Metabolus rugensis (Hombron and Jacquinot)

Truk Monarch

Muscicapa Rugensis Hombron and Jacquinot, Ann. Sci. Nat. Paris, (2), 16, 1841, p. 312. (Type locality, Roug = Truk.)

Monarcha rugensis Hartlaub, Archiv. f. Naturgesch., 18, 1852, p. 133 (Gruppe Roug. = Truk); idem, Journ. f. Ornith., 1854, p. 168 (Carolinen = Truk); idem, Proc. Zool. Soc. London, 1867 (1868), p. 829 (Hogoleu = Truk); Gray, Hand-list Birds, 1, 1869, p. 321 (Caroline = Truk); Giebel, Thes. Ornith., 2, 1875, p. 614 (Carolinae = Truk); Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, p. 353 (Ruk).

Colluricincla rugensis Pucheran, Voy. Pôle Sud, Zool., 3, 1853, p. 62 (Ruk); Hartlaub, Journ. f. Ornith., 1854, p. 162 (Roug = Truk).

Metabolus rugensis Bonaparte, Comptes Rendus Acad. Sci. Paris, 38, 1854, p. 650 (no locality = Truk); Sharpe, Cat. Birds British Mus., 4, 1879, p. 238 (Ruk); Finsch, Proc. Zool. Soc. London, 1880, p. 575 (Ruk); Tristram, Cat. Birds, 1889, p. 197 (Ruk); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 19 (Ruk); Nehrkorn, Kat. Eiers., 1899, p. 26 (Ruk); Hartert, Novit. Zool., 7, 1900, p. 4 (Ruk); Matschie, Journ. f. Ornith., 1901, p. 112 (Ruk); Reichenow, Die Vögel, 2, 1914, p. 262 (Karolinen = Truk); Takatsukasa and Kuroda, Tori, 1, 1915, p. 54 (Ruk); Wetmore, in Townsend and Wetmore, Bull. Mus. Comp. Zool., 63, 1919, p. 203 (Truk); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 63 (Ruk); Mathews, Syst. Avium Australasianarum, 2, 1930, p. 470 (Ruk); Yamashina, Tori, 7, 1932, p. 404 (Truk); Hand-list Japanese Birds, rev., 1932, p. 178 (Truk); Hand-list Japanese Birds, 3d ed., 1942, p. 197 (Truk); Mayr, Birds Southwest Pacific, 1945, p. 295 (Truk).

Monarcha (Metabolus) rugensis Gray, Cat. Birds Trop. Is. Pacific Ocean, 1859, p. 19 (Caroline Islands).

Geographic range.—Micronesia: Caroline Islands—Truk.

Characters.—Adult male: White feathers (with dark bases) throughout except for black ones on forehead, lores, chin, and throat; chin and throat with steel-blue gloss; tips of second to fifth or seventh primaries black, black coloring extending along inner webs; shafts of primaries and basal half of tail feathers black; bill and feet black.

Adult female: Resembles adult male, but generally sooty-black, darker above; under tail-coverts and sometimes rump splotched with white; white coloring may also be present on tips of secondaries, on chin, and on tail.

Immature: Resembles adult, but bright cinnamon on upper parts and on wings and tail; inner webs of primaries grayish or dark brown, shafts of primaries lighter on basal half; lores, chin and throat white or washed with creamy-buff; breast and abdomen whitish, washed with cinnamon, sides darker rufous, under wing-coverts, axillaries, and under tail-coverts usually light rufous although somewhat variable in color; basal part of bill yellow, tip of bill horn colored. Immatures may be observed in all stages of color change toward the adult condition.

Measurements.—Measurements are listed in [table 40].

Table 40. Measurements of Metabolus rugensi

Table 40. Measurements of Metabolus rugensi

Number and SexWingTailCulmenTarsus
8 males103912726
(98-105)(88-93)(26-28)(25-27)
6 females100872726
(97-101)(86-89)(26-28)(25-27)

Specimens examined.—Total number, 27 (14 males, 13 females), as follows: Caroline Islands, USNM—Truk, 2 (Feb. 16, not dated); AMNH—Truk, 25 (Jan. 29, Feb. 1, 8, 10, 11, May 6, 9, June 11, 13, 14, 15, Oct. 11, 31, Nov. 2, 11, Dec. 3, 12, 17, 20).

Nesting.—Yamashina (1932a:404) reports on the taking of a nest containing one egg at Natsushima, Truk Atoll, in May, 1931. According to Hartert (1900:5) Owston's collectors obtained nests on June 1, 4, and 12. Two were in breadfruit trees about twenty feet above the ground. Each nest contained one egg. Hartert writes, "The eggs are cream-coloured, speckled with brownish red, more frequently and often very thickly on the large end, and with some deeper lying pale purplish grey patches, and one has some very fine black lines on the large end."

Molt.—A study of adult specimens obtained at various times of the year indicates that Metabolus normally molts in the period from about October through January.

Mayr (1933e:1-10) has studied the variation of immature and adult plumages in Neolalage banksiana (Gray) and other birds pointing out the occurrence of "retarded" and "progressive" plumages. Bogert has followed this work in interpreting the condition of the plumages in Metabolus, and through the kindness of Ernst Mayr I have examined Bogert's unpublished manuscript on the series of Metabolus at the American Museum of Natural History, from which the following account of the plumage is taken.

In the series of skins, there are specimens of non-molting, immature males with "normal" plumage (that is to say, plumage with upper parts cinnamon-colored and lower parts whitish and darker buff) taken in October and in February. There are also specimens of non-molting, immature females with "normal" plumage taken in November and in May. These immatures are in fresh or slightly worn plumages. In addition, there is one non-molting, male specimen (November) which has some white on the crown and throat, some black on the lores and chin, but because the black feathers are fresh, the specimen is considered to be a "transition" bird and may be either a "retarded" adult or a "progressive" immature male. One non-molting female (October) shows some sooty-black mottling on the chin and throat and a few black feathers on the crown; this is apparently a "progressive" immature because the lower mandible has a yellow basal part, characteristic of the immature. Another female (June) shows black feathers on the crown, nape, chin, throat, and breast; this bird is in the process of molting with the black feathers representing new growth and is an immature assuming the adult condition—in "progressive" plumage. One non-molting male (January) has an intermingling of white feathers in the cinnamon coloring of the head and body, black on the forehead, chin and throat, primaries black with cinnamon edges, and bill similar in color to that of the adult; it is considered to be an adult with "retarded" plumage. Two molting males (December) resemble adults except for cinnamon coloring on shoulders, back, primaries, retrices and a slight cinnamon wash on breast feathers; these may be "retarded" adults. One molting female (June) has mixed cinnamon and sooty-black feathering; this may also be a "retarded" adult. Another molting female (December) with more sooty-black feathering and less cinnamon feathering is also considered to be a "retarded" adult. In fully adult birds there is considerable individual variation, especially in the males where the amount of black on the throat, the extent of the black on the terminal part of the primaries, and the extent of the black on the basal part of the tail feathers is variable. Scattered white feathers may be present on adult females.

Remarks.—Hombron and Jacquinot first obtained the Truk Monarch, but it was not until the time of Kubary and of the Japanese collectors of Owston that very much was learned concerning the bird. In 1945, McElroy of the NAMRU2 party reported that he found no birds at the several islands of Truk that he visited in December. Some of the Japanese residents of the islands told McElroy that they did not know the bird. Evidently, its numbers are low or it has been eliminated, at least on the islands then populated by the Japanese.

Metabolus belongs to a group of flycatchers including the genera Pomarea, Mayrornis, Neolalage, Monarcha, and Clytorhynchus. The different plumages of the adults and the immatures are not unusual in this group of genera, this feature being observed in many of the flycatchers of Oceania. Mayr (1933c:1) points out some of the relationships between Metabolus and some of these other genera; he comments that all of them have rather thin bills, in contrast to those of other flycatchers.

Metabolus became established at Truk probably as the result of an independent colonization. It is a well differentiated genus showing little resemblance to Monarcha godeffroyi of Yap. In looking over the genera found in the Pacific area, it appears that Metabolus is closest to Clytorhynchus of the Melanesian region, especially to Clytorhynchus hamlini Mayr, which is resident at Rennell in the Solomon Islands. The bills of these two birds are similar, both being long and thin, with a pronounced hook. In coloration there is some resemblance; C. hamlini has the blackish forehead and chin like the male Metabolus and also the burnt-orange underparts. In C. hamlini, however, the sexes are similar, Metabolus also resembles C. nigrogularis. Like Metabolus, the immatures of this latter species are different in color from the adults.