Gallinula chloropus guami Hartert
Gallinule
Gallinula chloropus guami Hartert, Novit. Zool., 24, 1917, p. 268. Type locality, Guam).
Fulica chloropus Quoy and Gaimard, Voy. "Uranie," Zool., 1824, p. 703 (Guam); Kittlitz, Obser. Zool., in Lutké, Voy. "Le Séniavine," 3, 1836, p. 305 (Guahan).
Gallinula galeata var. sandwichensis Oustalet, Nouv. Arch. Mus. Hist. Nat. Paris, (3), 8, 1896, p. 34 (Saypan, Tinian, Guam).
Gallinula chloropus Hartert, Novit. Zool., 5, 1898, p. 62 (Guam); Seale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 31 (Guam); Safford, Osprey, 1902, p. 67 (Marianas); idem, Amer. Anthro., 4, 1902, p. 711 (Guam); idem, The Plant World, 7, 1904, p. 265 (Guam); idem, Contr. U. S. Nat. Herb., 9, 1905, p. 79 (Guam); Prowazek, Die deutschen Marianen, 1913, p. 101 (Marianen); Cox, Island of Guam, 1917, p. 21 (Guam); Wetmore, in Townsend and Wetmore, Bull. Mus. Comp. Zoöl., 63, 1919, p. 177 (Guam); Strophlet, Auk, 63, 1946, p. 536 (Guam).
Gallinula chloropus guami Hartert, Vögel pal. Fauna, 15, 1921, p. 1843 (Guam); Kuroda, Avifauna Riu Kiu, 1925, p. 199 (Guam); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 43 (Guam, Tinian, Saipan); Mathews, Syst. Avium Australasianarum, 1, 1927, p. 99 (Mariana Islands); Takatsukasa and Yamashina, Dobutsu. Zasshi, 44, 1932, p. 226 (Pagan); Hand-list Japanese Birds, rev., 1932, p. 197 (Guam, Tinian, Saipan, Pagan); Hachisuka, Birds Philippine Islands, 1, 1932, p. 241 (Guam); Peters, Checklist Birds World, 2, 1934, p. 204 (Marianne Islands); Bryan, Guam. Rec., vol. 13, no. 2, 1936, p. 15 (Guam); Hand-list Japanese Birds, 3d ed., 1942, p. 222 (Guam, Tinian, Saipan, Pagan); Mayr, Birds Southwest Pacific, 1945, p. 288 (Marianas); Downs, Trans. Kansas Acad. Sci., 49, 1946, p. 92 (Tinian); Stott, Auk, 1947, p. 525 (Saipan); Baker, Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 49 (Guam, Tinian, Saipan).
Geographic range.—Micronesia: Mariana Islands—Pagan, Saipan, Tinian, Guam.
Characters.—Adult: Head and neck sooty black; upper back dark, bluish slate-gray; lower back and wing-coverts brownish; tail blackish-brown; wings dark brown, outer edge of first primary white; breast and upper abdomen dark slate-gray, feathers on sides of breast with longitudinal white streak; under wing dark with white edges; lower abdomen grayish with white-tipped feathers; vent black; under tail-coverts white; bill and frontal shield red, tip of bill yellowish; legs and feet olive-green.
Adult female: Resembles adult male but usually with smaller frontal shield.
Immature: Resembles adult, but forehead mottled white and brown, with sides of head less distinctly speckled with brown; crown, neck and upper back dusky brown; back, scapulars and upper tail-coverts olivaceous-brown; chin and throat whitish; breast feathers pearly-gray tipped with white; abdomen white; sides gray, washed with buff. Older birds are darker above and more brownish-gray below; frontal shield small.
G. c. guami resembles G. c. indica, but upper wing-coverts darker and near "olivaceous black"; back, rump and scapulars darker and less olivaceous brown, although not so dark as in G. c. orientalis. From G. c. lozanoi, G. c. guami differs in: slightly darker upper wing-coverts; richer olivaceous-brown on back, scapulars and rump; thinner culmen with possibly less yellow coloring on tip. G. c. guami resembles G. c. sandvicensis Streets of the Hawaiian Islands, but has less olive wash on the feathers and a smaller frontal shield.
Measurements.—Measurements of Gallinula chloropus are presented in table 18. In general, females are smaller than males.
Table 18. Measurements of Gallinula chloropus
Table 18. Measurements of Gallinula chloropus
| Location | No. | Wing | Bill from rictus | Bill from nostril | Tarsus |
| G. c. indica | 15 | 164 | 27 | 14.4 | 48 |
| 158-173 | 24-29 | 13.1-18.1 | 44-50 | ||
| G. c. orientalis | 3 | 152 | 27 | 13.8 | 45 |
| 146-152 | 26-29 | 13.1-14.4 | 44-46 | ||
| G. c. lozanoi | 11 | 164 | 27 | 14.5 | 50 |
| 153-170 | 24-29 | 13.1-15.2 | 45-57 | ||
| G. c. guami | 11 | 164 | 27 | 14.7 | 49 |
| 156-171 | 24-28 | 13.1-16.2 | 47-56 | ||
| G. c. sandvicensis | 2 | 150-158 | 27 | 13.4 | 52-56 |
Weights.—From Guam an adult male weighed 291 grams and an adult female 256 (Baker, 1948:49).
Specimens examined.—Total number, 42 (16 males, 22 females, 4 unsexed), as follows: Mariana Islands, USNM—Guam, 5 (Feb. 24, May, June 5, 7, 18—Tinian, 3 (Oct. 12, 18)—Saipan, 3 (Sept. 28, 30); AMNH—Guam, 25 (Feb. 21, April 6, July 13, 28, 30, Aug. 1, 3, 6, 7, 13, 19, 23, 30, 31, Sept. 3, 17, Dec. 11—Tinian, 5 (June 11, Sept. 12, 13, 14).
Nesting.—Hartert (1898:63) reports nests of the Gallinule at Guam in grass and on swampy ground in December and March. A male with enlarged gonads was taken by the NAMRU2 party at Guam on June 7. Marshall (1949:219) is of the opinion that this bird breeds all year.
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.