Tachypetes aquila var. minor Oustalet, Nouv. Arch. Mus. Hist. Nat. Paris, (3), 8, 1896, p. 65 (Rota, Carolines, Marshalls); Hartert, Novit. Zool., 5, 1898, p. 68 (Marianne).
Fregata ariel Ogilvie-Grant, Cat. Birds British Mus., 26, 1898, p. 447 (Marianas, Carolines); Seale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 25 (Guam?); Safford, Osprey, 1902, p. 70 (Marianas); Bryan, Guam Rec., vol. 13, no. 2, 1936, p. 15 (Guam).
Fregata ariel ariel Mathews, Birds Australia, 4, 1914-15, p. 285 (Carolines, Marshalls); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 36 (Yap, Ngoli, Rota); Hand-list Japanese Birds, rev., 1932, p. 186 (Rota, Yap, Ngulu, Uluthi); Hand-list Japanese Birds, 3d ed., 1942, p. 208 (Rota, Yap, Ngulu, Uluthi).
Geographic range.—China coast and Philippines south to Australia and east to Pacific islands. In Micronesia: Mariana Islands—Guam?, Rota; Caroline Islands—Yap, Ngulu, Ulithi.
Characters.—Adult male: Resembles F. m. minor, but smaller and blacker with upper parts lustrous greenish-blue and white patch on lower flank.
Adult female: Resembles adult male, but browner with paler nape and white breast. Immature: Resembles adult, but with head, chin, throat, and belly white washed with rufous.
Remarks.—Like F. minor, the Least Man-o'-War has not been observed often in Micronesia. Marche obtained one female at Rota in June, 1888. D. H. Johnson saw a bird thought to be of this species at Agfayan Bay, Guam, on 4 June 1945. Records from the western Carolines are few. There are no reports of this bird from the Palaus and the Marshalls. It may breed on some of the atolls in the Carolines.
The two species of man-o'-war birds may be difficult to distinguish in the field. The smaller size of Fregata ariel is perhaps the most useful character although it may be easily recognized also by the presence of the white flank patch, if it can be observed.
Both of the species of Fregata discussed in this report have representatives in the Atlantic, Indian and Pacific oceans. Murphy (1936:920) has shown that the man-o'-war birds are able to cross the Isthmus of Panamá between the Pacific and Atlantic oceans. This route may also be the means of dispersal for other species. The irregular distribution of these birds as well as of other sea birds in the oceanic islands of the Pacific may be caused by their remaining over waters which contain preferred foods and their avoidance of waters which lack preferred foods.