Phaëthon lepturus dorotheae Mathews
White-tailed Tropic Bird
Phoethon lepturus dorotheae Mathews, Austr. Avium. Rec., 2, 1913, p. 7. (Type locality, Queensland.)
Phaeton candidus Kittlitiz, Denkw. Reise russ. Amer. Micron. und Kamchat., 1, 1858, p. 382 (Ualan); Hartlaub and Finsch, Proc. Zool. Soc. London, 1868, pp. 9, 118 (Pelew); Finsch, Journ. f. Ornith., 1872, p. 57 (Pelew); Hartlaub and Finsch, Proc. Zool. Soc. London, 1872, pp. 90, 114 (Pelew, Ualan); Finsch, Journ. Mus. Godeffroy, 1875, pp. 6, 47 (Palau); idem, Proc. Zool. Soc. London, 1877 (1878), p. 782 (Ponapé); idem, Journ. f. Ornith., 1880, pp. 296, 309 (Ponapé, Kuschai); idem, Proc. Zool. Soc. London, 1880, p. 577 (Ruk); Schmeltz and Krause, Ethnogr. Abth. Mus., Godeffroy, 1881, pp. 281, 299, 330, 353 (Ponapé, Mortlock, Nukuor, Ruk); Finsch, Mitth. Ornith. Ver. Wien, 1884, p. 52 (Kuschai); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 73 (Pelew, Ruk, Luganor, Nukuor, Ponapé, Ualan, Marshalls); Oustalet, Nouv. Arch. Mus. Hist. Nat. Paris, (3), 8, 1896, p. 62 (Agrigan, Palaos, Ruk, Kushai, Marshalls); Hartert, Novit. Zool., 5, 1898, p. 68 (Marianne).
Phaeton flavirostris Finsch, Ibis, 1880, pp. 329, 333 (Ratak Chain); idem, Ibis, 1881, pp. 105, 109, 115 (Kuschai, Ponapé).
Phaethon candidus Salvadori, Ornith. Papuasia, 3, 1882, p. 426 (Pelews, Carolines, Marshalls); Seale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 23 (Agrigan); Safford, Osprey, 1902, p. 70 (Mariannes); Takatsukasa and Kuroda, Tori, 1, 1915, p. 50 (Pelew, Ponapé); Uchida, Annot. Zool. Japon., 9, 1918, pp. 489, 492 (Palau).
Phaëthon lepturus Ogilvie-Grant, Cat. Birds British Mus., 26, 1898, p. 453 (Pelew, Carolines, Marshalls); Hartert, Novit. Zool., 7, 1900, p. 10 (Ruk); Safford, The Plant World, 7, 1904, p. 268 (near Guam); idem, Contr. U. S. Nat. Herb., 9 1905, p. 80 (northern Marianas); Mayr, Birds Southwest Pacific, 1945, p. 17 (Palau); Strophlet, Auk, 63, 1946, p. 535 (Guam); Borror, Auk, 64, 1947, p. 416 (Agrihan); Stott, Auk, 64, 1947, p. 524 (Saipan).
Phaeton lepturus Schnee, Zool. Jahrbücher, 20, 1904, p. 390 (Marschall Inseln).
Leptophaethon lepturus dorothea Mathews, Birds Australia, 4, 1915, p. 309 (Pelew).
Phaethan lepturus Cox, Island of Guam, 1917, p. 22 (northern Marianas).
Leptophaethon lepturus lepturus Kuroda, in Momiyama, Birds Micronesia, 1922, p. 33 (Agrigan, Saipan, Pelew, Ruk, Luganor, Nukuor, Ponapé, Kusaie, Marshalls).
Phaethon lepturus dorotheae Yamashina, Tori, 7, 1932, p. 407 (Ponapé); Hand-list Japanese Birds, rev., 1932, p. 187 (Agrigan, Pagan, Saipan, Agiguan, Palaus, Truk, Luganor, Nukuor, Ponapé, Kusaie, Marshalls); Hand-list Japanese Birds, 3d ed., 1942, p. 209 (Agrigan, Pagan, Saipan, Agiguan, Babelthuap, Koror, Urukthapel, Angaur, Unusuto, Truk, Luganor, Nukuor, Ponapé, Kusaie, Namorik); Baker, Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 38 (Guam, Peleliu, Ulithi, Truk).
Geographic range.—Islands in the southwestern Pacific area. In Micronesia: Mariana Islands—Agrigan, Pagan, Saipan, Agiguan, Rota, Guam; Palau Islands—Babelthuap, Koror, Urukthapel, Peleliu, Anguar, Unusuto; Caroline Islands Truk, Ulithi, Luganor, Nukuor, Ponapé, Kusaie; Marshall Islands—Namorik.
Characters.—Adult: White often with pinkish shade but lores and eye streak black; feathers of head, flanks and under tail-coverts with bases black; black on outer and subterminal part of inner webbing of primaries; black, subterminal coloring on scapulars and secondaries; black on shafts of elongated tail plumes; bill horn yellow, dark basally; tarsus dark yellow; feet blackish.
Immature: Resembles adult but upper parts barred with black, bill black on terminal part.
Measurements.—Measurements of adult birds from Micronesia are given in [table 15].
Weights.—The NAMRU2 party recorded weights of five adult males from Guam as 294 (267-321) grams.
Table 15. Measurements of Phaëthon lepturus from Micronesia
Table 15. Measurements of Phaëthon lepturus from Micronesia
| No. | Wing | Tail | Exposed culmen | Tarsus | |
| Marianas: Asuncion, Guam | 6 | 264 | 107 | 47 | 21 |
| 256-287 | 97-117 | 44-50 | 20-21 | ||
| Palaus: Peleliu | 11 | 257 | 108 | 45 | 21 |
| 242-270 | 98-122 | 40-49 | 19-21 | ||
| Carolines: Ponapé, Kusaie | 11 | 261 | 105 | 47 | 21 |
| 252-271 | 97-114 | 44-49 | 21-22 | ||
| Total: Micronesia | 28 | 260 | 107 | 46 | 21 |
| 242-287 | 97-122 | 40-50 | 19-22 |
Specimens examined.—Total number, 37 (22 males, 10 females, 5 unsexed), as follows: Mariana Islands, USNM—Guam, 5 (June 11, July 21); AMNH—Asuncion, 1 (June?); Palau Islands, USNM—Peleliu, 5 (Aug. 29, 31, Sept. 5, 6); AMNH—exact locality not given, 7 (Oct. 13, 26, Nov. 15, 23, Dec. 18); Caroline Islands, AMNH—Ponapé, 9 (Dec. 8, 9, undated)—Kusaie, 10 (March 1-8, April).
Nesting.—The NAMRU2 party observed nests of the White-tailed Tropic Bird at Peleliu in August and September, 1945. Several nests were seen in hollows of the Australian pine (Casuarina equisetifolia) between 20 and 30 feet above the ground. Birds could be seen in the nest hollows because the plumes of their long tail usually extended well out of the entrance. One nest was found in a dead tree in a battle-cleared area; others were observed in jungle habitat. Coultas observed nesting at Ponapé between November 1 and December 30, 1930, and found nests in the tops of trees and in hollow trees; a few were observed in holes in cliffs. Yamashina (1932a:407) records the taking of one egg at Ponapé on August 18, 1931. At Guam the NAMRU2 party found birds along the high cliffs which edge the beach. There was no evidence that they were nesting from May to July; nevertheless males taken in June had enlarged gonads. The bird is known to breed at Namorik in the Marshall Islands, according to the Hand-list of Japanese Birds (Hachisuka et al., 1942:209).
Food habits.—The NAMRU2 party found small fish in the stomachs of these birds taken at Peleliu.
Parasites.—Uchida (1918:489, 492) records the bird lice (Mallophaga), Colpocephalum epiphanes and Menopon eulasius, from the White-tailed Tropic Bird from Palau.
Remarks.—Birds taken in Micronesia differ only slightly from those from other areas in Oceania. Within Micronesia (see [table 15]) the birds from the Palaus have the shortest wing and shortest exposed culmen.
The White-tailed Tropic Bird appears more numerously in western and northern Micronesia than in the Marshall Islands. This distribution may be correlated with a preference for the "high" islands; especially those which have rocky cliffs, including Guam, Rota, Peleliu, Angaur, and Truk. Reports were received in 1945 that the birds were only infrequently seen at Ulithi, a low atoll. Stott (1947:524) observed birds flying into rocky crevices at Saipan on December 18. Gleise (1945:221) also recorded the bird in the vicinity of Saipan. Borror (1947:416) reports seeing birds at Agrigan on July 29, August 5 and 6, 1945. Coultas (field notes) found tropic birds common at Ponapé in November and December, 1930, in forested regions and along the cliffs. He made similar observations at Kusaie and Palau. At Ponapé and Palau, Coultas noted the use of the eggs, young and adults as food by the natives. At Palau the plumes are used in headdresses worn by the natives, the birds being taken with the blowgun.
Murphy (1936:807) states that the principal enemy of the White-tailed Tropic Bird at Bermuda is the introduced rat (Rattus rattus). Introduced rats, particularly Rattus mindanensis on Guam, may prey on the nesting birds. Baker (1946c:404) writes that this rat is a good climber and may spend considerable time in trees. The rat was trapped also in rough coral jungle at the edge of the cliffs, where tropic birds, Micronesian Starlings and other species, may have been nesting.
Little has been recorded concerning the post-breeding season wanderings of these tropic birds in Micronesia. They seemingly spend considerable time at sea, but whether they move as far from their breeding areas as do birds in the Atlantic, as reported by Murphy (1936:803), Baker (1947a:253) and others, is not known.
Murphy (1936:796) notes that the northward distribution of the tropic birds in the Atlantic is dependent on the warm currents of water. In the western Atlantic, the poleward-flowing, warm currents of the Gulf Stream allow for the northern extension of the range of these birds to Bermuda. In the eastern Atlantic, cool currents flowing toward the equator restrict the northern range. The same condition prevails in the eastern Pacific where warm current flowing toward the pole enable the birds to range north to the Bonins and other islands.
The three species of tropic birds known from Micronesia overlap very little in their ranges in this area. The White-tailed Tropic Bird has become firmly established in the western part of Micronesia, but there are only a few records from the extreme eastern part. The Red-tailed Tropic Bird appears to be resident only in the northern Marianas although it has been recorded in the Carolines and Marshalls. Interspecific competition may prevent considerable intermingling of breeding populations in Micronesia, or it may be that each species requires different ecologic conditions.