Food habits.—Seale (1901:31) found grass, insects, and larvae in stomachs obtained at Guam.
Remarks.—The subspecies G. c. indica, G. c. lozanoi, G. c. guami, and G. c. sandvicensis bear a close resemblance to one another in size and color. G. c. guami and G. c. lozanoi resemble each other so closely that it would be difficult to separate unlabeled specimens of the two subspecies. G. c. orientalis differs from all of the gallinules in smaller size and darker color. Study of these forms indicates that the Gallinule has colonized the Marianas from Asia probably by way of Japan and the Bonin and Volcano islands. The Hawaiian subspecies is probably of American origin, as pointed out by Mayr (1943:46), and is not a close relative of the Mariana subspecies. The fact that these insular subspecies have not undergone much differentiation does not necessarily mean that they are recent arrivals, but probably is a reflection of the lack of plasticity of the species; as a whole the species does not exhibit anywhere a great amount of geographic variation. A thorough study of all insular populations of this species (including specimens from the Azores, Seychelles, Réunion, Mauritus, and the Greater and Lesser Antilles) might reveal the effect of isolation on the species in general. Its ability to become established on isolated islands is apparent, although it is indeed peculiar that the species has not reached the Caroline Islands.
The Gallinule in the Marianas is restricted to fresh water lakes, marshes and swamps on the islands of Guam, Tinian, Saipan and Pagan. Coultas (field notes), on visiting the island of Tinian in 1931, comments that the bird is rare and found at only one lake on the island. Downs (1946:92) noted the species in 1945, and Joe T. Marshall Jr. obtained three specimens at Lake Hagoya in October of the same year. Gleise (1945:220) estimated the population of Gallinules on Tinian in 1945 at 70 individuals. Stott (1947:525) reports that the birds were abundant at Lake Susupe, Saipan, in 1945. Seale (1901:31) found the Gallinule to be abundant at Guam in marshes and taro patches. In 1945, the NAMRU2 party found fairly large populations of the Gallinule in fresh water marshes and fallow rice paddies at Guam. The greatest concentration of birds appeared to be in the Agaña Swamp and along the Ylig River. They seldom ventured out into open water but preferred weedy edges into which they could suddenly dart when disturbed. It was interesting to note such wary behavior, for an observer would think that after the bird had been in an environment virtually devoid of birds of prey (except for an occasional migrant) for a number of generations, it would have lost such behaviorisms as a result of the absence of the selective processes involved in predation.
Porphyrio porphyrio pelewensis Hartlaub and Finsch
Purple Swamphen
Porphyrio melanotus Temm. var. pelewensis Hartlaub and Finsch, Proc. Zool. Soc. London, 1872, p. 107. (Type locality, Pelew Islands.)
Porphyrio melanotus Hartlaub and Finsch, Proc. Zool. Soc. London, 1868, pp. 8, 117, 118 (Pelew); Gray, Hand-list Birds, 3, 1871, p. 64 (Pelew).
Porphyrio melanotus pelewensis Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 61 (Pelew); Bolau, Mitteil. Naturhist. Mus. Hamburg, 1898, p. 70 (Palau); Dubois, Syn. Avium, 2, 1904, p. 976 (Pelew); Mathews, Birds Australia, 1, 1911, p. 241 (Pelew); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 43 (Pelew); Mathews, Syst. Avium Australasianarum, 1, 1927, p. 100 (Pelew); Hand-list Japanese Birds, rev., 1932, p. 197 (Palau); Hachisuka, Birds Philippines, 1, 1932, p. 245 (Pelew).
Porphyrio pelewensis Finsch, Journ. Mus. Godeffroy, 8, 1875, pp. 5, 39 (Palau); Salvadori, Atti Accad. Sci. Torino, 14, 1879, p. 1169 (Pelew); Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, p. 407 (Palau); Finsch, Deut. Ver. zum Schutze der Vogelwelt, 18, 1893, p. 459 (Palau); Sharpe, Cat. Birds British Mus., 23, 1894, p. 206 (Pelew); Nehrkorn, Nat. Eiers., 1899, p. 205 (Palau-Inseln); Matschie, Journ. f. Ornith., 1901, p. 113 (Palau); Reichenow, Die Vögel, 1, 1913, p. 216 (Palauinseln); Takatsukasa and Kuroda, Tori, 1, 1915, p. 51 (Pelew).
Porphyrio cyanocephalus Elliot, Stray Feathers, 7, 1878, pp. 10, 13 (Palau).