The Avifauna of Micronesia, Its Origin, Evolution, and Distribution

by Rollin H. Baker

Nycticorax caledonicus pelewensis Mathews

Rufous Night Heron

Nycticorax caledonicus pelewensis Mathews, Bull. British Ornith. Club, 46, 1926, p. 60. (Type locality, Pelew Islands.)

Nycticorax caledonicus Hartlaub and Finsch, Proc. Zool. Soc. London, 1868, pp. 117, 118 (Pelew); Sharpe, Cat. Birds British Mus., 26, 1898, p. 158 (Pelew); Hartert, Novit. Zool., 7, 1900, p. 10 (Ruk); Reichenow, Die Vögel, 1, 1913, p. 255 (Palauinseln); Takatsukasa and Kuroda, Tori, 1, 1915, p. 50 (Pelew); Uchida, Annot. Zool. Japon., 9, 1918, p. 486 (Palau); Wetmore, in Towsend and Wetmore, Bull. Mus. Comp. Zoöl., 63, 1919, p. 172 (Uala, Truk Atoll); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 37 (Pelew, Ruk).

Nycticorax manillensis Hartlaub and Finsch, Proc. Zool. Soc. London, 1872, pp. 89, 105 (Pelew); Finsch, Journ. Mus. Godeffroy, 8, 1875, pp. 5, 33 (Palau); idem, Proc. Zool. Soc. London, 1880, p. 577 (Ruk); Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, p. 353 (Ruk); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 69 (Pelew, Ruk).

Nycticorax caledonicus pelewensis Mathews, Syst. Avium Australasianarum, 1, 1927, p. 200 (Pelew, Carolines); Peters, Proc. Boston Soc. Nat. Hist., 39, 1930, p. 271 (Pelew, Carolines); Peters, Check-list Birds World, 1, 1931, p. 115 (Pelew); Hand-list Japanese Birds, rev., 1932, p. 183 (Palau, Truk); Hand-list Japanese Birds, 3d ed., 1942, p. 204 (Babelthuap, Koror, Coracel, Truk); Amadon, Amer. Mus. Novit., no. 1175, 1942, p. 6 (Palau, Ruk); Mayr, Birds Southwest Pacific, 1945, p. 285 (Palau, Truk); Baker, Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 43 (Angaur, Peleliu, Garakayo, Truk).

Geographic range.—Micronesia: Palau Islands—Babelthuap, Koror, Coracel, Garakayo, Peleliu, Ngabad, Angaur; Caroline Islands—Truk.

Characters.—Adult: Size medium; head and nape dark slaty-black; occipital plumes white with dark tips and shafts; back dark reddish-brown, lighter on sides of neck, wings, wing coverts, rump, and tail; under parts whitish with light reddish-brown on sides of neck extending to throat and upper breast; tibia with some brownish feathers; underwing pinkish; feet yellowish-brown; bill black.

Immature: Resembles adult, but upper parts mottled black with reddish-brown; underparts with lighter streaks of brown and whitish on breast; feet yellowish; bill black above, yellowish below.

Adult resembles N. c. manillensis Vigors, but is duller above.

Measurements.—Two adult males from Peleliu measure: wing, 293, 299; tail, 105, 107; culmen, 82, 89; tarsus, 79, 81; seven adult females from Peleliu: wing, 269-286 (280); tail, 101-106 (104); culmen, 76-84 (80); tarsus, 78-83 (80); one adult female from Truk: wing, 280; tail, 97; culmen, 83; tarsus, 79.

Specimens examined.—Total number, 27 (5 males, 18 females, 4 unsexed), as follows: Palau Islands, USNM—Peleliu, 9 (Aug. 31, Sept. 1, 5, 6, 8, Dec. 6); AMNH—exact locality not given, 16 (Nov. 7, 8, 13, 23, 25, Dec. 1, undated); Caroline Islands, USNM—Truk, 1 (Feb. 16); AMNH—Truk, 1 (May 25).

Nesting.—The NAMRU2 party observed a nesting colony of these night herons at Peleliu on August 29, 1945. Approximately eight nests were observed in a grove of saplinglike trees at the edge of a mangrove swamp. These nests were 15 to 20 feet above the ground; most of them contained one or two nestling birds. Two subadults and three nestlings in postnatal molt were obtained; no eggs were found. Marshall (1948:219) records breeding in August, September and December.

Food habits.—Baker (1948:43) reports that stomachs of night herons obtained by the NAMRU2 party at Peleliu contained a great variety of animal foods, including eels, fish, lizards (skinks), crabs, shrimp, and insects. The stomach of one adult contained 14 large grasshoppers and four fish, totaling about 15 cc. in volume. The nestlings had eels, skinks, and insects in their stomachs.

Parasites.—Uchida (1918:486) found the bird louse (Mallophaga), Lipeurus baculus, on the night heron at Palau.

Remarks.—Amadon (1942:4-8) has made the most recent study of the species Nycticorax caledonicus and recognizes eight subspecies from Australia and New Calendonia north to the Caroline and Bonin islands. This is one of the few tropical and subtropical species which has extended its range to the Bonin islands. The discontinuous distributions of this species prevents an accurate estimation of the route by which it reached the Bonins. The presence of the bird at Palau and at Truk makes it difficult to account for its absence at Yap and other intervening, and seemingly suitable, islands. Populations at Palau and Truk appear to be similar and are placed in the same subspecies, but when adequate material is available from Truk, further study may reveal that the populations on the two islands (Truk and Palau) are recognizably different.

At the southern Palau Islands, night herons were found by the NAMRU2 party in mangrove swamps, lagoons and on beaches. I found them to be inactive during the daytime; the birds were usually perched singly in trees or at the edge of the water. The birds appeared to have special roosting places and were observed sitting in the same place on several different occasions. McElroy of the NAMRU2 party reported seeing three night herons at Truk in December, 1945.