). The simplest diagnostic feature determining that all five birds were Fairy Terns is the pattern of their outermost primaries. The following analysis is based on Higgins & Davies (1996: p. 722) and Johnstone & Storr (1998: p. 346). The outermost primary (p10) in Little Terns in all plumages has black on both webs adjacent to the shaft. That on the inner web tapers, increasing from twice the width of the outer web at about mid length to three times or more towards the tip of the feather. In juvenile Fairy Terns, the black outer web is similar but the amount of black on the inner web is constant in width for almost the full length and is much narrower, being no wider than the width of the outer web at any point except for a small bulge at the extreme tip. This pattern is retained in some immatures VOL. 24 (4) DECEMBER 2007Fairy Tern: Another Form Breeding in Coral Sea 171 for several months, as the juvenile outer primaries can be retained into immature plumage. In adult Fairy Terns, the pattern is similar to that of the juveniles but the black is replaced by grey so the leading primary in this species is considerably paler than in the Little Tern. The limited amount of black in the younger birds on East Diamond Islet, and its absence in the adults, was most obvious when the birds were in flight as evident in Plate 37 (D) and (F). Other features identifying these birds as Fairy Terns include the following: 1. Small amount of dark grey or black in the other outer primaries (Higgins & Davies 1996; Johnstone & Storr 1998). 2. Paleness of the upperparts: their backs and wings were very pale grey, creating little contrast with their white underparts. Little Terns have distinctly grey upperparts, several shades darker than these birds (Carter 1970; Hill et al. 1988; Higgins & Davies 1996). 3. Their relatively robust, stocky build. Fairy and Little Terns are similar in length but Fairy Terns are heavier, and this is evident in the field (Carter 1970; Hill et al. 1988; Higgins & Davies 1996). Higgins & Davies (1996) gave the weight of the subspecies nereis of Fairy Tern as ~70 g but that of Little Terns as only 50 g. Only four weights are available for the subspecies exsul (Higgins & Davies 1996); they range from 57–72 g and, as this is the smallest subspecies of Fairy Tern, it seems likely that it shares the stocky build of nominate nereis. 4. Little Terns have relatively longer legs (Carter 1970; Hill et al. 1988; Higgins & Davies 1996). In the Little Tern, the length of the exposed tibia approaches 70% of the tarsus but, as in these birds, is only about 35% in Fairy Tern (MC pers. obs.).

Age of subadult birds The incompletely developed bill and the extent of buff on the head, mantle, scapulars, and wing-coverts of the fledged juvenile suggest that it was between 4 and 7 weeks old. Because of the faint cubital bar and white crown, the two older subadult birds are considered to be in first-immature non-breeding plumage, i.e. between 3 and 12 months old. According to Hannecart & Letocart (1983), in New Caledonia Fairy Terns lay their eggs between September and December. This is ~3 months earlier than in southern Australia (Higgins & Davies 1996). Assuming that the breeding season in the Coral Sea is similar to New Caledonia, these birds could be 3 months in advance of their southern relatives and thus in a plumage equivalent to that of a southern immature Fairy Tern in April (Higgins & Davies 1996). These immatures appeared to be a little more advanced than that because the flying bird in Plate 37 (D) seems to retain only one juvenile primary, the outermost. However, it is impossible to be certain of the exact age as, apart from this observation, nothing is known about the local breeding season and little regarding that in New Caledonia. The simultaneous occurrence of a newly fledged juvenile and immatures in first non-breeding (winter) plumage suggests that the breeding season for this population is longer than in southern Australia. AUSTRALIAN 172CARTER & MUSTOE FIELD ORNITHOLOGY

Subspecific identification The subspecies davisae is most readily eliminated because it is a darker bird. The grey of the upperparts is a similar hue to that of the Little Tern and the black loral patch adjacent to the eye in adults is considerably larger than that in the East Diamond Islet birds (Higgins & Davies 1996). Moreover, a study of numerous photographs taken by Ian Southey of specimens from various museums around the world reveals that the grey in the outer primaries in davisae is several shades darker, tending to black, and more extensive than in these Diamond Islet birds. The occurrence of this taxon, which is restricted to New Zealand (Higgins & Davies 1996), is highly unlikely in this region. According to Higgins & Davies (1996), the few useful characters for distinguishing exsul from nereis in the field are as follows: Exsul in first-immature non-breeding plumage differs markedly because the crown is wholly white, not streaked with black. This isolates the black band that runs from the eyes around the nape, creating an appearance similar to that of the Black-naped Tern. The absence of crown streaks in the immatures present on East Diamond Islet is apparent in Plate 37 (B) and (D). This pattern is very clear in a series of photographs taken by Ian Southey of specimens from the Muséum Nationale d’Histoire Naturelle, Paris. Three characters distinguish adults in breeding plumage. The first of these is that exsul has a slightly larger black loral patch. Comparison of the adult birds in Plates 35, 36, and 37 (A) and (C) with photographs of mainland Australian birds (S.n. nereis) from many sources, including Harrison (1987), Pringle (1987) and Hill et al. (1988), shows that the loral spot was indeed larger in the East Diamond Islet birds but the difference is not very obvious. Comparison with a photograph by Ian Southey shows that this spot was also larger than that in the type-specimen of exsul in the British Museum at Tring, UK, but was similar in size to that in Fairy Terns photographed in New Caledonia (Hannecart & Letocart 1983). The second is the timing of the moults. As revealed in the photograph of the flying adult [Plate 37 (F)], primaries p1 to p5 are new and fresh but p5 is not yet fully grown, whereas p7 to p10 (outermost) are old and worn. Primary 6 cannot be discerned, suggesting that it was missing or in a very early stage of growth. This accords with the moult schedule for exsul and conflicts with that of nereis. Moult of primaries in adults of the nominate subspecies does not begin until January at the earliest. The primary moult score for this adult, calculated in accordance with Marchant & Higgins (1990: p. 30), is estimated to be 26–28 (Danny Rogers in litt. 12 January 2007). This compares with 21–45 for three exsul specimens collected in December–January (Higgins & Davies 1996). That for nominate nereis would be zero or thereabouts. Moreover, the inner secondaries are new whereas a few of the outer ones are old and worn. However the black crown, although a little faded, is as extensive as in full breeding plumage. Higgins & Davies (1996) apparently had less confidence in the third distinction, bill colour. They stated that subspecies exsul is ‘said’ to have a larger black tip to the bill, and the author of that text (Danny Rogers) found one specimen with 15 mm of black at the tip in support of that claim. The type-specimen also has a large black tip to an otherwise bright-yellow bill, as has a specimen from the Museum of Comparative Zoology, Harvard University, Massachusetts, USA (photographs by Ian Southey). Adult nominate nereis may retain a small black tip to the bill from non-breeding into the early stages of breeding plumage, but by this date VOL. 24 (4) DECEMBER 2007Fairy Tern: Another Form Breeding in Coral Sea 173

Fairy Terns on East Diamond Islet, 13 December 2006: Adult, begging juvenile and immature. Plate 35 Photo: Andrew McCutcheon

Fairy Tern on East Diamond Islet, 13 December 2006: Adult showing head pattern and bill colour. Plate 36 Photo: Kathy Wilson

(December) the whole bill would be bright orange-yellow (Higgins & Davies 1996). The bills of the adults on East Diamond Islet were almost entirely black, a condition possible in subadult nereis but unknown in nominate adults (Higgins & Davies 1996). The adult in Plate 37 (C) appears to have a wholly black bill, but in the field MC noted that there was a small paler area on the cutting edges of both mandibles near the base. However, this was neither as extensive nor as obvious as AUSTRALIAN 174CARTER & MUSTOE FIELD ORNITHOLOGY the pale sides of the bill in the second adult shown in Plate 36. An adult exsul, photographed with a juvenile, in a photograph in Hannecart & Letocart (1983) has a similar bill colouration. In a second photograph in that work an adult in breeding plumage has a mainly yellow bill with a large dark tip and a little black at the base. The implication from a series of six specimens of adults in various plumages in the Paris Museum (photographs by Ian Southey) is that typically exsul has a darker bill than nominate nereis although rarely as dark as in the East Diamond Islet birds. Leg and foot colour was also a surprise, being bright orange-red in the juvenile, dull yellow-orange in the first-immature non-breeding birds and very dark red, appearing almost black, in both adults. According to Higgins & Davies (1996), leg colour of nominate nereis is brown to yellowish brown in juvenile and first- summer non-breeding birds (with an orange tinge to the toes by mid winter), and orange to dark orange in all adult plumages. Both the juvenile (a more developed bird than the one that we saw) and the adult exsul with it in the photograph in Hannecart & Letocart (1983) have dull-orange legs, as does a first-year non- breeding bird in the second photograph. The adult in the background of the second photograph (a blurred image) appears to have pale-orange legs with darker joints. Higgins & Davies (1996) made no mention of differences in leg colour between subspecies exsul and nereis, and the legs were not visible in any of the photographs of specimens from museums around the world provided by Ian Southey. From the above we suggest that either both bill and leg colouration in exsul differ from that of nominate nereis more profoundly than currently realised or that the East Diamond Islet birds are an undescribed taxon. The former seems more likely. It was apparent in the field and to many who have viewed the photographs of the birds in flight, Plate 37 (D) and (F), that the tail looked abnormally short and with the fork ‘square’ rather than a graduated ‘V’ shape. Examination of the Heron Island specimens considered to be exsul confirmed Danny Rogers’ recollection that they too had short tails. In both specimens the tails were too worn to provide accurate measurements.

Call When flushed by approaching observers, one adult uttered a harsh, low-pitched kek-kek call. On first hearing this, Frank O’Connor, familiar with the calls of breeding Fairy Terns in Western Australia, declared that this alarm call was not that of a Fairy Tern but, after subsequent hearings, conceded that it probably was not very dissimilar.

Genetic status of subspecies Recent mitochondrial DNA work on the three subspecies has found exsul from Southern Lagoon, New Caledonia, to be genetically distinct with a single unique haplotype (n = 16) that is not shared with either of the other subspecies. Gene flow between New Caledonia and Australia is estimated at <0.01 migrant per generation (p <0.001) and exsul is considered to be more closely related to davisae than it is to nereis. Exsul is therefore considered endemic within its range and does not interbreed with southern Australian or New Zealand stock (Brunton 2005). VOL. 24 (4) DECEMBER 2007Fairy Tern: Another Form Breeding in Coral Sea 175

Status and significance Because of differences in geographic range and morphology, birds found breeding in the Coral Sea Island Territory are extremely unlikely to be subspecies nereis or davisae. By inference they are most likely to be exsul and, if so, this record would extend this subspecies’ global range 800 km west and well into Australian territorial waters. This would afford it recognition and protection under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999, which defines species as ‘a group of biological entities... that includes: a subspecies’. It would also bring it under the jurisdiction of the Lihou Reef National Nature Reserve, which is listed under the Ramsar Convention on Wetlands of International Importance. It is possible that the birds breeding in the Coral Sea are a separate genetic haplotype from those recorded in New Caledonia. Much less likely would be the possibility that they are a new subspecies; however unlikely, this cannot be ruled out with current evidence. Either way, their conservation is important. Based on some circumstantial data and anecdotes from previous research-trip reports, it is possible for us to speculate on their population and recent status, as follows. In recent years, the Commonwealth’s seabird-monitoring program for the Coringa–Herald group (north of East Diamond Islet) has not found any Little Terns or Fairy Terns (King 1993; Limpus 1996; Barry Baker unpublished data). Neither has the Fairy Tern been reported from more frequently visited regions of the Coral Sea, such as Marion and Frederick Reefs situated about 150 km to the south (Bourne et al. 2005), nor in the Swain Reefs (Clive Minton pers. comm.), where since 1999 there have been regular expeditions to study Roseate Terns Sterna dougallii (O’Neill et al. 2005). The Little Tern, on the other hand, breeds occasionally on the inner Great Barrier Reef islands (King 1993). To the east of East Diamond Islet is the remote Lihou Reef, a National Nature Reserve comprising 19 small cays between 30 and 120 km from East Diamond Islet. It is very rarely visited and has not been included in the Commonwealth’s seabird-monitoring program in recent decades. There are few sources of data from this reef and none in recent years. In their account of a pelagic survey from 15–26 May 1981, Stokes & Corben (1985) reported no Fairy or Little Terns in the Coral Sea Island Territory. The cruise included Lihou Reef (specifically Turtle Islet) and, although not reported, counts of breeding birds were done on all islands visited. No Fairy Terns or Little Terns were found (Chris Corben in litt. 28 April 2007). Reports of visits to Turtle Islet and Anne Cay on 3 October 1987 (Scotney & Jeffs 1987) list several breeding species, including Sooty Tern and Common Noddy but no Little or Fairy Terns. The most recent surveys of Lihou Reef National Nature Reserve occurred in the mid 1980s. Data are summarised in ANPWS (1989), which reported ‘Little Terns’ on 11 out of 17 islands, including breeding at both extremities of the reef. Breeding was reported for Georgina Cay in August 1984. The authors stated ‘21 adult Little Terns and 10 downy chicks were observed on the western sand spit of the major Cay’ (part of Georgina Cay) and referred to a second breeding record at Observatory Cay from Hindwood et al. (1963), which stated ‘The nesting of the species on the Lihou Reefs, some 400 miles east of the Queensland coast, could be exceptional’. We postulate that all records of Little Terns breeding in Australia’s Coral Sea Island Territory are likely to have been Fairy Terns. It seems probable that Fairy AUSTRALIAN 176CARTER & MUSTOE FIELD ORNITHOLOGY

A

B

C D

F

E

Fairy Terns on East Diamond Islet, 13 December 2006. A: Adult and immature. B: Immature with adult Black-naped Tern behind. C: Adult facing. D: Immature flying. E: Juvenile begging. F: Adult flying. Plate 37 Photo A: Kathy Wilson, B: Grant Penrhyn, C: Mike Carter, D: Mike Carter, E: Andrew McCutcheon, F: Paul Walbridge VOL. 24 (4) DECEMBER 2007Fairy Tern: Another Form Breeding in Coral Sea 177

Terns have been overlooked because of the difficulty of identification and thus frequent confusion between these species. As already discussed, the exsul subspecies of the Fairy Tern bears a closer resemblance to the Little Tern than it does to either nominate nereis or the davisae subspecies of the Fairy Tern. Hindwood et al. (1963) referred to Serventy (1959), who documented anecdotal records of breeding ‘Little Terns’ on Willis Island as far back as 1922 when the ‘first detailed description of bird life was given by Captain J. K. Davis who visited the island between October 16, 1921 and April 15, 1922’. Willis Island is located ~180 km north-west of East Diamond Islet and has no published records of either Fairy or Little Terns in recent decades. Serventy (1959) stated: In 1952 one bird was seen by Hicks. I saw one bird on my visit. February. [Serventy refers to visiting in June 1954, so it is probable that this ‘February’ refers to Hogan, who was there from 29 October 1922 to 20 April 1923, and from 14 November 1923 to 7 May 1924.] Hogan mentioned the birds being first noted in December 1922, although they were not seen landing on the island till March. None nested that season, but in the next year the first eggs were seen on April 19. These were found near the nests of the Sooties. Reithmuller gives no details of the nesting behaviour but mentions the fact they do nest on the island. On my visit 10 pairs were found nesting. Half the eggs had hatched. The nests were on bare sand and surrounded by Sooties with which they often fought. The birds were shy, but permitted approach to about five yards’ distance before flying. Mr Hicks... informed me the terns have only begun nesting on the island during the last few years. Apparently Mr Hicks was a wireless operator who visited the islands from 1944 to 1954 and his report of ‘Little Terns’ on Willis Island is particularly significant. Even though ‘Little Terns’ had been reported breeding there intermittently since 1922, they have apparently been lost as a breeding species since the 1950s. The first occupants of Willis Island were transferred there in November 1921 aboard the steamship Innisfail with 150 tonnes of cargo and it is possible that rats would have been introduced to the island at that time. However, Bureau of Meteorology staff based on Willis Island in early 2007 were unaware of any need for rat eradication in the past (Garry Sugrue in litt. 13 March 2007). Rat infestation was certainly a problem on other Coral Sea islands such as South West Coringa Islet between the mid-20th century and about 1991, before an intensive eradication program (DEW 2001). The detrimental effect of rat predation on ground-nesting bird populations of offshore islands is well known and we might assume that this contributed to the loss of the Fairy Tern as a breeding species, if not on Willis Island perhaps on some adjacent islands. Whatever the real cause, the absence of recent records of small terns gives us some indication of the conservation status of the species. If we assume, as is likely, that historic records of Little Terns in the Coral Sea were in fact Fairy Terns, the loss of the species from Willis Island would represent a significant contraction of its range in the Coral Sea Island Territory, given that there have been no recent reports of small terns much beyond Lihou Reef National Nature Reserve. The limited distribution and number of breeding locations mean that the population is now likely to be smaller than it was 50 years ago. The small number of individuals may make the Coral Sea population inherently vulnerable. It should also be noted that because of the decline in the mainland population of the nominate subspecies the conservation status of the Fairy Tern in Australia has been changed from Least Concern to Vulnerable (Garnett 2007). AUSTRALIAN 178CARTER & MUSTOE FIELD ORNITHOLOGY

Conclusion Our findings appear to correct a significant identification error in the literature from previous studies of Lihou Reef National Nature Reserve, indicating that the Fairy Tern, and not Little Tern, breeds in the region. We reveal the presence of a new but hitherto unknown subspecies of Fairy Tern for Australia, that is most likely the New Caledonian subspecies exsul, but could conceivably be a new subspecies or genetic haplotype. Further investigation is needed to ascertain this. The distribution and abundance of the Fairy Tern in the Coral Sea may have significantly altered since the 1950s with its apparent loss from anywhere other than the region of East Diamond Islet and Lihou Reef, possibly as a result of introducing rats into other former breeding areas. Hence, the Fairy Tern is now likely to be the most notable terrestrial vertebrate fauna component of the Lihou Reef National Nature Reserve. Although at present there is no reason to suspect that remaining breeding colonies are under immediate threat, their long-term status is less certain. Mainland Fairy Terns are reported to have a high natural rate of breeding failure (Garnett & Crowley 2000). If this is also the case in the Coral Sea, expected sea-level rise and increasing El Niño and cyclone frequency could significantly affect the population. Efforts to establish the size of the population and its sensitivity to further environmental change are necessary to realise Australia’s obligations to the Ramsar Convention and Biodiversity Convention.

Acknowledgements We thank all of the following for their assistance. Besides the authors, those who took part in the expedition, providing essential observation effort and expertise, were Chris Brandis, Dave Donnelly, Matt Edmunds, Jason Edwards, Jean Froelich, Andrew McCutcheon, Ian Montgomery, Bill Moorhead, Chris Morris, Frank O’Connor, Grant Penrhyn, Chris Seers, Paul Walbridge, Nathan Waugh and Kathy Wilson. Chris Pike of Tura Charters organised the logistics, and provided the vessel and navigational skills. Those who provided images used in the preparation of this paper were Jason Edwards, Andrew McCutcheon, Grant Penrhyn, Paul Walbridge and Kathy Wilson. Ian Southey provided photographs of specimens from many of the world’s museums. Dianne Brunton supplied copies of unpublished reports on conservation genetics. Guy Dutson reviewed an initial draft and provided regional contacts. Barry Baker referenced historical data. Astrida Mednes of the Department of Environment & Water Resources provided hard-to-access literature. Rory O’Brien of Museum Victoria arranged with Walter Boles of the Australian Museum in Sydney for the loan of the Heron Island specimens so that we could inspect these in Melbourne. Danny Rogers, Chris Corben, Jim Reside, Greg Clancy, Guy Dutson, Chris Doughty, Alan Morris, Richard Schodde, Andrew Silcocks and Margaret Cameron provided verbal information, advice and some texts.

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Received 17 June 2007 !