The red-tailed tropicbird (Phaethon rubricauda) is a seabird native to tropical parts of the Indian and Pacific Oceans. One of three closely related species of tropicbird (Phaethontidae), it was described by Pieter Boddaert in 1783. Superficially resembling a tern in appearance, it has almost all-white plumage with a black mask and a red bill. The sexes have similar plumage. As referenced in the common name, adults have red that are about twice their body length. Four subspecies are recognised, but there is evidence of clinal variation in body size—with smaller birds in the north and larger in the south—and hence no grounds for subspecies.
The red-tailed tropicbird eats fish—mainly flying fish and squid—after catching them by plunge-diving into the ocean. Nesting takes place in loose colonies on oceanic islands; the nest itself is a scrape found on a cliff face, in a crevice, or on a sandy beach. A single egg is laid, then is incubated by both sexes for about six weeks. The parents make long food-foraging trips of about 150 hours during incubation, but once the chick has hatched, the parents specialize their foraging: one forages for the chick for a few hours at a time, while the other makes much longer trips to feed themselves.
This bird is considered to be a least-concern species according to the International Union for Conservation of Nature (IUCN), though it is adversely affected by human contact. Rats and feral cats prey on eggs and young at nesting sites. The bird's tail streamers were once prized by some Hawaiian and Māori peoples.
Taxonomy The British naturalist Sir Joseph Banks encountered the red-tailed tropicbird on the Pacific Ocean in March 1769 on James Cook's first voyage, noting that it was a different species to the familiar red-billed tropicbird. He gave it the name Phaeton erubescens. It was the French polymath Georges-Louis Leclerc, Comte de Buffon who formally described the species in his Histoire Naturelle des Oiseaux in 1781, noting it was a native of Isle de France (Mauritius). The bird was also illustrated in a hand-coloured plate engraved by François-Nicolas Martinet in the Planches Enluminées D'Histoire Naturelle which was produced under the supervision of Edme-Louis Daubenton to accompany Buffon's text. Buffon did not include a scientific name with his description but in 1783 the Dutch naturalist Pieter Boddaert coined the binomial name Phaethon rubricauda in his catalogue of the Planches Enluminées. The genus name is derived from Ancient Greek phaethon, "sun", while the species epithet comes from the Latin words ruber "red" and cauda "tail". English ornithologist John Latham wrote about the red-tailed tropicbird in 1785 in his General Synopsis of Birds, recording it as common in Mauritius and the South Pacific. He also reported a black-billed tropicbird collected from Palmerston Island that ended up in Banks' collection. Latham did not give them binomial names, however. It was left to German naturalist Johann Friedrich Gmelin to describe the species, which he did as Phaeton phoenicuros and P. melanorhynchos respectively in the 13th edition of Systema Naturae in 1788. Latham later described this black-billed specimen as the New Holland tropicbird, giving it the name Phaethon novae-hollandiae.
The British naturalist Walter Rothschild reviewed the described names and specimens in 1900 and concluded that the original use of P. erubescens was a nomen nudum. He concluded that the populations of Lord Howe, Norfolk and Kermadec Islands belonged to a distinct subspecies which he named P. rubicauda erubescens, due to their larger overall size, more robust bill and prominent reddish tinge to their plumage. He also classified P. melanorhynchus and P. novae-hollandiae as juveniles. The Australian amateur ornithologist Gregory Mathews then applied the name P. rubicauda roseotinctus to Rothschild's P. rubicauda erubescens.
"Red-tailed tropicbird" has been designated the official name by the International Ornithologists' Union (IOC). Other common names include red-tailed bos'nbird or silver bos'nbird, the names derived from the semblance of the tail feathers to a boatswain's marlin spikes, and strawtail. The New Zealand Māori call it amokura, and the native Hawaiians koae ula.
Its closest relative is the white-tailed tropicbird (P. lepturus), the split between their ancestors taking place about four million years ago.
Four subspecies are recognised by the IOC:
P. r. rubricauda Boddaert, 1783 the nominate subspecies, from the western Indian Ocean. Subsequent specimens from the Cocos (Keeling) Islands were allocated to this taxon. P. r. westralis Mathews, 1912 from the eastern Indian Ocean. Mathews described it as separate on account of its larger wings. More extensive analysis in 1989 showed that the wing and beak size overlap between this and the nominate subspecies, leaving intensity of colour as the only distinguishing feature. P. r. roseotinctus Mathews, 1926 from the southwestern Pacific Ocean, including populations on Kermadec, Lord Howe, Norfolk and Raine Islands. P. r. melanorhynchos Gmelin, 1789 from the western, central and southern Pacific Ocean, including populations on the Cook Islands, Tonga, Samoa, the Marquesas and the Society Islands.
The ornithologist Mike Tarburton reviewed the known subspecies in 1989 and concluded that none were valid, noting that there was a clinal change in size in the species: those from Kure Atoll in the North Pacific being the smallest; ranging to those from the Kermadec Islands in the South Pacific being the largest. He also noted that the pink colouration was more intense in new plumage and faded after a few years in museum specimens.
Description
The red-tailed tropicbird measures on average, which includes the , and weighs around . It has a wingspan of . It has a streamlined but solid build with almost all-white plumage, often with a pink tinge. The sexes are similar in plumage. A dark brown comma-shaped stripe extends back from the lores, through and over the eyes and reaching the ear coverts. The iris is dark brown. The bill is bright red, slightly paler at the base and black around the nostrils. The legs and base of the toes are pale blue-mauve, while the webbing and rest of the toes are black. The white feathers of the head and rump have concealed dark brown bases, while those of the mantle, back, tail rectrices and tail coverts have dark brown shaft bases. The two long tail feathers are orange or red with white bases for around a tenth of their length, and can be hard to see when the bird is flying. The white wings are marked by dark chevron-shaped patches on the tertials, and the dark shafts of the primary flight feathers are visible. The pink tinge is often more pronounced in the remiges of the upper wing. Moulting takes place outside the breeding season, the streamers being replaced before the rest of the feathers. Streamers are replaced at any time, one growing while the other is shed, and old streamers may litter the area around a breeding colony.
Newly hatched chicks are covered in thin, long, grey-white down, which is paler on the head. The lores are bare. The down is greyer in older chicks. The primaries, rectrices and scapulars are evident in the third week, and chicks are mostly feathered with residual down on underparts and under the wings after six weeks, and fully feathered by 11 weeks. Juvenile birds have a glossy white forehead, chin, throat and underparts, and prominent black barring and scaling on their crown, nape, mantle, back, rump and upper wing coverts. Their bills are blackish grey with a light blue-grey base, and grey legs and feet.
In Australian waters the red-tailed tropicbird could be confused with the silver gull (Chroicocephalus novaehollandiae) or various tern species, though it is larger and heavier-set, with a wedge-shaped tail. Its red bill and more wholly white wings distinguish it from the adult white-tailed tropicbird. Immature red-tailed tropicbirds likewise can be distinguished from immature white-tailed tropicbirds by their partly red rather than yellow bills.
The red-tailed tropicbird is generally silent while flying. Aside from during courtship displays, birds may give a short greeting squawk to their mate when arriving or leaving the nest. Birds give a low growling call as a defence call, and young chatter repetitively as a begging call—made whenever the parents are nearby.
Distribution and habitat The red-tailed tropicbird ranges across the southern Indian, and western and central Pacific Oceans, from the East African coast to Indonesia, the waters around the southern reaches of Japan, across to Chile, and the Hawaiian Islands, where they are more common on the northwestern islands. It frequents areas of ocean with water temperatures from and salinity under 35% in the southern hemisphere and 33.5% in the northern hemisphere. In the Pacific Ocean, the southern boundary of its range runs along the summer surface isotherm.
The birds disperse widely after breeding. Evidence suggests birds in the Indian Ocean follow prevailing winds westwards, young individuals banded in Sumatra and Sugarloaf Rock, Western Australia, being recovered at Mauritius and Réunion respectively. Banding on Kure Atoll suggests birds in the North Pacific disperse in an easterly direction, following prevailing winds there. Strong winds can blow them inland on occasions, which explains some sighting records away from the coast and their preferred habitats.
Johnston Atoll It is the world's largest colony of red-tailed tropicbirds, with 10,800 nests in 2020. In the Pacific area, it nests on the Australian offshore territories of Norfolk and Lord Howe Islands, and on Queensland's coral islands (including Raine Island and Lady Elliot Island). In mid-2020 Australian scientists found a bird on Lady Elliott Island that they had banded 23 years earlier as a chick, but had not seen since, which had come back to breed on the island. In New Zealand territory it breeds on the Kermadec Islands. Elsewhere in the Pacific it breeds in Fiji, New Caledonia, French Polynesia, Hawaii—with a large colony on Kure Atoll—the Cook Islands, Pitcairn Island, and islands off Japan and Chile.
There are large breeding colonies on Europa, Aldabra and Christmas Island in the Indian Ocean, with smaller colonies in Madagascar, where it nests on the tiny island of Nosy Ve, the Seychelles, and Mauritius. It is also found on the Australian territory of Cocos (Keeling) Islands in the Indian Ocean. The warm waters of the Leeuwin Current facilitate the species nesting at Cape Leeuwin in southwestern Australia, yet is only a rare visitor to New South Wales at corresponding latitudes on the Australian east coast. It also nests at Ashmore Reef and Rottnest Island off Western Australia, as well as Sugarloaf Rock at Cape Naturaliste and Busselton on the Western Australian coastline itself.
It is an occasional visitor to Palau, breeding being recorded from the Southwest Islands, and was first recorded from Guam in 1992. It is an uncommon vagrant to New Zealand proper, where it has been recorded from the northern reaches of North Island, especially Three Kings Islands. It is a very rare vagrant to North America, with records from California and Vancouver Island.
Behaviour The red-tailed tropicbird is a strong flyer, and walks on land with difficulty using a shuffling gait.
They can hover in midair by flying into the wind; pairs may even fly backwards and circle each other during courtship displays.
Breeding