Poliolimnas cinereus micronesiae Hachisuka

White-browed Rail

Poliolimnas cinereus micronesiae Hachisuka, Bull. British Ornith. Club, 59, 1939, p. 151. (Type locality, Yap.)

Ortygometra quadristrigata Hartlaub and Finsch, Proc. Zool. Soc. London, 1868, pp. 8, 118 (Pelew); idem, Proc. Zool. Soc. London, 1872, pp. 90, 107 (Pelew, Uap).

Ortygometra cinerea Finsch, Journ. Mus. Godeffroy, 8, 1875, pp. 5, 38 (Palau, Yap); idem, Proc. Zool. Soc. London, 1880, p. 577 (Ruk); Salvadori, Ornith. Papuasia, 3, 1882, p. 273 (Yap, Pelew); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 61 (Pelew, Yap, Ruk); Finsch, Deut. Ver. zum Schulze der Vogelwelt, 18, 1893, p. 459 (Palau).

Ortygometra cinerea = quadristrigata Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, p. 353 (Ruk).

Poliolimnas cinereus Sharpe, Cat. Birds British Mus., 23, 1894, p. 130 (Pelew, Yap, Ruk); Hartert, Novit. Zool., 5, 1898, p. 64 (Guam); idem, Novit. Zool., 7, 1900, p. 9 (Ruk); Scale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 30 (Guam); Safford, Osprey, 1902, p. 67 (Mariannes); idem, The Plant World, 7, 1904, p. 265 (Guam); idem, Contr. U. S. Nat. Herb., 9, 1905, p. 79 (Guam); Cox, Island of Guam, 1917, p. 21 (Guam); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 42 (Guam, Pelew, Yap, Ruk).

Porzana cinerea Stresemann, Novit. Zool., 21, 1914, p. 54 (Guam, Truk).

Porzana cinerea ocularis Hartert, Novit. Zool., 31, 1924, p. 264 (Ruk, Guam).

Poliolimnas cinereus collingwoodi Mathews, Syst. Avium Australasianarum, 1, 1927, p. 95 (Pelew, Marianne, Carolines); Hand-list Japanese Birds, rev., 1932, p. 197 (Guam, Koror, Yap, Truk); Hachisuka, Birds Philippine Islands, 1, 1932, p. 236 (Marianne, Pelew, Caroline); Peters, Check-list Birds World, 2, 1934, p. 198 (Marianne, Caroline, Pelew); Bryan, Guam Rev., vol. 13, no. 2, 1936, p. 15 (Guam); Mayr, Birds Southwest Pacific, 1945, p. 288 (Guam, Palau, Yap, Truk, Bikini); Delacour and Mayr, Birds Philippines, 1946, p. 64 (Micronesia); Baker, Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 48 (Ulithi?, Truk).

Porzana cinerea collingwoodi Rensch, Mitt. Zool., 1931, p. 468 (Marianne, Karolinen, Palau).

Poliolimnas cinereus micronesiae Yamashina, Tori, 10, 1940, p. 679 (Bikini); Hand-list Japanese Birds, 3d ed., 1942, p. 221 (Guam, Babelthuap, Koror, Yap, Truk, Bikini).

Geographic range.—Micronesia: Mariana Islands—Guam; Palau Islands—Koror, Babelthuap; Caroline Islands—Yap, Ulithi?, Truk; Marshall Islands—Bikini.

Characters.—Adult: A slightly built, long-legged rail with forehead and anterior crown light gray with darker, slate-colored feather shafts; color more olive-brown on occiput and nape; eyestripe dark slate extending to occiput; superciliary from bill to eye, and stripe below eye, white; chin and throat ashy-white; sides of head, neck and breast ashy-gray, lighter on breast and whitish on abdomen; sides of abdomen ashy-brown becoming more buffy on tibia and under tail-coverts; mantle olive-colored becoming lighter and more brownish on back, rump, and scapulars; wing-coverts similar in color but feathers with broad dark brown shaft-marks; wings brown, first primary with whitish outer web; under wing gray with some lighter streaks; tail dark brown, lighter on edges; bill horn colored, tan below; feet brown; iris vermillion.

Immature: Resembles adult, but head more rufous, upper parts marked with buffy rufous; eye stripe light rufous-brown; underparts tinged with rufous.

P. c. micronesiae differs from P. c. collingwoodi Mathews of the Philippines by having more pale gray and less olivaceous-brown on the nape and shoulder; darker on the under tail-coverts; and having a shorter culmen. P. c. brevipes (Ingram) of the Volcano Islands differs from P. c. micronesiae by being paler on upper parts, particularly back and wing-coverts and more washed with buff below; by having a shorter, thicker culmen; and by having a shorter tarsus.

Measurements.—Measurements are shown in [table 17].

Table 17. Measurements of Three Subspecies of Poliolimnas cinereus

Table 17. Measurements of Three Subspecies of Poliolimnas cinereus

LocationNo.WingTailFull
culmen		Tarsus
Poliolimnas cinereus collingwoodi
Philippines, Talaut. Celebes		13 98 22.538.0
92-108 21.0-24.035.0-41.0
Poliolimnas cinereus micronesiae
Guam		10 955121.037.0
91-10250-5320.0-22.534.5-39.0
Palau
10 935121.037.0
89-9551-5320.0-23.034.0-38.0
Truk
5 955121.036.0
94-9751-5320.5-22.535.0-37.0
Poliolimnas cinereus brevipes
S. Dionisio Island		8 96 19.030.0
94-97 17.0-20.029.0-32.0

Specimens examined.—Total number, 25 (11 males, 13 females, 1 unsexed), as follows: Mariana Islands, AMNH—Guam, 10 (July 13, Aug. 1, 5, 7, 13, 19, 23, 31); Palau Islands, AMNH—exact locality not given, 10 (Nov. 11, 13, 15, 23, 25); Caroline Islands, AMNH—Truk, 5 (June 3, 8, 16, 17, 18).

Nesting.—Hartert (1900:9) describes two nests found on swampy ground. One contained three eggs, the other four eggs. He writes, "The eggs are pale buff, or cream-colour, speckled all over with brownish rufous, more frequently near the broad end. In some eggs, these spots are larger, in others minute, and there are often some, underlying pale purplish gray spots."

Remarks.—Superficially, the White-browned Rail of Micronesia is distinct from its near relative, P. c. collingwoodi, but the differences are not so well marked as they are between insular populations of other species of rails. It is probably a comparatively recent addition to the Micronesian avifauna, and its pattern of distribution may represent an early stage in the development of endemism in contrast to the pattern of later stages in the development of insular forms shown by the isolated rails, Rallus owstoni and Aphanolimnas monasa. The fact that Poliolimnas cinereus is found only on widely separated islands in Micronesia does not necessarily mean that it has become "extinct" on the intervening islands, but that it may be partial to the larger, "high" islands, or that it is actually present but remains to be discovered on these intervening islands when more intensive field investigations are made. Hachisuka (1939a:151), in naming the Micronesian form, comments that it has a shorter bill than P. c. collingwoodi of the Philippines and Celebes, and that it is intermediate between this subspecies and P. c. brevipes of the Volcano Island to the north. Within these three subspecies there are trends toward a shorter culmen and shorter tarsus and, less markedly, toward a shorter wing. From the evidence at hand, it can be concluded that Poliolimnas first colonized Micronesia probably from the Philippine area (or Papuan area) through the Palaus and Carolines, to the Marianas and north to the Volcano Islands. Further, this has probably been a relatively recent invasion, although the subspecies in the Volcano Islands shows marked change in length of tarsus and culmen. This extension of range to the islands north of the Marianas is unusual and resembles somewhat the distribution of Nycticorax caledonicus in the same general area.

The Micronesian White-browed Rail is a shy bird with the typical skulking habits of most rails. The NAMRU2 party did not find the bird at Guam, although reports were obtained that it was present in the marsh and swamp areas. Coultas (field notes) tells of observing the rail at Palau at a fresh water lake on Babelthuap, where it was difficult to obtain and apparently rare. Seale (1901:30) obtained a female specimen at Guam from native boys who snared it in a sweet potato patch near the Agaña River. This bird, taken in June or July, had eggs ready for laying. McElroy of the NAMRU2 party observed rails at Truk in brackish swamps, where he found them to be fairly common. A male which was taken in December had enlarged gonads. At Asor in the Ulithi Atoll, the NAMRU2 party learned that a small rail (possibly of this species) was found at taro patches in the early days of occupation, but that it was apparently eliminated by clearing operations. The taking of a bird at Bikini, as reported by Yamashina (1940:679), is further evidence that these birds may subsist on coral atolls as well as on the high volcanic islands; possibly the bird of the Marshalls may have been derived from the south rather than from the west. Unlike Rallus owstoni, this bird is apparently restricted to swampy areas, and may be eliminated from its habitat by drainage or clearing by man. It may always persist, however, in the taro patches maintained by the natives.